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I am at the end of my rope trying to get to the bottom of my brake fluid leak. I replaced the master cylinder with a Raybestos MC39621. This is the SECOND one of these I have installed and it made absolutely no difference.......still leaks like the one I replaced. I bench bled it before installing and there was no indication of any leak. I have checked all lines and checked all around the ABS area behind driver seat. I have checked all calipers when I bled the lines. No leaks anywhere.
Now onto the master cylinder:
This is where I see fluid.
All the paint is eaten away here from the leaking.
And of course the very familiar area of leaking fluid. Notice how much has leaked from the reservoir. This is from only driving it mostly in city driving for a total of maybe 4 hours. Any ideas what I need to be looking at here?
There's an adjustment on the rod coming out of the power booster. I wonder if it's adjusted too far out and pushing on the plunger further than it should.
There's an adjustment on the rod coming out of the power booster. I wonder if it's adjusted too far out and pushing on the plunger further than it should.
And how does a person determine if the thing needs adjustment? And how is it adjusted?
I fought with it on my 89 several years ago. I do not remember the specifics. Do you have a FSM? Or possibly try searching this forum for the procedure.
I fought with it on my 89 several years ago. I do not remember the specifics. Do you have a FSM? Or possibly try searching this forum for the procedure.
I disconnected the master cylinder from the booster and there is absolutely no sign of fluid leaking out the back of the master. I am going to order a new master cylinder reservoir diaphragm and see if that might be the source of the leak.
Make sure the warning switch in the inboard side isn't leaking, mine leaked, 86 also. Otherwise there are ways to determine where it's leaking from, I recommend you do that, rather than keep replacing the same part, MC's themselves seldom just leak externally.
If you think it's leaking on the back side (not sure from your pictures) make sure that when bleeding you use short strokes on the pedal rather than long ones, there are many reasons for doing that actually.
Make sure the warning switch in the inboard side isn't leaking, mine leaked, 86 also.
There is no leak there.
If you think it's leaking on the back side (not sure from your pictures) make sure that when bleeding you use short strokes on the pedal rather than long ones, there are many reasons for doing that actually.
I bled all four corners using a Motive Power Bleeder. I ran a full quart and 1/2 through the lines.
I know, one of the worst master cylinder designs I can think of. And to think they used to tell us Harley riders back in the day about our leaks.
1986 Brake Master Cylinder Problems
