Experience with master cylinder rebuild?

[d3vi@nt]

Both masters on my MTS are needing repaired or replaced.

OPP Racing informed me that Brembo no longer makes rebuild kits for OE masters and they no longer have any. Gotham has the seal rebuild kits for $50 per side. A different vendor (kurveygurl) said seal repairs must be done by a Brembo service center. RCS replacement units would be a little under $600.

Has anyone attempted the seal repair process? Is it tricky enough to require service center expertise or special tools?  It's obviously not a part you would want to fail.

Any thoughts appreciated.

[Speeddog]

Are they leaking or ?

[d3vi@nt]

Are they leaking or ?

Clutch requires bleeding every 200-300 miles. After that, friction zone begins to disappear. Bleed and it's perfect again for another 200-300. I replaced the slave with an Oberon unit thinking that was the culprit, but still the same.

Front brake is similar, though I tie it back for 24-hours and it's great for a while until lever travel begins to increase and brakes get a bit mushy. Rinse and repeat.

Thought it might be a pinhole in the line or something, but since its affecting both brake and clutch, I'm leaning toward MCs. Bike has 38k miles on the clock, and these MCs were rumored to be not super.

[koko64]

Down here I take m/c and caliper rebuilds to specialty auto brake shops insured for that work. Sometimes the margin on a rebuild is so small replacement is a better option as long as you dont get too fancy. I may provide the shop the rebuild kits, but sometimes they find matching generic seals (depending on the bike).

Specialty small bore honing tools are expensive here but I dont know your prices up there.

Maybe the next level down in radial m/c's from oem monsters or superbikes will give the feel you need at a better price rather than the top of the range stuff?

[Speeddog]

I've seen Brembos where the rubber grommet around the plastic elbow fitting will crack and allow the MC to pull air.

They won't leak fluid from that crack, as one might expect.....

Radial masters won't self-purge air at all, as the reservoir feed comes in the side.
So the master itself needs to be bled from it's bleeder fitting as well.

[d3vi@nt]

Thanks, guys. I'll take a closer look and see if I can find any cracks anywhere.

The clutch (PR16) I've been bleeding at the master with good results. The front brake (PR18/19) I've also bled at the master with good results. The times it's gone a liitle bit soft, seems like tying the lever back overnight has firmed it up and works for a time. It's definitely not as bad as the clutch.

@koko64 I assumed replacing the cylinder seal would suffice, but if honing is required, I'd definitely have to find a shop. Though I don't know of any that do that kind of work. At $100 in repair kit + labor, I might be better off just replacing them with new.

Thank again.

[d3vi@nt]

I've seen Brembos where the rubber grommet around the plastic elbow fitting will crack and allow the MC to pull air.

They won't leak fluid from that crack, as one might expect.....

Fittings and tubing all seem to be good --no cracks visible, nor fluid. The dust boot on the clutch has a few small tears, which makes me wonder if some dirt has been introduced and is causing the issue with the clutch. Not sure if that part can be found, either.

Don't really know what direction to go with this...

[stopintime]

Yes, you do    There are ENORMOUSLY important reasons to have a trustworthy and confidence inspiring brake master. You won't get there on your own (?)   Try to fix the clutch master if you really want, but not the brake side.

Back to OPP 

[d3vi@nt]

Yes, you do    There are ENORMOUSLY important reasons to have a trustworthy and confidence inspiring brake master. You won't get there on your own (?)   Try to fix the clutch master if you really want, but not the brake side.

Back to OPP 

Pretty frustrating; after reading and watching, the procedure is pretty simple and the issue could potentially be fixed with a few inexpensive rubber seals. That apparently aren't available.

Of course, there's still a chance it could be something other than the master 

[stopintime]

.... such as the ABS unit? 

[d3vi@nt]

.... such as the ABS unit? 

Specific to the clutch, I suppose there's a chance of a leak in the line somewhere. The stock line doesn't appear to be braided stainless like the brakes, apparently just rubber. I haven't found any pre-made, so would have to measure and custom order. New crush washers probably wouldn't hurt, either.

ABS was implicated in the issues with the rear brake that plague these bikes. Mine has been good after a good bleed/abs cycle/bleed process, though. Front brakes honestly aren't bad, but the clutch is a PITA when it starts to go, creating challenges at stop/start intersections.

[koko64]

Sometimes a hairline crack occurs on the slave cylinder bleed nipple. Some models had quite a small diameter threaded section prone to cracking under the stress of repeated bleeding.

[koko64]

For the brakes there are probably stubborn bubbles lodged in the ABS unit and you need to put a banjo bleeder there at some stage. You could search for other bleeding methods like syringe and vacuum methods or the sonic method that might dislodge bubbles in various nooks and crannies. I use retired hair clippers with the blades removed which are taped to the brake line. It works like a parts cleaner vibrating the bubbles into the fluid stream while you bleed them. Stubborn jobs have required me to use the regular method and both syringe and the sonic methods to remove trapped air. The final factor is patience as it is tedious to say the least, pita is more like it. You're probably sick of it already from the effort and it shows some of the engineering downfalls of modern ABS systems without enough thought to maintenance. I once fixed someone's brakes that others failed to by bleeding them with alternate methods over two solid hours. The brakes felt and worked great after the sustained effort. I'm sure you've racked up some hours already.

[koko64]

How's it going?

[d3vi@nt]

How's it going?

Well... when my ST2 started giving me fits, I solved the problem by getting the MTS. Now the MTS is giving me fits, I've alternated between working on it and my ST2. And I believe new fuel pump relays for the ST2 have solved that problem.

So if I hold true to form, I may let the MTS sit for a year, pretend I'm shocked that the battery died in that amount of time, and postpone buying a new one because I'm a cheap-a$$ (or more accurately, a dumb-a$$).

Long story, short; I plan to button the ST2 back up tomorrow and either ride it or bleed the MTS again and ride it.

I'll probably go the RCS route with the levers. The clutch has to be leaking somewhere and I still feel both masters are suspect. Time and money will tell!