Mysterious front end shake at speed
 

We're dealing with a front end shake on SPF1833 vintage mark III. Starts at 65 and seems to end above 85. Seems to reduce when power is applied or going into a corner. Balance is perfect, tires new, wheels new, alignment perfect. All double checked.

Could it be the infamous Ford Death Rattle?

Stumped and looking for ideas...

%/

Front wheel bearings ?? or switch the front tires from one side to the other and see what happens....

Cobra Valley designed and built some new upper and lower balljoints that they say addresses this problem.

I know Randy takes a lot of time proving out what he does, and from what I have read on the SCOF site, everyone is very happy with the new balljoints.

Cobra Valley's R/T Super High Performance Ball Joints

This topic has been beaten to death over the years. It's the tires, they're not really round. Are they BFGs perhaps?

Even a square tire can be balanced. Many tires leave the factory with either (or both) a dimentional or dynamic out of round. If you have a set of those you get a harmonic at the speeds you mentioned.

Get the tires "trued". There are machines to do this.

Major Racing Traction in Bridgeport. They're at 20 Union Avenue, 203-367-7223, talk to Dave.

Bob

It's probably the tires, if you can get a set off another one and see if it's still there. I had the same problem and my rims were bent.

If you are convinced that your tires/wheels are not the cause, then you may want to look at tightening up your rack/pinion. I've been fighting a high frequency steering wheel shake what only occurred between 60 and 70MPH. My tires are not out of round and neither are my wheels. The entire front suspension was analyzed, and the root cause of the problem was that the steering rack adjustment was set a tad too loose. Once it was tightened up a bit, then high speed shake disappeared. Hope this helps...

YMMV,
Randy...

From my notes from Dennis O.
On the front of the rack at 90 degrees to the pinion input is an adjuster.
Loosen the locknut (17mm) and turn the center stud down a little (7mm).
This adjusts a nylon pad onto the back side of the rack and pushes the rack onto the pinion taking up any slack in the gear mesh. If you over tighten the stud the steering will be stiff, so only make small adjustments. The nylon pad wears quickly in the first 1000 miles. This should fix most of your shimmy problems. If it still persists your tires are at fault.

I've got the same vibration problem where excessive shaking occurs approximately in the 60MPH to 75MPH range. I've had the problem from day 1 of buying the car and have tried dynamic road balancing of my wheels/tires three times with no measurable improvements. I also replaced one of the wheels and tires as it was questionable whether one of the Michelin tire was out-of-round. The front wheel was also replaced in the process as an idiot changed the tire and wreck the original wheel in the process. In summary, I've been struggling for two years with this car with no progress in resolving the issue (very frustrating)! After reading through the various cobra forums, I see a recurring theme with the shaking issue and yet many of the folks reporting the same problem are running wheel sets varying from 15" up to 18" ... so I'm not convinced it's a wheel/tire issue anymore.

To make matters worse, I've never raced or tracked the car or even spun the tires ... this car has been pampered it's whole life. And now the latest ... while driving 30 MPH down a crowded city street last Friday, my right front caliper and bracket somehow came off the car causing me to loose my brakes and almost have an accident. Fortunately, neither myself or anyone around me was hurt and I managed to get the car off the road with hitting or killing anyone. While all of the damage is still being assessed, I know that the right front wheel, the caliper of course, and possibly the upper control arm were damaged and will need to be replaced. For anyone out there with later model Superformance Mark III cobras, I recommend that you have your car checked over carefully as this kind of brake caliper failure at speed could prove deadly. Safe driving to all!

Thanks for all the replies on this. Certainly some good ideas for us to look into. I will come back with our solution given we actually find one. I am all ears in the mean time...

Since most of our cars do not use "rag joints" in the steering column the problem is more pronounced.

Most production cars, both past and present, come with "rag joints". Go out in the garage and take a look.

Bob

drthomas999,
There was a known problem with caliper bolts on a series of Superformance cars a while back in 2009 I believe..
Cars in the range of chassis #2600-#2975 is where the problem occurred. "Inadequate thread locking compound was installed by the factory."
The solution was to remove the mounting bolts inspect and re-apply Loctite #271 on the bolts and then reinstall.
There was a thread or two here on CC about it, just like your experience as I recall.
Contact me if you have questions...my contact info is below.

For all you guys that think rag joints or tightening up you gear boxed will solve this----you are kinda missing the obvious--while it might stop the steering wheel from shaking--the root cause is in the design of the front end and suspension/wheel size/offset etc.

It will take a dedicated effort to individually solve and correct the issues car by car

Jerry, while I agree with most of your comments, on this one I do not. Maybe it's just the verbiage but if the root cause of a mechanical problem is a "design flaw" then the cure for all affected would essentially be the same. If the cure for each is different, then that means that the problems were also different.

By extension if the problems are different, then the root cause of the problems would be in the manufacturing, not in the design.

If the design is at fault then once a definitive fix for a given fault is found then, within a window of manufacturing tolerances, that same fix would apply to other cars built with the same design.
Steve

OK Steve----I think the verbage led you to reaD THAT i MEANT THE DESIGN WAS BAD(sorry about the caps lock)

Here's where I am pointing the finger---A RAG JOINT won't fix the PROBLEM!!! neither will tightening up the adjustment of the rack( Sorry Blas)

The shake is coming from something that can generate a force back thru the steering parts---this can be from wheel balance, out of round, etc---it also can come from caster, ball joint to tire patch alignment, etc----

There are systimatic processes to determine when it does it( 60-85 mph)---is that in a straight line??? how about a long turn to the left??? right??? under braking???these are just some basic examples of ways to isolate this vibration/shake---

In addition to all the suspension sources for shake/vibs---aero can play a big part at those speeds---a small panel can cause enough buffet to shake a 2-3000 lb car---

While some people may have different or additional steering issues...
Over the years the people (Owners of SPF's, VW's, etc) who have adjusted their rack adjustment bolt and have had success with this issue and had no additional problems since. It's a cheap and easy thing to try...and has worked for many in the past. It's a internal wear issue on the nylon washer.
Perhaps if you substitute the word "adjusting" for the word "tightening" this will suffice.

I've got SPF 2932 and I had a front end shimmy that was only solved by balancing the wheels and tires while they were on the car. The vibration does return when the car has been sitting on the cold cement. It disappears after a few miles or if the weather is hot. Thus, I think the tires are flat spotting. Nothing to do about that except to buy some tire cradles so that they never sit flat on the garage floor. I did adjust the steering as suggested just now. Will let you know if this helped any. Also checked the caliper bolts. I could barely turn all of them. Obviously they had no lok tite but they were pretty tight. I have 7500 miles on my car so, I'm not that concerned.

BLAS has a good point if there is clearance between the rack bar and pinion gear then the wheels are free to move due to the free play. The adjustment is there to push the rack bar against the pinion so that there is no play. Normaly there is a spring or a spring washer to help with maintaining the lash. Not sure if ours have that.
One other thing that I found on my car is the I Shaft joint to the steering column shaft was not tight. The bolt was tight but I could move the shaft in the splined U Joint. I did tighten mine up and I do not have the issues that are mentioned. I also have my origonal BFG's and the original balance. The car is a 2003 SPF.

I just tried the adjustment on the rack and pinion. It did tighten up the steering a bit and feels much more solid and smoother now.

Thanks for the suggestion, Blas.

Blas,

On #2613, I see a 17mm nut and two smaller nuts holding what looks like a cover plate on either side opposite where the steering shaft enters the rack. It doesn't look like the center stud is adjustable. I didn't jack the car up, so maybe I'm not looking in the right place.

I'm with GTB, I don't see the 7 mm nut to tighten up. The 17 mm nut is on top of the pinion. Can you just screw the bolt in that the 17 mm nut is holding? My 2608 started to shimmy at about 3,500 miles. I was going to get the front tires balanced, but now maybe I'll figure out how to tighten up the steering first.