1100RT Mastercylinder Q

[Rollifahrer]

I replaced brake lines recently and overfilled the reservoir (front). After a bit of riding lever pressure didn't feel right, soI removed some fluid, but noticed fluid around the plastic cover that conceals the boot and BL switch. Took it off, cleaned it up, then a bit more came back. Removed lever and boot. There's a thin coating of fluid inside the boot, but no pools or obvious signs of a leak.

Is it likely overfilling caused the seepage? The level didn't drop and the brakes feel right.

I plan to clean it up and replace the boot, then check it. Even if it doesn't come back, I'm curious about the cause.

Anyone had brake fluid leak out around the boot?

[flars]

Overfilling usually won't cause it to leak down there as far as I know since the m/c piston only allows x amount of fluid to flow through the system.
Was there dried up brake fluid (green stuff) around that area also? If so, you probably have a leak around the m/c piston. Clean it off completely and watch it for a short while. If it leaks even a little bit, you should get a m/c rebuild kit and fix it. Mine started to spray brake fluid all over the place when those seals decided to give up.

[Rollifahrer]

Thanks.

No dried green stuff; just fresh oil, and much less this time than the first time I noticed it.

Clymers doesn't have instructions for a rebuild. I'm guessing you pull the MC off the bike and replace O rings on the piston. Any harder than that?

[RTs4me]

Seal failure is fairly common. It seems to occur more on bikes that are not frequently used. A slight film of brake fluid dries out and the crusty deposit rips up the seal. Constantly-used bikes don't develop this deposit so the problem doesn't appear. It's probably worse in high-temperature areas.

The cure is to strip the old piston and seal out, clean the bore thoroughly and rebuild with a new piston and seal. The rebuild kits comprise of a new piston with new seals already mounted. It's a good idea to replace the bellows/dustcover at the same time. Seal replacement can be done without removing the reservoir assembly off the bike, but protect the paintwork with old towels in case any brake fluid drips.

[lazywizard02]

Seal failure is fairly common. It seems to occur more on bikes that are not frequently used. A slight film of brake fluid dries out and the crusty deposit rips up the seal. Constantly-used bikes don't develop this deposit so the problem doesn't appear. It's probably worse in high-temperature areas.

The cure is to strip the old piston and seal out, clean the bore thoroughly and rebuild with a new piston and seal. The rebuild kits comprise of a new piston with new seals already mounted. It's a good idea to replace the bellows/dustcover at the same time. Seal replacement can be done without removing the reservoir assembly off the bike, but protect the paintwork with old towels in case any brake fluid drips.

+1, not much cost or time. A Common failure for an RT at this age. Great brake response after. If you are careful, you will have low risk of inducing air. Take car with the small screws, don't lose them.

[Rollifahrer]

Thanks guys. At 133K, I think that's the way to go.

It's not obvious how the piston comes out, and Clymer says it can't be taken out. "...intergral to MC assembly and can not be replaced seperately."

Are there threads behind the grease in the tapered recess? Or something in there to grab onto?

BTW: I think I found the cause. I had a brake line leak not too far from home, so I topped off the res. with synthetic fluid that said it was compatible w DOT3 and DOT4. (It was the fifth place I went that had brake fluid, but not DOT 4. Now I carry some.) I went to syn. oil in my airhead, then back to break in new rings. HES canister O ring shrunk, dip stick O ring shrunk, and I'll be replacing the oilpump seal for the third time this winter (gotta pull gearbox to get to it!). Could be the little bit of syn. brake fluid I had in there for a couple days screwed up the seals.

Thanks again for your help,

Rick

[Rollifahrer]

Hey Guys,

According to the dealer's fiche, Clymer is right, they only sell the MC as a unit. The parts guy thought there might be Brembo parts or knock-offs that will work. Any ideas?



Thanks,


Rick

[RTs4me]

I buy a lot of parts from 'MotorWorks' in the UK. I think they will ship to the USA. See this link to the 'brake parts' page of their parts ordering website:

http://www.bmwandguzzispares.co.uk/bmw/products/product.php?f=i&code=BA_15_30_HA_40&shnew=New&model=R850%2F1100%2F1150+%26+Cruiser+%288+valve%29&shnewcode=15&part=Brakes&sub_part=Master+Cylinders+and+parts&modelcode=30&partcode=HA&source_code=BA_15_30_HA_40&header_text=&header_text_image=0

Replacement piston/seal unit is part number BRA11141.

The next page shows the bellows/gaiter. Part number BRA10756.

Could you get similar parts from a USA-based supplier? (Beemerboneyard, Bobs BMW, etc).

[flars]

Beemerboneyard sells the kit:
BB32722332037 $42.95 fits all R1100 except R1100S.

[Rollifahrer]

Hey Tim,

I found the part on the link you gave me.

Now I still have to figure out how to get the old one out. I'm thinking I can remove the banjo bolt and blow it out, like blowing pistons out of calipers.

I'd cover the whole MC with a zip lock bag to contain the BF mist that follows the piston, then put a couple shop rags over that to catch it if it comes out with force. I'd use the pressure Clymer recommends to blow out caliper pistons.

Do you know a better way?

[RTs4me]

I just put some small pointed-nose pliers into the recess of the piston, where the brake lever normally sits to push the piston into the mastercylinder. Have a look at the diagrams on RealOEM or MaxBMW parts listings to see how it all fits together. Open the pliers out to grip the piston internally and pull gently. Once the piston clears the bore, it can be gripped externally and pulled clear. Beware of fluid spillages. If you empty the reservoir first, there shouldn't be much fluid around.

Clean up, rebuild and refill. Bleed and pressurise the brakes to settle the pads against the discs. Ensure that there are no leaks and verify correct operation of brakes before riding the bike. Don't take chances with brakes!!!

[Rollifahrer]

Hey,

Thanks again for all your good info., but I still can't get it out.

I tried needlenose pliers, then external snap ring pliers. They got a better grip, but the thing won't budge. I cracked the banjo bolt and opened the resevoir, thinking that might relieve any vacuum, but it won't go even with firm pressure. It feels like a retaining ring is holding it back. It rotates freely, and moves forward easilly, but will not back out.

It seems odd there would not be a circlip, even though the piston is trapped, by the lever, just to be sure. But I haven't seen any mention of one anywhere.

Hmmm, haven't been stumped like this in a couple years. Not since trying to align the FD U joint and driveshaft spline. Ended up using a rolled up rag with a corner sticking out.

[brainfish]

Try using a grease gun. Put the nozzle up to the where the banjo bolt screws into the housing. You get some grease but it should push the piston out. Did this in Tenn. in the ball field where I rebuilt my friends Master Cylinder.

Brian

[Rollifahrer]

I'm wondering if I have a stock master cylinder.

The piston is spring loaded, which I expected, but a spring is not part of the rebuilt "kit". When I compress the spring and let go of it quickly, the piston's return travel is stopped by a metal to metal clunk. I can't see anything in that end of the bore that would stop the piston, and don't see any other access to the bore beyond what I can see when the spring is compressed.

It's definitely a BMW part, but I bought the bike w 68K on it and don't know the history. I can see why dealers and Clymers say it's not serviceable, but I can't figure out how you guys are having the piston slide out with a gentle tug, or some grease pressure. I used air, and only created mist where air blew back out of the banjo bolt opening.

The piston seems to be retained by a metal part somewhere.

[brainfish]

go here and look at the view part number 20 there is a small screw that holds the pston in place, it limits the travel. you have to remove it

http://www.maxbmwmotorcycles.com/fiche/MainDiagrams.asp?mospid=48862

[Rollifahrer]

That was the problem. Thought I looked at every possible place for a screw; can't believe I didn't see that little bugger.

Thanks to all,


Rick

Brainfish: great link! I'll keep it handy to study other stuff I take apart.

[AntonLargiader]

There's an article on my website describing the whole rebuild process.

[Rollifahrer]

There's an article on my website describing the whole rebuild process.



I think i'm over the hump, but I'll use you're article to make sure I get it reassembled correctly.

One more Q: 2 parts suppliers have the notation "annodized" and the pistons are about 70 bucks. 2 do not have that notation and run 40 -50. The picture of the 40.00 part looks just like the one I removed, which is annodized. Is there any real difference? Are they interchangeable?


thanks,

Ricj

[AntonLargiader]

Sounds like a great question to ask the vendor!

[Rollifahrer]

I asked my guy at Re-Psycle. He didn't know, but after some research suggested there might have been a safety recall, and the annodized piston might be the revised version. Called the dealer, no open recall, and no info on pistons because BMW only sells the MC unit complete.

I have 3 more places to call, but thought maybe someone on this thread might have been down that path.

[Rollifahrer]

For those interested:

According to the guy at Beemerboneyard, early MC's internal surfaces were not coated and the bores pitted, allowing fluid to leak past the seal.

Mine is annodized, but the seal is dull and rough and deformed vs the shiny pliable front seal that does all the work and is bathed in fluid on both sides.

I'm guessing the bore on the outside of the rear seal dried out and the seal wore against the bore. Just speculating, but it looks like wear on a part that wasn't lubed. I know, the front side was always wet and there should be a film even after the seal sweeps the bore, but it looks like it dried out. Maybe inspecting and wiping with brake fluid on a q-tip every few years would help?

Anyway, I learned a lot about hydraulic brakes. Thanks again,


Rick