3 Link- Twisted sister

[ehansen007]

Hey guys,

I just experienced this with my 33 and thought I'd put it up here. It appears most haven't had this issue thus far with the 33 but it's somewhat common for the roadster guys considering how much racing is done (and the sheer number of roadsters on the road). Bolting on the 3 link bracket is simply not enough. While some will say that cars with more torque than stock, drag race applications, etc, etc, will cause this, I'm hear to say that 300HP and 300 lb/ft appears to be enough to twist the rear into submission and bend the bracket. Personally, I bought a used rear end and I"m not sure how well it was treated before I got it but I think my axle housing may have twisted as well inside the pumpkin as I had tranny oil coming out the seam. You could see the paint was worn off and the bracket was twisting on the axle but I my have broken the tack welds on the axle/housing interface as well.

So, after doing the research on the roadster forums, it seems that Breeze and VPM have solutions for this. The VPM will work with the factory dog ears on the housing- but I cut these off. DOH!. As for the breeze method explained here http://www.breezeautomotive.com/imag...stallation.pdf, dependable sources are telling me that this much welding to the axle housing (pumpkin) can cause significant damage via heat and will take the axle out of alignment which can ruin the bearings and the driveshafts. So, I'm going to do a couple of tack welds at 180 from each other on the housing/axle interface. and then install the 3 link bracket and do a few tacks there as well. So I'll be doing a light weight version of the Breeze setup which will allow me to remove the bracket with an angle grinder if this should ever happen again.

I appreciate and welcome any input here. Wish me luck!

[myjones]

Hey guys,

I just experienced this with my 33 and thought I'd put it up here. It appears most haven't had this issue thus far with the 33 but it's somewhat common for the roadster guys considering how much racing is done (and the sheer number of roadsters on the road). Bolting on the 3 link bracket is simply not enough. While some will say that cars with more torque than stock, drag race applications, etc, etc, will cause this, I'm hear to say that 300HP and 300 lb/ft appears to be enough to twist the rear into submission and bend the bracket.
I appreciate and welcome any input here. Wish me luck!
]

Erik
Looks like that bracket should have been boxed or at least had a gusset or two. A few tack welds would have helped as well.
I intend to stress my 4 link with over 500/500 and as near perfect anti squat as I can produce. Plus I hated to lose the space for the big banana bracket since that's where my fuel tank sits. I did add swivels on every control arm to reduce binding in an attempt to have the best combo back there. I was discouraged from welding the axle tubes to the pumpkin because of the cast iron to steel joint and they said under 700 HP typically doesn't damage that connection. Can you tell if side load had any part in the damage or if it was all rotational stress?
Dale

[ehansen007]

Well, the markings on the axle seem to indicate that it rotated quite a bit until it got bound up but I can't really be sure how it all went down. I think it was hard launches out of the corners at the autocross that did it.

[Tom Veale]

Hi Erik, When we installed the 3-Link on my Challenge series roadster we tack welded the bracket to the axle tube. That car's been through a lot and never bent up the bracket. That said, it also only produced about 250 rwhp and maybe just shy of 300 lb-ft torque.

So far I've not had any issues with the '33, but then again I only have 7K miles on it and only a few track days. I've never been to the drag strip with the car and also am running a "touring" type compound tyre, so that might have saved it from the dreaded "Banana Bend." When the salt's off the roads here in WI, I'll give it a good inspection. Thanks for the heads-up.

Best regards, TV

[michael everson]

Tom. I'm not positive but pretty sure I welded yours.
Mike

[Olli]

I welded mine.

Olli

[esff32]

That really blows Erik. Stack used this one from Vintage Performance. It won't help you because of the dog ear mounting design but I wasn't sure if you were going to replace the rear end or not. It is $115 plus shipping.

[frankeeski]

Erik, I think while I was at it, I would box the bottom portion of the back of that bracket as well. What ever forces you are putting on it, it is twisting.

[Arrowhead]

Wow that sucks Erik. Like I always used to say, "beat till it breaks and then fix it so it don't" Course that got pretty expensive and that's why I "used" to say it. I think there was another case of a hot rod spinning a three link posted recently also.

[ehansen007]

Yeah Stack hit me up via text with the VPN solution which of course won't work. I'll box in that lower section as well. I think it's left open so you can get to the bolt on the bottom. Most seem to believe that if you just make a few strategic tack welds, none of this will happen.

[sheephearder]

Erik, I have a bolt on bracket that came with my kit that I don,t use cause my 3 link rear end from Mosier came welded. If needed, let me know. I could get it to you in a couple weeks as I'm getting my 2nd knee replacement Monday. Thanks for your information on this problem as we all will learn something from it.

[Arm7419]

Erik

Check out the Banana Bracket Brace Kit on www.vintageperformancemotorcars.com. I used this on my car.

Chuck

[peakengineering]

That looks pretty nasty and with only a few hundred ponies, Im thinking about fitiing a second banana bracket and rod to the other side of the housing, effectively turning the 3 into a 4 link, any thoughts on this modification ?

[erlihemi]

Hey guys I'm new to the F5 world, but this rear diff issue is something that occurred to me at the Howell build school. The weight transfer and torque characteristics for these cars is much different as a corner turner than as a sticky launcher. If you have a combination that is getting the rear to "hook" and you have sticky tires I don't think the F5 set up is beefy enough. I would like to know if anyone is setting these up for drag racing and if so how they are getting enough weight transfer to "plant" the tires. I would like to be able to build a 3 link for cone weekends that is robust enough for Friday nights at the local drags also. maybe that's not achievable with this chassis??

[Doutie]

Ehansen, To address the issue of welding on the housing, some simple information needs to be applied. As the weld cools from a liquid metal state to a solid it shrinks. This shrinkage can cause issues but doesn't have to. If you weld around the tube, say for an inch on one side of the tube and nothing on the other side of the tube, The weld shrunk one side but not the other. This causes the tube to bow and can put the axle turning inside the tube out of alignment. If you weld along the length of the tube there is far less distortion. Take a moment to look at big truck suspension and note how the spring perchs or suspension hangers are welded to the housing, along the length and never across the tube.
I deal with truck suspension for a living and what I see happening to this brkts, tells me they are too light and anchor poorly for the loads being applied. If mine bends or comes loose I will upgrade the outboard plate of the bracket to 3/8 and add two 1/4 gussets which weld to the outboard plate and to the axle along the length of the tube. None of the bracket itself would be welded to the tube because those weld would be across the tube. The gussets would be placed, angled so prevent rotation of the bracket on the tube. The gussets would provide the stiffness to prevent the bracket from bending to the side as in the picture.
I'm no engineer , but I hope this gives you some ideas to throw around. Doutie

[Arrowhead]

Hey guys I'm new to the F5 world, but this rear diff issue is something that occurred to me at the Howell build school. The weight transfer and torque characteristics for these cars is much different as a corner turner than as a sticky launcher. If you have a combination that is getting the rear to "hook" and you have sticky tires I don't think the F5 set up is beefy enough. I would like to know if anyone is setting these up for drag racing and if so how they are getting enough weight transfer to "plant" the tires. I would like to be able to build a 3 link for cone weekends that is robust enough for Friday nights at the local drags also. maybe that's not achievable with this chassis??

I don't think the chassis is the problem, in fact the frame is much stiffer than a traditional ladder type frame. I haven't heard of anyone ripping off the suspension mounting brackets either for that matter. Even FFR will tell you if you want to drag race, go with the 4 link rather than the 3 link. A serious drag racer will probably build their own rear suspension anyway as the supplied upper and lower links are non adjustable for length or angle. Personally, I have the 4 link and frankly, I think I would need to toa lot of upgrades before I would see the handling improvements of a 3 link.

BTW, where are you located in upstate NY?