I recently did a full brake job on my 99 M3. Rotors, pads, lines, rebuilt calipers, and so forth. The issue I'm troubleshooting right now is with the front rotors, specifically the front right. It squeaks once per rev while coasting or if I spin the wheel while it's jacked up. Oddly, it only does it while spinning the wheel forwards.
Here's what I just did, unsuccessfully, to try and fix it:
- Took caliper and rotor fully off, brushed the hell out of any grime on the hub (there wasn't really much since I'd already cleaned it), and reinstalled the rotor with copper anti-seize in between
- Torqued rotor set screw to spec (12 ft/lb)
- Reinstalled carrier bracket and torqued bolts to spec (81 ft/lb) with some loc-tite just for grins. I tested to see if these bolts were loose before I took it apart and they didn't appear to be.
- Inspected pads and they all looked fine and were seated properly, with grease on the backs as usual. The pad attached to the piston was securely attached.
- Wheel bearing seems fine
- I spun the wheel once I had it on and torqued and it was quiet, but once I took a test drive the same behavior returned. Likely because the caliper was looser since I had just taken it off, and tightened up once I pumped the brakes.
Here's a video of it with sound as I spin the wheel (before I did any of the things above):
Any ideas? My best guess at the moment is that maybe this rotor has excessive runout. It's brand new and I haven't even bedded in the rotors/pads yet. I'm hesitant to until I get this figured out. These rotors are Performance Friction V3 two piece rotors ($$$) so it'd be surprising to me if there's a quality issue, but I suppose it's possible. They are slotted, and I've never had slotted rotors before. Do slotted rotors normally do this sort of thing prior to being broken in? I'd expect some noise under braking, but it's odd to me that something seems to be hitting while coasting.
Last edited by TostitoBandito; 02-11-2017 at 10:59 PM.
Thinking about this overnight, it's clear that the only things that could be causing this are the rotor being either warped or unevenly seated on the hub. If it were a pad or anything in the caliper or carrier bracket being stuck or uneven and the rotor were true, it would be dragging/catching equally the entire revolution. This only catches for a short period each revolution, and spins freely otherwise.
So, the only things I have control over which could've done this are:
- The thin layer of anti-seize applied to the hub somehow making it sit unevenly. I'm skeptical about this because I applied anti-seize to all four hubs just the same, and only this one seems to be having any issues.
- The rotor set screw is too tight, resulting in the rotor sitting unevenly. I've only been torqueing it to 12 ft/lb per spec, and I think the last time I put it on it was even less than that (just snug with a ratchet). All it needs to do is line up the holes and keep the rotor roughly in the right place. The lug bolts serve the purpose of evenly seating it once you put the wheel on.
Any other causes have to be manufacturing defects on the rotor itself. My prior OEM rotors never had this issue, so it has to be the new equipment and not something like the hub face.
The rotor screw only serves to hold the rotor in place while you put the wheel on. The lug bolts themselves are what actually hold the rotor to the hub with any serious force. I dont even have my rotor retaining screws anymore. The pad is definitely dragging on the rotor to cause the squeak. Why the pad is dragging I have no idea.
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Did the new brake equipment have a break in period on it? Like 10-15 hard stops from 60 mph
Yeah the noise is definitely from the pad dragging at one small point in the revolution (the same each time). Either because the rotor is sitting at a slight angle, has too much runout, or maybe from some sort of slight high point on the rotor. Maybe the edge of one of the slots is slightly high.
Yes there's a bedding procedure for the rotors and pads. It's similar to most other high performance rotors:
5 light snubs from 50 to 30
5 medium snubs from 70 to 40
3 hard snubs from 100 to 30
5 minute cooldown period with minimal braking
It's possible that this will even out whatever's rubbing if it's just something on the rotor, but I wanted to make sure that nothing was genuinely crooked before I went and hammered my brakes like that.
Ceramic or metallic pads ?
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My next step I think is gonna be to re-lube the guide pins. They're all brand new in new bronze bushings, but maybe the silicone lube (silaramic) I used is sticking or something, causing a pad to drag excessively. I'll hit them with copper anti-seize instead since it's metal on metal and that seems to be what teams like TMS and Bimmerworld use.
So this might be stupid, but is that sound coming from your breaker bar? Certainly seems to be in one place. Does it make that sound going forward and backwards? (from a rotation standpoint)
Can you spin the wheel by hand and have the brake make the same noise? That to me doesn't sound like pad drag...I think that would make a more of a sandpaper sound or something not a squeak?
Ok, finally found it.
The front right caliper was slightly twisted because one of my freshly-installed ECS bronze guide pin bushings had somehow backed out slightly. This caused the caliper to not sit flush on the carrier, causing my pad dragging issue and the noise. Only the single bushing on the front right caliper had moved. The rest were fine.
I fired an email off to ECS with the info, because the bushings were all installed correctly exactly as their guide said. No idea what happened. There's a retaining ring that pops into a groove on the end that the guide pin inserts into, but there's enough space between that ring and the caliper for it to move about exactly as much as it did before it catches on the caliper. I'll need to pound out and replace the two bushings on that caliper since their internal O-rings are all cut up from the guide pin threads hitting them at a slight angle and there may be damage to the bores.
Fun times. At least my OCD about the noise led me to find the problem before anything beyond the bushings were damaged.
To close this out, ECS was great and they overnighted me a replacement for free.
Unlike many other brass bushing kits, these have an internal o-ring which sits in a groove in the end facing the caliper carrier bracket in order to help keep dirt out, and also has a rubber dust cap on the other end. The o-ring has a square profile and is slightly wider than the bore of the bushing so if you slide a guide pin in there right after installing it, it wants to stop once the main body of the guide pin hits the o-ring. In order to fully screw in the guide pins they must slide past the o-ring, and when that happens they tend to actually scrape off some of the o-ring material. This shouldn't really compromise any of the functionality of the bushing, since it basically just levels off the o-rings. Slathering a bunch of extra grease in there might help, but I don't think would eliminate the issue.
What I think happened is that when I screwed in the guide pins they briefly caught on the o-ring as they were being screwed in, and the force happened to be enough to dislodge this bushing (but none of the others) before the pin popped past the o-ring. Once it was dislodged, the act of further tightening the guide pin twisted the bushing and got it stuck in that position. That bushing must have been slightly looser than the others in its bore.
I made some suggestions to ECS including using a slightly smaller o-ring, or an o-ring with a round profile to allow the pin to slide easier past it.
If the pin was catching the square-cut o-ring it seems easy enough to file a small chamfer on the end of the pin to guide it through.
Glad this solved it for you.
I've also found that the bronze bushings are also soft enough that if you have to force them to seat in the caliper that the bore can become distorted. I haven't used the ECS bushings, but some of the others have required some emery paper to make sure the guide pins operate fully smoothly. Binding can get worse as the brakes heat up since the pins and guides are different materials. I like the feel of them on track, particularly the fronts and they do help a bit with pad taper, but invariably, particularly with worn pads, something binds up. So, I keep going back to rubber guides the way the factory intended them - with no lubrication on the guide pins so that at least for street cars, the rubber tension actually helps retract the pads when the brakes are released rather than waiting for the rotor to knock them back.
+1 on ECS
I've looked at those guide pins a few times because in theory they should be easier to take out compared to other brands that might sieze in the caliper. I've run Bimmerworld brass guides for years and have never run into an issue...even on my track car. I haven't had an issue with the pins getting stuck or the brass bushing getting stuck in there.
Copious amounts of antisieze has helped I think and some routine cleaning while you're in there also would go a long way.
Glad you got it sorted out and ECS got you squared away!
The Bimmerworld kit uses clips to hold the guide in place rather than the friction style of your ECS guides.
The ECS bushings have similar retaining clips. They sit in a groove in the long end of the bushing. In the pics I posted, it's what's preventing the bushing from sliding out anymore since it was hitting against the caliper bore (you can just barely see the clip in the properly-seated bushing in the overhead shot). Ideally the retaining rings would sit closer to the caliper bore to not allow any movement, but they have to allow wiggle room for fitment in different calipers with different amounts of clearance available. The only better solution would be some sort of clip or ring which could clamp on to the smooth surface of the bushing without the benefit of a fixed groove, and could be placed anywhere for custom fitment, but I'm not sure how that would work.
I also want to give a shout out to Performance Friction. I had emailed them earlier when I thought it might be their rotors, and they gave me a call yesterday to check in and discuss with me. They're very responsive and helpful for a small manufacturer who does most of their business with various racing series and not plebs like me.