Severe steering wheel shaking under low/high speed braking

[Aus323i]

Hi everyone,

Firstly, I just wanted to thank everyone for the amount of help I've been given on this forum, its great to see this community being so supportive of people with less knowledge of certain E21 related things.

Secondly, and why I am posting, is the problem I am having with my brakes. I recently installed a 15" Wilwood brake kit up the front of the car, while also replacing the wheel bearings and tie rod ends at the same time. I have a friend thats been a mechanic for a few years give me a hand with the bleeding and fitting of everything to spec and as far as we can tell we have done everything correctly although there is a major problem we have experienced. Today, I took the car out for the first drive since installing the brakes, I was trying to go and do the 'break in' procedure on the brakes but instantly was stopped but the severe shaking I experienced through the steering wheel. There is a very loud shuddering and the wheel is very hard to stop from shaking. This happens all the way from 60km/h down to 20km/h. From what I have read this is apparently 'warped' rotors but as they're new I thought this had to be wrong especially coming from Wilwood as they are a reputable company. Through doing a little more research apparently it can just be 'hard spots' on the rotor which may need to be machined down to true. So, would anyone have an opinion as to what this could be and any solutions to fix the problem?

Max

[Jeroen]

I don't really suspect the rotors, never experienced that myself. But they are a decent make and run freely between the pads? Usually that spot is good for inspecting rotors and calipers for possible alignment issues as well.

As per FAQ section this could also be the common E21 shimmy, usually caused by worn front trailing arm and anti roll bar bushes causing the trailing arm to move excessively. Other options are the usual common suspects on most cars I guess: unbalance in the wheels/tyres, brake discs or wheels not centered correctly on the hub, brake disc bolt sticking out preventing correct alignment of the wheels, steering rack freeplay, etc.

[Aus323i]

I do know that the rotors and pads make very slight contact all the time with them installed. I didn't know how to remedy this and thought it would go away after being worn in. I will try replacing the roll bar bushes and get someone to do the trailing arm bushes (unless they're quite simple to do). Another point is that it only happens under braking, it is not constant. The wheels have been balanced last week, but I have not had the brake discs centred. I may have a look at the alignment of the calipers and rotors. Is there any way that a un secured rotor is aligned on a hub?

Thanks, Jeroen.

[nas80]

What about your wheel bearings?

[e21-Mark]

Steering rack mounting bushes are also well worth checking.

[Jeroen]

Agree, the round ones that go around the rack, in case of a non-powered rack btw

[Reck]

Definitely check rack bushes. Mine had turned into some sort of black gloop!!

[TopCat]

I had exactly the same problem on Herman

Turned out it was a sticking calliper

Now all fixed with new callipers and pads

[Aus323i]

Thanks for all the replies

I've replaced and greased the wheel bearings and they're all seated in the hub correctly but I will take another look at them.
If the steering rack mounting bushes are the ones that sit in the rack next to where the headers would be then they are fine as well. (Doesn't seem to have any cracks or have turned to sludge)

A few extra bits of info that may help:
- My engine mounts and transmission mount are completely compressed
- The car from 80km/h to 5km/h under quite hard braking doesn't seem to make the shudder as much as 60km/h >
- The rear callipers are stock. They work but I don't know whether they would be the cause to the shudder just because of how much is does shake.
- Wheel alignment is out as I can visually see a difference in the way both front tyres face when the wheels are straight. (I assume that this wouldn't be it as it would just effect the tyre wear and general ride)

After speaking to my specialist BM garage they said I may be experiencing brake run out which will need to be looked at to fix. But from reading how they remedy this I do not want them to machine the rotors back though as this will be expensive and ruin perfectly good rotors that were also expensive

If they are brand new Wilwood's would the front's be sticking? I'm sure thats something they would have checked before selling the callipers, but maybe I bought an anomaly. Would putting copper grease on the rotors help in anyway to stop a sticking caliper?

[trash-berd]

If your steering rack bushings haven't ever been replaced to your knowlege they are almost certainly shot.
Also check rear rotors, if your rotors aren't catching on the front that's a definite suspect

[Jeroen]

Max,

First things first, brand new Wilwood calipers won't be the issue, they are surely not stuck and they don't need any copper grease. Is the setup centered correctly, meaning there is just the same room between the pad and the rotor on each side of the rotor?

The new wheel bearings, are they adjusted correctly without any freeplay?

The rotors are new, or existing ones but were good before? When you turn them it should be pretty easy to see if they're not centered or seated correctly, especially with a tight reference point like between the brake pads.

Do you have the idea its the right, left, of both?

A bit of a puzzle but if problems start after work is done, something didn't go well. Even though suspension bushes are a known weakpoint I don't believe in other parts that just happen to break at the same time.

Since you had the tie rod ends replaced as well it may very well be that wheel alignment is way off at the moment. This will become more apparent at higher speeds and needs to be adjusted anyway so perhaps that would be a good start at this point.

[Aus323i]

I agree with you that it won't be the new pads or rotors, so scrap that idea.

When the wheel bearings were put on they seemed fine and didn't have the free play that they did before. Although, I am going to check just how tightly I did the nut up that holds the hub and bearings on.

The problem I have with the brake system is that when I bought the car it had no working brakes as one of the front calipers was leaking. So, I have no idea if before this was happening or not. The new rotors are sitting perfectly between the brake pads and are easily turned with out much force.

I'll get back to you soon on how everything goes. I'm sure it is something small that I have missed, and I will check the steering rack bushes now to see how good they look.

Thanks everyone again

[Aus323i]

Just after talking to another E21 guy I met with the other day to buy some parts he was telling me that any slight difference in weight or alignment in the front end from what it should be will put a slight vibration through the whole steering under braking. My front wheels have a ridiculous amount of positive toe and I don't know how long it has been since they were last aligned. My wheel bearings are tight, and quite a few of the front bushes are worn or dry and starting to crack so I think this could also be a cause.

Cheers for all the help, its good to know what to look out for.

[Jeroen]

So a round of trailing arm and sway bar bushes, alignment and fingers crossed but that's likely to sort things out, good!

[Aus323i]

I never continued this up. Unfortunately I think I could actually have a problem with my Wilwood's as all the bushes on the front end have been replaced and an alignment done but it seems to be happening just the same.. My next step is I'm checking the run out of the discs with a dial gauge my friend is bringing up from his workplace. Hopefully, there is a problem with them.

If that isnt the problem, the only other thing I can think of is the upper strut mounts/bearings. If not I am stumped -.-