front brake issue - steering wheel wobble - 2003 E-39

I have a 2003 540i with the M-5 Sport pkg that now has 180k miles and runs great, but for a brake issue:

I keep getting steering wheel wobble in the steering wheel. Here is a brief summary of what I have done and the issue keeps coming back.

Replaced the front thrust arm bushings twice in the last 12 months
replaced the front control arms
replaced the front struts
replaced the outer tie rods and center tie rod link
replaced the front sway bar bushings
replaced the front calipers twice in the last 12 months
replaced the front brake flex lines
replaced the front wheel hubs
replaced the brake caliper slide pins and bushings more than once
vacuum bled the entire braking system
replaced the front rotors 4 times in the last 12 months. two sets of Meyle rotors, one set of BMW rotors (turned them twice), and currently have a set of Brembo rotors

The last time I replaced the front brakes, pads and calipers (two months ago) I had them installed by a BMW factory tech.

The issue is that I keep getting a wheel wobble about a month after I replace or turn the rotors. For about a month, it drives and brakes perfectly and then slowly but surely the wheel wobble comes back. It was so bad last summer when this issue started that I actually shredded a set of new thrust arm bushings..

The only pattern I am beginning to see is that the pins seem to getting gummed up. I started using synthetic brake caliper pin grease and am currently using silicone for the pin grease.

Recently it was suggested that I use "copper never-seize" as it may hold up better and not gum up.
I plan to try that this weekend.

I have been working on cars for decades and never encountered anything like this and no-one has given me any clues as to what to do.

Any intelligent input would be greatly appreciated.

Best Regards

Chris

Ok, weird - if brakes cause a problem, seems to me the typical issue is a pull to one side or the other, not a wobble in the steering, and a pull is uneven clamping or drag for some cause or another, which your efforts should have covered (hanging caliper, caliper piston sticking, slide pin issue, etc. - &, stock slide pins are pretty squishy, even if they get sticky or dried out, kinda hard for metal to get hung up much on new or old rubber, considering the forces involved with the braking system). If your rotors weren't warped, I'm not sure how it could be a brake rotor problem, and usually, you only feel rotor warpage when you brake as a shake in the steering wheel. Now being on your 4th set with all sets you tried being quality brands, seems unlikely that rotors themselves are an issue.

Not clear on that point, are you getting steering wheel shake only under braking, or all the time, after awhile?

If it's only under braking, then sounds like it's some really oddball issue. Typically if there was a problem with the ABS system you'd expect a warning light, but complicated electronic systems, who knows what can go haywire - if you're in the situation where you're getting the wobble, maybe disable the ABS on the theory one front wheel ABS circuit is freaked and pulsing rapidly under braking (which I'd think shouldn't be warping rotors, if it was doing that) Presumably though, you'd feel ABS pulsing in the brake pedal when braking.

If it's all the time, I'd be suspecting something other than everything you've replaced, maybe a loosey/worn steering box, although that would manifest itself all the time and would seem unrelated to anything brakes, although I suppose a shake could be worse under braking due to the front loading.



You've replaced the tie rods (9,10 & 11), so that leaves 1 & 5, the pitman & steering arms, but, having done the tie rods, seems like having had eyes & hands-on 1 & 5 would have already covered that. You did front struts, if you'd seen any issue with the top strut bearings, would have addressed that... If it's wobble under braking only, the flexible rubber coupling on the steering shaft would seem unlikely, if that's deteriorated it should be an all-the-time issue...Any chance of metal fatigue cracks on any kind of mounting tabs, say off the front axle support? I could think wheel bearings, but since you've done those, only if they weren't gotten back on completely, which seems unlikely since it sounds like you have plenty of experience...

I've used a vacuum bleeder for years, but have found it to be less than ideal in some situations for getting air out of the brake system - if you haven't needed to replace the master cyl. then I wouldn't suspect air in the lines to be an issue, even of itself, and even less to be doing something that ends up as steering wheel shake. I'd say maybe try a pressure bleed or foot-pump-the-brake-pedal bleed although kinda hard to think that would make any difference. Can't quite imagine how some air in the lines might cause an issue, perhaps with the ABS system, that could get you a steering shake - besides which, you'd have a squishy brake pedal with air in the lines.

Some additional parts diagrams for a memory jog, although not covering everything you mention...



Ok, to step outside the mechanical for a moment - since you mention turning rotors, are you finding that you're getting warped rotors?

If perchance with no luck landing on a mechanical cause, that would mean they're getting hot somehow - any chance you're doing anything different driving-technique-wise? If you have an automatic and habitually brake with your left foot, it wouldn't be unheard of to be unawares of lightly dragging the brakes; human muscles won't stay in tension/contraction all the time, and it would be easy in trying to hold one's foot up that the foot muscles relax slightly without even realizing it. 5'ers are big cars, if you're driving around regularly with some degree of, uh, 'exuberance', I could see an easy possibility for ending up with hot brakes and warped rotors. I'm kinda guessing though you'd be aware of the human-induced possibilities here also. Sorry not to have anything singularly specific to suggest, maybe Charlson will have some ideas.

Thank you so much for the response. This is comprehensive.

Just to be clear. The issue goes away if I turn the rotors or replace the rotors.

1. It is not an ABS pulse.
2. The wheel shimmy is only felt under braking and the wheel shimmy is most felt around 50 mph.
3. the car is an automatic and I do not brake with left foot....
4. I commute approx. 150 miles per day and most of it is highway. I do not race the car but am not afraid to use the brakes. I have never experienced anything like this....I am 52 so I have been driving for a while.
5. As an example. If I am going 90 and apply the brakes to gently slow down, I do not feel any wheel shimmy until I get down around 50-60 MPH.
6. Any thoughts on the copper never seize instead of silicone or synthetic slide grease?

Best Regards

Chris

Hey Chris - hrrmrmrrrm... I'm kinda hard pressed to think different lubing on the slide pins makes a whole lot of difference; the rubber slide guides/sleeves that go into the caliper (if E39 is similar to what I'm familiar with) are what, like almost an inch in diameter? And the slide pins run through the middle hole of those, which are a good bit smaller diameter (1/4" or so?) - since the guide inserts are rubber, and there's that much space for some movement (motion restrained by the positioning and compressibility of the pin guide rubber), relatively speaking, there's a good bit of room for the slide pins to move/vary their position. That being the case, most any appropriate lube I'd think would work alright, and obviously you've tried application-appropriate lubes so far. There's certainly no harm, as far as I know, in trying the never-seize, I'm skeptical it would make a difference or solve the issue. As for the pins getting gummed up, to some degree the lube/grease always gets dirty, that shouldn't be hanging up the slide pins, at least I wouldn't expect so.

I've had uneven pad wear on single-piston BMW calipers, I attribute that primarily to the flex in the rubber slide pin guides/sleeves/inserts - typically, you should be seeing similar wear on both sets of front pads, not unusual to have the piston-side pads worn a bit more than the outboard pads, maybe that's something to look at, obviously if one set of pads is substantially more worn than another, that would indicate some sort of caliper issue. But, seized calipers or sticking pistons (presumably eliminated by caliper replacement already) would also typically show up as a pull.

No pull from high speed braking would indicate even braking pressure to the rotors, so that would seem to rule out higher up the chain - master cyl., ABS unit, hard & flexible lines to the calipers.

Hitting a shimmy at a specific speed range under braking that seems to be fixed by new or turned brake rotors... some vibration harmonic perhaps presenting itself at that speed for some reason... if rotor warpage is the problem, from what you're saying, I'm at a loss to think what might be making rotors warp, even more stumped if both fronts are warping.

I'm gonna hold for Charlson's input before further speculation for the moment, he's a tech with experience across a broad range of bimmers, hopefully he'll have some insight, he'll probably be checking in later in the evening.

Chris,
This is quite a crazy issue you having since you have replaced a lot of things. So the first thing is to check is how the rotors surface looks front and back. You need to see if there is any blueing of the rotors this would be a sign of overheating from say a hung up caliper or sticking slide. When you say you replaced the hubs did you also replace the wheel bearings? Suspension and steering should not effect this system. If no blue is found on the rotors you need to see if the rotors are actually warping or are the pads causing the issue. This can be done by a test cause rotor thickness variation. What you do is get one vernier brake caliber tool and divide the rotor into 8 different sections basically like pie slices. Measure each one and record it if any two measurements are over .030mm then the rotors are warped. Also take you measurements 25mm in from the edge of the rotor. If the rotors are under that spec then most likely the pads are causing the issue. What type of pads are you using? Another test is to burnish the pads and see if the shaking get better. To do this you need to do 60mph to 10 mph stops around 10 times of course waiting enough time in between to cool the brakes. If it gets better then the pads are causing the issue. Lets start with this stuff and let us know how it goes.

1. The hubs and bearings were replaced as a set.
2. No blueing.
3. Have used Paged pads and BMW pads. Was planning to try Brembo next if I change again...Currently have Brembo rotors and Pagid pads installed.
4. Will check rotors with caliper as described.
5. Have not burnished the pads as described. Let me check rotor thickness first and get back to you.

Appreciate the help...Yes I agree, this is nuts.

One consideration is something wrong with huh/bearings replacements. I had a similar issue at certain speeds. I have 160k on mine, and it boiled down to the hubs/bearings on my driver side. I have heard of replacements needing to be replaced very shortly after being installed. No idea what can go wrong other than a manufactures defect. Of course these cars seem to chew through bearings for some reason. I do them myself, so it doesn’t cost me much other than the bearings. Plus, you know all the bolts will be new and therefore easy to remove relatively speaking when you do the job.
Just one guys opinion of course. I say that having looked through your extensive problem-solving work and myriad other attempts. Replace one bearing at a time, and you might get lucky.

I also had a control arm go bad after installation because my shop did not load the suspension effectively before tightening up the bolts, but it looks like you’ve eliminated that in your extensive work.