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DesertTech 04-08-2019 11:56 PM

4.8is wiggly rear end
 
Just picked up a 2004 4.8is last fall and absolutely love it. Put a full new front suspension on, and new brakes, along with BC racing coils. After the installation of all the parts, it seems like the car keeps falling out of alignment and now drifts slightly to the left. The major concern is when going over bumps and ice the back end becomes completely unsettled! Over highway dips, it has a lot of side to side movement on the rebound, and going over ice the rear seems to slide around trying to align itself before getting grip again. Its a really unsettling feeling and quite scary when there's traffic around.

The car isn't slammed at all, but the shop that did the alignment said one of the rear bushings can cause extra camber outside of spec. They found one side was a little worse than the other and one side had a little more camber. Searching parts now and it seems like theres a lot of common issues shared between all of the rear components (ball joints, swing arm bushings, upper control arms, etc), so not sure how to narrow this down without having to do the entire rear end at the moment since its my only car at the moment where I live. Need it back on the road as soon as possible, and can refresh the entire rear end this summer. As of now, just need it safe to drive.

EODguy 04-09-2019 07:54 AM

I'm interested in the answer too, as mine gets squirrelly as hell and after replacing joints, bags, etc. For awhile I was starting to think that it was some sort of delay in the DSC.

I can be on just rained on pavement where it's squirrely and can stop and punch it and it grabs right away without any slippage.

One mechanic said it's possible that the bag could have some wrinkle or alignment issue:dunno:

Let me know if you have done anything to the rear end...

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StephenVA 04-09-2019 08:10 AM

I would recommend a recheck of the actual bolts holding the rear suspension arms to the body. Note this Torque must be checked on the arms with a load on the rear suspension.
I would also check the lower arm swings at the frame as these bushing are a known weak point. The bushings themselves are available in the aftermarket saving huge costs.

SlickGT1 04-09-2019 08:17 AM

You essentially have to get a jack or some other thing that can compress spring from the spring perch.

What this means, is that you have to release the tension on all the suspension by compressing the spring, then you can grab the wheel and start wiggling. Probably the upper control arm.

There is a video on YouTube in some shop where they show how it’s done.

andrewwynn 04-09-2019 11:04 AM

I thought all the V8 were air spring so if air spring you just release the air pressure at the joint abive each bag.

Check your Alignment with a string: stretch a string at the widest part of the tire where it will clear the body around both front and rear tires.

You can. Tie/tape the string onto something including around back to itsf.

Put a 1/16" shim at the front of the front tire.

Now: the back edge of the front tire should just barely touch and the front edge of the back tire should be 1/6" away.

I'm betting that the toe angle is wide it will make the back end horribly loose: basically the car is literally over steering on the back end: when the front is going in a 50' radius the back is turning a 70' radius which will make the back end feel like it's on casters.

Front and back are spec for I think like 0.15° toe in, that works out to exactly 1/16" over 24" so with the tire being close to 24" wide where the string touches that's a very good estimate.

The last guy I helped with this problem. The wheel was toe out more than 1/4". He set his own alignment with a string and his car handles like a sports car again.

andrewwynn 04-09-2019 11:06 AM

But: first take the pressure of the spring off and wiggle the tire and determine what part broke to allow the gemoetry to change. You may be able to adjust the tie into spec while waiting for the part and redo when the part comes


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SlickGT1 04-09-2019 11:42 AM

Quote:

Originally Posted by andrewwynn (Post 1159523)
I thought all the V8 were air spring so if air spring you just release the air pressure at the joint abive each bag.

Check your Alignment with a string: stretch a string at the widest part of the tire where it will clear the body around both front and rear tires.

You can. Tie/tape the string onto something including around back to itsf.

Put a 1/16" shim at the front of the front tire.

Now: the back edge of the front tire should just barely touch and the front edge of the back tire should be 1/6" away.

I'm betting that the toe angle is wide it will make the back end horribly loose: basically the car is literally over steering on the back end: when the front is going in a 50' radius the back is turning a 70' radius which will make the back end feel like it's on casters.

Front and back are spec for I think like 0.15° toe in, that works out to exactly 1/16" over 24" so with the tire being close to 24" wide where the string touches that's a very good estimate.

The last guy I helped with this problem. The wheel was toe out more than 1/4". He set his own alignment with a string and his car handles like a sports car again.

I thought he said he did BC coils. Am I thinking of wrong coils?

I don’t think it matter if you have coils or springs though. The only way to release tension on all those arms is to compress the spring. If you jack up at the arm or at hub, the tension still stays at the spring.

StephenVA 04-09-2019 01:58 PM

The OE poster said BC coil overs, so he has indeed converted to coils on all four corners. Toe in the rear should be as close as possible to Zero toe in, to keep the rear tires from premature tire wear. Yes, you will trade off some turn in capability in exchange for longer tire wear. But then again the life of rear tires is approx 15-20K anyway...

andrewwynn 04-09-2019 03:09 PM

You can use a spring compressor to remove the spring pressure or a jack in the right place. I would probably attach a spring compressor while car is on the ground then lift it up. Any luck that's enough to remove the pressure for testing.

I have a feeling the spec for toe in makes for zero angle under throttle

DesertTech 04-09-2019 05:01 PM

Quote:

Originally Posted by StephenVA (Post 1159551)
The OE poster said BC coil overs, so he has indeed converted to coils on all four corners. Toe in the rear should be as close as possible to Zero toe in, to keep the rear tires from premature tire wear. Yes, you will trade off some turn in capability in exchange for longer tire wear. But then again the life of rear tires is approx 15-20K anyway...

I think there is too much toe on one side. About a month ago the shop write up said both upper ball joints are loose and recommend replacing the upper control arms. I might start with that, and also have bushings for the rear swing arm but just need to correct the camber and toe angles. The toe is way out of wack, and currently at

left: .11
right: -.09

Camber
left: -2.27
right: -2.84


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