3 Link, 4 Link, What Link???

[skullandbones]

OK it's not another thread to talk about which is better just to get your attention!

I've decided to migrate back to the rear of the car for some upgrades that I've been thinking about since day one of the build. At the time just getting it on the road was the priority so now I've had time and money to change the 4 link out for something a little more adjustable. That's the operative word: adjustability. I've decided on a Watt's link after spending some time with James Watt's patent application on his improvements to the steam engine. I'm not sure when it was first applied to suspensions but I'm glad it was. I plan on a style of Watt's link that is mounted on the chassis instead of the pumpkin kind of like the Fays2 that Mustangs use. I have a good reason for that. There are pros and cons for any suspension system depending on what you need it for so I have done my best to design it for street/ auto cross.

I plan on using the quad shock brackets as the main support for the cross member with some added support to tie it to the 2x2 rail above so it will not be fully loaded on the welded bracket. The member will be a simple rectangle with triangulated arms to handle the lateral loads of the chassis. The bell crank or propeller is going to be made of 6061 aluminum with vertical mounting plate that will have several adjustment points for raising and lowering the roll center in the rear. I like that the roll center is exactly where the pivot point of the propeller is so there is no calculation involved. The lateral links and diff mounts are probably coming from Speedway since they have the best variety of pan hard bar brackets I've seen so far.

I like the idea of having the roll center mounted rigid to the chassis so I can adjust it up/down with ride height as well as the cross member adjustment. So the next step is to put the roadster back on the lift for mockup and tacking the pieces then remove and weld it up. This is supposed to be a completely bolt in project so I can remove it if I wish and return to the present system without any modification. Also, I will be driving the car so there will be no downtime as with the front suspension project I did. At some point I will be adding a third link in the center of the diff but the Watt's link will be first. I will in effect be running a 6 link suspension. Then as I've discussed before, I can remove one UCA and do a little experiment to see how the "poor man's 3 link" works. The final goal is to fab a 3rd link that will use the mounting points of the 4 link UCAs (diff and chassis) but in the centerline of the chassis. There may be a few days of downtime when that happens but first things first.

I had to show my pic of the metal I got at industrial metal supply. You can get some great deals from remnants or you can go custom and pay more. I got these for $48 dollar. If I had had the aluminum cut to size it would have been $30 just for one piece. I love a good deal. The shiny aluminum plate is for a dead pedal.


Any thoughts or other input is always appreciated and usually educational.


WEK.

[CraigS]

Have you seen this? Good for reference as you design yours.
http://fays2.net/fays2_watts_link_20_.html

[skullandbones]

I did see that eventually. I have looked quite a while but probably wasn't searching as efficiently as I thought. It turns out that what I thought was kind of an odd ball approach to the Watts link is actually the most common application at least for Mustangs. I think Fays2 is the most used by a long margin for the Mustangs. When I was looking at sites and other forums, I got confused, thinking the Fays was mounted on the diff cover but it must have been another one like Whiteline. So I ignored it since I was looking for something different. They mount on the quad shock brackets just like in a Mustang. I'm glad we have those brackets now as I have a good use for them. I believe I can make this work without removing my trunk mounted battery. If I used the Fays I would have to move it. That was one of the things I didn't like about most of the systems out there. I also wanted a clean uncovered diff cover so I can possibly change the gears if I wish. We will see if there is enough space for that once I get mine installed. Of course, that would be after removing the bell crank.

Thanks for the link.

WEK.

[Gumball]

I had the Fays2 set-up on a '65 Mustang I built as a vintage racer - it's a great part and may be of help in designing yours. I think I have some pics of it, but they'll be either old paper photos or on CD somewhere. Let me know if you need them.

Also, a friend of mine has the Fays2 on a car he currently owns - I'd be happy to take some measurement or other photos if you need them.

[skullandbones]

I have a design path already that I had in my head but after describing it to a friend he was nice enough to do a rendering of it from a description which turned out exactly like I had envisioned it. The only critical measurements were the distances between the inside edge of the quad shock brackets at the front which is ~36.25 inches and the length of the vertical members which is ~13.5 inches. That will place the bell crank about an inch below the diff/axle center line at my present ride height. From reading and talking with actual users of the Watts link, that position seems to be a very good starting point. It coincides with the generally accepted height of between 4 and 10 inches above the ground level. I have a pic of that rendering.

I'll include some pics of the real thing when it is tacked and welded.

Thanks,

WEK.

[skullandbones]

I started on the fabrication after cutting the bracket pieces to size (6 x 2.5 inches). The support brackets that ride on the 2x2 frame rails are just some angle cut about 3 inches long. These brackets are set at compound angles so they have to be fitted on the car. I am tacking the bracket pieces in place then measuring and cutting the main cross member to the right width and tacking it up. Since the member will be slightly canted forward at the bottom, I will compensate for the propeller support by installing it on the cross member on a perpendicular plane with the ground. It's turned out to be more challenging due to the close quarters of this area of the car. However, it is going forward slowly but surely as planned. I think I'm opting to have this welded by my friend who has a welding business and can do a much better job on this rather strange configuration. I measured carefully and still managed to weld up the cross member with a 1/4 inch variance from side to side. It probably would have been fine but I undid one side and adjusted it to make it perfectly level. That was a lot of work of a 1/4 inch. Next I will fab the triangulation supports on the cross member and the center propeller support and it's triangle supports. Here some pics.

Thanks for looking,

WEK.

[CraigS]

I am glad to see the words "triangulation supports" since that was what immediately came to mind when I saw the 4th pic. I am looking forward to following your thread.

[skullandbones]

Craig,

It seems like this is going incredibly slow. I think it's our hot weather. I slow down a lot when it gets above 100. It's not too bad in the garage but if it gets too much hotter the AC is coming on.

Anyway, I thought I would stop and account for what I had done. Then after going back it only took me about fifteen minutes to cut and tack the support bars in. I still have to cut the propeller support into the main member and angle it properly. Some of these little things are quite tedious. I also fit the piece back on the car each time I do something and check the 1/2 bolts for fit. I have to drill six 1/2 holes and tap them for the propeller holes (adjustment positions to raise or lower roll center). So it's off to the hardware store to get new bits. I've been working with aluminum but these steel pieces don't drill as easily. More pics to come.

Thanks,

WEK.

[CraigS]

I am not sure of the wall thickness of your square tubing but are you going to weld in a sleeve for each bolt position? I just looked back at the cad drawing and realized that maybe that piece is solid so no sleeves needed.

[skullandbones]

That's correct. There are no holes in the cross member except the center propeller mount or that would be a real concern with all the back and forth lateral forces on the holes. The center mount is 1 x 1/2 x 8 inches of steel and cut into the member for more welding surface. That mount will be drilled and tapped. It should be strong enough with some triangles built in. I was trying to keep the weight down. So far the cross member is 12.5 lbs. I'm thinking it will be half unsprung and half sprung weight and the CG of the device is pretty low. Once the cross member is in place, I will get a better feel for the lateral link positions. I want to fab the diff brackets off the shock brackets by boxing the bracket and adding a bung. I'm not sure that will work yet (may be too low). The alternative is the ugly axle housing mount that Speedway has. That is a good plan B though. As I said before, the Fays system uses them. I think that was a cheap and easy way to keep the price point down for them. I keep thinking, the only thing that will see it anyway are the insects crawling under the car as there is no good way to view it without putting it on a hoist or jacking it up! Maybe I need a viewing window of Plexiglas in the truck floor. Some people would appreciate it.

Thanks,

WEK.

[skullandbones]

Things are going rather slow but it's summer in AZ so we slow down. I don't see a need for this until I can get a track day or AX next season so it's OK to take my time.

I finally got the cross member tack and sent to the welder. He TIG welded the thin stuff and I wire welded the heavier pieces. So it's cleaned up and painted. Now I will install and leave it in as it will be convenient to measure the other stuff when I put it on the lift. Here are a few pics. I had to angle the propeller mount a little forward at the top to stay perpendicular with the ground. I figured the links and other brackets would be easier to mock up with the cross member finished.

I'm having the machine shop guy do the propeller as he has a milling machine and I don't. That will be the most critical part to get right!

Have to get the propeller back before mocking up the rest with some hiem joints I have on hand.

WEK

[CraigS]

I think you would be better off using a through bolt and nut than threading the holes. If you thread the bolt into a threaded hole your bending load is right on a thread. If you pass the bolt through the hole you can size the bolt length so all the load is on the solid shank.

[Mike N]

Craig is right on that bolt, if you allow the bolt to take shear. Unless you have a partially threaded bolt and the plain shank engages the hole you want the friction at the joint to react the shear and not the (threaded) shank of the bolt.

Obviously pre-load on that bolt is important. Use a good bolt and torque it to 80% of yield. I have a threaded hole on my watts and used one of these http://www.mcmaster.com/#standard-cap-screws/=sjponi

[skullandbones]

Hi guys,

I appreciate the input. This has been a concern from the beginning since it would be the most likely break point in the system. Having said that, I am taking some risk that this will work well enough for the application I have planned. I'm using a 5/8 - 18 screw partially threaded. There is another component that has not been shown because it hasn't been made yet. That is a 1/2 inch spacer between the mount and the propeller. I need that for 1) space to clear the mount and 2) to help close the gap for the lateral links and the propeller to line up in the same plane. There is about 6.5 inches difference so to keep from triangulating the system, I am using whatever little fudge factor I can. The 5/8 inch screw should provide a little more "meat on the bone" so to speak. Don't know for sure if the spacer will help spread the shear load. I think it will but don't have documentation to prove it. Plan B is to redrill/tap the holes for 3/4 - 16. I have a Plan C, also. I did think about what to do in case of failure. I think with a few extra components if the system fails I can attach one lateral link and drive home with a make shift PHB. Anyway, it's something that will get regular attention during the under the car inspection routine.

WEK.

[CraigS]

Take a look at these spacers for a design guide.
http://www.jegs.com/webapp/wcs/store...od+end+spacers

[skullandbones]

Craig: thanks for the link. That's exactly what I need (shoulder and all).

Installed the cross member for the last time today. It is tight in that space between the gas tank and the diff especially with a rear mounted sunken battery box. It fits and bolted up nicely. I will add another bolt thru the vertical components of the cross member. That would have been nearly impossible with the multiple angles so I will remove the tires and drill though the already existing forward hole on the quad shock bracket. That will capture the main frame of the cross member and add to the stiffness of the unit. The rest of the project is measuring, cutting, and bolting things up. Propeller is being machined except for the pivot hole which is waiting for the roller bearing from McMasters just to make sure of the size (press fit). The car weighs an extra 13.5 lbs now but the benefit is supposed to "out weigh" (ha) the weight.

Note to self: wait patiently for parts.

WEK.

[skullandbones]

Had no idea I would be getting parts in less than 24 hours from McMasters. I have hear they are fast but that's ridiculous! No complaints here.

Since I have the chance, I mocked up the bearing/sleeve on the 5/8 - 18 screw. I used some hardened washers as spacers and some 0.003 shims. This is the first attempt. I may have to re shim and/or go with a slightly longer bolt to match up with the lateral link brackets. But it doesn't look bad for a first fit. I don't know how much shimming will be necessary to get the right spacing for the sleeve and room to torque the bolt down enough for preload. It's a little like adjusting a wheel bearing by feel except it's a little more tedious. I want the bearing and propeller to move smoothly and still not have enough play to move along the screw shaft. I'll have to trial fit and torque it with some different combinations of shims until I get it perfect. I've heard that any extra play you get in the bearings or spherical rod ends will transmit as a loud "clunk". Sure don't want that.

Propeller should be ready at the machine shop tomorrow.

WEK.

[skullandbones]

Don't have the brackets and other hardware yet. That will be here next Tuesday. So all companies do not ship at the same speed. Unfortunate for a company called "Speedway" should be pretty fast you would think.

Anyway, I did get the propeller back from the machine shop. Love machined aluminum. Here's a couple of pics.

Thanks,

WEK.

[skullandbones]

I received the brackets and rod ends so I did a mock up of the components to check for fit and see how I would have to adjust for final spacers, jam nuts, shims, etc.........

I was very impressed with the clamp on PHB brackets from Speedway. It got a 5 on their top rated list. I can see why. It's a little expensive but for the amount of fabrication it saves, it's worth every penny. The welding was perfect; maybe robotically done. Had to think outside the box by fitting some sleeves under the clamps as the brackets are really for a 3 inch axle housing. A 3 inch 1/8 thick exhaust tube worked perfectly. Just cut it 3.7 inches split into halves and installed under the clamps. I also had to install the brackets in reverse so the orientation of the DS bracket would miss my battery box. It takes care of the bottom link on the watts. The other one is oriented up. There are several adjustment positions with 3/4 inch holes. It's for a PHB so the holes are in a small arc but that's no big deal. I will just adjust to fit when moving the links up or down.

Everything is close since I moved the cross member as far forward as I could when welding it up. So there is a near perfect alignment with the rod ends on the brackets and the rod ends on the propeller. I will have to do some small spacing to clear jam nuts and space the propeller perfectly but it is doable. I used some electrical conduit to simulate the lateral links which I could not order at the time. I needed to measure them with the rod ends installed in the mock up. Those are now ordered. I ended up moving the brackets in slightly from extreme outboard so that the links will be 12 inches long each.

When I lowered the roadster with the mocked up unit, everything cleared at ride height but just barely. In the future, I may replace the cross member with an aluminum clone so I can move it back a half inch then.

Here are a few pics of the mock up. I will have to remove, paint, and re-install when my lateral links arrive.

Thanks,

WEK.

[skullandbones]

I was hoping for more feedback as there hasn't been a lot of discussion about watts links and how it's affected the handling. I've gotten some on other threads I've done but it's usually a comparison like, "IRS is better for overall comfort" or "here's the hierarchy: 5 link, IRS, 3 link, 4 link". How about when I go into a turn now I know when the rear end is going to let loose. Before it was a guessing game. I'm OK with criticism too. Not the "yellow bullet" kind though. I usually learn at least one thing I didn't know before from these kinds of discussions. So feel free.

Thanks,

WEK.

[Mike N]

Bill, you know my experience but I'll post here for reference.

I went from the 4 link with FFR uppers/lowers with urethane bushings to my own fabricated 3 link plus watts. I had the 4 link for 4 or 5 years before the switch and made many 1/4 mile passes and AutoX runs. For straight line use the 4 link was really never a problem. It hooked well at the strip and handled pretty good on the road. However for Auto X the 4 link was very difficult to find a nice balance at the limit of lateral traction. Once you reached the limit the rear end would almost always break loose in such a way that I couldn't catch it. The rear wouldn't just get into a nice slide it would snap loose.

Many detailed theories out there as to why exactly this is but it seems to be commonly agreed that the 4 link triangulation actually binds up in roll. What this means is that the 4 link rear suspension has an associated roll stiffness in it's characteristics (like a sway bar). So what happens when the rear starts to slide is that the built up roll stiffness releases and unloads the outside tire reducing traction in such a significant way that there is very little chance of saving the rear of the car. There are a few guys who seem to have had success with racing the 4 link but my theory is that they slide the rear of the car in such a way even entering a turn so that the roll stiffness never really gets built up.

Driving the car with the 4 link at the limit you can almost feel the rear of the car raise up slightly as you start to pull lateral G's, and then as the rear end breaks loose you can feel the rear drop slightly. This doesn't happen with the FFR 3 link plus panhard bar or a watts link in place of the panhard bar. For anyone who does anything more aggressive than cruise around in their FFR (and who doesn't?) just about any upgrade to get away from the 4 link 'bind' will provide a very nice improvement in the way that the rear of the car behaves under cornering loads.

I'm waiting to hear Bill's reports on how the watts behaves with the 4 link still in place. It may actually introduce another source of binding that could make things worse. A partial fix is to remove one of the upper links (poor mans 3 link).

[skullandbones]

I'm just waiting for those lateral tubes. I may have to get a couple of things from McMaster as well but it should be possible to do some preliminary testing within a week or so.

Re: the guys sliding around the turns sounds like a pretty good work around. Maybe they are drifters so it comes naturally. Also, I find it interesting that you stayed with the 4 link as long as you did. I have had a lot of motivation to change earlier than later mainly from the discussions here and on ffcar. I know the 4 link gets bashed a lot due tot he design shortcomings but it is OK for a lot of uses and is very simple and reliable.

I will as promised try the "poor man's 3 link" but I will do some driving with the "new 6 link" when I finish the Watt's link. I really can't wait to see if the PM3L really works. It does on many Mustangs according to the forum so it should with this application too. We will see.

One more thing: I was wondering if the third link (when I fab that portion) should be a bit heavier than the lateral links on the Watt's link. I was thinking of a 1 or 1.25 rod end. Does that sound like overkill or sound reasonable. I was going to possibly use the tube/rod ends for the PML experiment. I might have to shorten the tube or change to a much shorter tube but I could still use the other parts for the final third link. Any thoughts?

Thanks,

WEK.

[Mike N]

Bill, I used 3/4" rod ends for the suspension links and 5/8" for the watts. The 3/4" are plenty strong enough.

[skullandbones]

OK, Mike. I will go with the 3/4 rod ends. It's funny that Speedway has the larger rod ends but don't seem to carry the larger tubes to fit them. Maybe it's on their website. The catalog probably can't hold all the parts. I'm finding that the choice of certain components can complicate the process by having to make accommodations for them when they create a clearance issue. But that's why it is so much fun, right?!!!!!!

Thanks,

WEK.

[CraigS]

I am pretty sure that the FFR 3rd link and panhard rod are 5/8 rod ends. I know the jam nuts are 15/16.

[skullandbones]

That's great to know. So the 3/4 rod ends should be fine. So Craig: do you have any insights to share about your 3 link? Is it an FFR 3 link? I've heard a lot of good stuff about them but not too much negative. I'm headed in that direction with my watts link which will substitute for the PHB.

Thanks,

WEK.

[frankeeski]

I was hoping for more feedback as there hasn't been a lot of discussion about watts links and how it's affected the handling. I've gotten some on other threads I've done but it's usually a comparison like, "IRS is better for overall comfort" or "here's the hierarchy: 5 link, IRS, 3 link, 4 link". How about when I go into a turn now I know when the rear end is going to let loose. Before it was a guessing game. I'm OK with criticism too. Not the "yellow bullet" kind though. I usually learn at least one thing I didn't know before from these kinds of discussions. So feel free.

Thanks,

WEK.

Bill, I'll try to be kind but just remember you asked for it. Your 4-link with Watts link is not going to react any different than the standard FFR 4-link. I can't predict but it might even perform worse because of the inherent arch the upper control arms react in and also the stiffness of the poly bushings. I applaud all those who choose to look outside the box and fabricate themselves. I would however ask why you didn't just go with a pre-fabricated piece like the FFR 3-link or a Levy 5-Link? When you consider all of the parts you are buying and /or having fabricated by outside fabricators I just wonder how much money you've saved? Again, I get it, I fabricate much of my own stuff. Moving on, I haven't seen Mike's setup but I know he also fabricated his own Watts link setup. I have the Levy 5-link with the billet aluminum upper and lower control arms with Heim joints on both ends of each control arm. This system offers suspension flexibility that the FFR solid poly control arms will never be able to compare to. Granted, on the street the system will never see the limits of the Heim joints. The 5-Link is the best riding suspension out there for the FFR provided the proper springs are used, the rear suspension has no bind whatsoever. Now you could do a 6-Link, as you are calling it, but to do it right you would need to use control arms with heim joints on both side of all of the control arms. That would give you the flexibility in the suspension similar to that of the Levy 5-Link. The next thing I am going to tell you is to ditch the FFR springs on the coil overs. The rates on the springs is far from consistent. When corner weighting the car with the FFR springs we found close to a 70 lbs difference in the rear #350 springs and 50 lbs difference in the front #500 springs. I switch over to Eibach springs and they were within a few pounds of one another or close to perfect. On a car with a chassis as stiff as the FFR is, a 70 lbs difference is huge. I also dropped the rears down from 350 lbs to 250 lbs and the fronts from 500 lbs to 425 lbs. I know this goes against the conventional track wisdom but with the front anti-swaybar the car plants well and the 5-link keeps the rear on the track surface as well. Running 18" wheels and tires the drop in rating also give a bit better ride on the street. The last thing I would tell you is that tire pressure is a huge issue with the dreaded snap spin. 1 lbs of pressure for every 100 lbs of car is a good starting point but not ideal. Tire wear is going to tell you what pressure to run your tires at. The sweet spot on my 18" tires for the street is 18 lbs in the rear and 19 lbs in front. Track temps allow a little bit less pressure. Mike is a great resource, he has allot of track time so keep his # handy.

[Mike N]

Frank.

My rear set up is very similar to Gordon's. I am a tinkerer as you know and I studied, CAD modeled and analyzed the rear suspension and as a result there were a couple of things I wanted to do a little differently to Gordon's. I'm very happy with the result. Even with a couple of pieces that I paid to have machined I have less than $600 in my rear suspension. Of course I have about 100 hours of fab time in it so it wasn't 'cheap' if you include labor.

I'm curious to see how Bill's rear suspension works with the watts link and 4 link. With the soft rubber Ford bushings I have a feeling that it might actually work quite well. I'd love to make a couple of auto X runs with the watts disconnected and then a couple with it in place to see what sort of changes it makes.

[skullandbones]

Hi Frank,

You were right, I haven't saved a lot of money by doing the DIY version of the watt's link. I may have about $550 in it with some extra parts and metal left over in the project. I did it mainly as I needed a customized cross member to fit with my sunken battery box. Did not want to change that an re-route electrical at all. Fays2 was a good value but just would not work. I also wanted a strictly bolt in system. So far that is following plans. My plan was to go from the 4 link to the "6 link" for a short time period to experiment. I don't expect any life changing results but it will be interesting to have that knowledge. I feel the 4 link is severely limited by design so fixing it is unlikely. However, adding the rod ends to everything would be another interesting experiment. I don't want to invest that much in parts and modification of the UCAs and LCAs to prove it. Sticking with the transitional aspect, I will try the Poor Man's 3 link which will consist of removing one UCA. I think that will be most interesting. It would be nice to stop there if it worked well except for changing the UCA for the sphericals and swedged tube. If there are observable limitation to this setup, then it's on to the custom 3rd link mounted off the old 4 link brackets. This is easier for me as I do short projects much better. I noticed from a picture of Mike's system that he migrated to lower control arms that fully articulate. So that is a logical move, as well.

This was supposed to be a summer project so I think it will take most of the summer to evaluate this stuff as we don't have a lot of opportunities to get out in this heat (my personal opinion). I hope to have enough progress made by the time I track down an AX event that I can benefit the most.

I told you I always learn something from these conversations. I did not know that FFRs springs varied that much from published values. I have a MKIII with 450/250 front/rear springs. The kit was delivered on Apr, 2007. So I don't know where FFR was getting the springs they included in the kit. I'm a little early in the process to worry too much about them as I have lots of other "fish to fry" for now. Thanks for your data and input. It will be considered as I get deeper into the project.

Note: Would you mind how you are measuring the spring rates?

WEK.

[CraigS]

I went from 4 link to ffr 3 link. The first most obvious change was that the car rolled more. This is to be expected when you lower the roll center. It was also much more stable particularly in entering corners. I wouldn't say that a surprise over steer couldn't happen but it seems to be more gentle when it does.I quite soon added a vpm rear swaybar. There are a couple of things to look at in the rear suspension. I'll call one the rear view which is where roll center shows up and affects how much the car rolls and also the handling balance when compared to the front roll center. The other is side view. The angles of the links determines anti squat and roll steer. Of course these overlap in real world driving since you are often cornering and, either accelerating or decelerating, at the same time. One thing to note when comparing an ffr 3 link to a similar setup but w/ a watts link. In theory, if the roll centers are the same, the handling should be the same w/ either the watts or panhard. One advantage to the watts is that the roll center stays the same in either a right or left turn. A panhard varies in right vs left depending which side is mounted to the frame. A disadvantage to the watts comes when you want low rollcenters. The height of the panhard determines RC in that setup. But the height of the propeller pivot determines RC height in the watts. But you have the lower half of the propeller hanging below the RC, so that limits how low it can be.
WEK said... "I feel the 4 link is severely limited by design so fixing it is unlikely. However, adding the rod ends to everything would be another interesting experiment. I don't want to invest that much in parts and modification of the UCAs and LCAs to prove it"
Sure wish I could find it again but 4-5 yrs ago I saw one of the top Mustang aftermarket firms mocked up a 4 link w/ rodends in both ends of all four links. They found that the rear axle wouldn't roll at all. The original design needed rubber bushings to work.

[skullandbones]

Hi All,

I have heard some individual reports of bad behavior of the 4 link that goes away when changed to another type suspension. One thing that Mike mentioned was that he noticed less skittering (paraphrasing) on wash board with a 3 link. I guess that means it's staying on the ground a little longer than with the 4 link. Craig you are saying the rear end movement is more predictable. I have a question. At what speed (minimum) and type of turn will give you the first indication that there is a real difference? When I'm driving the roadster it is so stiff, it doesn't feel like it is giving at all. I know it is but there doesn't seem to be much movement like dive, squat, or roll in any direction. Maybe it will be easier to recognize than I think but right now, I have no idea what to expect.

Regarding the 4 link experiment with the hiem joints, I wonder if they used rod ends that will take a lot of misalignment. The "rock ends" that Speedway carries are made by QA1 and operate at a misalignment of 36 degrees. The rod ends I have for my watts link do not articulate very much at all. However, they are nearly perfectly aligned and don't need that travel. I can see how that exercise would fail miserably if they didn't use the right stuff. It would probably bind worst than the bushings.

Thanks for the accounts of your exploits!

WEK.

[Jeff Kleiner]

Bill,
RE: the lack of roll or movement with rod ends in the control arms. No matter how much articulation the rod ends allow with the splayed upper arms it becomes an impossibility for the axle to move freely in any axis other that straight up and down...think of it as a triangle with the chassis forming the wide leg at the forward mounts and the two UCAs creating the other sides, meeting at the axle. The wide base (chassis mounts) is a fixed distance. If you were to try to raise one side of the axle one of the arms would have to get shorter while the one on the opposite side would have to get longer. Obviously with solid arms and rod ends that can't happen (well, without bending things anyway!). With rubber or poly bushings the compression & extension of the upper arms as they move through varying motions occurs in the bushings themselves. When those bushings reach the limit of their allowable movement the suspension binds fully and changes the loading of the chassis which usually produces that much referenced snap spin.

Jeff

[skullandbones]

Jeff:

That's a good way of looking at the problem in the design. I've seen 4 links that worked a lot better than this one (racing and hot rodding) so when I saw the "Mustang" 4 link on my roadster when I was assembling it, I thought it rather odd. My logical side was saying, can this even work? So I guess it is what it is. That's why I will be going to some type of third link eventually. I'm hoping I will be able to figure out a good fabrication for the mounts. They present a great solid platform but they are arranged at odd angles so it will take a little bit of imagination.

I don't know where the ideal location is for the roll center for the rear end of this car but I am betting that it is just south of the centerline of the pumpkin/axle. That's why I followed the other style watts link systems out there and put most of the adjustment for the bell crank higher. I also have a little limited adjustment on how far I can move the lateral links to match the location of the pivot point. The clamp on brackets have 6 adjustment holes but they are pretty close together. We will have to see how it plays out.

Thanks,

WEK.

[skullandbones]

Received the tubes for the lateral links and started putting it back together for the nth time. What I spent most time on was rearranging the spacers, washers, and shims on the bell crank to get it functioning without too much play (hand fitted) and clearancing the rod ends at the axle brackets and the bell crank. The last surprise was when I lowered it to the ground. One of the lateral links does not line up like I expected so that will have to be moved to another adjustment point. I think getting the links lined up for each adjustment will take some documentation so I don't waste time doing by trial and error. I probably won't need the full range of adjustment but being able to raise/lower the chassis and adjust the bell crank along the 7 adjustment holes on the cross member is an advantage. Once the lateral link is moved to get it parallel, I will do my first test drive. I found a place to do a test drive. Will do a video to give you a look. Thanks, WEK.

[CraigS]

I haven't done a re- research of Watts links but, as I remember it, the links do not need to be absolutely parallel to the ground. The RC is determined by the height of the propeller pivot and not by the link attachments to the axle. Of course, w/ your style of attachment to the propeller, you need them well aligned so the rod ends don't bind. As quick tests, I think you could move your propeller up or down one hole w/o moving the end attachments. BTW, the RC on the FFR 3 link is about at the height of your lower propeller link in the second pic when the ride height is somewhere in the 4.25 area. So your RC as shown is somewhat higher. BTW2. Sorry I can't give more details as my last 4 link to 3 link conversion was in 2008 so memory of details is gone. I had done it first on my MkI in 06 and then wrecked that car in 07. In 08 there was no question I would also do the MkII I had bought. I did run a couple of autocrosses w/ the 4 link. Ran pretty soft rear springs (250?) and all rubber control arms w/, I think, 550 front springs and a 3/4 front bar. The car wasn't terrible that way but that was back when I was running street tires so it wasn't very good test.

[skullandbones]

Today was the first day back on the road after installing the watts link. I found out by accident (should have figured it out before) that the clamp on axle PHB brackets become mirror images of each other when you invert one. So I had not figured that out until after a couple of adjustments with the lateral links. Long story short, I can put the rod ends in the bottom bracket hole on each side (or 2 up on each side, 4 up on each side) and it puts the links in the correct position. It was a happy accident I guess that the spacing between the two brackets matches well with the length of the bell crank. That's nice!

I drove about 40 miles today on varying surfaces and some freeway driving. The object was to see if I have any issues with the installation as far as rubbing, binding, etc..... There was no evidence of that. I still have to raise it on the lift to check for any damage or rubbing but it was super quiet in the rear for the entire time. I didn't expect anything spectacular as it is the same 4 link with the added watts link or my first "6 link". There were two instances when I felt like there could be some change but it's too early to be sure. One was when rounding the tight curves in my neighborhood. I tried taking them as quickly as possible without sliding too much. I think there was a little difference in the way the whole car rounded the curve. It just seemed more precise and I had trouble getting it to slip sideways at all. I was not at high speed but faster than you would drive it normally. I also noticed on some wash board and loose gravel that the car did not skitter around like it has in the past. I am reserving judgment on making any definite claims until I can remove the watts link and drive the same territory tomorrow or the next day. There is a cool drive with finished streets and no houses and a circle I can use as a "test track" but today the sheriff's deputy was using it as a radar post so I couldn't take the opportunity.

I didn't notice any negative feedback from the rear suspension from this little drive. But I really can't absolutely confirm any differences until I check it with just the 4 link and then again with the watts link hooked up. I'm hoping that I will see some variation between the two setups. After that, we will go on to the Poor Man's 3 link to compare that change.

Thanks,

WEK.

[skullandbones]

Took the roadster out for a drive with the Watts link disconnected. So I've had one drive with and now seeing if I can tell any difference. I rubbed bar soap in the inside edges of the fenders where they would contact the tires. There is a 5/8 inch space between the fender edge and tire at ride height. I have not experienced any tire rub on compression, rebound, or against the fender so far. This was just to verify that the tires were not hitting the fender even a little with lateral forces applied. I saw no white tire marks and honestly after driving the roadster once with and once without the Watts link within a day that I can 't really see a difference. If there is, it is not significant. So I will make another pass with the Watt's link attached (then it will remain installed) just to check again. My goal is to transition to a 3 link in steps but this will give me some evidence if asked about the experiment in the future. Right now, I would have to say the Watts link doesn't have an effect either way with the 4 link. If I had the place to test it (higher speeds safely), I would see if the Watt's link helps to reduce the chances of a "snap spin" but that is not doable at this time.

WEK.

[skullandbones]

Took another drive. This time with the Watt's hooked up for the final time. After two days of on and off the lift; attaching and un-attaching links, my conclusion based on the three drives is that the Watts link does not have a significant effect on the 4 link suspension. I will now go forward with my plan to fabricate a 3 link that will replace the UCAs on the 4 link. However, there is one more step before the change to a custom 3 link. There has been discussion about a suspension solution that the Mustang community has used called the "Poor Man's 3 Link" (PM3L) which consists of removing one of the UCAs of the 4 link. Since the suspension points are the same as a Mustang's, I thought I would do it. Of course, this requires installation of a PHB, Watts Link or some other lateral link that will stabilize the lateral motion of the chassis. I decided to try out the PM3L since it was the next logical progression toward a 3 link. I will be fabricating the brackets for the third link while I am driving the roadster with this change. I'm using the ends from the UCAs for part of the bracket so I will have to stop driving for a while when it's time to weld up the differential bracket. The diff end of the UCA will be used on the OEM bushing attached to the diff with a bar welded across the top of the diff to connect the two bushing brackets. A tab on top and centered on the diff pumpkin will receive the spherical rod end at the diff connection point. Another bracket will use the connection points of the UCAs at the chassis side with a similar tab for the other spherical rod end and link that make up the third link. The third link will be app. 10 inches long. My plan is to make it as level as possible with the ground to avoid any pinion angle issues. Not sure how long it will take me to finish the fitting and welding as it is tight and tedious in that area. But I will be driving with the PM3L until the custom link is ready. Thanks,

Note: one reason the PM3L may work better for the roadster is that the attachment point is directly connected to a frame. On the mustangs inherent weak points were where the UCAs attached to the unibody. Serious racers usually had to reinforce those areas with backing plates. Even if the PM3L works, it is just a temporary setup. Wish me luck!

WEK.

[CraigS]

I wouldn' t use two ends from the 4 links. You need at least one end w/ a rodend so the car can roll in relation to the axle. Here is a source for steel and aluminum threaded tubes etc.
http://www.afcodynapro.com/store?sea...&=Search+Store

[Mike N]

Bill

Your top link will be quite short and even though roughly the same as the factory upper still not ideal. Because of the difference in lengths of the lower and upper link the pinion angle will change with suspension travel. I don't know that this will be an issue or not. I agree with Craig, rod ends would be my choice to the upper link ends.

By the way I don't think you would expect to feel any real difference with the watts until you get to the limits of lateral traction. Any big empty parking lots near you?