[oldred]

On my old '88 F250 diesel the brake pedal pressure began to get heavy then shortly after when depressing the pedal the brakes would hold (with far too much pressure required) but only for a few seconds then the pedal would slowly drift to the floor. I suspected the brake master cylinder since this seems to be a common symptom of a bad MC, at least the drifting down part anyway, but after replacing it (I bench bled it first) and bleeding the brakes I still have the same problem, no change. There are no leaks in the lines or wheel cylinders and it is not losing fluid so where should I look next?

[Rob Keller]

The Hydro boost unit itself.?.?

Or a defective replacement master.

Just because its new don't mean its good.

Do all wheels stop?

Could be a flex line that is swelled almost shut & slowly letting fluid to that wheel .

I'm really reaching here




R

[oldred]

Rob you were right it was the "new" Master cylinder I pulled all the wheels and checked for leaks then removed the MC and checked for leaks on the piston end, finding nothing I took it back to Auto Zone and they gave me another one which solved the problem.

[Rob Keller]

EEEWW the dreaded Auto bone!


I think auto parts is getting like politics
choose the lesser of the evils.


UGH!

glad your stopping



R