51 Merc Brakes Not Releasing

C

captmidnight

New member
I've got the strangest problem, hoping somehone can help me diagnose. When the car is sitting the brakes work fine, plenty of pedal and nice and firm when pressed. But after driving for a while, once the car warms up, the rear brakes seize up tight and I have no travel on the pedal, in other words there is pressure in the rear line even when I have not depressed the pedal, it just builds up. In fact even when I get the car warmed up and it is just sitting, over time the rear brakes develop pressure, the pedal gets hard and the rear brakes bind up.
Anybody know what the heck is going on? I took apart the master and cleaned it, I did not rebuild it. Is my problem in the master or in one of the wheel cylinders? Is there a rebalancing valve in the master that is hanging up? It's driving me nuts and I don't want to start throwing money around replacing stuff until I know where the problem lays. The car is in concours condition and in very good shape mechanically.
Thanks for this and to all those who responded to my previous threads on sourcing parts.
 
Sounds like you answered your own question. Your problem sounds like you created it. And I would have to say that it is in your master cylinder the last thing you touched. Although I would not rule out wheel cylinders or partialy seized e-brake cables. You probably should let the fella that does that for a living look at it for you. Brakes are cheap your well being is worth a lot more.
 
If the brake shoes get wet with brake fluid or with wheel grease, they'll swell up and bind the drums.

The MC should also have a tiny return port for pressure release which may be clogged. Although I never inspected my Merc MC for one, I encountered this problem once before on an OT master cylinder.
 
The tiny return port will shut of if the pedal adjustment is to tight ,back of the adjustment between the pedal and M cylinder
 
Check the flexible rear brake hose on the driver side that feed into the junction block on the rear brake line that feeds across the rear wheels. It might be collapsed.
 
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