I came across this old girl and gave her a new hime

[Kyle_in_Tex]

So the old girl looses her brakes ... Pump them up bleed them out and I have brakes ... Then she sits and I loose them ... Pump them up bleed them and brakes again .. Not leaking any fluid ... So any ideas???

Pitted internal cylinder walls letting fluid past a seal in the master cylinder?

 

[sixdogs]

Pitted internal cylinder walls letting fluid past a seal in the master cylinder?

I'll go with the master cylinder as well.

 

[blueriver]

I wouldn't think so ... I thought that and put a new MC on it.

 

[Kyle_in_Tex]

So the old girl looses her brakes ... Pump them up bleed them out and I have brakes ... Then she sits and I loose them ... Pump them up bleed them and brakes again .. Not leaking any fluid ... So any ideas???

Somewhere, fluid is getting either out, or past a seal. Or maybe air getting in system from somewhere?

 

[sixdogs]

Somewhere, fluid is getting either out, or past a seal. Or maybe air getting in system from somewhere?

If air comes in, fluid has to come out and he said none was missing. The only other thing I can think of is that the brakes were not fully bled and some air is in the system. After the master cylinder that's my next choice.

 

[the old grind]

I had air get in rear lines for a few years without losing a drop. Truck was an '84 K2500 HD with ~13"x2 1/4" drums aft. What eventually got me thinking was that 68-82 Corvette rear discs are known for 'pumping air' into the lines with fixed rear calipers and discs that run out axially if not turned still on their stub-axles or seated properly on an arbor when faced while detached. (..'stacking' tolerance, whatever... there are actually tapered shims to correct Vette disc 'wobble'..)

Turns out that drum or disc doesn't matter, and btw replacing wheel cylinders had done nothing to help. A drum was out of round from me prying it off once before, and as the linings oscillated air got in with no loss of fluid. (cyl seals hold pressure one way, not both) I'd bleed & it'd last only a few miles. :banghead: I only had a few k mi on the linings and only replaced the drums. Man, was it great to get a firm pedal under foot again, and for 4 more yrs till I traded. Maybe this isn't what's happening with the OP's sweetie pie, but stuff happens. I sure wouldn't have believed it if I hadn't seen it, done it.

Anyway, a guy who could 'turn' those drums could check for radial runout in a heartbeat. :2cents:

 

[blueriver]

I read on another forum that the Vacum booster / hydrovac may need rebuilding ... a fellow who had a 55' (I believe) International experienced the same problem ... so I'm looking at that possibility.

Sure sucks wanting to stop the old girl when she's loaded ... I have grain on it and just back up to the grinder mixer and dump into the auger ... until it wouldn't stop !!! Now I park it and block the wheels and back the grinder mixer to her !!!