123 Brakes won't release
 

'80 300D. New master, calipers, brake hoses.
Brakes drag slightly when warm. If I loosen the master/booster nuts they release. I have free play on the booster rod and there is NO adjustment on this car in the pedal or booster area. The booster is working.

This happened a yr or so ago and the only solution, I could find, was to drill about 3mm down into the master cylinder's piston where the booster rod makes contact. It was a temporary fix. The dragging problem has returned. :confused: What now???

Brakes won't release
 

If I remember correctly the pushrod inside of the booster is adjustable, I think it's an 8mm hex.
Mike

I never found the adjustment nor is it mentioned in the factory manuals.
It would sure make this a simple fix if so...

Anyone know if the free play is adjustable? It seems odd for a booster to fail this way.

brakes
 

how old is the master cylinder?

Its new. I even swapped another out to make sure it wasn't a manufacture flaw.
I picked this car up with a leaking brake hose. I replaced all the hoses, brakes dragged, I replaced a couple of calipers, still dragged.
Further trouble shooting (which is what I should have done originally) revealed the brakes would release if I pull the master cylinder from the booster rod creating freeplay.
I measured the portion of the rod sticking beyond the booster housing to be about 3mm more than another 123. This car is an '80, the other was an '83. I don't know if there's a difference or not.
I temp solved the problem by drilling the master cylinder's piston 3mm. I was concerned about "punch thru" of the piston so I made several very hard stops. Seemed to work ok.
Now I get back to this project and find they are dragging slightly again.
Stumped.

Any suggestions?