front brake stuck on !

[skidlydog]

Hi all, 1200gs 07 plate and both of the front brakes are stuck on. after releasing the bleed nipple by the lever it releases but after a few pumps its locked solid again . any thoughts foltks ?

 

[Slipperyeel]

You don't mention if it has the servo?

Does it have rubber hoses? Could it be early breakdown of them internally?

 

[Rusty Bolts]

Hi all, 1200gs 07 plate and both of the front brakes are stuck on. after releasing the bleed nipple by the lever it releases but after a few pumps its locked solid again . any thoughts foltks ?

Assuming that it is not a very late servo bike, check the master cylinder piston isn't getting stuck down the bore. Take the lever off and rod and push the piston in and out a few time to see if there is corrosion stopping it returning to the 'off' position. If that is all lovely then it may be your calliper pistons sticking. After removing one from the fork leg carefully pump the pistons out and squirt brake cleaner around and scrub with a tooth brush (I find my sons electric tooth brush works a treat) to get rid of the gunk and smear some red rubber grease around the pistons. They should go back in under firm thumb pressure. Repeat for the other side. If its all groovy then I can't think of a reason why it would be sticking.

 

[Bendy toy]

I usually find its best to pop each piston out in sequence clean and replace. leave it too long and you will need new seals. Done in time with care and you'll be able to re-use the seals.

I made a clamp from two M6 bolts and strips of 25 x 3 steel to hold one piston in place. Use block of wood to stop the other pair moving too far. Pop out the one remaining piston with a bicycle tyre pump. Clean, replace move the clamp and repeat until all four are done. I block the banjo bolt hole with a suitable bolt & PTFE tape and blow air in via the bleed nipple hole.

Only use red rubber grease. NEVER use silicone grease or silicone spray. Its too slippery and causes the brakes to bind.

BMW charge £60 per caliper for seal kits which come with 4 new pistons. You can't buy seals only for the fronts.

 

[Slipperyeel]

Bendy. When you say use the red rubber grease. Do you mean on the pistons? I've always considered doing that just makes them into a dirt magnet. I've only ever smeared them with brake fluid on reassembly...so once washed there's nothing for crud to stick to and what does get on there washes off just as easily.

Am I missing something?

 

[NZRalphy]

Correct eel. Only use brake fluid. The grease will likely be wiped off as the piston is re-inserted anyway.

 

[JJH]

Try opening the bleed nipple. JJH

 

[Bendy toy]

Bendy. When you say use the red rubber grease. Do you mean on the pistons? I've always considered doing that just makes them into a dirt magnet. I've only ever smeared them with brake fluid on reassembly...so once washed there's nothing for crud to stick to and what does get on there washes off just as easily.

Am I missing something?

Ive never had much success with simply cleaning the pistons. If they are cruddy enough to not clean easily they may well be due for replacement. By the time that happens, the seals will be shot or the seal grooves have corroded and crushed the seals. Either way they only fix is a rebuild.

I would not use grease on a clean up job - frankly no point. I do use red rubber grease for calliper rebuilds. It goes into the seal grooves, around the seals and a thin smear over the pistons. I always push pistons right to the bottom so almost all grease gets wiped off. Ive never had an issue with it attracting dirt. Ive done this ever since I had Yamahas with quick rot callipers. BMWs being anodised (and Yammie Blue Spots) are less of an issue.

I once used silicone grease (on an old Honda brake) and caused the pistons to not retract properly. It's too slippery and can ruin a set of pistons.