Braking Wobble

[djbock]

Been getting an occasional braking wobble between 50-70 mph. Figured that I would replace the wishbones (control arms) and have a question. How imperative is it that I have an alignment done after I install the new parts?

If an alignment is needed after the control arm replacement, should I replace the tension struts as well that way I don't have to do it twice?

Just not sure how far the alignment will be out of specs with the parts replacement.

[vivanov1]

seems like you need to cut your rotors. had that on my Fx35, when you break at high speeds and it shakes, usually due to rotors.

[djbock]

Originally Posted by vivanov1

seems like you need to cut your rotors. had that on my Fx35, when you break at high speeds and it shakes, usually due to rotors.

Rotors are new, no help.

Mileage is 116,000 btw.

[TurnAround]

Originally Posted by djbock

Rotors are new, no help.

Mileage is 116,000 btw.

Definitely get the alignment, any time you are replacing steering or front susp parts. It takes very little to alter the alignment.

On the shimmy.. what kind of pads do you have? I have Axxis Deluxe Plus pads. Nearly zero dust. I love these pads, except.. they develop a brake shimmy after 5k miles. If I remove the pads and sand them.. its all perfect again for 5k miles. New rotors.. all that.

What's going on is that I am using high performance pads that are designed to be used much harder than what I am. The new rotors... they're about 10k old now, but they look brand new. Brand spanking new. Its because the pads aren't removing ANY metal at all. Zeeeero. So the rotors, and the pads, build up deposits that don't get burned off / ground off. Big heavy vehicle, zero healthy rotor wear, performance pads = shimmy braking at 70+ mph. The solution... replace the pads with ones that grind just a little bit off of the rotors and the pads, and deal with the front rims getting dusted out a little.

Actually, there might be another solution. Use the same no dust pads, but go with slotted drilled rotors so that they are less prone to deposits themselves, and, scrape the pads some. This is what I should have done!

Both of my Z3's have these same pads and have no issues.

[JCL]

djbock:

I recommend you get an alignment if you replace the control arms. What leads you to believe that the control arms are the problem? Anything slightly loose in the front suspension could set off a wobble upon braking.

Turnaround:

Here is an article on brake pulsing/shudder due to rotors. The underlying cause is pad deposition on the rotor surface. I used Axxis Deluxe pads with no issues for 40,000 km, but they do need to be properly bedded in. I suspect that your shimmy after 5000 is due to them not being properly bedded.

StopTech : Brake Pulsing

Slotted and/or drilled rotors would be a step backwards for your problem. The scraping that they do is for debris caught between the rotor and the pad, essentially a non-existent problem. You need the deposits on the disk surface for proper braking, you just need those deposits to be even. Your X is heavier than your Z3s, and so this becomes more critical.

[TurnAround]

Originally Posted by JCL

djbock:

I recommend you get an alignment if you replace the control arms. What leads you to believe that the control arms are the problem? Anything slightly loose in the front suspension could set off a wobble upon braking.

Turnaround:

Here is an article on brake pulsing/shudder due to rotors. The underlying cause is pad deposition on the rotor surface. I used Axxis Deluxe pads with no issues for 40,000 km, but they do need to be properly bedded in. I suspect that your shimmy after 5000 is due to them not being properly bedded.

StopTech : Brake Pulsing

Slotted and/or drilled rotors would be a step backwards for your problem. The scraping that they do is for debris caught between the rotor and the pad, essentially a non-existent problem. You need the deposits on the disk surface for proper braking, you just need those deposits to be even. Your X is heavier than your Z3s, and so this becomes more critical.

I've been through all that with Dave Z. That's who I bought the new rotors from, and have always bought my pads from. Working towards an alternate solution; Bedding the brakes fully on an X5 3.0i has resulted in boiled brake fluid.. to fully bed performance no dust pads. No problem when bedding higher dust pads.

But, thanks for the feedback... really. :-)

[vivanov1]

and in terms of alignment, GET ONE, my arms were changed, and i purchased the car with a 9 degree lean to the right, an alignment is usually around 85 and well worth it

[motordavid]

Imo, the brake wobble feel is very hard to diagnose...a quick search shows pages of threads on the topic with no really clear,
succinct diagnosis and repair. There seem to be several possibilities, and at the risk of "part replacing" to death, I have no real
answer. And, I suffer from the same common malady.

I had new front brakes and rotors, (dlr done under Maint.), 20K miles ago, and I bedded them very carefully by the rec'd methods.

I had an Indie do "InspII" and a few other things 18 months ago, which included them going over the front suspension with a fine
tooth comb...as I was under Warranty Direct's warranty then, I know the Indie was looking for stuff to R&R. His honest opin was
the front end, while not "new", was in very good shape.

My wobble is not always there, but generally appears after "some time" of highway driving; a hard hit on the brakes at 60+ produces
it through the steering wheel, brake pedal to a lesser degree. Less speed usually does not produce it, and it comes and goes, even at
higher speeds.

My point is, even in the threads of similar wonderments, the "obvious" things are diagnosed/pointed out, but there are very few follow
up posts that say, "I got this _____ fixed and now it's fine".

I'm thinking tension struts and, maybe in combo with some other part(s). When I get back to the Mtn I'm hitting my Indie in Asheville
with a directive for him to pour through the front end, as my WD warranty is nearing its run.

To DJBock, Good luck on your diagnosis and repair and please let us know!

And, glad you are home/stateside and safe...thank you for your service to our US!
GL,mD

[TurnAround]

Hi MD! How you bin?

Your experience, is the exact experience I've had.
This is my 3rd or 4th trip around the play pen. I've tried lots of stuff. I think the assessment is; BMW uses ATE brakes which are not as high precision as Brembos. They have movement to the calipers and the "conventional" pads. With pads that dust some, they wear nicely and have no shimmy. The no dust pads are simply not cleaning off the deposits on the rotors in good order. Rebedding the brakes every 4k to 5k is a little impractical at best, and impractical with a 3.0i litre X5 that takes a weee bit longer to get up to 60 on the bed in runs.

Like I said, this same brake part combo works great on the Z3's. One bed in, with a revisit once in a rare while and they seem to be good.

My next experiment is slotted drilled rotors.. which will clean the pads a little.. which will prevent the deposits in the first place. If that doesn't work, its back to the "medium dust" pads.. so they can keep those rotors wearing slightly!

[djbock]

Originally Posted by motordavid

And, glad you are home/stateside and safe...thank you for your service to our US!
GL,mD

Prob the main reason that I am trying to narrow it down. Due for another stint in the not so distant future and want to make sure all is well for the CEO while I am gone.