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Brake System Woes - Help


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Good Morning/Afternoon,


Recently picked up this beauty that has been sitting idle for an unkown period of time, found some parts in the trunk (always a clue there) including new brake master, clutch master, and clutch slave. Went ahead and swapped out everything in the brake system, new calipers, all parts of the drums replaced, new pads, and installed the new masters and the clutch slave. While attempting to bleed the system I found that there is no fluid comign out of the brake master (disconnected the lines out of the brake master and nothing coming out) even when pressing on the brake pedal. Brake pedal feels firm but no fluid is reaching any of the brakes. Any ideas? Am I missing something? Brake booster seems to be okay, no major leaks and pedal is returning.





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Did you also replace all the brake hoses?  4 fronts and 2 rears...Good insurance.

Old, unused hoses full of junk can look OK on the outside but plugged internally.

Use compressed air to blow out the hard lines before reassembly. Then plug one end and pressure check for leaks.



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23 minutes ago, Santawillis said:

May need to bench bleed the master!

Not really.  Just loosen the lines at the installed MC one at a time after someone pumps and holds the pedal down.  Put a rag under the MC to catch the expelled brake fluid.

BMWCCA  Member #14493



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16 hours ago, halboyles said:

Put a rag under the MC to catch the expelled brake fluid.

This is important because a leaking M/C (or reservoir, for that matter) will dribble fluid down the frame rail until it reaches its end point under the driver's floorboard, where it will proceed to rust out the frame rail.  I learned this the hard way around 1982 or so...



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But if no fluid's coming out, then either the booster pushrod's

not seated in the piston stack, per Hal,

the piston is well and truly jammed,

the depth of the piston is wrong,

or something else is sticking.


I avoid the 'bench bleed' for the reason Mike states- brake fluid gets channeled into 

places that rust.  If that happens, get the garden hose and flush the hell out of ti.


The original main cylinder had a guide to get the pushrod into the right place-

but not all replacements had it.  That might be what's going on.


For further troubleshooting, take the main cylinder off, and cycle it on the bench

with a screwdriver seated in the piston recess.

It should move a bit more than an inch.

Likewise, cycle the pedal- the pushrod

should move a bit more than an inch.




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"I learn best through painful, expensive experience, so I feel like I've gotten my money's worth." MattL

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  • 2 weeks later...

Okay, here is an update. 


Got new braided lines for the front and rear to isolate that problem and found no fluid coming to those hard lines at all (albeit these hoses were very swollen so I am glad I got that going). This led me to a rabbit hole related to either the "T" or the master. I tried to bench bleed and found no fluid is reaching the furtherst line on the master (see photo) and also bypassed the proportioning valve found on the the 76s to isolate that as well. 


@TobyB I think it may be the master not being installed correctly. Will try to remove it tomorrow to take a look, may even try the old master to see if there are any improvements!


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Sorry you are having the problems.  Fixing brakes sucks.  I have gotten to the point with mine that I got a brake pressure tester and will be digging into it shortly as mine I felt never quite worked at 100%.


I will post the results on line pressure as a reference for others (not to say that mine will be representative of known good pressures). 


In the FWIW category you can get a pressure bleeder cap that fits on your reservoir.  You need to regulate the air pressure to about 7lbs.  It makes it much easier to bleed things yourself.  If you don't have an air compressor you could use something like a 12v tire pump that allows you to adjust the pressure.  There is very little volume used. 


You can also do something like the one below, but it won't have the correct cap (I don't think).   Some other folks will be able to provide the part for you. I can't remember where I got mine.     It may be worth as could save you ten's of hours of frustration. Only you can put a price on your time.  










"Goosed" 1975 BMW 2002


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