Cobra swerves when backing off the throttle!!

[commercialcobb]

When I put the 429 under power, a great deal of power, when I lift to make a turn or any other reason for that matter it swerves like crazy.. Scares the hell out of me! It always seems to want to dive left when I lift off the gas. Is that something with the torque and rear tires?? Maybe the suspension/alignment? Or do I need to get a swaybar to stiffen the suspension? Kind of a broad question but has anyone encountered this before and if so what was your fix? I am just looking for a place to start narrowing down the diagnosis to what ever may be the culprit.. Any help would be great, you guys have help me so much already in the past..

[Jac Mac]

Someting is moving in your suspension to make it do that, like a bush deflecting etc. Its 'normal' for some types of LSD, Traction Lok's etc to cause this to a certain degree, but if the problem is really bad then some part of the suspension needs a rethink. We call it torque steer where as you accelerate it requires a bit of input by you on the steering wheel to counteract ( possibly without realising ) and then when you lift off the two combine to make the reaction of deceleration & your countersteer so violent.

[Bob In Ct]

I'm no chassis expert but I would be very careful about making the back end any stiffer than it is now.

Bob

[392cobra]

Originally Posted by commercialcobb

When I put the 429 under power, a great deal of power, when I lift to make a turn ..

Lift Throttle Oversteer ?

[Cobrabill]

"Stiffness" only effects ride quality & weight transfer.I'd look into that issue PDQ.Something isn't right under your car.And if the suspension un-loads at the wrong time,it could get deadly.

[commercialcobb]

It does it for the most part on straight shots, we are a little timid about trying this in turns and its not on a track. It just a dead shot out of a stop sign and when I hit 60 or so and lift its looking for oncoming traffic.. Front end supsension or Rear or both?? I know the bushings in the rear are sub par and am assuming that is the problem..

[Jac Mac]

Its in the rear, thats where all the action happens when you lift off the throttle, if the bushes etc are suspect like you mention thats a good place to start looking, but look for any loose brackets, bolts etc as well, does not take much play in a bush etc to allow a lot of movement at the wheel.

[commercialcobb]

here is a shot of the rear and fromt bushing.. The rear is pretty bad as you can see a piece of it is laying on the frame below it!

[Jac Mac]

Thats the top bush for the RR Coilover, doubt that is the culprit although it would give a similar action to a dud shock in your case. Check the links that run forward from the axle housing to chassis for similar problems or broken brackets etc, probably easier on a lift or over pit etc.

[FatBoy]

It may just be the angle of the photo, but that top bolt looks like it's half way out. If so, that may also account for the broken top bush if it is moving and flexing.
You can't possible start fine tuning your suspension until everything is sound and bolted up tight.

Paul

[RICK LAKE]

commercialcobb.What have you done to the car? Built it, brought it new assemblied, brought it used? I am trying to get get a base to work with. To start with are you runnning a complete iron 429-460 motor in the car?
Have you started at the front of the car and check and tighten every nut and bolt?
Do you have the correct tire pressures in all 4 tires?
Have you measured the ride height in all 4 corners and is it level with your weight in the drivers seat?, If not you need to adjust it.
What shocks and spring rate are on the front springs?
Are the motor mounts tight and not split where it goes to the frame?
Any chance you have an alignment sheet of specs for the car?
Any change of a short video of this happening? can you get it here on the forum? this would be a big help in seeing what happening.
If you have a dirt track friend in the area, see if he will let you weight the car in 4 corners to start. Make sure your body weight is in the drivers seat. After this, go and align the car, About +1/2 degree of camber each side, +3.0 degres of caster l/s. +3.3-3.4 on the r/s. toe in the car about 1/16" and road test it. See if the car is still all over the place. If not you are good to go.
If you still have a problem I would be looking at the front shocks and spring rates. Both are too soft of the car. If that motor is all iron, thats about 700 lbs. You could have the wrong setup in the front end or the shock valving could be broken. Springs being too soft will also cause this problem.
Let's start at the top of the list and get the basics done first. Check for arms for play when you check for the bolts and nuts to be tight. Check the wheel bearings, ball joints, and bushings for play. If you find some repair and recheck. Tierod end play for none and play in the steering rack or dead spot on center. You would feel a small knocking noise through the steering wheel. The picture you showed us, is the suspension under load? IMO there is not enought clearance between the spring coils for them to work correctly and cause the car handling to be all over the place with coil bind. You should have about 4" of travel from loaded to unloaded in each corner. I am getting ahead of myself. Let's look at the beginning and go from there. Rick L.

[Bryan Wilson]

That shock looks coil bound where the coils are close together not allowing the shock to travel in a downward direction. Just my 2c worth.
Cheers,
Bryan

[madmaxx]

Possible related. I had a lexus do the exact same thing after tire replacement. It was crazy, every time i gave it gas or let off it would pull to the left. I immediatly returned since it was not doing when I took the car in for tires. They had mounted "s' speed rated tires when the car called for "v" rated and said they see it all the time. They said the sidewall stiffness was the culprit, they changed to "h" rated since that is all they had and it immediatly went away. This leads me to beleive it is in the bushings or sway bar in the rear, you compress them under acceleration and they are not rebounding equally causing the car to swerve. Rember the rear tires track the car, the front turn it.

[commercialcobb]

Originally Posted by RICK LAKE

commercialcobb.What have you done to the car? Built it, brought it new assemblied, brought it used? I am trying to get get a base to work with. To start with are you runnning a complete iron 429-460 motor in the car?
Have you started at the front of the car and check and tighten every nut and bolt?
Do you have the correct tire pressures in all 4 tires?
Have you measured the ride height in all 4 corners and is it level with your weight in the drivers seat?, If not you need to adjust it.
What shocks and spring rate are on the front springs?
Are the motor mounts tight and not split where it goes to the frame?
Any chance you have an alignment sheet of specs for the car?
Any change of a short video of this happening? can you get it here on the forum? this would be a big help in seeing what happening.
If you have a dirt track friend in the area, see if he will let you weight the car in 4 corners to start. Make sure your body weight is in the drivers seat. After this, go and align the car, About +1/2 degree of camber each side, +3.0 degres of caster l/s. +3.3-3.4 on the r/s. toe in the car about 1/16" and road test it. See if the car is still all over the place. If not you are good to go.
If you still have a problem I would be looking at the front shocks and spring rates. Both are too soft of the car. If that motor is all iron, thats about 700 lbs. You could have the wrong setup in the front end or the shock valving could be broken. Springs being too soft will also cause this problem.
Let's start at the top of the list and get the basics done first. Check for arms for play when you check for the bolts and nuts to be tight. Check the wheel bearings, ball joints, and bushings for play. If you find some repair and recheck. Tierod end play for none and play in the steering rack or dead spot on center. You would feel a small knocking noise through the steering wheel. The picture you showed us, is the suspension under load? IMO there is not enought clearance between the spring coils for them to work correctly and cause the car handling to be all over the place with coil bind. You should have about 4" of travel from loaded to unloaded in each corner. I am getting ahead of myself. Let's look at the beginning and go from there. Rick L.

To start off: My step dad said this problem existed 4 years ago before it entered the shop. Yes the guys in the shop had it 3 years before I came into there shop to finish the job. They have lost their arse on this complete overhaul and wouldn't put anyone on it so I stepped up. Reason I posted this question is because he has expressed major concern about it but I have not seen it myself. It will be on the road this week and he swears it will still do it, and the pic I showed it is the shock under load and the bolt has since been tightened. Old pic.

1. Yes, Iron 429-460.. 2. Bolts will get an entire recheck.. 3. Tire Pressures will be exact.. 4. Ride Height has not been checked.. 5. Shock and spring rate unsknow.. 6. Motor Mounts are new and tight.. 7. No video yet.. 8. No alignment yet.. 9. Do know some dirt track guys, will have them weigh it.

[FWB]

the rear spring, as someone else had mentioned, has no travel, when it crushes the force is transferred to the frame, the frame then twists under torque and the car torque steers. let off the gas and torque is removed spring relaxes frame relaxes. springs are wrong at the least. the bushings are toast because they are first in line receiving all of the pressure.

[kitcarbp]

I agree with Rick and FWB having "pinned" it as rear coil spring bind and as FWB pointed out with no spring travel (if fully compressed at normal ride height) , the shock bushing is being hammered to a pulp. In any case it has to be in the rear suspension for such a drastic change in yaw under power.

[commercialcobb]

Originally Posted by kitcarbp

I agree with Rick and FWB having "pinned" it as rear coil spring bind and as FWB pointed out with no spring travel (if fully compressed at normal ride height) , the shock bushing is being hammered to a pulp. In any case it has to be in the rear suspension for such a drastic change in yaw under power.

I think your both right and this will be my first course of action that I take to fix this dangerous condition. Also "kitcarbp" I like your use of the term "yaw" as I am a pilot and that makes perfect sense to me. In aviation "yawing motions" can have dramatic affects on aircraft perfomace and handling so now you have given me my first clue as to the extent of what all this means. I'll let you guys know what the outcome is. By the way, how can I tell what the spring weight is? Is it stamped on the spring? Also by loosening the adjustable spring, is that only going to raise up the rear end?? The car already sits higher than I'd like. Are springs universal or do I need a spring to fit my coil? Let me know what to do first and I can take it from there I think.. Thanks fellas again for everything!!

[bigmike]

Commercialcobb:
I empathize with you, I had exactly the same problem with my shell valley. Here's what I found: A. My locker had seized up, allowing no coasting action. Having replaced that it was still pretty squirrly, but not on coast. I blew a u-joint, and while replacing it, discovered 3" of play fore and aft on the rear axle. The rear was turing with the front!
B. When cleaning up to install new bushings, I discovered that no 2 trailing arms were the same length. I ordered 2 long and 2 short adjustable arms from speed way motors, making my rear axle fully adjustable for tracking and pinion angle. It now handles like a dream, as solid as can be. Only took 9 years to get it right!
BigMike

[commercialcobb]

Originally Posted by bigmike

Commercialcobb:
I empathize with you, I had exactly the same problem with my shell valley. Here's what I found: A. My locker had seized up, allowing no coasting action. Having replaced that it was still pretty squirrly, but not on coast. I blew a u-joint, and while replacing it, discovered 3" of play fore and aft on the rear axle. The rear was turing with the front!
B. When cleaning up to install new bushings, I discovered that no 2 trailing arms were the same length. I ordered 2 long and 2 short adjustable arms from speed way motors, making my rear axle fully adjustable for tracking and pinion angle. It now handles like a dream, as solid as can be. Only took 9 years to get it right!
BigMike

Is there a way to test if the locker has siezed?? Raise it off the ground and turn the wheels or no?? Where did you get the play 3" on the rear axle?? I'lll check my new adjustable trailing arms for lengths and make sure that the axle is square to the frame.. Let me know what you think..

[bigmike]

I'm not sure of the "correct" way to test the locker, but I had no differential action; just both wheel locked in sync. ( I replaced it with a Detroit helical gear Locker). When I was repairing the bad u-joint, I took off the rear wheels, and could move the spindle 3"fore and aft,, at the ouboard point. My shell valley did not have adjustable trailing arms, just machined aluminum bars....not good. The rear axle needs to be correctly aligned...there are to many variables in the manufacturing process (welded brackets, drilled holes, etc).
With the adjustable arms, the lower (longer) arms square the axle up to the chassis (not necessaarily the body), and the angled upper (short) arms adjust the angle of the rear axle pinion relative to the driveshaft.
I would, if I were you, disassemble the entire rear suspension, and double check everything. You should especially check the alignment of things, and, if you don't have adjustable arms, get some (about $200.00). It appears to me that your springs are not correct...they appear to be coil bound. I can provide pixs of my new setup if you would like.
BigMike