[Zap]

Thought I'd ask some of the more seasoned experts - any thoughts on ruling out what would be causing this? The steering wheel shakes only when braking fairly hard AND generally at a moderate or higher speed of travel.

The brakes work great, and most of the time don't vibrate. Tons of life still left in them, so I'm not really keen to shotgun all the parts just to see if that fixes it. I put the car up and the front wheels spin freely without any spots that seem to drag (such as from a defective rotor).

My thought is that maybe the brakes are fine and I've got a weak part in the suspension such as a tension strut. Car has close to 88k.

Any thoughts or even better, any way to diagnose what is at fault here? Thanks for the advice!

[Shoooter_j]

Upgrade to the front m3 control arms. Had this exact issue happen and its due to the bushing being worn.

[cpie168]

+1
Exact same issue for me. Worn control arm bushings. Upgraded to M3 front control arm and never looked back.

[Zap]

Excellent - thanks for the responses! Does that means it is suggested to upgrade both the upper and lower arms, or is it just one of them that is generally needed? Is there any alignment needed after this work?

Anything else that should be swapped while apart? I was looking around and saw that Turner has a kit, for instance, that also includes the headlight adjusting rod and front upper inner bushings.

[VTECaddict]

The upper control arm (tension strut) from the M3 is pretty much physically identical to the non-M RWD one, just stiffer bushings on it. It's an improvement over stock, but probably not too noticeable.

The lower control arm is the one that makes a huge difference because it adds -0.7 camber to the front. This gives you much sharper turn in and lateral grip in the front. If you do the M3 lower front control arm, you will need a new headlight adjustment rod because it connects differently.

Alignment is absolutely required afterwards.

[justpete]

Originally Posted by VTECaddict

The upper control arm (tension strut) from the M3 is pretty much physically identical to the non-M RWD one, just stiffer bushings on it. It's an improvement over stock, but probably not too noticeable.

The lower control arm is the one that makes a huge difference because it adds -0.7 camber to the front. This gives you much sharper turn in and lateral grip in the front. If you do the M3 lower front control arm, you will need a new headlight adjustment rod because it connects differently.

Alignment is absolutely required afterwards.

And the lower control arm has a sealed spherical bearing at the body end which makes a lot of difference to steering feel and quickness. The same bearing is available to be installed in the upper control arm but might be too much for most drivers.

[feuer]

... and none of it (control arms) will remedy the brake issue, it will only disguise it. On older generation BMW's yes, due to suspension design, on newer no. Since you don't experience vibrations all the time I would say is brake pad deposit. Solution would be more aggressive pads and change of your braking habits.

One could read hundreds of threads about people replacing the control arms and still experiencing brake pulsation. Why?

Also, why most of the time OP doesn't have brake vibrations.

If bushing is gone, worn out, is permanently gone. It will not sporadically get better and not cause brake vibrations.

In fact just the opposite would happen. Vibrations would be regular occurrence and more violent in time.

That is why I say is brake pad deposit and OP braking habits.

[feuer]

Originally Posted by VTECaddict

If you do the M3 lower front control arm, you will need a new headlight adjustment rod because it connects differently.

One can easily mod the existing rod. I have done plenty. But you are correct, connects differently.

[gavronm]

I'm with feuer on the brake pad deposit side of this. Before you start tearing into your suspension, find an empty country road and do 6 or 7 max braking events from 80 to 40 and see if that helps. Free and fun.

Had to do this every now and then when I was running yellowstuff pads on old OEM rotors over the summer.

[fravel]

New control arms fixed this problem for me.

[Zap]

Wow, quite a discussion! For the record, the car has done this since I got it. In hindsight, I should have pressed harder about the issue.

Re: pad deposits, I've tried the country road braking procedure already and the problem still remains. If it made any difference in the feel of the brakes, it wasn't significant. That's why I checked to see if the wheels turned freely - but I didn't encounter the drag I would have seen on other cars in the past (which had cheaper or inadequately sized rotors that had warped).

So, if the max braking exercise didn't yield anything would you still suspect brakes over suspension? The big problem with seeing suspension wear increase in severity over time is that I don't drive a ton. I've had the car almost 3 years, but it has only had about 7k of mileage in that time so if something is degrading, it isn't as obvious as with someone that racks up that amount of mileage in less than a year.

[Jklad]

It could also be warped rotors if they are worn

[rothwem]

Originally Posted by feuer

... and none of it (control arms) will remedy the brake issue, it will only disguise it. On older generation BMW's yes, due to suspension design, on newer no.

I've got to know, what's so different about newer BMWs that causes us to be immune from bushing wear?

[feuer]

Originally Posted by rothwem

I've got to know, what's so different about newer BMWs that causes us to be immune from bushing wear?

You are missing my point. Is not that is immune to busing wear but is less prone to brake vibration due to suspension component failure, and that is due to suspension design which is completely different than previous generations.

[mojobmw_e90]

What rotors do u have? I had the same issue and fix was oem brake pads and rotors

[Zap]

Originally Posted by feuer

You are missing my point. Is not that is immune to busing wear but is less prone to brake vibration due to suspension component failure, and that is due to suspension design which is completely different than previous generations.

This is something I wouldn't be aware of (this is my first BMW) - so thanks for clarifying this point. FWIW, the car handles and feels great anyway. Out of curiosity, is the service life on the suspension parts different on these cars from others?

Originally Posted by mojobmw_e90

What rotors do u have? I had the same issue and fix was oem brake pads and rotors

Everything is OEM - services were performed at the dealership by the previous owner.

[feuer]

Originally Posted by Zap

This is something I wouldn't be aware of (this is my first BMW) - so thanks for clarifying this point. FWIW, the car handles and feels great anyway. Out of curiosity, is the service life on the suspension parts different on these cars from others?

From suspension components the struts and shocks are extremely short lived compared to other cars. The rest of the suspension is OK

[armansiu]

how about XI? are they compatible?

[feuer]

Originally Posted by armansiu

how about XI? are they compatible?

Is this question for me? Compatible? Please explain further.

[armansiu]

Originally Posted by feuer

Is this question for me? Compatible? Please explain further.

oh sorry. forgot to quote.
just wanna ask if the m3 upper control arm would fit XI non-M?
thanks.

[feuer]

Originally Posted by armansiu

oh sorry. forgot to quote.
just wanna ask if the m3 upper control arm would fit XI non-M?
thanks.

No, it will not.

[armansiu]

Thanks, feuer