Tyres, Brakes and Suspension » What a saga, binding rear brake

Warning, a long post.......

I did my annual (36,000 mile) service last week. All good, valves in spec, no sign of anything untoward and I changed the rear axle oil as I do every service. I also cleaned the brake callipers, an annual task. They were all clean and good and the rear pads were close to the limit (originals at 30,000) so I ordered some new sintered Ferodo's from Motoworks. I didn't do the forks on advice from a friendly BMW trained technician. Front pads have loads of life from new.

Then the saga began....

New pads in after having cleaned around the pistons with brake cleaner and an old tooth brush. Caliper floating pins cleaned and lightly greased. Level in reservoir dropped to upper line. Wheel slightly tight to turn. Took it for a spin to bed the pads in and at a 5 mile stop it was still tight. After 11 miles it was an effort to push it back into a parking slot! Slow ride home.

Pads out, pistons pushed out a few mm and cleaned with very hot soapy water and another old, clean tooth brush. Back together, felt better. Test run. Still binding. Bugger!

Pads out, rethink every possibility, push pistons out almost to the point of no return and again clean them. Put them back together, check free play in master cylinder actuator, same, same. It's hot and I'm getting a bit fed up with getting riding kit on and off, sweating etc....

Pads out (recurring theme) pistons out, all looks good. Clean cylinders, pistons and seals in situ and reassemble with red rubber brake grease as I've always done back in the day when I was a motor tech (an awful long time ago). Same, same. if I had hair, I'd consider pulling it out!

Call main dealer for advice. They go through all my steps and can't come up with anything. They even measure some OEM pads for me to make sure mine aren't oversize, they aren't.

I go round to see my local bike shop. He's very busy but gives me a couple of minutes. He thinks the master cylinder piston may be stuck but says that I probably wouldn't have been able bleed my brakes if that was the case.

Home and strip and clean my rear master cylinder. All seems good. Brakes still binding. I'm dehydrated to the point of feeling ill, I've got band practice in an hour, a 260 mile day trip with friends to Scotland tomorrow and I'm mega frustrated about the bike. My wife says I can use her nearly new Ninja 650 Kawasaki which is great but I'm not feeling enthusiastic. I've not ridden it before and it's got chicken strips a mile wide to remove... Also, I love my RS!

I get home late after band practice. It went very well. I'm knackered, feel ill and can't sleep. I read a comment on the inter web that suggests that using brake grease on the seals and pistons can cause the seals not to grip on the pistons and retract them the minute fraction required for clearance as the piston just slips on the seal.

Get up, raging migraine headache, my friends go off without me and I go back to bed dosed up with Migraleve. I eventually get up feeling better, strip and clean calliper removing the seals which thankfully remained unharmed and were in good condition. Rebuild calliper using just brake fluid.

Sorted? Well so I thought. The wheel turns freely as it did before the new pads (oh I also tried the old pads back in and they still bind) but after a few miles it begins to bind slightly, and the disk gets hot.

I can only guess that initially the issue was some fine debris causing a piston to stick (front piston methinks). After cleaning it was probably the grease stopping the seals from retracting the pistons.

I watched Youtube videos of manky old calipers being rebuilt with dubious cleanliness and they worked fine…… Sigh.

I’ve a trip tomorrow to see how it goes. New calliper seals should arrive and if miles don’t sort it they might. The bike's sat in the garage and the wheel spins just fine.

Otherwise I’m stumped – unless pressure from the front is getting to the rear????

Any ideas? I ride with my toes on the pegs so I'm not putting any pressure on the lever.

What a saga trying to get to the meat of the thread!

That is my personal style. We are all different. If you have no useful suggestions then perhaps refraining from criticising my way of explaining the problem and what I’ve currently done to resolve it might have been better.

I feel your pain Sanemancured. My brother is going through exactly the same predicament, but with his GS, and on his rear brake.

Twice the dealers had it in, after he had to be recovered. They've had to replace the discs because they got scorched the first time, and the dealer is now fighting my brothers corner for BMW to replace the caliper under warranty, as they're messing him about.
Either way, they still don't know what's causing the problem...................

Zitat von Sanemancured im Beitrag #3

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That is my personal style. We are all different. If you have no useful suggestions then perhaps refraining from criticising my way of explaining the problem and what I’ve currently done to resolve it might have been better.

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You might try releasing pressure at the rear caliper. Put a piece of clear hose on the bleed nipple and open it just far enough to allow any static pressure to bleed off, then close nipple. don't stroke the brake pedal while doing this. If you see fluid come out of the caliper (it won't be much) the system has some residual pressure.
Chris

I know this level of frustration. It is brutal. I think you are on the right track with the master cylinder, but that is all I've got. Best of luck and let us know how it turns out.

YUP.

I had this with my 1150. Only figured it out because I was getting horrid MPG and eating rear pads. It is Part of what prompted me to remove the ABS. But, Ultimately, I believe it was just "goo" in the line that made it into the caliper, that stopped fluid from returning to the line when releasing brakes, leaving the caliper tight.

Zitat von Philbuck im Beitrag #4

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I feel your pain Sanemancured. My brother is going through exactly the same predicament, but with his GS, and on his rear brake.

Twice the dealers had it in, after he had to be recovered. They've had to replace the discs because they got scorched the first time, and the dealer is now fighting my brothers corner for BMW to replace the caliper under warranty, as they're messing him about.
Either way, they still don't know what's causing the problem...................

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I've been out for a 135 mile day. The binding has almost gone but it's not completely resolved. When you spin the wheel it spins easily enough but there is a scraping sound that shouldn't be there. It gets hot while the front disks don't.

The residual pressure thing. A good idea and I'll try that 1st. I got to thinking (while riding) about the floating calliper mechanics. If I push my knee on the calliper it frees right off. That is moving the fixed pad away from the disk. So maybe it's the fixed pad that's binding? The calliper itself slides easily on it's pins but I'm wondering what the mechanism/force is that produces this movement away for the fixed pad. I mean I know the calliper itself is free to move but there should still be means of producing a small clearance once you've released the pressure, as the seals do on the other side. The back of the fixed pad has a stainless plate with an inner pad. I transferred this from the old pads. I'm wondering if that somehow achieves this?

I'll have a careful look at this plate and inner pad. I'll post some photos too. I have new seals and pistons and I might end up trying new seals. I'll leave the old pistons in for the time being as changing 2 things is often folly.

The system has been bled through with new fluid at least 3 times front and rear so I don't think that debris will be an issue. Whether pressure from the front brake can pressurise the rear I'm not sure. The front brakes are fine.

I can't find the stainless plate in any of the spares online which is strange.

The saga continues.

Zitat von Sanemancured im Beitrag #13

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I Whether pressure from the front brake can pressurise the rear I'm not sure.

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