Unstable steering at speed

[EZ$]

Haven't been taking the car on many longer trips, but this past Sunday I went to a C&C about 65 miles from home with a friend. I'm running PS with a stock Mustang PS pump that I modified the internal spring by cutting, I believe, 7/16" off to lessen the pressure and the amount of assist it provides. Anyhow, when on the freeway I noticed that the car wanted to dart back and forth in the lane, but what was concerning was that it didn't seem to be from input to the steering wheel, and when correcting it seemed to over-correct, thus making the movement worse. I don't think that it's the PS because during a previous long trip it did not manifest itself and was in fact quite stable. The car ran great otherwise so I need to correct this unstable issue to make the car more pleasurable to drive. I'm just not sure what could be causing the problem.

I could really use some help in determining the problem, so if you've had this issue and solved it, or you have some recommendations of things to check let me know.

As a note, I had the car aligned at Roger Krause Racing in June of last year. Here's the printout. 20240424_142909 by Rick Paul, on Flickr
Not sure if this will show anything that might be causing the issue.

Thanks for the help.

[65 Cobra Dude]

I would check tire pressures. You only want about 23lbs and it sounds to me like you’re running much higher pressures.

Henry

[Jeff Kleiner]

As Henry said, no more than 23 PSI. You could stand to have a little more positive caster, say 7 to 8 degrees positive but the ~6 that it shows isn't too far off. Ideally I like to see about 3/32" (0.10 degree) total toe in.

Jeff

[rich grsc]

Am I reading that incorrectly, or is that toe out?

[EZ$]

I'm only running 20-22 lbs pressure. I'm not sure if that is toe in or toe out. It seemed to be driving OK, but this trip it was like a squirrel!

[Jeff Kleiner]

I'm only running 20-22 lbs pressure. I'm not sure if that is toe in or toe out. It seemed to be driving OK, but this trip it was like a squirrel!

If it was good and now is not I'd be giving it a good going over to see what has changed, come loose, or???

Jeff

[Nigel Allen]

Could be a loose part of the steering/ suspension components. Worth going over front and rear components. As the handling of the car har recently changed, it could be a warning that something is coming loose.

[EZ$]

Thanks Nigel! That is on the agenda.

[BEAR-AvHistory]

Did you put a trace line on all your nuts & bolts to see if any moved? Part of my inspection routine is checking that all the lines are still perfectly aligned.

[EZ$]

It's been quite a while since I assembled that area, but I'm sure I did. I plan on getting it in the air tomorrow to check all that out.

[Alan_C]

I bought a Saturn Sky Redline Turbo late last year. The car exhibited the same darty behavior you describe. The alignment was off and all four tires were 14 lbs over inflated. Just goes to show how lame some dealership mechanics can be and the crappy driving manors two issues combined can generate.
In addition to a thorough mechanical check, take a look at the tires to see if you have a tread separation in progress. If the tires are 7 years old or more, time to replace them. Mechanical items rarely change when a car is simply not used. Maybe you hit a pot hole before putting the car away. Do you have a copy of your prior alignment specs for reference. Obviously changes were made to the alignment, but were they good changes, like it was said regarding toe in or out. Just changing the toe number does not mean it was changed enough.
When I had my MK4, I always did a beginning of the driving season mechanical check as it had been recommended by several members. On one trip, a rear caliper bolt came loose and fell out. I missed that one and made sure it was installed with Locktite after it was replaced. I suggest you consider you were experiencing bad driving manors and you did not return home, kind of dangerous no? Sometimes we need to be reminded that these cars are not our daily drivers. When they start talking back to us, we should listen because, as we all know, these cars can bite and bite hard if not respected. It will be interesting to hear what the cause turns out to be. I ordered a Gen 3 coupe a couple of weeks ago and I will do more to make sure the car is in good condition before getting out on the road. The comment about torque stripping the nuts is a good one as you can visually verify something is as it should be very quickly visually rather than have to retorque each and every fastener.

[ydousurf]

If you have ever experienced the speed wobbles or a.k.a. “the wobble-of-death,” you’ll sh!t your pants! Especially if you’re moving at a high rate of speed. On my jeep, I previously had Super Swamper’s and decided when I bought new tires I went with the BF Goodrich brand. The BFG’s were a much softer compound and worked great for wheel’n and snow, but they brought on the w-o-d and I had never experienced it prior on my other tires.

I agree with everyone saying validate anything that may have changed or has become loose on all steering components. Your tire pressures and factor the age of tires as well. However, two questions:
Does the “darting” occur all of the time or was it just sporadic?
And if so, do you recall what that section of highway or stretch of road was like. Meaning, was it asphalt or cement and the possible age too?

Why I mention the road is and you we all know this, but when semi trucks and just normal traffic especially on older asphalt together will create grooved impressions and that has to be factored-in. My BFG’s only tend to be affected by the grooved asphalt. I had been on this particular stretch of highway a couple times on my older tires and never experienced the death wobble.

Now, I’m not knocking the BFG’s. The other variable was my older tires, and they were definitely old and “hardened-up” over the years... So, that has to be factored into the equation.

Anyway, good luck, I hope you solve the issue and let us all know. Stay safe Rick!

Doug

[F500guy]

I would just add, jack up each corner and try to wobble the wheels like previous posters stated to look for loose suspension. Rear steer problems could cause the car to dart. I mention this because even though I am still in my build, A couple months ago (may Update my build thread about this) the driver side wheel seemed to have a clunk and moved a bit. Went through all the bolts and finally narrowed it down to the heim joint on the toe link, frame side. Took it apart and it was very poor quality and the inner race was loose with 0 miles on it. I upgraded both sides to a higher quality heim joint and also the bolt that is used in that spot.

[Al_C]

A little late to this party, but I can share my experience. Same issue on my roadster a couple of years ago. The car felt loose and wobbly at Interstate speeds. My issue was the tie rod/steering rack ends were not tight. They weren't really loose, but they weren't tight. IIRC the torque spec for those are 40 lb/ft. My steering rack is the stock FFR power steering unit. Once they were tight the problem went away.

[Rdone585]

I know you probably have different steering components than I have with a MK II, but I would start by checking the ball joint connections with the spindle. I've had issues and I know others here have as well with them being fully tight, but not fully seated. Then through some exercising of the steering it suddenly becomes loose when it magically seats into the proper place.

[Jeff Kleiner]

... I would start by checking the ball joint connections with the spindle...

Also check the screw in ball joint in the upper control arms. I had one come in for paint a few years ago and when I pulled the wheels I found that one of the upper ball joints had backed almost completely out of the control arm!

Jeff

[J R Jones]

EZ$ There is a potential problem that is most often experienced as darting side to side on pavement with longitudinal grooves cut in the pavement. It is also felt on bridges with steel mesh deck.
The problem is a bent wheel that wobbles enough to "search" on the grooves.
To a lesser extent you will feel the "search" on longitudinal slab edges in the pavement.
Spinning the unloaded tire will reveal a bent wheel.
jim

[MPTech]

Hey @Jeff Kleiner. would you mind sharing you alignment specs? I searched and couldn't find them.

[Jeff Kleiner]

Hey @Jeff Kleiner. would you mind sharing you alignment specs? I searched and couldn't find them.

Mark,

Power steering street car:
7 to 8 degrees positive caster
.5 to .75 degrees negative camber
3/32" total toe in

If manual steering back the caster down to 3 to 4 degrees.

Jeff

[GoDadGo]

Mark,

I'm running the specs Sir Jeffski outlined and have no stability issues.
4 degrees on the caster since I'm utilizing a manual rack.
My rear is a 3-Link and tire pressures are set at 23.

Steve

[EZ$]

Hey guys, a lot to digest here. I'm going to try to go through this over the next few days. Once I find something I will definitely post it here. Thanks for your concerns. As a note, Alan, you are spot on regarding my continuing on the trip. When I first noticed it, I thought I was overreacting and that the steering was just faster than I remembered, but it probably was not.

Thanks again everyone.

[MPTech]

Mark,

Power steering street car:
7 to 8 degrees positive caster
.5 to .75 degrees negative camber
3/32" total toe in

If manual steering back the caster down to 3 to 4 degrees.

Jeff

THANKS Jeff!

[CraigS]

Since you show negative camber in the rear I assume you have irs. If so, check the camber adjuster in the rear uca. The intermediate adjuster likes to work loose in the uca. FFR recommended red loctite there. I ran mine for several months until I was sure I had camber in a range I could use and welded the piece vs loctite. That meant I had only the rod end to make adjustments with and had to take the bolt out of the spindle but camber adjustment was so infrequent it wasn't a problem.

[EZ$]

Craig, I have the T-Bird IRS, and I don't remember any adjustability in the uca, but I'll check it out while I'm under there.

[Railroad]

Don't forget about the spindle and half shaft nuts. I have read, some did not get torqued properly and became loose.
good luck,

[EZ$]

I'll need to add that to my list!

[Its Bruce]

I had an inner tie rod go bad within 250 miles (cheap repo and probably not in the best shape when i installed it). Play in left/right of wheel is typically tie rod. Play in top/bottom is typically ball joint.

[EZ$]

Thanks Bruce. I can't do anything until tomorrow. When things go bad they go bad. My DD F150 decided that today was a good day for the battery to take a dump on me. It's parked close enough behind the cobra that I can't get a jack into the back of the car to jack it up. Hopefully the battery is charged back up in the AM so I can access it, and I will add that to my notes of things to check.

[Ford & Jeep Fan]

Could be a loose part of the steering/ suspension components. Worth going over front and rear components. As the handling of the car har recently changed, it could be a warning that something is coming loose.

I was just thinking this.

[EZ$]

OK, so I'm finally tearing into this. Why did it take so long? Don't ask. Anyhow, I had torque marked all of the bolts and nuts in the front suspension, and nothing has moved. There is no movement of the wheel assembly when off the ground and trying to move it. The more I search, I'm thinking that it may have been the loose nut behind the wheel!

I'll keep looking since I have it in the air, but at this point I'm not sure what else to look for. It may have been the road surface. I680 and Hwy. 101 are a disaster and may have contributed to the situation. If anyone has any other ideas, I'll take them. I'm not the best mechanic, and I don't have much experience. I really tried to be as careful with the build as I could. I'm also wondering if the PS still has too much boost, even though I cut that spring according to a thread from way back. If that is the case, is there any way to maybe add a heidts valve in the system somewhere to dial it down when driving on the freeway?

Thanks again guys.

[AC Bill]

I have read numerous reports of driving issues similar to what you describe, car seems to be darting, over sensitive steering, etc., and they were all related to the toe settings. It's been a year since your alignment was done. It may be worthwhile having it checked again now you have put a few more miles on it. I see you had it done with only 500 miles. I would think that would have been enough miles for everything to have settled into place.
Did the IRS rear have all new bushings? I know that worn bushings in the rear can have a factor on steering, and how the car tracks.

I also notice the vehicle listed on the alignment print-out is for mid 60's Mustang. Perhaps the specs should be for a different year? Otherwise they have really nothing to work with, since it's all computerized these days.

When I had my alignment done I brought my FFR build manual that had the specs listed for it. They adjusted everything based on them, and the roadster tracks like it's on rails.
Good luck.

[EZ$]

Bill, I was thinking along these lines as well. I'll contact Krause Racing and see what can be done. I drove it today and the steering seemed a bit quick, darty is the only description I can come up with. Since my DD is an F150 which is anything but darty, I may not be the best judge! One good thing is that I had a squeaky DS rear brake that has been driving me a bit crazy lately, and it appears that I got that corrected, YEAH!

I'll have the alignment double checked and see if that corrects it. If not, I guess I'll have to look into some way to lower the sensitivity of the PS to see if that helps. can't think of anything else to check.

[CraigS]

I cut a bit more from my spring than the accepted 7/16". I actually cut a little too much but no problem. I took the spring to the hardware store and found some nice SS washers that matched the OD. Used them as shims. Previously I had a Heidts valve. I didn't like it because, when I adjusted it to give the assist I liked on the road, it would sometimes lose assist in a parking lot when idling along in 2nd. One other thing to experiment with is drop front tire pressure to 18#. Yep, I know that is low, but try it and maybe you will settle at 20-21#. BTW, is your rack a 3.0 turns lock to lock? If it happens to be 2.5 turns, find a new rack. I tried a 2.5 and it was just wonderful in an autocross. But I didn't like it on the street. Had it in the car in April and figured I would get used to it on the street. About Sept I decided I would never like it so I took it out and went back to the 3.0 rack.

[Jeff Kleiner]

Rick,
RE: reducing PS pressure. I run a Heidts valve and vary the assist depending on what I'm doing with the car; full boost for autocross, reduced on the street HOWEVER whether turned up or down the car drives the same. The only thing that changes is the amount of effort it takes to turn the wheel. The car doesn't become more "twitchy" or unstable at full assist than it is with it reduced...I just have more resistance at the wheel with it turned down which is my preference for everyday street driving. BTW, I'm using the 2.5 turn rack and it's one hand rock solid at 85-90 MPH.

Jeff

[rich grsc]

You never replied to my question, do you have toe-in? Your spec sheet shows a positive toe number, so is that just how the print out records a toe-in setting?

[EZ$]

Craig, I'll have to double check on the rack. It was a PS rack out of a Mustang, (have to check the paperwork as to what year). I'm currently running 20 lbs all around

Jeff, that was what I had hoped for. It just seems too sensitive at speed, but like I said, it may just be me.

Rich, I was actually hoping that someone with more knowledge about those printouts would answer that. I had told them the specs that Jeff had listed, and I assumed that they had worked towards them. And yeah, I know about assuming!

I think I'm going to start with having them tweak the numbers, increasing the caster to at least 7, and confirming that it is toe-in. From there I'm not sure what I'll do. Maybe just drive it a bunch more and see if it's just a matter of getting used to the way the steering feels.

[ProfessorB]

Regrding rack ratios (see thread entitled "Mark II steering Upgrade" for more details) I did quite the dance changing racks to a slower ratio. One problem is that lots of parts suppliers do NOT list the actual ratio in their specs. The do list turns lock-to-lock, but that can SOMETIMES be misleading and sometimes not. My own original rack was just over two turns lock-to-lock. My replacement rack was three turns lock-to-lock. But the way to compare them FOR SURE was to measure tie rod travel for one turn. I cant remember now the measurements, but the replacement rack had less linear travel (of the tie rod) compared to the old rack (each rack being operated exactly one turn). Also, lots of autoparts suppliers mix and match the racks indiscriminately. They have different part numbers for slow and fast ratio....but you don't necessarily get what you order. A dozen phone calls to BBB (O'Reilly's rack supplier) confirmed this. I finally got the correct rack thru Unisteer. They DO understand the difference in raio and you WILL get the ratio you order. Get it thru Summit because their price is cheaper than Unisteer direct.