My snake is slithering

[my427cobra]

My Snake is slithering.
I’m experiencing a strange suspension movement in my Cobra. It’s slithering from side to side. It just started a week ago .

To be more specific, I’m experiencing a slight yaw (right to left motion) at low, moderate and highway speeds.

It seems to manifest itself as a slight right hand yaw when I ease up on the throttle and a slight left hand yaw when I apply the throttle again.

I’m not talking about full throttle changes, but even at small throttle applications.

Maybe a 1 inch movement in the steering wheel, the car moves over 6 inches to a foot over a 50 to 100 ft distance of travel.

At even throttle speeds, low, moderate or highway speed I experience a slight side to side wandering.

I’ve checked all 4 tire pressures and BFG’s are all at 22 psi. I’ll try bumping them up to 24 and 26.

But I don’t think it’s tires because it just started out of the blue last week. Although BFG's have had reported tread problems.

Doesn’t seem steering or front suspension related as it’s manifesting itself as throttle changes.

So I’m thinking rear suspension movement side to side.

I have a Ford Lincoln Versailles 9 inch rear axle with 2 lower forward swing arms about 20 inches long (hiems at the axle and urethane solid rod ends at the front attachment to the frame). A center link , about 8 inches long at the top of the pumpkin is centered on the axle and attaches to the upper frame hoop (works as a center swing arm and pinion angle setting). And a 24 inch panhard bar from the bottom of the pumpkin to the right hand frame member with hiem joints at both ends

All the bars are parallel to the ground when the car is sitting on the ground at normal ride height.

So I’m thinking, if the rear axle is “steering the car” as the throttle is released or applied, could the axle be rotating slightly due to a bad joint somewhere?

Shocks are Carrera adjustable with 275 lb adjustable 10 inch coil overs. Don’t think it’s the shocks because the ride and handling seems the same.

I also have a rear sway bar but unlikely that would cause the problem.

So I’m asking if any of you have any other suggestions.

I’ll get the car in the air and start checking all the joints and their fasteners.

Cheers
Greg

[t walgamuth]

I'd bet on the heims being worn or a bad one, but the sway bar being loose on some cars will cause yaw on throttle changes. The cobras are so short and wide they'd move around much more than most cars.

[my427cobra]

Hi t walgamuth. I would think that a "loose" sway bar might cause a yaw problem in a cornering situation, but my problem does not seem to be evident in cornering, just occurs in a straight line.

Cheers
Greg

[Chilibit]

i would inspect rear wheel bearings Start with right side.

[Jerry Clayton]

Are the lower links parallel or angled? How much?/ what is mounting distance width front and back ?
I had a 3 link drag car and it was complicated

[my427cobra]

Hi guys. I will check the axle shaft bearings.

I'm sure it's will be some wear problem in a joint or bearing as the car has performed/handled flawlessly for the past 7 years since I completed it.

I'll get to work on it in a couple of weeks and let you know what I find.

Cheers
Greg

[66gtk]

Originally Posted by Chilibit

i would inspect rear wheel bearings Start with right side.

Yes, easy to assess. Don't drive that car until you figure out what's going on. Should be obvious when you find it.

[my427cobra]

Good advice and thanks guys.

Cheers
Greg

[patrickt]

Or, you could just ignore it, run the car real hard, and whatever it is that is starting to go will eventually fail catastrophically and then it will be easy to spot.

[my427cobra]

I don't know Patrick. Sounds like an expensive repair process.

Cheers
Greg

[Jerry Clayton]

so no answer to my question about lower link angles??

Also with a very short drive shaft, an extreme amount of u-joint angle change up on acc/decell can cause thst---

My 74 Pantera had one bad joint in the drive axle and it was very wierd accel/decell in corners!!!!!!

aLL BARS BEING PARALLEL does not help ------angles are what stabilize things

[my427cobra]

Hi Jerry. I was offline for a while.

All the links are parallel to the ground.

The longer, lower leading links angle in slightly to the car's centerline.

It will be tomorrow or Tuesday before I get under the car to get an exact measurement/angle.

Cheers
Greg

[CHANMADD]

Your thrust angle is off...

[my427cobra]

Thanks CHANMADD. I will check that also. It could be possible it went out of adjustment (the top center link).

The problem has just manifested itself after perfect driving for years.

Cheers
Greg

[xlr8tr]

Originally Posted by my427cobra

Thanks CHANMADD. I will check that also. It could be possible it went out of adjustment (the top center link).

The problem has just manifested itself after perfect driving for years.

Cheers
Greg

Possible bad shock, or one has worn more than the other. This would translate into more suspension travel on one side with throttle application, and with your suspension type that creates rear steer. Think about the geometry: if you push one side up, with parallel upper and lower links that are both parallel to the ground, the side being pushed up is effectively getting shorter, pulling the axle forward. This is what Jerry is talking about above... lots of crazy stuff going on that is hidden by springs and shocks, until something goes off.

[my427cobra]

I'll get the car up in the air Wednesday and trouble shoot it one step at a time.

1) I'll start by checking all the rod ends/heims/bushings

2) replace as necessary

3) check the shocks

4) check the sway bar links

5) check all fasteners, replace as necessary and retorque all fasteners

6) remeasure for square/alignment/pinion angle

I'm pretty sure it's one of the urethane bushings as I can see the shoulder of the one on the passenger side is broken /missing and may be causing some side to side play in the lower arm where the forward end attaches to the chassis/frame bracket.

We'll see.

Cheers
Greg

[hauss]

Just a thought but if you have a limited slip try adding more additive are better yet change the diff oil and add the additive . I had a jeep that would do exactly what you are describing .they too are short wheel base.

[my427cobra]

OK Egg on my face!!!!!!!

Went out today to work on the Cobra and the drivers side rear tire was FLAT!

Seems the valve stem seal has a crack in it and was leaking air.

I may have been driving home from last weeks car show on a "soft" tire and most likely this was causing my strange handling.

How did I not guess that???????

I'll check everything else just as a precaution and will get the valve stem replaced.

Thanks for all the inputs.

Cheers
Greg

[patrickt]

Originally Posted by my427cobra

OK Egg on my face!!!!!!!

Went out today to work on the Cobra and the drivers side rear tire was FLAT!

These cars are more sensitive to tire pressures than most people think. Kind of like the Corvair….

[t walgamuth]

It is always easy to overlook the simple. Good solution for you and your pocketbook!