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1974 R75/6 Front Brake System

4

44006

Member
I need to bleed this front brake system on a very clean cosmetic restoration bike with new or new looking parts and clean looking fluid.

Front brake sticks after applying front brake by lever and will release to free if bleeder at wheel caliper is opened to release a small amount of fluid.

I am a knowledgeable and experienced airhead and /2 rider and servicer but mostly bikes of the cable brake era.

The routing of brake hoses looks to me like it may be difficult to get smooth rising path upward to master cyl so I am looking for advice before starting. I understand how these brakes work and how to bleed brakes. I am just looking for specific hints to help with this specific model to get quickest and best result. THIS IS NOT MY BIKE AND I DO NOT WANT TO MAKE A MESS!

There must be many past posts on this topic but I apparently do not know how to use the search feature on this forum. A few hints or tutorial on that issue would also be appreciated.
 
Please define: "Front brake sticks after applying front brake by lever and will release…" Does this mean it drags or that it literally locks up?

To my experience, the ATE calipers are going to exhibit some drag at the caliper, regardless of how much effort you put into bleeding them. There is a substantial difference between the drag on my '78 R80/7 (ATE; fair amount of drag in spite of a complete overhaul of the system including replacement of several components) and the brakes on my R100RS and K75C (both Brembo; little drag-K75- to no drag- RS).

If they are locking, the the master cylinder has a pressure relief port (hole) that may be clogged. This is a useful thread: http://forums.bmwmoa.org/showthread.php?68148-Sticking-front-brake-master-cylinder-or-caliper


44006 said:
I need to bleed this front brake system on a very clean cosmetic restoration bike with new or new looking parts and clean looking fluid.

Front brake sticks after applying front brake by lever and will release to free if bleeder at wheel caliper is opened to release a small amount of fluid.

I am a knowledgeable and experienced airhead and /2 rider and servicer but mostly bikes of the cable brake era.

The routing of brake hoses looks to me like it may be difficult to get smooth rising path upward to master cyl so I am looking for advice before starting. I understand how these brakes work and how to bleed brakes. I am just looking for specific hints to help with this specific model to get quickest and best result. THIS IS NOT MY BIKE AND I DO NOT WANT TO MAKE A MESS!

There must be many past posts on this topic but I apparently do not know how to use the search feature on this forum. A few hints or tutorial on that issue would also be appreciated.
Click to expand...
 
Last edited:
If you have the possibility of air in the m/c, such as when it is drained of fluid, the m/c must be tilted forward so that air trapped at the front of it can rise towards the reservoir.
So I learned fiddling with mine for way too long.:banghead:
 
Ditto on the ATE sticking. Is it sticking after riding and using the brake for a bit? If so that's likely air and it's likely at the front of the MC. Detach the MC and rotate it forward so that the air will rise toward the reservoir while bleeding. If it just sticks without riding, you should rebuild the whole system. If you do the latter, get the piston out of the caliper and examine it before buying a new one. You likely only need gaskets for that. And get some red grease for reassembling the caliper (a guy in the UK sells tiny tins on ebay; it's enough to do a dozen jobs).
 
Thank you folks - Jeff 488 tripped my memory of why I had a bad feeling about this brake. I have a 1977 R80/7 that I have not used in a long
time and I remembered some difficulty but not exactly what. Jeff's comment about tilting the master cyl brought it all back to me.

The solution then was and I think now also was to simply hoist up the back of the cycle so it is pointed downward about 20 degrees or so and then
bleed the system - that will give a continuous path upward through the tubes and master to the fill reservoir.

Again - thanks

This will probably solve the problem and the purpose for this post
 
44006 said:
The solution then was and I think now also was to simply hoist up the back of the cycle so it is pointed downward about 20 degrees or so and then
bleed the system - that will give a continuous path upward through the tubes and master to the fill reservoir.

Again - thanks

This will probably solve the problem and the purpose for this post
Click to expand...

That's too scary for me.
I unclamped the m/c and tipped it fwd.
Might be more fiddle, but less anxiety.:)
 
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