New Front Brakes - Shimmy after 1 month - why me?

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E9KNZ047

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Hi - Some advice please. I have recently (twice) had new front pads put in - first time the discs were also machined and the second time the discs were replaced. In each case after about one month of daily commuter use when braking I would start to feel a shimmy(Aussie expression ?? or accepted mechanical term ??) through th steering wheel - i.e a very obvious wobble only when braking. The pads installed were Lucas initially then Bendix - I have been told these pads are too hard and therefore causing heat build up and glazing on the discs leading to the shimmy or wobble developing only when braking. Does this sound correct or are there other potential causes?
I have ordered BMW supplied Techstar now and hope this will rectify - do I need a specific brand of disc rotor as well perhaps ?
Has anyone else had a similar problem or can offer any advice I would be very grateful.
 
Shimmy is also used in the US to describe this, who knows what the Brits and Scots my call it. :roll:

It sounds like a case of very bad luck. Many times if your disks become warped (usually due to extreme heats - long down grades without engine braking) they cannot be successfully machined. The disk metal can winds up with different hardnesses in different spots. I suspect that this was the case the first time you had your brakes serviced. With new disk being installed it is unlikely that you have heat stress them unless you've done some serious mountain driving or pulled heavy load (image that with a coupe?) More than likely you just got a bad disk (soft spot that wore quickly) - it would only take one bad disk to telescope shimmy into the steering column.

IMHO it is unlikely that that hardness of the brake compound had any major bearing on with this. Hard compound simply wears out the disks faster than the pads.

There are a few other possible sources of shimmy during braking; however, none I can think of that would wait a month before re-appearing after brake service.

Since it has only been a month could you ask for a set of replacement disk?
 
A comment on the article by the gentleman who has never seen a warped disk rotor, I have in my possession one very warped rotor recently removed from TBL. Yes it is possible to warp a rotor but on a daily driver it is, indeed, very unlikely. You can check the rotor for warpage or buildup by removing the road wheel and turning the hub (remember the caveat to lower all the windows slightly before jacking the car up). Also check wheel bearings, steering linkages and ball joints for excessive play.
 
A comment on the article by the gentleman who has never seen a warped disk rotor, I have in my possession one very warped rotor recently removed from TBL. Yes it is possible to warp a rotor but on a daily driver it is, indeed, very unlikely. You can check the rotor for warpage or buildup by removing the road wheel and turning the hub (remember the caveat to lower all the windows slightly before jacking the car up). Also check wheel bearings, steering linkages and ball joints for excessive play.
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Which is the crux of the article. Yes on a racecar this is possible but look at the extremes in temperature that a rotor endures at a typical track session. This rumor got started on the track circuit and moved over into the mechanics shops for daily drivers. The vast majority of brake wobble comes from pad material that is not evenly distributed due to improper pad bedding. And from the OP's original post he is having this problem "only when braking" which would probably rule out a suspension issue. Although go ahead and check everything just to be sure.
 
Shimmy Shimmy

I concur with the sentiments regarding warped rotors, irregularly bedded/glazed pads, but there are a few other things you may wish to consider.

It may sound counter-intuitive, but I would not be surprised if your new found shimmy is only indirectly related to braking. If you have a "newly" out-of-round or out-of-balance tire(s), your braking may only be exaggerating one of those issues. Have you hit a pot hole, curb or road hazard recently? Missing a wheel weight? Have you locked a wheel up (skidded) so that a tire may have developed a flat spot? Are you certain all of your lug nuts are properly tightened?

All of these things can contribute to some of the shimmy you describe. In fact, but for the "only-when-braking" that is the first place I would look. It is also possible for a tire to have a belt separation that you may have previously overlooked; the tread may be harboring a lot of road gravel, or you may even have a bunch of hardened mud on the inside of your rims.

Another thought is loose wheel bearings, worn/loose upper strut bearings/mounts. or worn struts.

Again, I am not saying for certain this is the root of your braking issue, but it is within the realm of possibility and simple, if not inexpensive, to eliminate as a contributing factor.

If possible, consider rotating the tires to see if it changes the shimmy. Maybe you will get lucky and everything will be fair dinkum . :)
 
I think we are struggling with a semantic issue. A warped rotor is generally not truly warped. They become unevenly worn; that is they have non uniform thickness. As for it happening, I have personally had a few in my life and I have discarded more than a few customer rotors after unsuccessfully attempting to turn them back to specifications (way back when I was a mechanic).

Also in my experience incorrectly bedding the pads almost never results in "warping" but rather it results in glassed over pads which have little stopping power. The notion of unevenly deposited brake material on the surface of the rotor is interesting but I am not sure I believe.

The notion of an existing problem being amplified makes sense only if the problem occurred almost immediately after brake service.
 
Shimmy shimmy followup

With respect to those who may have far more experience than I, I have suffered my fair share of warped/burned/blued and even cracked rotors. Try heating your brakes on a downhill grade when another vehicle manages to splash the contents of a cold mountain stream on your heated brakes. Not mine, but I witnessed it.

Have also seen brake disks seemingly etched with brake pad residue well after they were supposedly bedded in. (personally think the friction material was poorly manufactured.) My point is that while not the most probably scenario, these things happen. Ever see brake pads rust to the rotors? One night in inclement weather may be all that it takes with the right metal master pad - despite all of the added graphite!

As to nonbrake issues manifesting themselves as braking issues, consider the possibility of a few loose lug nuts thereby increasing the runout of the front wheel(s). If you are lucky and travel only in a straight line, shimmy might be the only consequence you or your car suffers. Torn, broken or decomposed braking strut bushings may also change the suspension dynamics when braking. Then there's always loose caliper bolts or other slightly worn suspension parts that only seem to show their respective weaknesses/wear under braking.

Again, this is not a criticism of the other's opinions, just merely my humble observations.

Respectfully.
 
It really isn't about semantics, nor is it about flat spots, loose lugs, or suspension issues. I too came from the old school train of thought that brake shimmy is the ubiquitous "warped rotors", until I saw the light.

These issues have been researched by some pretty astute, DIY'ers, racers, and companies including Bentley who no longer advocates turning rotors and BMW itself, which no longer turns rotors.

These coupled with the links that i provide (I have more if interested), show that there is something else at play here other than "warped rotors".
 
until I saw the light....something else at play
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What light was that? What is at play? From your article...which talks about measurable thickness variations (TV)...
This uneven deposition results in thickness variation (TV) or run-out due to hot spotting
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Sounds like semantics to me. Call it what you will: flat spots, warpage, metallurgic change due to heat and cooling, pad material deposition, thickness variation. Back in the day, there were plenty of non-metalic pads so I don't think metal deposition was the cause of all of these warpage problems despite what the article might imply. I would suggest that "depostion" problems and simple non-uniform tangential wear is due mainly to minor variations in the metal grain crystallization of the rotors when they are manufactured (cast). This could explain both hard and soft areas as well as a tendancy to accept metalic pad deposits under certain conditions.

So, with all due respect, have you ever turned a rotor? I have. When they do not have a smooth surface it is obvious, whatever the cause. The lathe with not cut smoothly. This is when I would toss them as they will never be right again. Perhaps the "astute people" don't advocate turning rotors because once there is a problem with rotor, turning won't help! It never did for me. On the other hand, turning is great for removing uneven radial wear and ridges.

To E9KNZ047's particular problem, there is also the mundane possibility that the pads were not properly cut or mounted and they are hitting the little nub whose job it is to make the brakes vibrate and cause people think their brakes are shot so they take the car to the shop before real damage occurs. I've never seen it but is it possible.
 
So, with all due respect, have you ever turned a rotor? I have.
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I used to do so religiously. I used to have my NEW rotors turned to remove any errant debris or casting imperfections. And I still have nothing against turning rotors.


When they do not have a smooth surface it is obvious, whatever the cause. The lathe with not cut smoothly. This is when I would toss them as they will never be right again. Perhaps the "astute people" don't advocate turning rotors because once there is a problem with rotor, turning won't help! It never did for me. On the other hand, turning is great for removing uneven radial wear and ridges.

To E9KNZ047's particular problem, there is also the mundane possibility that the pads were not properly cut or mounted and they are hitting the little nub whose job it is to make the brakes vibrate and cause people think their brakes are shot so they take the car to the shop before real damage occurs. I've never seen it but is it possible.
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One thing is for sure brakes and brake work is one of those topics that will engender heated debate (no pun intended) wherever you go.
 
Thanks to all for your advice and opinion - I have learnt a good deal more about brakes than I expected. I intend to get the existing rotors refinished given they are only a month old and the vibration is only just recurring , have the BMW supplied pads mounted and follow the brake bed in process supplied- which I had not done previously. Will also get the mechanic to eyeball the front-end, w/bearings to cover off although I am pretty sure that area is fine.
Will advise the outcome in a months time..hopefully not sooner :)
One other very important note I picked up - when jacking, hoisting the car to ensure the windows are slightly down - guess this is due to chassis twist and cracking the windows..better safe the sorry.
Thanks again
 
Not sure I'd blame the brakes. Check your tie rod/control arm ends and wishbone bushings for cracking rubber or excess play. Try it with the wheels on the ground and in the air. Any extra play in those will result in shimmy, especially on braking.

Leaking oil from motor seals, power steering hoses or strut towers will destroy rubber in no time, so if there's a leak, fix that first.
 
Thanks to all for your advice and opinion - I have learnt a good deal more about brakes than I expected. I intend to get the existing rotors refinished given they are only a month old and the vibration is only just recurring , have the BMW supplied pads mounted and follow the brake bed in process supplied- which I had not done previously. Will also get the mechanic to eyeball the front-end, w/bearings to cover off although I am pretty sure that area is fine.
Will advise the outcome in a months time..hopefully not sooner :)
One other very important note I picked up - when jacking, hoisting the car to ensure the windows are slightly down - guess this is due to chassis twist and cracking the windows..better safe the sorry.
Thanks again
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I think you are on the right track. The brakes are the logical thing to check off your list first. If you have gone through the procedures outlined above and you still are having problems then you can move on to other areas in the front end.
 
Oh yeah - forget to mention that if paint your calipers red and you'll shave at least 10 feet off your 60mph stopping distance. :twisted:

... that may only be for Corvettes and Porsches through, I can't always remember these things correctly.
 
Know as runout to us on this side of the ditch

Besides the checks mentioned before take the roadwheels off and using a dial gauge measure the runout/ warp/shimmy/ variance as you slowly rotate the disk on the hub.
Place the dial gauge at the outer edge of the disk and then in the middle of the swept area.
I can't remember the specs but I can look them up for you if required.

When a new disk is mounted the mounting face on the hub and the disk must be clean and free of rust etc

Malc
 
This is a very common problem on the 535i and it is directly related to worn out bushings. Replace the rotors and a month later the problem returns. I rebuilt the suspension on my old 535i and the problem went away. Another thing to keep in mind is the torque on the lug nuts. The heat transfer from the rotors to the wheel is a function of the lug nut torque; you don’t want to over torque the lug nuts (75 ft-lbs). Don’t use an impact hammer for tighten the lug nuts, use a torque wrench! Most likely it is the bushings. A quote from the E28 forum “A very common problem with the e28's. The bushings in the control arms tend to wear out pretty quick, causing the car to vibrate violently when braking at high speeds. The upper control arms have always been more noticeable(to me) when braking because they tend to "thunk" and move the entire shock assembly every time enough brake pressure is applied - While the lower control arms have always had the distinct vibration quality”

HTH

Scott
 
This is a very common problem on the 535i
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And that relates to the Coupe how?
I really don't understand the logic in this forum. The OP clearly stated that he encountered a shimmy when braking RIGHT AFTER doing front brake work on his coupe. Why would you take that information and glean that the problem must be with the front suspension? The first thing I would check if I had just done the brakes and then encountered a shimmy during braking would be...ummm, the brakes.
 
What‘s to understand? It is about sharing knowledge and experience to help each other out. What I don’t understand is the arrogance of your post! This forum is to help people not lambaste other members because you think you have the only correct answer to someone’s problem. My experience was identical to his except it was a different BMW. How does that relate to a coupe? I don’t know how many BMW’s you have been under but suspension is very similar on all of them, they just keep improving their basic design. I had a shimmy during braking on my 535i so I also assumed the rotors were warped. I replace rotors and pads and guess what, about a month later the shimmy returned. It turned out to be the control arm bushings were worn out. I replaced the all the bushings, ball joints rotors and pads and never had the problem again. So does “And from the OP's original post he is having this problem "only when braking" which would probably rule out a suspension issue” this problem must only apply to the coupe suspension? Doesn’t it make sense to you that if the bushings are worn there is excessive slop in the front end and applying the breaks would cause a shift in the location of the control arm starting a vibration in the front end? MichaelP suggested the same thing as I did, maybe he knows something too?

I’ve been on this forum long before it migrated over from Road Fly the intent has always been help each other out with information not chastise people. It is because of my past experience I’m 90% certain it is the suspension and not “pad bedding” yet I didn’t write a nasty post lambasting you four your suggestion did I? In general our posts should be limited to helpful advice and the arrogance should be left out. This poor guy has done his brakes twice now maybe it is time to consider other possibilities besides the pads?

Ummm,

Scott
 
Shimmy

I only scanned over this string and did not see any mention of the possibility that the shimmy is being caused by a worn out steering stabilizer. The steering stabilizer is sort of a shock absorber for the steering system. I have seen them in the past create exactly the symptoms described. I don't own a coupe yet and am not sure if they are so equipped. But when they are worn out they create a shimmy when the brakes are applied, especially when traveling downhill.

The other possibility that I have personally experienced is that worn out brake calipers can create a shimmy. The bolt holes in the caliper can be worn enough to cause this when brakes are applied.

The last item I would suggest is worn ball joints. This condition can bypass a good working stabilizer and create a shimmy.

Good luck with your troubleshoot,

Cheers,

Eddie E.
 
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