E90 Suspension Gurus: Yes ANOTHER Help Me Fix The Rear End Thread.

[PrematureApex]

'08 135.

Stock Springs
Bilstein HDs
Front M3 H&R Sway
Strongflex Front CA/TS Polys
Whiteline rear subframe bushings
Monroe rear upper shock mounts

The car still has the dread rear end steer/jumpiness over bumps, particularly mid corner but also going straight.

Is this still all the bump steer built in back there?

Has anyone identified a proper solution for this?

Is it in the rear trailing arm bushings (toe arms?)?

The spring arm inboard bushing?

Not really looking for the "install M3 rear arms" answer...but something more specific.

If I'm going to start replacing bushings back there, want some first hand advice on where to start.

What bushing(s) are responsible for that mess back there?

The RSF bushings helped, as did the shocks, but that certainly didn't fix the issue.

[lowbudgethero]

Stiffer Springs, tires, and alignment go a long way

[houtan]

You could ask dcarron as well, but when i switched upgraded the toe arms, the rear end got much more stable. I went with the bimmerworld toe arms which comes with durable aurora bearings. they are top notch and their customer service is awesome. The manzo arms are also popular but the bushings are a hard rubber.

My preference was to use something OEM like the ones fe1rx made for his car, but he is not ready to sell any so i went with the bimmerworld arms.

[PrematureApex]

OK, thinking of starting with bushing replacements in the toe arms and the trailing arms, then going from there.

[dtla1]

What are your alignment specs?

[PrematureApex]

Originally Posted by dtla1

What are your alignment specs?

Started factory, then 0 toe all around.

But this illustrates the problem. A car blatantly hopping around, completely and inexcusably unsettled...

Is not an alignment issue.

Hence, looking for first hand experience of those who've actually tackled the issue.

Not meant to be insulting, but trying to, if I'm honest, bypass the BMW forum BS.

[ShocknAwe]

From Fe1rx thread, rear guide rod on M3 has bearings rather than bushings. Toe arm was different as well.

I've always felt the RTABs were rather soft, I can manipulate them by hand, but theyre the same on the M3.

I'd probably start with guide rod and toe arm bushings.

[chris82]

Even with M3 RSFB the stock suspension bump steers really bad, when I had coilovers it was minimal. My guess is it's the shocks. Has it always done this with the Bilstein HDs? How many miles on them. Also, do you get any harshness back there?

[PrematureApex]

Yup, really always done it. They have about 25k on them. No leaks, and at least from attempts to compress them, they still have life in them. No harshness beyond the firm feel of the monotube shocks.

Obviously, a stiffer spring is going to reduce the bump steer. Sinks no one makes a set with minimal drop. Have to locate a set of BMWPSs I guess.

I'll start with the tow and trailing arm bushings, finger's crossed.

[RyanDavies]

Plenty of manufacturers allow "minimal drop".

I can run my JRZs in the rear 2 inches above stock ride height at the wheel if I chose to do so.

[fe1rx]

Originally Posted by PrematureApex

Yup, really always done it. They have about 25k on them. No leaks, and at least from attempts to compress them, they still have life in them. No harshness beyond the firm feel of the monotube shocks.

Obviously, a stiffer spring is going to reduce the bump steer. Sinks no one makes a set with minimal drop. Have to locate a set of BMWPSs I guess.

I'll start with the tow and trailing arm bushings, finger's crossed.

Do you have a GoPro? It would be interesting to have it aiming at your rear wheels to see if you can see toe and/or camber changes under braking, accelerating and over bumps. If you can see what is happening it might help you figure out where the problem is coming from.

[PrematureApex]

Originally Posted by RyanDavies

Plenty of manufacturers allow "minimal drop".

I can run my JRZs in the rear 2 inches above stock ride height at the wheel if I chose to do so.

With coilovers, of course. I was referring to stock-sized springs.

[PrematureApex]

Originally Posted by fe1rx

Do you have a GoPro? It would be interesting to have it aiming at your rear wheels to see if you can see toe and/or camber changes under braking, accelerating and over bumps. If you can see what is happening it might help you figure out where the problem is coming from.

I do have access to one. I'll look into that, thanks for the idea.

[dtla1]

Originally Posted by PrematureApex

Started factory, then 0 toe all around.

But this illustrates the problem. A car blatantly hopping around, completely and inexcusably unsettled...

Is not an alignment issue.

Hence, looking for first hand experience of those who've actually tackled the issue.

Not meant to be insulting, but trying to, if I'm honest, bypass the BMW forum BS.

Never underestimate the affects a good/bad alignment can have.

Do you know your exact alignment specs? and when was the last time it was done? By which shop?

[MightyMouseTech]

Originally Posted by PrematureApex

Started factory, then 0 toe all around.

But this illustrates the problem. A car blatantly hopping around, completely and inexcusably unsettled...

Is not an alignment issue.

Hence, looking for first hand experience of those who've actually tackled the issue.

Not meant to be insulting, but trying to, if I'm honest, bypass the BMW forum BS.

0 tear toe is going to make for a very "lively" rear end.

[AlexR6]

Originally Posted by PrematureApex

Started factory, then 0 toe all around.

But this illustrates the problem. A car blatantly hopping around, completely and inexcusably unsettled...

Is not an alignment issue.

Hence, looking for first hand experience of those who've actually tackled the issue.

Not meant to be insulting, but trying to, if I'm honest, bypass the BMW forum BS.

0 toe usually is the worst choice... car tends to tramline (or whatever you call it) and the rear end moves very easily.

I would start with some positive toe in the rear and if you want a reactive front end, a little negative front toe!

This setup works good for me for both street and track use.

[PrematureApex]

Just got it inspected this morning, and had it put up on the rack. 1/16" in the rear. For shits and giggles, I had them set it at 1/8".

This is 100% NOT an alignment issue.

It is an extension of the slop that's been in the car forever, and all E90s for that matter.

[PrematureApex]

Originally Posted by MightyMouseTech

0 tear toe is going to make for a very "lively" rear end.

Originally Posted by AlexR6

0 toe usually is the worst choice... car tends to tramline (or whatever you call it) and the rear end moves very easily.

I would start with some positive toe in the rear and if you want a reactive front end, a little negative front toe!

This setup works good for me for both street and track use.

I actually like closer to 0 toe on most rwd cars. I like a car that's easy to rotate. 0-1/16" is what many here run.

Not talking about tramlining.

Rear end behavior of a car running 0 toe, or some toe out even, is not what's going on back there, unfortunately.

[MightyMouseTech]

On my 1er, the RSFB's were the biggest culprit to the back end sway over bumps, especially hitting a small bump mid corner. The car would literally swing left to right.

Installing the M3 rear bushings eliminated this completely.

Now I just get a bounce from hitting the bumpstops if hitting a bump mid corner. Adding some suspension travel should cure that. Should know this summer.

[The Wind Breezes]

You have 0 toe in the rear? Bad idea, try a small bit of toe in back there.

[ShocknAwe]

If I recall correctly, dinan springs have a higher rate than bmwps. Could try those instead. Think the drop is still minimal.

[PrematureApex]

Originally Posted by The Wind Breezes

You have 0 toe in the rear? Bad idea, try a small bit of toe in back there.