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Sticky Front Calipers


cali_beemer

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So some of you may have followed my last post on fuel economy. Its become clear that my front brake calipers are not releasing like they should. I can only spin the front wheel by hand, about a 1/4 turn before the brake pads stop it, with a very noticeable pressing sound from the pads. I recently removed the wheel and pulled the pads to scuff the surface, clean the pads and greese the slider pins. This seemed to make the brakes feel a bit better but now I have noticed they arent free. I have a feeling that the calipers are sticking (and possibly the casue of my low fuel economy). The original owner has had one of the rotors replaced for being warped at 12k miles. The bike had 15.5k miles on it and the front is feeling as if one or both rotors is becoming warped. I have replaced calipers on cars before but I know the BMW servo brakes cant be serviced like a normal brake. So I have a few questions. Is it best to rebuild these calipers or replace them with something from beemerboneyard? What would the process be to rebuild these and flush the brakes? I planned on having the brakes flushed but I dont think a brake flush would fix a sticking caliper. I had planned on taking the bike to the dealer for the brake flush but if the calipers need attention i would prefer to do this myself becasue money is tight and I have tools and a lift at home. Also, the bike is still under an extended warranty, does anyone have an idea if that would be covered? The bike is a 2004 R1150RT.

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I have been unable to find a rebuild kit for the Evo callipers. I find that a good clean around the pistons using an old toothbrush keeps thing free there - I like to gently squeeze the lever with the ignition off to extend the pistons - be careful not to expel them from the cylinder.

 

Then be sure that the rubbing surfaces for the pads are clean, smooth and lightly lubed with brake grease.

 

Andy

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I had a similar problem on a Honda years ago. I dismantled the calipers and cleaned everything and lubed it up, no more problem.

I used no rebuild kit, I reassembled with the original parts after I cleaned it all.

Like Boffin said.

 

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I have been unable to find a rebuild kit for the Evo callipers. I find that a good clean around the pistons using an old toothbrush keeps thing free there - I like to gently squeeze the lever with the ignition off to extend the pistons - be careful not to expel them from the cylinder.

 

Then be sure that the rubbing surfaces for the pads are clean, smooth and lightly lubed with brake grease.

 

Andy

 

Did you use any particular cleaner when you did that? Did you lube the pistons at all? I have a toothbrush and I would prefer to do that instead of rebuild them.

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Use brake cleaner. Look for signs of corrosion in the piston bores. You can clean the pistons and bores up with extra fine steel wool (make sure to all traces of steel wool afterwards). Lube with clean brake fluid only.

 

This could be air in the system. Do a thorough bleed. Also, have the front pads worn evenly?

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Use brake cleaner. Look for signs of corrosion in the piston bores. You can clean the pistons and bores up with extra fine steel wool (make sure to all traces of steel wool afterwards). Lube with clean brake fluid only.

 

This could be air in the system. Do a thorough bleed. Also, have the front pads worn evenly?

 

My understanding from Boffins post was that a complete rebuild may not be needed. Is there a link to aplace to read up on the brake fluid flush procedure for the evo brakes?

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Well, I pulled the calipers tonight. Once I got the bike on the lift it was apperant that the seized caliper was on the bikes left side by all the brake dust on the bikes fairing. Oddly enough, thats the rotor that was replaced at the dealer by the original owner. I got the pads off and extended the pistons. I cleaned them up with brake cleaner and a toothbrush as outlined here. I lubed them with fresh brake fluid. It was very recognizable that there was one piston in particular very seized. It took serveral cycles of cleaning and lubing, compressing the pistons and re-extending them but it finally free'ed up nicely. I scuffed the pads, greased the slider pin and hole in the pads after cleaning every thing. I did the other side and now the wheel turns nicely. it can turn 1-2 full turns before stopping, while before it couldnt go more than 1/4 turn. The bad news is that the rotor is slightly warped. You could here it intermitenly touch rub the pads on rotation. Of course you can feel the slight pulsation in the lever so I already knew it was warped a bit. Its not real bad so it should be fine for now. The other bad news is that I had 2 pistons expel and lose a bit of fluid. Not much, and I was able to catch it early and push it back in. I would think I need to bleed them after that mishaps. I checked the fluid level and the master cylinder is still at the proper level so I couldnt have lost much. I plan on riding it this week before doing a brake bleed. It should be okay.

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Fluid level in the reservoir won't tell you if you have introduced air behind the pistons. I'd do a full bleed before riding too far. Were the brake pads worn unevenly? You should really replace all four pads too.

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Fluid level in the reservoir won't tell you if you have introduced air behind the pistons. I'd do a full bleed before riding too far. Were the brake pads worn unevenly? You should really replace all four pads too.

 

The pads were worn evenly. I realize I need to do a brake bleed but I would like to ride to work and back. I may just take my truck.

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.... The other bad news is that I had 2 pistons expel and lose a bit of fluid. Not much, and I was able to catch it early and push it back in. I would think I need to bleed them after that mishaps. I checked the fluid level and the master cylinder is still at the proper level so I couldnt have lost much. I plan on riding it this week before doing a brake bleed. It should be okay......

 

On your bike, which has iABS, the brake lever hydraulic systems are totally seperate from the wheel cylinder hydraulic systems. Even if you lost all the fluid from a wheel cylinder, the handlebar one would still look much the same.

You NEED to tupperware off and do a flush bleed of the servo unit. Your brake system IS compromised.

Andy

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Unless you removed the pistons out of the housings you are not getting at the innards properly. One needs to remove the rubber diaphragm that is pushed by the brake fluid to clean inside.

You are only playing with part of the system and not getting at the crux of the problem.

Take the caliper all apart, clean, reassemble and bleed. Don't hafass it.

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This is beginning to sound like one of those incomplete jobs by a wisher wanting to avoid doing it right.

Pistons have to come out to do a full clean and the seal(s) should come too. Truly cruded seals are sometimes embrittled and approaching failure- no way to know that short of looking. If they're good you could reuse them. Otherwise, better to find out while you're not riding. New seals are better and whether or not BMW sells them, you ought to be able to match them from a good brake supply place. While calipers can typically be serviced and last the life of a machine, replacement of a really bad one may just be a fact of life. Maybe yours is slightly mis-machined and a fit is off a little- it happens.

No way to get the crud out of there otherwise- you're just diluting its remnants with solvent.

Any time a piston is out for any reason you need to bleed. Its generally good practice to bleed anytime you do anything at all to a system. It would be surprising if this system has a decent lever feel and actually works after your description of work so far unless you bleed it.

Prevention of future episodes will come from sticking to factory recommendations for periodic fluid changes. Some combos are corrosion prone if they see any road salt or similar- don't know if this has any relevance to your immediate problem- such corrosion is quite visibly different from old brake fluid crud.

Does this bike still have a working ABS unit? Cruded calipers indicate a good chance of problems elsewhere if its old gummed fluid doing it.

It is also generally wise to do both calipers at a vehicle end for anything with dual front discs. What caused one to have issues is likely developing in the other.

Your "rotor warpage" might be just pad material deposition. A little light sanding of that disc won't hurt and might (or might not) help. It would be a rare rotor indeed that feels totally uniform in a hand spin- riding is the test.

Now is a good time to measure the rotor and be sure its in spec- or at least look for visual wear as a check. I would not expect yours to be worn out based on your description.

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Buy a couple of HD Scotchbrite pads (the thin green ones about 4 x6) and soak them in denatured alcohol. Then fold them in half and pinch them against the disk while spinning the wheel. This should remove any crud on the disks. Sometimes pad material can be compromised by chemicals and, when heated up, will put deposits on the disk.

 

 

 

 

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While calipers can typically be serviced and last the life of a machine, replacement of a really bad one may just be a fact of life. Maybe yours is slightly mis-machined and a fit is off a little- it happens. No way to get the crud out of there otherwise- you're just diluting its remnants with solvent.
Agreed. A friend noticed uneven pad wear on his still-warrantied R1200RT. Dealer ordered a complete caliper assembly and 4 new pads, saying that sometimes these calipers/pistons come from the factory too tight. He also had a seized rear caliper on a new F650GS. The rotor ended up blue from overheating. Same thing: new caliper assembly plus rotor.

 

Brakes keep you alive. As others mentioned, you may wish to reconsider finishing the job before you go riding.

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Well I ended up parking the bike until I can bleed them. I am ordering the parts to bleed them today. I may see if beemer boneyard has a used rotor while I am at it.

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There are not a lot of miles on your bike. Depending on how badly your rotor is warped, you may be able to have your rotors turned to even them out, while still being withing minimum tolerances for wear. Could save a bunch of money.

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Having experience of this , turning of drilled or slotted discs is a lottery due to the perforations and the thickness ( lack of rigidity in the disc ) The only sucessfull way ahead is a machine shop with a surface grinder and a magnetic table to keep them flat and true.

 

And will stillsave on the price of replacements.

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What racer7 said...

I've had to use an air gun to push the pucks out of the caliper housing. Yep, you gotta pull them loose from the hoses. Use a rag to pad the puck when you hit it with air, you can crush you fingers this way, be careful. Then you can check the bore and the pistons and the diaphragms.

Sounds like you may have a build up of brake fluid cottage cheese in there.

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So, if I am doing a bleed, whats the best procedure to remove the calipers to clean while not hurting the servo system? Doesnt there need to be fluid in there constantly? On cars, I have just pinched the line, removed, and re-installed followed up with a brake bleed. I am not sure yo ucan pinch the lines of the hoses on the bike.

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Don't ever pinch a brake line, you'd weaken the tubing. Simply plug it or let it drain. You are going to do a bleed, no? just pump pkenty much new fluid through the system.

MAybe best you take it to a dealer or bonified mechanic to rectify your dragging brakes.

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I don't see how draining the servo would cause problems during maintenance. Obviously, the servo needs fluid in it if it is powered up. There are instructions on this site on how to make a funnel to fill the servo.

 

There was a recent post from a fellow who had a chunk of rubber blocking the rear brake line, likely due to the lining of the brake line having gotten brittle and breaking. As mentioned above, you don't want to be bending these brake lines to pinch them off.

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Draining the servo is a big no-no, unless you have access to a MoDiTec. Basically, if you drain it, you then need to activate the ABS (the internal chambers/pistons) to run fluid throughout the system. You can't do that unless you have a MoDiTec or you button everything back up and then go jam on the brakes a couple of times :eek: !

 

 

 

 

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