Front brake & steering wheel vibration shudder solved

[TurnAround]

This might jynx me now that it appears solved but... here goes; You guys were really great over the years in helping me to diagnose this problem so I wanted to report back some good results, benefit others having the issue, and generally say Thanks for the assistance!

Problem: When using after market low dust pads; Steering wheel shudders fairly violently, and can feel front brakes shuddering as well, when braking above 50 mph. Faster you're going, more violent the shake. Once 'heated', re-braking within a few second does not produce the shudder. Wait one minute or more and brake again.. the shudder is back. Substantially ruins driving pleasure. Makes you hate your boss and that crummy sandwich you had for lunch.. ha..

Troubleshooting Work: Replacing pads, or, removing existing pads, sanding them, and remounting... either will result in eliminating the shuddering / vibration during braking... for about 2 months. Then it returns.

Diagnosis: Normal brake surface deposits are building up on the pads and rotors. Happens with all cars. Happens more with low dust pads because they're not burning off the deposits. Central to issue tho; Because brake deposits form unevenly (normal / expected), when braking the deposits set up an opposing pattern of "Grab a little more / Slip a little more" Grab, Slip, Grab, Slip... on each wheel. Now, because the two wheels can't possibly have the same deposit pattern ever, they're grabbing micro harder at different instances. Chaos pattern sets in and steering wheel vibration starts (steering is 'caught in the middle' of the uneven deposit 'fight'). Now add in that 5 series suspension design for this era uses a forward facing strut, and that has rubber bushings that are a semi hollow triad design and easily wear out. Great handling and ride qual, but wear out in 40k miles. The worn bushings allow, encourage and amplify the chaotic shuddering pattern set off by the uneven deposits, and now the steering wheel vibration is near violent.

Partial Solution #1: Replace every suspension part that uses rubber! Done that. Car drove like new again. Still had some 30% shudder though. Some folks report that all shudder is gone. Not for me though.

Partial Solution #2: Replace low dust pads with BMW OE recommended high dust pads. They keep the rotors and pads free from uneven deposits. That dust you see on people's wheels.. that's the grave yard for the now dead brake surface deposits! Me... can't handle the high dust. Tried partial metalics and more of the shudder when away (almost all of it), but then had unacceptable amounts of dust still.

Final Solution: Went with Centric StopTech SportStop Slotted & Drilled rotors. They're keeping the uneven deposits from forming .. at least.. below the threshold of enough of them to cause shudder. Or, the deposits may still be there at the same levels, but (I think this is key) the slots and drillings 'cancel' the chaos pattern set up by normal rotors (Google Chaos theory and how its in every day life but we don't see it). I suppose other brands of slotted and drilled rotors would work too. Not necessarily saying that only these will do the trick.

Results So Far: Its been over a year now. I wanted to wait that long before posting, because, in the past simply replacing the rotors or pads would 'seemingly' eliminate the problem, but it would come back months later when the uneven deposits inevitably formed again and the 'fresh surface' of the low dust pads had aged and 'filled up' and couldn't keep up with removing the deposits.

Maybe the shuddering will come back at 18 months or something like that. Who knows. Just saying, its been over a year now and the X brakes like it did brand new. Zeeeero shudder. Very positive and responsive brake feel. I'm using Centric Posi-Quiet Ceramic pads. SUPER low dust. Basically zero dust.

My suspension is all up to date ('cept for some front sway bar guides) and the car handles great. But I learned from you guys, that work should just be done no matter what to get your German machine back to day one handling anyway.

Cross yer fingers.

Thanks for the TONS of information on suspension you all provided. I learned sooOOOooo much. Thats what I love about this forum. I've always wanted to understand suspension better and now I do. Excellent "Brain Trust" here on this board!