[keith k]

I drug my '70 T/A out of the barn to work on it this week. Brake master cylinder losing fluid in the back reservoir, and it seems to be running down the front of the booster under the cylinder, so I assume it's a master cylinder problem.

Before pulling the master cylinder, I wanted to suck the fluid out of the cylinder and lines using a vac pump at each of the bleeder screws. I get good fluid flow on the left (driver side) front, but at the two rear wheel cylinders I can't pull anything. Vac pump will pull great vacuum with the bleeder screws loosened, but it just holds the vacuum and no fluid (or air) flows.

It's a stock system with the mess of combo/metering valves up front. I tried depressing the switch on the back of the cast iron valve (per the service manual), but that doesn't seem to help.

Any ideas?

I was sort of hoping not to have to disassemble the whole system and check for blockages...

Note the brakes on this car worked beautifully before the master cylinder started losing fluid - best pedal feel of any old car I've had.

[skunkwerks]

Keith,
sounds like your rear hold off valve is sticking in your proportion brass block. Remove the rear brake line where is joins with the proportion valve and start bleeding from there. you will need to genereate at least 25 psi vacuum. once you get fluid out of that then re-attach the brake line and bleed from the rear pass side then rear drivers. should get you going.

[TA455HO]

Another possibility - if I'm reading that right - is the bleeder screws are clogged up - try pulling one of them out completely and see if anything happens - be prepared for fluid to flow if that is it. Sometimes if they sit for a long time or are not bled for a while the fluid in the end causes some corrosion and the hole gets plugged with that.

I hope that helps some. I have had luck removing the bleeder screws completely, digging out the hole with dental picks and cleaning with pipe cleaner brushes and back in business,

Chad

.

[keith k]

Originally Posted by skunkwerks

Keith,
sounds like your rear hold off valve is sticking in your proportion brass block. Remove the rear brake line where is joins with the proportion valve and start bleeding from there. you will need to genereate at least 25 psi vacuum. once you get fluid out of that then re-attach the brake line and bleed from the rear pass side then rear drivers. should get you going.

Yes, this was one of my problems. Original fluid loss was in the rear reservoir, which tripped the switch in the block, and it stuck. I managed to un-stick it and get the fluid flowing to the rear again.

Originally Posted by TA455HO

Another possibility - if I'm reading that right - is the bleeder screws are clogged up - try pulling one of them out completely and see if anything happens - be prepared for fluid to flow if that is it. Sometimes if they sit for a long time or are not bled for a while the fluid in the end causes some corrosion and the hole gets plugged with that.

I hope that helps some. I have had luck removing the bleeder screws completely, digging out the hole with dental picks and cleaning with pipe cleaner brushes and back in business,

Chad

.

I had one that had this problem, too. I pulled all four and cleaned them up good. Before I did that, I replaced them all with the Dorman "Quick Bleeders"... the kind that have the internal check ball/spring to enable one-way flow. That aspect sort of works, but when I was done and snugged them up... two of the four kept leaking (slowly, but leaking...) out the nipple. So I fixed up the originals and put them back on.

So I think I'm back in business. Firm pedal, and fluid flowing at all of the bleeders. Car is still up on stands while I tick through the rest of my long list of service needs for it, though, so I haven't had it out for a road test.

[skunkwerks]

Better to use the original bleeder valves. Glad you got it back up and working. I hate doing brake bleeding. Always fear getting fluid on the paint.