Issues with my rear end "walking/torquing" - Need advice

[Intervention]

OK so I have been trying to narrow down a certain issue with my car as of late. I feels as if my rear end "walks" when I step on it in 5-6th on the highway. Let me explain more... (Sorry if this is long as I am trying to give as much info as possible... I thank anybody now for offering advice)

Last season I blew out some BMR bushings. BMR quickly shipped me a brand new set and I installed them no issues. This happened at the track, you can imagine how the rear end felt with all bushings like that.


Later that season I ended up popping my diff in half (damn drag radials...) Replaced the diff with an Eaton Posi.

I had my mechanic(very experienced) install a Trutrac first to no avail. The thing sounded like a damn air impact at any speed. It literally shook the car, it sounded as if I was riding on the rumble strips on the highway. Had the thing torn down, replaced every bearing, called their techs... Had my mechanic tweak a few things and grand a few thousandths off some spacer. Still no dice. Ended up returning it for an Eaton Posi.

So fast forward to today and this season. I have been having an issue with the rear end walking when you step on the gas for the past few months. It feels as if it is the rear end. When you tap the gas, the car pulls to the left and when you let off it goes back to the right. I figured my bushings went bad so I had BMR again ship me new ones(THANKS BMR!!!) Problem is, I go to change them and the ones in their were fine. I replaced them regardless...

When I put my drag radials on, the issue is exacerbated by 2-3x the motion.


Food for thought:

1. Can it be diff related? The diff works fine though and even if it was stuck open/locked that shoudlnt result in allowing my rear end to torque.

2. Lower Control Arms? The bushings are brand new, installed correctly... I'm not sure if anythign can be related to the LCA's. I will try putting the stock arms back in tomorrow

3. Upper mount? Should have no say in left to right rear end motion right?

4. Panhard bar? It is stock and I am lowered 1.25". Any issues here?

5. When my exhaust was installed, the Kmember was removed. I am 98% sure the motion is from the rear end. Bot possibly maybe something is loose up front?


Long story short, this is driving me crazy. It is going back to my mechanic and he will double check everything. I have checked everything I can think off and it all looks/feels fine. THANKS to anybody who responds.

 

[frarmar]

I'm no help, but I have the exact same thing. Right down to it being a lot worse with DR's on... Mine feels like the car kind of slightly veers a bit left when you get on the gas and settles back when you let off (only in 5th gear at highway speeds)... I recently had a true trac put in also, but haven't had the DR's back on yet...
About the only thing I haven't replaced back there is the UCA..

 

[Intervention]

I'm no help, but I have the exact same thing. Right down to it being a lot worse with DR's on... Mine feels like the car kind of slightly veers a bit left when you get on the gas and settles back when you let off... I recently had a true trac put in also, but haven't had the DR's back on yet...
About the only thing I haven't replaced back there is the UCA..

The issue is, it didnt do it stock... So I know something is up

I cant pin exactly when it started to happen, but it is recently

And that is pretty much spot on what I am experiencing

 

[kenneth]

Could it be something as simple as an alignment, being that your lowered?
Just guessing

 

[Intervention]

Could it be something as simple as an alignment, being that your lowered?
Just guessing

I thought that... But I have had the alignment done just last year after I was lowered. Everything was adjusted to spec

 

[frarmar]

We're definitely in the same boat.

I put a new panhard on, retorqued lca's, put in new lca bushings, had my DR's rebalanced and put my stock shocks back on.... nuthin'... Haven't had the DRs back on since the true trac went in, so we'll see.

The issue is, it didnt do it stock... So I know something is up

I cant pin exactly when it started to happen, but it is recently

And that is pretty much spot on what I am experiencing

 

[Intervention]

We're definitely in the same boat.

I put a new panhard on, retorqued lca's, put in new lca bushings, had my DR's rebalanced and put my stock shocks back on.... nuthin'... Haven't had the DRs back on since the true trac went in, so we'll see.

Panhard was my next idea... But maybe not now...

Pinion angle shouldnt mean much here?

This is bugging me. It HAS to be something

 

[frarmar]

Panhard was my next idea... But maybe not now...

Pinion angle shouldnt mean much here?

This is bugging me. It HAS to be something

I'm not sure on the pinion angle thing to be honest.

The odd thing to me is why it's so much more pronounced when the DR's are on.

Hopefully your mechanic can shed some light when you take it back in... maybe it'll end up being something stupid we're overlooking.

 

[dysan]

I can't remember exactly how my car was but it was sloppy as hell and it turned out my upper bushing on top of the diff that the UCA mounted to was trash. I put a poly one in there and it tightened it up considerably.

Definitely something to check if you've blown out LCA bushings launching it hard.

 

[Intervention]

I'm not sure on the pinion angle thing to be honest.

The odd thing to me is why it's so much more pronounced when the DR's are on.

Hopefully your mechanic can shed some light when you take it back in... maybe it'll end up being something stupid we're overlooking.

I have faith we can get this worked out. It must be something

I can't remember exactly how my car was but it was sloppy as hell and it turned out my upper bushing on top of the diff that the UCA mounted to was trash. I put a poly one in there and it tightened it up considerably.

Definitely something to check if you've blown out LCA bushings launching it hard.

HMMM, stock UCA though? What sort of bushings are up there? It just doesnt make sense though. I thought the UCA solely deals with up/down rotation?

I'll check it out

 

[KJGT]

You dont have LCA relocation brackets do you? If they/moved bent or werent on right when they were welded the whole rear could be off and thats why its pulling one way hard under power.

A four wheel alignment to check the thrust angle would be the first thing I would be doing. Only other thing that will do that is two different diameter tires. If the bump steer was way off the rising of the front could cause it on crowned roads as well when the front end rises.

 

[Intervention]

You dont have LCA relocation brackets do you? If they/moved bent or werent on right when they were welded the whole rear could be off and thats why its pulling one way hard under power.

A four wheel alignment to check the thrust angle would be the first thing I would be doing. Only other thing that will do that is two different diameter tires. If the bump steer was way off the rising of the front could cause it on crowned roads as well when the front end rises.

No it has stock LCA brackets/none at all...

I am going to check into that UCA and recheck the alignment. The mechanic will take a look at everything else

I appreciate the help so far guys!

 

[erat]

Had this problem on a truck. Check the spot welds were the differential housing meets the axle housings. That weld can crack under stress and will cause crabbing when under acceleration.

 

[pdmusgt]

Still running stock panhard with it lowered even stock setup the rear to the left alittle. You need adjustable panhard bar

 

[rojizostang]

whenever i've worked on the rear end and experienced something as you describe, it turned out to be the panhard bar hadn't been tightened up sufficiently. i had put everything back under the car and tightened everything up but missed tightening the bolt on the panhard by the driver side wheel. just a thought. or perhaps you have a bad bushing in the panhard bar itself?

 

[Sky Render]

It sounds to me like your limited slip isn't working right. In a straight line, it's sending more torque to one side than the other, creating a yaw that feels as if the car is pulling to one side.

 

[Boozshey]

What suspension mods do you have? Just springs? Everything else is stock to include sway bars?

 

[Intervention]

It sounds to me like your limited slip isn't working right. In a straight line, it's sending more torque to one side than the other, creating a yaw that feels as if the car is pulling to one side.

But how about an open diff car? They would pull like crazy with that theory?

What suspension mods do you have? Just springs? Everything else is stock to include sway bars?

Steeda Ultralite springs and BMR LCA's are my only mods suspension wise

 

[GeorgeInNePa]

But how about an open diff car? They would pull like crazy with that theory?



Steeda Ultralite springs and BMR LCA's are my only mods suspension wise

An Open diff, typically, sends power to the wheel with the least traction.

What he's describing is what happens with a spool or locker when an axle breaks. The car will try to make a turn because there is no slippage on the unbroken side.

Due to the clutches in the LSD and how it works, I doubt that's what happened here.

 

[94tbird]

that happened to me once at the track. Whenever i hit the gas, the car would immediately pull to the right. If i let off the gas, the car would straighten out and ride normally. That was with my bogarts on. I went to the pits to call it a day and prepare for an easy drive home. Changed the wheels back to my stock wheels and magically the problem was gone. Never happened since. been 3 years i think since it happened.