Front Brake Master Cylinder Question

[Warthog]

After having my 91 K100LT painted and after getting it back together I had to bleed the front brakes. Afterwards I noticed it leaking on the glove compartment lid. It appeared to be coming from the plastic resivoir so I pulled it and replaced the "o" ring at the bottom. While I had it apart I noticed there was alot of brake fluid coming out of the piston that is articulated by the hand lever. I looked at the book and it indicates that there are rubber bushings and I'm thinking these are probably the problem. I have also heard that you can't rebuild the master cylinder. Can I just replace the piston or do I need to replace the entire assembly? I looked on Max BMW and it does not look like you can buy the entire assembly.

[Hodag]

I replaced mine last year and had to buy an entire assembly, rebuild kit no longer available

[boomyr]

I experienced the same problem with my '96 K11. I bought just the plunger from Eurotech, http://www.eurotechmotorsports.com .

I didn't hone the cylinder for fear that I would increase the size of the bore to the point that it wouldn't seal. Instead I used fine steel wool to clean and polish out any burrs, deposits or rough spots that might damage the plunger.

I then flushed out the cylinder very thouroughly with rubbing alcohol ( to get good evaporation after I cleaned it) to remove whatever steel wool particles were left.

Somewhat of a small gamble to try the plunger (about $50) first, but my master cylinder appeared to be in pretty good condition after I cleaned it up.
It ended up saving me from spending about $300 for a complete unit.

After a couple thousand miles, no sign of any further leaking or other problems.

I'd clean up the cylinder to see what you have there. I ran my finger back and forth through the cylinder to feel for rough spots until they were smoothed out with the steel wool, then make a decision. If it doesn't take much to get it smoothed out, I'd be inclined to try replacing the plunger.

Good Luck!

[Warthog]

I was thinking about trying that but am having a problem getting the clip off that retains the piston. How did you get yours off.

Don

[boomyr]

I was thinking about trying that but am having a problem getting the clip off that retains the piston. How did you get yours off.

Don

Yours will be different than mine I think. K11 has a screw that prevents the piston from coming out of the cylinder. I'm sure someone that is familier with your unit will chime in.

[jdiaz]

I was thinking about trying that but am having a problem getting the clip off that retains the piston. How did you get yours off.

Just get a set of circlip pliers at Sears.

[Warthog]

Got a set of circlip pliers at PEPBOYS and was able to remove the piston. The cylinder looks pretty good but the rubber on the piston seemed very stiff which could be the problem. I used very fine steelwool (000) to clean the cylinder and will order the piston from Eurotech tonite.

Will keep my fingers crossed.

Thanks