Rear End Wag After Spring Install

[esco11]

So I had somewhat recently installed the BMR 082/089 spring combo and I’m now noticing a big of wag from the rear end when accelerating. I first noticed it when downshifting to pass on the highway but also had it happen during some city driving today.

I had an alignment done right after the spring install, will try to post the specs tomorrow. I still haven’t clocked the bushings due to lack of time and I’m hoping it might be related to that. If anyone has any other ideas of what this could be I’d appreciate the input.

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[rayban1]

think you should of clocked first, then had alignment done.

 

[esco11]

Very true, I wish I had come across the BMR tech tip thread before that.

 

[BmacIL]

Need to see alignment settings. Another member posted similar recently and it was entirely alignment. Also, did they trim the bumpstops per the instructions?

 

[esco11]

Need to see alignment settings. Another member posted similar recently and it was entirely alignment. Also, did they trim the bumpstops per the instructions?

I did the spring install and I trimmed the bumpstops down to the BMR listed lengths.
Here are the values off of the alignment sheet:

Front Left
Camber: -1.7
Caster: 7.0
Toe: 0.01

Front Right
Camber: -1.6
Caster: 7.2
Toe: 0.02

Front
Cross Camber: -0.1
Cross Caster: -0.1
Total Toe: 0.03


Rear Left
Camber: -1.2
Toe: 0.15

Rear Right
Camber: -1.8
Toe: 0.13

Rear
Cross Camber: 0.5
Total Toe: 0.28
Thrust Angle: 0.01

 

[wildcatgoal]

Rear camber really shouldn't be so different - but without the Steeda camber bracket it's kind of hard to adjust, so I get it. But that's probably not the issue, anyway.

Rear toe is best at 0 or slight toe IN and even on both sides IMO and IME. I'm not honestly sure if the difference between your toe in the rear is actually significant, but when I get alignments done, I get (often) the exact same number on each side (or damn close). Well, I run 0 toe in the rear, so... haha. A little toe in is fine in the rear.

But that alignment doesn't seem terrible, so I'd try and clock bushings and make sure all bolts are tight, the springs are seated properly, and your wheels have been torqued.

 

[BmacIL]

I'd generally agree with wildcatgoal here. The rear camber is off enough left to right to cause some handling inconsistencies, though not necessarily the kind you're seeing. Clock the bushings for sure.

 

[NightmareMoon]

Those toe settings should be alright. The car should self-center a bit if the rear steps out, but toe won't solve traction issues.

In addition to the good suggestions above, make sure there is no wiggle in the hubs.

Make sure everything in the suspension is torqued properly (you've got a torque wrench, right?) If you hear any banging or pops at any point, that's a sign something may be loose. If your car requires different amounts of steering to go straight under different circumstances (such as accelerating versus braking) that's also a sign something may be loose and shifting.

That's all I've got. If you believe the car is misbehaving and acting unstable under power, then be very very careful driving it until you diagnose the issue. You don't want to hit a barricade or something.

 

[SVT-DADDY]

I could be wrong here but isn't the spec for total toe in the rear .20?

I know some toe will help stabilize the rear of the car under power, but I believe too much can actually have the reverse effect and start to make the rear end a little wonky. It's also too big of a difference for my liking. I am calling on my experience running a tire center 20 years ago. lol I am not saying it will fix your problem for sure but I'd have that rear toe fixed.

 

[SVT-DADDY]

Found the specs. You're right at the max.

 

[BmacIL]

I could be wrong here but isn't the spec for total toe in the rear .20?

I know some toe will help stabilize the rear of the car under power, but I believe too much can actually have the reverse effect and start to make the rear end a little wonky. It's also too big of a difference for my liking. I am calling on my experience running a tire center 20 years ago. lol I am not saying it will fix your problem for sure but I'd have that rear toe fixed.

You have to go much further than ~0.1 deg per side to feel those kinds of effects.

 

[esco11]

Thanks for all the suggestions guys, I'll for sure give all of this a shot as soon as I can.
Unfortunately it might be a bit since it looks like I'll have to take it in for a CEL popping up.

 

[Grintch]

I have a similar issue.

Installed the Track Suspension (with the smallest Steeda rear spring spacers). Car felt good and rear felt more stable than stock (maybe because of the new rear toe link bushing). a month later I did my first track day in the car. Everything felt great and I outran the 3 Corvettes and 1 Z28 that came out. My only issue was not enough front camber (because FR doesn't address the lack of camber adjustment with the Track kit) that ate up my outside front tire pretty bad.

So order some front camber plates, HD trans & diff fluid, and a set of square wheels and tires thinking I am going to have a fun part time track car. But a month or so later the car starts feeling skittish over bumps and on narrower roads with lots of crown. Gets worse till I get the camber plates installed and re align the car & check/tighten up all the suspension bolts. Car feels better after that, but not 100%. But then starts feeling worse again, getting worse over time. Got it aligned again and checked over by my race mechanic, and it didn't seem to help much if at all.

As it is today its a bit scary to drive (really scary in the rain, but not much rear tread left), and there is no way I would trust it at speed at the track. The rear end seems like it has a different agenda from the front. But I still can't find a cause. Another side effect is it is really eating up the rear tire life, but the wear pattern is normal.

 

[Rebellion]

I'd clock everything on the rear and check for integrity, first, then get the alignment done to have similar camber and toe on both sides on the rear.

Never happened to me, but it has happened to a comp orange friend of mine. I would have a good shop/technician look at it, this is important stuff.

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