Seizing caliper?

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Originally Posted By: OVERKILL
I don't think I'll have time for that in the next few days however, as I have a VERY busy month coming up unfortunately

I kinda wish you'd waited until you actually had time to carry out the advice you're receiving.

Some Googling indicates that your M5 has 2-piston floating calipers. This complicates things greatly, for now you have twice the probability of a seized piston on either side. Plus you have the standard floating-caliper bugbears of seized pads and seized pins

And you definitely need to check for trueness of the rotor. I see your rotors are slip-on over the hub. This adds yet another variable: rust buildup between rotor and hub. This can make the rotor wobble as it spins. To confirm the presence of that, you need a dial indicator (cheap Grizzly one will do).

Pistons can rust (or are yours stainless?) and old brake-fluid can cause really thick gum to build up. You MUST check for all the above things or you're wasting your time and everybody else's.

Considering that you live in the Rust Belt, and considering the age and the unknown maintenance history of the vehicle, anything anybody tells you now is a guess. You need to do what I've said, and actually look at the parts in question the way I said to.
 
Originally Posted By: Tegger
Originally Posted By: OVERKILL
I don't think I'll have time for that in the next few days however, as I have a VERY busy month coming up unfortunately

I kinda wish you'd waited until you actually had time to carry out the advice you're receiving.

Some Googling indicates that your M5 has 2-piston floating calipers. This complicates things greatly, for now you have twice the probability of a seized piston on either side. Plus you have the standard floating-caliper bugbears of seized pads and seized pins

And you definitely need to check for trueness of the rotor. I see your rotors are slip-on over the hub. This adds yet another variable: rust buildup between rotor and hub. This can make the rotor wobble as it spins. To confirm the presence of that, you need a dial indicator (cheap Grizzly one will do).

Pistons can rust (or are yours stainless?) and old brake-fluid can cause really thick gum to build up. You MUST check for all the above things or you're wasting your time and everybody else's.

Considering that you live in the Rust Belt, and considering the age and the unknown maintenance history of the vehicle, anything anybody tells you now is a guess. You need to do what I've said, and actually look at the parts in question the way I said to.


- The Car has single piston calipers. The next generation M5 after mine has twin-piston.

- As in the original post, I had the caliper OFF the car. The pins slide freely and do NOT BIND.

- The pads move freely, and I cleaned and lubricated their contact points, as indicated in the opening post.

- I have a dial indicator, I'll dig it up.

- The hub and mating surface are clean, I checked that. They were off recently.

- The pistons are rusty as heck inside where the pad clips slide in, so I'm going to go out on a limb here and say they aren't stainless
wink.gif


- I've looked at everything except the inside of the caliper, because I can't take it apart without risking making the vehicle undriveable. That's WHY I created this thread, to get some idea BEFORE I dug in any further so that I'm not wasting MY TIME by giving myself a vehicle I can't drive while waiting for replacement parts. I'm sorry if you took this as wasting your time and that of other members, that was not my intention.
 
It is NOT the brake hoses. If the BMW was 20 yrs old, maybe. I am running on original hoses.

I have developed a process of fixing sticky calipers.First, I free up the bleeder. Then, I take the caliper off the carrier. Next, I slowly pump the brake pedal to ease the piston out until I can grab it with pliers. I pull the piston out and wire wheel the rust off its top. If there are any corrosion blisters on it, I file them smooth. I use Syl- Glyde to re-assemble. I make sure the bleeder is clean . I use a 6" C clamp and a hammer to start the piston back in. Twist, twist, tap, tap. The piston seal is at the top, corrosion in the barrel wont affect it. Bleed the system and you're done. The rubber parts are fine to re-use, so I don't even bother with the rebuild kits any more.
 
Getting any pedal pulse ?

Regardless if you had them done 6 months ago , one session of some hard braking that gets a rotor hot enough and it can warp .
 
Originally Posted By: OVERKILL
It is like the caliper is putting just a bit of pressure on the pad and it shouldn't be.


There designed to put a bit of pressure on the pad. That's why the wheel spins so much easier when the caliper is removed. You just need to spin both wheels with the same force and count the revolutions.
 
Originally Posted By: OVERKILL
- The pistons are rusty as heck inside where the pad clips slide in,

Then there is a very high probability that there is rust on the piston under where the dust boot covers it. And very likely gum from the old brake fluid as well. Something like this:
01.jpg


Yes, that's a Honda rear brake, but the principle is identical. Rust/gum causes the piston to stick and refuse to retract as it should. If you can get a Channel-Lok onto the piston, rotate/pull it out of its bore until you can peel the boot back. At that point any rust/gum will become abundantly evident.

BUT... you need to inspect everything properly, and check the rotor for runout with that dial gauge. With your car's age and lack of correct servicing, anything is possible. This is the sort of job garages hate, but that somebody like me would find to be fun.
 
Apply Syl-Glyde to the contact points between the caliper and the pads too. Specifically, on the inboard pad backing where the piston makes contact and on the outboard pad backing where the caliper fingers make contact. Also, IIRC your application contains a metal anti-rattle clip which maintains pressure on the caliper. Lubricate its contact points as well. HTH.
 
The brake hose can look good, but the damage is inside the hose and can actually prevent all the pressure from releasing. Bad hoses cause a lot of premature pad failures.
 
Originally Posted By: GSCJR
Apply Syl-Glyde to the contact points between the caliper and the pads too. Specifically, on the inboard pad backing where the piston makes contact and on the outboard pad backing where the caliper fingers make contact.

Sil-Glyde is a bad choice for the applications you mention. Molykote M-77 is the very best stuff to use in this case.
 
Originally Posted By: GSCJR
Apply Syl-Glyde to the contact points between the caliper and the pads too. Specifically, on the inboard pad backing where the piston makes contact and on the outboard pad backing where the caliper fingers make contact. Also, IIRC your application contains a metal anti-rattle clip which maintains pressure on the caliper. Lubricate its contact points as well. HTH.


That's all already been done yesterday
smile.gif
However I used the Permatex synthetic brake lube, not Syl-Glyde.
 
Originally Posted By: Tegger


BUT... you need to inspect everything properly, and check the rotor for runout with that dial gauge. With your car's age and lack of correct servicing, anything is possible. This is the sort of job garages hate, but that somebody like me would find to be fun.


I don't mind doing it either, I just figured that getting a 2nd (3rd, 4th, 5th....etc) opinion on what was going on would help
smile.gif
And your advice has been invaluable, so I thank you for that.

I'll update this thread once I've had a chance to inspect the piston.
 
my bet is either rotor warped or wobble from buildup, the dial caliper is your best friend, test the rotor surface, then remove rotor and test hub/bearing surface
 
Originally Posted By: Tegger
Originally Posted By: GSCJR
Apply Syl-Glyde to the contact points between the caliper and the pads too. Specifically, on the inboard pad backing where the piston makes contact and on the outboard pad backing where the caliper fingers make contact.

Sil-Glyde is a bad choice for the applications you mention. Molykote M-77 is the very best stuff to use in this case.


You've been on this forum long enough to know that the words "best" and "bad" are subjective. I have done more brake jobs than I can count and Syl-Glyde has never caused a problem when applied correctly to the brake pads. "Now back to our regular scheduled program." @Overkill, Perfect!
 
I was having almost the exact same problem on my dad's 2002 Jeep Wrangler that you are with your BMW. I did a pad and rotor job and everything went perfect. I even flushed the brake fluid and put anti-sieze on the new rotors to stop the rims from sticking. The jeep stopped great and the pedal feel was much better. After a week of normal driving, it seemed like the alignment was off and the brakes were squeeking when driving at low speeds. Over a period of 10 minutes, every time I stepped on the brakes, the whole jeep pulled to the right hard. It got so bad that I almost had to cut the steering wheel all the way left to make a hard stop and keep the truck on the road.

I took the wheels off and found the passenger side caliper locked and not wanting to release at all. I opened the bleeder and pushed the piston back again, inspected everything and everything looked fine. I put the wheel back togther and tested it out with the jeep still on jack stands. Sure enough, the piston would press out into the pad but it would only retract about 1mm. I replaced the caliper and everything has been working great since.

Before I turned in the caliper for the core charge, I took it all apart and found nothing really wrong. I then tested my brake hoses by pumping the brakes a bunch of times, releasing the pedal and then opening the bleeder to see if the fluid was pressurized by a failed brake line. Almost nothing came out, the brake hoses were fine.

Long story short, the caliper in a 2002 jeep wrangler randomly locked up and wouldn't release. No ryme or reason to it, it just didn't want to release anymore. Replacing the caliper fixed the problem. If just buying a new caliper is too expensive for you, a rebuild should fix it.
 
Originally Posted By: GSCJR
You've been on this forum long enough to know that the words "best" and "bad" are subjective. I have done more brake jobs than I can count and Syl-Glyde has never caused a problem when applied correctly to the brake pads.

I do not use the terms "best" and "bad" lightly; I mean what I say, here. Sil-Glyde does not prevent rust. If anything, it seems to promote rust. It's a rubber lubricant only.

The point of applying grease to the piston/shim interface and caliper/shim interface is to prevent rust in those locations. M-77 is the very best I've ever found for this application, and Sil-Glyde is the very poorest choice. I speak from personal Rust Belt experience on these things.

Since Honda brakes have had long-standing and notoriously awful problems with corrosion in the Rust Belt, Honda Canada did extensive research into a solution. They put out a TSB on the solution they developed. I've tried it, and it beats -- hands down -- anything I've ever tried in 20 years of fighting with brake rust. The principle of the Honda solution will work on any brake assembly.
 
When was the brake fluid last changed? Should be done at minimum every 2 years.

Also don't turn German rotors, they are probably right at the min spec. Also how old are the brake houses? Those are probably getting tired as well.

I assume these are fixed calipers? One of the pistons is probably just sticking a bit.

If you suspect one is sticking a bit after you drive the car shoot the rotors with a thermometer and see if their is a big temperature variation.

German cars, especially high performance German cars are very sensitive about the brakes being in spec. It doesn't take much, a tire shop with an impact set to a million foot pounds can warp a rotor.
 
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Originally Posted By: Tegger
Originally Posted By: GSCJR
You've been on this forum long enough to know that the words "best" and "bad" are subjective. I have done more brake jobs than I can count and Syl-Glyde has never caused a problem when applied correctly to the brake pads.

I do not use the terms "best" and "bad" lightly; I mean what I say, here. Sil-Glyde does not prevent rust. If anything, it seems to promote rust. It's a rubber lubricant only.

The point of applying grease to the piston/shim interface and caliper/shim interface is to prevent rust in those locations. M-77 is the very best I've ever found for this application, and Sil-Glyde is the very poorest choice. I speak from personal Rust Belt experience on these things.

Since Honda brakes have had long-standing and notoriously awful problems with corrosion in the Rust Belt, Honda Canada did extensive research into a solution. They put out a TSB on the solution they developed. I've tried it, and it beats -- hands down -- anything I've ever tried in 20 years of fighting with brake rust. The principle of the Honda solution will work on any brake assembly.


Substantial amount of info and photos here.

http://www.agscompany.com/lubricants/canadian/205
 
Originally Posted By: hattaresguy
When was the brake fluid last changed? Should be done at minimum every 2 years.


I'm going to say never, as I don't think it is part of BMW's "Scheduled maintenance" and the car was dealer maintained until I got it. If it IS part of that though, then it would have been changed whenever BMW called for it.

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Also don't turn German rotors, they are probably right at the min spec.


They are at the min spec now (after turning), but they aren't pulsing or doing anything funky.

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Also how old are the brake houses? Those are probably getting tired as well.


Original, but they look to be in great shape.

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I assume these are fixed calipers? One of the pistons is probably just sticking a bit.


Nope, floating. And they have big singles, not twin piston.

Quote:
If you suspect one is sticking a bit after you drive the car shoot the rotors with a thermometer and see if their is a big temperature variation.


Good idea, I'll see if I can borrow my buddy's IR gun.

Quote:
German cars, especially high performance German cars are very sensitive about the brakes being in spec. It doesn't take much, a tire shop with an impact set to a million foot pounds can warp a rotor.


And that has been a problem actually. The shop I deal with, who is great with pretty much everything, was using the torque stick on my wheels. They stopped doing that when the car had to go up to BMW to get one of the wheel locks off because the key broke, LOL! They now use a torque wrench, like I use, and put them at 88lb-ft.

BTW, the squeaking is less today. I'm wondering if the disassembly and cleaning up of everything has worked to alleviate the issue
21.gif
 
My first suggestion was going to be that you live with the noise for a couple of weeks and a couple of weeks of driving and see whether it doesn't fix itself.
Minor brake noise problems will often do that, and it's not as though you would have been creating any hazard for yourself or others, since you obviously have adequate clamping force to stop the car.
Leave this alone for another week and then post back as to whether the irritating squeal and stickiness are both gone.
I'd lay odds that they will be.
What's really causing this problem?
Who knows, but I do know that you could drop a lot of money, and have already dropped a lot of time on a problem that will likely resolve itself.
 
Originally Posted By: GSCJR
Substantial amount of info and photos here.

http://www.agscompany.com/lubricants/canadian/205

Well, my fairly extensive Rust Belt experience is that Sil-Glyde is decently good for rubber parts, but terrible for metal parts.

Perhaps it's a characteristic of silicones in general, but Sil-Glyde also has a tendency to be absorbed by rubber parts over time, and those rubber parts will swell from the absorption. Sil-Glyde doesn't actually have very much silicone in it for its volume, so maybe it's the fillers that cause the swelling.

For the ingredients of Sil-Glyde and dielectric grease, see this link:
http://www.bobistheoilguy.com/forums/ubbthreads.php?ubb=showflat&Number=2991606
Scroll down to message number 2991606.
 
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