K75S brake issues

[szabgab]

Dear all,

I have all these bloody ailments of my bike, all of which are starting to disappears, mostly thanks to you guys and the wealth of information, that is circulating on the forum. As of now my driveshaft is going to be a good one and the bike will not let me on the side of the road with stripped splines, it also idles smoothly, thanks to the multiple efforts, I have taken to get rid of of all the little air leaks I had, ignition is good, contacts are clean, alternator is better, fuel system is cleaner, fuel and vacuum lines are renewed, battery replaced, front wheel sorted, oil drip addressed on the front (but still waiting to be looked at at the rear weep hole). But there is  one more nagging issue, that is rearing it's noisy head every single time, I ride the bike, and that is a constant high pitched brake squeal at the front. The bike came with a brand new set of blue Brembo pads up front and it was squealing, when I bought it. The PO said, the mechanic advised him to drive the bike for an extended period of some hundreds of miles and the noise will go away. Well it did not. Since that time I have taken the calipers off, cleaned and sanded the pins, spring, inside of the calipers, even though the pistons inside their rubber protectors looked spotless, I have removed them and sanded them with 1000 grit + WD40, and put some fresh DOT4 brake fluid on them upon reassembly, this always helped with my other bikes in the past. Also put some copper paste on the back of the pads and the pins. Everything helps for 5-10 miles, than the squeal is back with a vengeance. The brakes are not sticky, pistons are not frozen, and the bike is not squealing, once I depress the lever, I let go, squeal is back. Sometimes it eases, but it always bad after a longer period of not using the bike, and seems to be worse on hard right turns. I have spoken to a few mechanics, including the one advising the PO and they all just scratch their heads. Did anybody experience something like this? If s, what helped? My rear brakes are an issue too, but first please help me with this annoyance of the highest dgree.

Thank you!

Gabriel

[Laitch]

Considering the pads came with your moto and the previous owner didn't seem to care much about maintaining the moto correctly, I would replace the pads with good quality pads I was certain were the correct pads for the moto—preferably organic-type pads like these. Use a thin film of copper anti-seize or brake lubricant on the backs of them like you did on the ones you have.

[szabgab]

Considering the pads came with your moto and the previous owner didn't seem to care much about maintaining the moto correctly, I would replace the pads with good quality pads I was certain were the correct pads for the moto—preferably organic-type pads like these. Use a thin film of copper anti-seize or brake lubricant on the backs of them like you did on the ones you have.

Latich, thanks for your reply. In this instance the pads are truly good, Brembo blue pads are the bees knees according to Brembo and BMW respectively, they are ceramic pads, again highly recommended. I do not trust the PO with anything anymore, so I measured the pads, and they are brand sparking new, not a millimeter worn, but again, there is nothing else I can try, apart from replacing the pads, is there?

[Laitch]

I've got nothing more for you. If the discs are within spec, and all other components are in good condition as you have described, I'd verify the part number is correct for your bike model's year of manufacture and for the pad's location. If all of that lines up, I'd still replace them with organic pads. :giggles

Other than that, find denser earplugs. To adapt a precept from the Harley Riders Bible, "Loud brakes save lives."

[rbm]

But Laitch, Harley drivers never use their brakes, they always have to lay 'er down.  Maybe the precept you meant to quote was "loud screeching noises saves lives."

[Laitch]

Maybe the precept you meant to quote was "loud screeching noises saves lives."

Yep. I always have trouble using that bible's concordance.

[Laitch]

Try this stuff and let us know how well it works. It adheres the pad plate to the piston. It has not yet been endorsed by Taylor Swift.

[rbm]

They should be using that stuff on Kanye West.

[szabgab]

Try this stuff and let us know how well it works. It adheres the pad plate to the piston. It has not yet been endorsed by Taylor Swift.

I was eyeing up these kind of products, but you guys being American have got access to all these goodies, proper spline lube, amazon with great prices and so on, whilst here I'm stuck with things, that are just about similar to the right stuff. ANyway, if I'm not mistaken, 3M has got some sticky pads, that do basically the same, glue the pads to the pistons.

Now to the rear brake issue, it was the only brake, that was functioning great, when I bought the bike. Ever since I have removed the final drive for lubing/inspection it is not good at all, braking is just so-so (before it was easy to lock the wheel, now I need to push the pedal down rather forcefully to achieve something similar), the rotor is overheating, and my fuel consumption shot up rather significantly, so I would guess, I have brake drag combined with something else. If I press the brake, it does not engage at the same time, but rather one side first, then the other. If I turn the wheel, the pad(s) is (are) touching, but it does not seem to be severe. If I use solely the front brake for city rides, my rear rotor still gets hot, I do not get it. I have undone the caliper a few times and retorqued, just in case I cocked up something there, cleaned the caliper really thoroughly, removing the pistons, cleaning them, etc., but the issue is the same, crap braking, hot rotor, bad fuel consumption. Any ideas? Are there some spacing shims between the rotor and mounting holes, I could have missed (given that the pads do not touch at the same time)? I'm baffled, to say the least... 

[rbm]

Sounds like the rear master cylinder is plugged.  There are a couple of small holes within the MC that allow transfer of the hydraulic fluid to the calipers, and provide pressure relief when the pedal is released.  One or both of those might be blocked. The blockage seems to be preventing the pads from returning.  Either a MC rebuild is in order or pick up one of the cheaper alternatives on Ebay for much cheaper than BMW.  Search the forums for suggestions.

[szabgab]

Sounds like the rear master cylinder is plugged.  There are a couple of small holes within the MC that allow transfer of the hydraulic fluid to the calipers, and provide pressure relief when the pedal is released.  One or both of those might be blocked. The blockage seems to be preventing the pads from returning.  Either a MC rebuild is in order or pick up one of the cheaper alternatives on Ebay for much cheaper than BMW.  Search the forums for suggestions.

Oh great, some new issue, but how come the issue raising it's head, when I removed the caliper? Although that could be anything I guess, moving the lines and getting some crap inside the mc, whatever.

Anyway, is there a way to clean it, or do I need to replace the mc altogether?

Thanks!

[rbm]

What I'm suggesting is a theory; I'm not stating for a fact that the MC is plugged.  When the systems on the motorcycle are disturbed, there is a chance something can be dislodged or broken given the age of the components in these bikes.  however, don't assume that my diagnosis is correct.  I'm a long ways away from Budapest and haven't seen the bike in question.

[szabgab]

What I'm suggesting is a theory; I'm not stating for a fact that the MC is plugged.  When the systems on the motorcycle are disturbed, there is a chance something can be dislodged or broken given the age of the components in these bikes.  however, don't assume that my diagnosis is correct.  I'm a long ways away from Budapest and haven't seen the bike in question.

But your suggestion sounds legit, so I might just go ahead, and try to clean the cylinder and piston first to see, if that achieves anything. If not, well, there is the $10 chinese replica route :)

BTW, cleaning stuff in the piston area is worth anything in this situation (obviously if it is a plugged mc)?

Thanks!

[bocutter Ed]

IIRC I read somewhere on this forum that if you adjust the pedal travel too far/tight the master cylinder can't return enough for pistons to release ...

[szabgab]

IIRC I read somewhere on this forum that if you adjust the pedal travel too far/tight the master cylinder can't return enough for pistons to release ...

Ed, that surely would interfere with the operation, but I did not touch the set-screw, and everything is exactly, as it was before (minus the well operating rear brake)

[Laitch]

Ed, that surely would interfere with the operation, but I did not touch the set-screw, and everything is exactly, as it was before (minus the well operating rear brake)

Get a quart of DOT4 brake fluid and bleed the hell out of that caliper.

[The Mighty Gryphon]

I had this problem with Moby II. 

[szabgab]

Get a quart of DOT4 brake fluid and bleed the hell out of that caliper.

I already tried that,  when I removed the pistons from the caliper I had to that anyway,  but I might give it another try.  Whilst at it,  I might go the master cylinder piston cleaning route just to see,  if rbm's suggestion works out...  Would a piston-bore cleaning sort out the possible mc blockage?

Thanks!

[natalena]

It sounds really silly, but I had a similar front squeal problem with a bike back in the day. After loosening up the triple clamps and realigning the forks, it mysteriously was exorcised and never returned. It wasn't a terrible noise, just really irritating. Good luck.

[Laitch]

Whilst at it,  I might go the master cylinder piston cleaning route just to see,  if rbm's suggestion works out...  Would a piston-bore cleaning sort out the possible mc blockage?

Both rbm's and natalena's suggestions have merit. Master cylinder pistons can seize in their bores if particles are in the fluid. The fluid passages within the container are easily blocked. The components also can be misaligned. Read all of this thread and look carefully at its remaining photos.

natalena's suggestion is simple to do and given your description of the bike's condition when you bought it—except for the spiffy, high-tech ceramic brake pads that are constantly whining for your attention—the likelihood of something being out of alignment anywhere on this bike is great.

[stokester]

Rob Fleischer has some suggestions on brake squealing here -> http://bmwmotorcycletech.info/brakes.htm

[K1300S]

overall....how old are the rubber brake lines?  they are not lifetime items.  they fail internally.  result is restricted fluid flow and dragging pads.  replace all of the hoses...

front squeal...is there a bevel on the leading and trailing edges of the pads?  if not, file one onto all the pads.  leading edge in partiular should not be "square" to the rotor.

[The Mighty Gryphon]

I had this problem with Moby II. 

Did you watch the video?  I had a pile of those mouse turds come out of the brake lines on a '91 K100RS.  They plugged up the banjo fittings and made the brakes drag.  It's a good reason to change to new stainless lines.

The good news is that it appears that the crap doesn't get past the banjo fittings, so there shouldn't be a need to disassemble the calipers or the master cylinder.

[szabgab]

OK, so rear brake is still an issue, but... I hang my head in shame, I had these stupid front calipers off the bike so many times for cleaning, wheel removal and so on, so forth, that the last time, when I did the really thorough cleaning of the pistons etc., I forgot to tighten one caliper. Today I returned to the gig to try to bleed the system once more and the caliper in question had a strange lateral movement, checked the bolts and they were... bloody finger-tight. Imagining, that I have ridden the bike for the last 100-150 miles like that fills me with terror. Anyway, once torqued to spec and taken for a good long test ride of 10-15 miles the squeal is not back. Once I thought, I have it again, but it was a streetcar instead :) So hopefully we can assume, that the pistons were somewhat dirty and really good cleaning + oiling helped, but not tightening the caliper properly resulted in misaligned and always slightly touching pads...

Now to the rear brake - I have done, what Laitch suggested, and pushed through the system a great amount of fluid. I have not seen any air bubbles or debris escaping, but the brake is now operating great, I mean, I can lock again the rear wheel with very little effort. But I am not completely lucky, as the pads are still touching and the rotor gets rather hot. I have not done, what Chris Harris and Gryphon did as of yet, as all the lines are brand sparking new, changed, when the front pads were changed, the rubber in the hose is still shiny new, banjo bolts too, not a crack in sight. But given, how a shop works, basically doing everything quickly, I might just disassemble the line banjo by banjo and see, if there was not any crud left in the MC or reservoir, that has got sucked into the new lines...

[szabgab]

Rob Fleischer has some suggestions on brake squealing here -> http://bmwmotorcycletech.info/brakes.htm

Blimey, this is quite a read. I thought I will get through it quickly before supper in the basement, my wife asked me three times already, if I'm still alive :) Invaluable info in there...