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Discussion Starter · #1 ·
My car is getting a mild to severe shimmy (left to right steering wheel shake) under hard braking. I first noticed this issue a while ago on my previous set of front rotors (the originals) which were operating fine initially but started to have this judder under firm brake applications which got progressively worse. These original rotors were previously heat spotted, so I ordered a new set of Zimmerman rotors and Textar pads which I installed earlier this year. The new components operated perfectly initially, but this judder has returned. First it was very minor and not bad enough to worry about, but it's getting worse again to the point where the steering wheel shakes quite violently when braking hard from high speeds.

I've inspected the rotors and cannot see any uneven wear patterns or heat spotting on either side. Both front upper arms have been replaced recently, the lower ones are original but there is no apparent issue with them. Tie rods seem fine also. The front left wheel bearing has a minuscule amount of play at 12 and 6 but it is so small it is barely appreciable. Given the severity of the shimmy under braking I think this can be ruled out.

Any ideas as to what this might be?

TIA
 

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Let me share another experience: from my 2008 Evo.
I had replaced front rotors and pads with some inexpensive carbon rotors and xyzzyd pads.supposed to be the greatest products.
However, no idea what happened, whether the installation was wrong or the pads didn’t “bed” into those carbon rotors properly, used to get crazy shimmy at heavy braking. Eventually, the brake calipers bolts got shredded and the calipers themselves were coming loose. Had to get new calipers (eBay used), and got used OEM rotors and pads and everything was perfect.
 

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Brake discs don't warp (let the flaming commence) 😂 - road going cars don't create anywhere near enough heat to warp discs...

It's generally brake pad deposits, bad discs from factory or uneven wear on the pads...

But; it can also be the suspension arms/bushes/ball joints and sometimes their failing is hard to see until you physically remove the suspect joint...

So; 7 series (but same principles); I had replaced all the suspension bar the main thrust arms as they'd been replaced 4 months before I bought the car and the car had just sailed through it's MOT

But started to get a vibration when braking & when driving at speed...

Double checked everything and no go; so stumped up and replaced those arms... And as you can see by the Google link in the post; that's how bad the ball joints were after 4 months of them being fitted! But, no play when they were in situ!

 

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I had a car that needed calipers rebuilt as pistons were sticking
So yes they can warp and it only took 4 mechanics and a year to work that out
 

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I had a car that needed calipers rebuilt as pistons were sticking
So yes they can warp and it only took 4 mechanics and a year to work that out
Pad deposits...

Calipers sticking is very common... But its pad deposits and poor pad wear that'll have been the issue
 

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Discussion Starter · #7 ·
Thanks for the replies.

I'm pretty confident that my thrust arm bushings and joints are fine so those can probably be ruled out. Wishbones are possible but would those create a brake judder unless bushings or ball joints were really bad (they're not)?

Sticking pistons is a possibility I guess but wouldn't I feel this happening? Is there any easy way to test if they are sticking?

As for pad deposits, a visual inspection of both rotors doesn't show any signs of anything abnormal and the pads seem to be making even contact on both surfaces.

The car was in a minor accident previously where the front right wheel struck something like a kerb fairly hard. The wheel, bearing and hub, thrust arm (with bushing and joint) were all replaced. Just wondering if maybe the knuckle got slightly bent enough to cause a vibration but not to have any visual signs of damage? I guess if that were the case the vibration would have probably been there from the start through, not gradually appearing over time.
 

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“Gradually appearing over time”…sounds exactly like my experience, and it was probably the rotor and pads not “bedding” correctly. Google these terms and see if there are signs of this happening in your case. I tried many times to “clean” up my rotors and get them to bed properly with the pads, following the bedding routines, but I guess they were not meant for each other and I failed. Tossed them all out, as I wrote before, and got used oem parts from eBay.
Check your calipers - make sure your bolts are not loose.
 

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I get what you're saying re the thrust arms

But as per my post, they were only 6 months old and zero play when in situ, but when removed the ball joints were buggered!

Absolutely check the inner CV joints and track rod ends too, they can seize and cause issues like this...

But agree with the above too, sometimes pads and discs don't bed in properly and you need to go through the whole procedure again.
 

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Discussion Starter · #11 ·
I get what you're saying re the thrust arms

But as per my post, they were only 6 months old and zero play when in situ, but when removed the ball joints were buggered!

Absolutely check the inner CV joints and track rod ends too, they can seize and cause issues like this...

But agree with the above too, sometimes pads and discs don't bed in properly and you need to go through the whole procedure again.
Given that I used OE Lemforder arms and not cheap chinese ones, unless the parts were defective from factory I'm sure these aren't the issue. I've jacked the car up and had a look at all the ball joints and yanked on everything to check for looseness and nothing had any play whatsoever. I'm aware that properly testing everything would require taking them off the car, but given my previous experience with the last set of rotors and having the replacement ones solved the issue (for a while anyway), it seems like rotors and pads are to blame.

Having inspected the surfaces of the rotor a bit more closley I'm thinking uneven pad deposits might be the culprit here.
Zooming in on these photos I took the other day you can actually see it from afar.

The next question is, do I try and re-bed them on the car by slamming the brakes a bunch of times, or do they need to come off and be resurfaced?
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your pads are not making full contact with the rotor surface.
a genuine BMW pad on a genuine BMW rotor will NOT do this.
there are two possible reasons for this:
1. Your pads are not having even surface - aka, defective.
2. Your pads are not getting squeezed uniformly to make contact with rotor(more likely). This means, your caliper pistons are not applying uniform pressure.

Lets see how to fix this.
1. Spread the pads, and apply brakes to get them back. do this multiple times to make sure the caliper pins are sliding easily. Sometimes, thats all it takes.
2. Next, if 1 doesn't fix, you have to take apart everything, re-grease your caliper pins, wipe everything clean absolutely, and re-install.
3. If 2 doesn't fix, you should get new pads.

In the meantime, avoid hard braking please. you don't want to create extreme stress on the calipers, they will rip the mounting bolts off(they are aluminum).

I spent lot of time examining your rotors. Your 4th hole on the outer perimeter is not getting covered at all by the pads. Compare them to mine, which is shiny clean. A brand new rotor and pad should "bed" 100% right from first application if the rotors, pads and calipers are all working correctly. I still have a good 15,000 miles on my front rotors.
 

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I'm with sunil on cheap pads prob being at fault here.

Other than that no, brake hardware is never aluminum. Newtis states to not grease the pins. And O'Reilly's turned my rotors after my first trackday long ago without any issue for cheap.

Bedding pads usually requires hard braking to ensure full pad contact. Obviously that hasn't happened here.
 

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Discussion Starter · #16 ·
I'm with sunil on cheap pads prob being at fault here.

Other than that no, brake hardware is never aluminum. Newtis states to not grease the pins. And O'Reilly's turned my rotors after my first trackday long ago without any issue for cheap.

Bedding pads usually requires hard braking to ensure full pad contact. Obviously that hasn't happened here.
I used Textar for pads and they're an OEM BMW supplier so I wouldn't call them 'cheap pads'.
The original ones that came off the car were ATE, but small differences in pad makeup material is really splitting hairs isn't it?
Zimmerman's bed-in instructions that came with the rotors went something along the lines of using medium brake force and avoid hard stops for the first 300km. Not sure if that's correct but I'm betting they know what they're talking about.

What I really want to avoid doing is throwing away the brakes and starting from scratch only to have this repeat itself, since I've already been through it once before. Seems like the only answer is to pull everything to pieces and test every component to rule them all out, then if everything tests well assume that the brakes did not bed properly and get different components next time and hope for a better result...
 

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A bad bedding will cause hot spots on the rotors, not uneven pad contact. Your rotors are fine.

The pad is the problem: either the pads are bad, OR the pistons are not pressing them evenly.

You have to make sure its not the calipers by spreading the pads and pressing them back and repeating this several times to make sure the pistons are acting correctly from both sides evenly. Just squeeze out the "dust/dirt" that may be in there. (This has nothing to do with M5 per se, can happen to any car). This whole "bedding" procedure doesn't make sense to me. I have never done this on new cars, or new brake rotors/pads that were genuine original components. The only time they went bad was with my 2008 Evo when i bought some carbon rotors and some nonsense pads and had to bed them over 100s of miles to get that extra stopping power, and they ripped apart my caliper bolts.

The shudder caused the caliper bolts to strip off:
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Discussion Starter · #18 ·
Just went for a short investigative drive and got some better photos of both rotors. With a number of firm brake applications I didn't feel the shaking as much as I recall the other day when attacking some twisties. It was still evident braking firmly in a straight line but definitely not as severe as coming into corners hot and carrying big speed. In other words, its not currently an issue in most driving, but only when properly getting on it.

I checked the temperature of both sides upon returning home (just with my hands, not a thermometer). There seemed to be more heat emanating from the front right (the side that was previosuly hit) rotor and wheel than the left, so maybe that points to a sticking caliper. I'm a little paranoid that maybe the knuckle or caliper carrier got bent in the hit and are causing this but I'm sure if that were the case the shaking would have been there from day one, right? And surely would have made the car impossible to align properly.



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Ah missed you've textar pads. Yes they supplied BMW for the first few years M5/6s, there was a discussion about that the other day. Pads should be good.

From experience those pads will leave deposits when driven at the track. I can see how a sticking caliper can get temps up there. You'd be getting smelling brakes at that point. Do you?

What I thought was not full pad contact is just different rotor shading.
 

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Just went for a short investigative drive and got some better photos of both rotors. With a number of firm brake applications I didn't feel the shaking as much as I recall the other day when attacking some twisties. It was still evident braking firmly in a straight line but definitely not as severe as coming into corners hot and carrying big speed. In other words, its not currently an issue in most driving, but only when properly getting on it.

I checked the temperature of both sides upon returning home (just with my hands, not a thermometer). There seemed to be more heat emanating from the front right (the side that was previosuly hit) rotor and wheel than the left, so maybe that points to a sticking caliper. I'm a little paranoid that maybe the knuckle or caliper carrier got bent in the hit and are causing this but I'm sure if that were the case the shaking would have been there from day one, right? And surely would have made the car impossible to align properly.



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The one thing I did when I had similar issues with Stoptech discs & Ferodo DS3000 pads is I went out for a very spirited drive, later at night when the roads were very quiet and did some hard 70-30mph braking (quite a few times) and then drove around for a good 20mins after that to let the brakes cool off back to normal temps...

That got the pads & discs bedded in nicely again and the deposits and worn off as they should have done and the full face of the disc was shiny...

Could be worth a try as you can see the outer face fine, but the inner face is harder to inspect...
 
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