The New And Improved Unofficial R65 Forum V2

Technical Discussion => BMW Technical Q&A, Primarily R65 => Topic started by: Redbaron on May 18, 2025, 08:54:24 AM

Title: Master Cyl Rebuild/Replace?
Post by: Redbaron on May 18, 2025, 08:54:24 AM
1980 R65, It sat for 10 years and I am trying to rebuild the ATE front brake "round" Master Cylinder.  The inside looks rust free but there was some junk floating in old brake fluid before I cleaned it out. I installed the Magura rebuild kit as instructed but still get no pressure when pumping brake.  No leaks, I notice 2 holes in the bottom of the master cylinder.  One appears open and the other does not. I would appreciate any suggestions. Thanks
Title: Re: Master Cyl Rebuild/Replace?
Post by: trips on May 23, 2025, 03:54:40 PM
Pretty slow here, interested but not knowledgeable on the subject. I also have a 1980 r65 in the shop getting the front brakes rebuilt due to sitting for a few years. Lot of knowledgeable people here, someone will respond eventually.
Title: Re: Master Cyl Rebuild/Replace?
Post by: Barry on May 24, 2025, 02:52:20 AM
Yes the two holes need to be clear.  The small hole is the fluid return for when the brake lever is released. You should see a small spurt from that hole to show the fluid is returning.

Hard to know if you have a fundamental problem or a bleeding issue. When I do a rebuild and complete fluid change from dry, I fill the system bottom up via the bleed nipple using a large syringe.  I usually get some firmness in the lever straight off doing it this way.