Rear Brake 1981 R100RT

[Whiskeychute]

'Ol gearhead her is stumped re: Rear Disc Brake on my '81 R100RT.
Rear brake inoperable.
Dismantled all items including master cylinder & caliper. Cleaned all components & installed new seals in caliper & new plunger on master cylinder. No bad corrosion anywhere & no pittting in calipers or master cylinder.
Used normal procedure for bleeding & used Dot 4 brake fluid. NO PETAL.
Took apart & nothing looked out of place. When putting pressure with brake petal & holding finger over end of the brake
line where it atttaches to the caliper, brake fluid will come out under petal pressure just as it should.
The pucks will seemingly move freely when applying air pressure to the brake fluid orofice.
After re-assembly, still no brakes. After air is removed from system, clean, clear brake fluid comes out the bleeder valve.
For some reason the pucks are not moving.......No leaks found anywhere..... HELP

[SteveD]

Two choices I see.

1. Flush new fluid into the bleed nipple in the opposite direction to a normal bleed. Reduce reservoir volume first, then slowly flush in the retrograde direction.
2. Remove the rear wheel, and rebleed the system in the normal manner, but have the caliper orientated so the bleed nipple is at a high point.

Reassemble and test.

[Whiskeychute]

Hey Steve,
Have already "Back-filled" the system, even utilized a hand-operated vacuum pump to check for leaks.......
Could the location of bleeder valve & the brake line be switched? No diagram of my rear brake is in manual.
Presently the bleeder valve is closest to the wheel & the fluid line is outboard from the bleeder right beside the
bleeder valve........
wt

[dougie]

http://www.realoem.com/bmw/showparts.do ... g=34&fg=10

[Whiskeychute]

Hey Dougie,
I have this dwg.....My rear calipers are a little different from this dwg in as much as the bleeder valve & the brake line
are side by side but his dwg shows the bleeder valve on the outboard side of the caliper & the brake fluid tube adjacent to the wheel....I'll try switching the line & bleeder & see what happens.
Thanks,
WT

[Dane]

I have more or less the same problem. I replaced the caliper pistons, seals etc and the entire master cylinder as the intake nipple looked suspect - and fitted a new braided soft brake line. I had some result with repositioning the caliper to get the bleed nipple as the high point - but I am not really happy with the action yet. Apart from the brake bleeding circus I must admit that I am not really impressed with the linkage arrangement. Lots of fiddly parts to do a very simple job. I renewed most of it and lubricated all of it, but there is still some friction in the system. By the way are all twin-shock (drum and disk versions) brake pedals the same? I suspect that a kinked pedal may be causing the friction issue.

[Whiskeychute]

Hey Dane,
Finally got rear brakes & just in time for a trip SOUTH
Never found anything out of place.......Big mystery but at least repaired as of now.
Do not know if the brake petals on drum & disc twin shock are the same.
Thanks good folks for all the good input.
Hope Florida is warmer than Tennessee....
WT

[Motorhead]

When I added a rear disc on my 1973 the only thing I had to do was add a mount for the rear master mount on my frame the peddle or lever is the same there as in my 1973 lever fits the system I added