HELP! Bleeding rear brakes, proportioning valve

[LouD500]

Need some help fellas with bleeding my rear brake.

'84 T-Type with Hydrobooster. Recently bought the car, brakes worked great so I never got around to checking the fluid level in the master cylinder. Went to pull it out of the garage and the brake light came on and the pedal went halfway down. Car still stops pretty good but I know I'm only running on the front brakes. Here's what I did:

-- Checked the levels in the master and I obviously ran the rear portion low, getting air into the rear system.
-- Filled it back up and bled the rear brakes. I get a good solid, steady stream of fluid from each rear wheel cylinder so I'm pretty confident they're bled.
-- Bench bled the rear portion of the master and when I disconnect the line for the rears at the master and pump it, I get a good solid, high pedal and solid fluid, no air. But when I hook it back up...and step on the brake...still goes halfway down and is mushy.
-- Jacked the rear up, and with the car running in gear, I step on the brake and the rear wheels slow down and stop for a second, then continue to spin with the pedal down. So, not getting any rear brakes.
-- Made sure the shoes were adjusted, slight drag on each drum, good shoes and hardware.

My assumption is that the prop valve still has some air in it and not activating the rear brakes. How do I bleed this prop valve? Seems to me my master cylinder is good and the wheel cylinders are good. I've had mostly older hot rods without prop valves so, it's causing me some grief. What am I missing?

Any help is greatly appreciated.

Lou

 

[TexasT]

Are you using a two person bleed or some kind of vacuum device?
If you are doing the two person method you could be "overstroking" the pedal. I always put a block of wood under the pedal as I can't control the helper and if they put the pedal to the floor it has been known to take on air.
With safety glasses or Goggles remove the mc cover. Have your helper push down the pedal while watching the reservoir. You may see some bubbles even little bitty ones mean the master cylinder isn't fully bled. Slow n steady on the pedal and cycle it until you don't see any bubbles then you can move on to the wheels.

 

[LouD500]

I was doing it myself using vacuum device. When I bled the master I was going slow and steady...but I was going all the way down. It may have taken back air thru the fitting at the mc....was just a push on type adapter...not threaded plastic adapter. I'll try with an actual mc bleeder adapter...my improvised piece may have been causing a prob. But when i bleed the mc i get a good firm pedal...is it possible air is getting back in when i let the pedal up thru the adapter...didnt think of that.

Whats the deal with the prop valve? Does anything need to be done with it when bleeding the rears? Or leave it alone?

 

[LouD500]

I should say...bleeding the rears with the vac device. The master i bled myself by depressing the pedal...but i was going all the way to floor and back...possibly overstroking like you said. I will try again without overstroking and using the right stuff.

For what its worth...i think i have the old cast iron prop valve. Ive read these are known to cause problems.

 

[Chuck Leeper]

AIRC, there is a procedure to clamp the prop valve pin in w/ a c clamp??
Here's a tool that may work..
http://www.carolinaclassictrucks.com/prop-valve-bleed-tool.html

 

[TexasT]

To me if you you are getting fluid out the back bleeders you are good. Maybe try the clamp but if it is spongy I think you still have air in the system.

 

[LouD500]

I get steady solid fluid out both rear bleeders. Just dont get it. Unless theres some air bubble trapped in that prop valve where bleeding the rears cant get it out. Like I said...good solid fluid out the back....but the rear brakes just dont hold. Maybe I blew a seal in the master and its leaking past. But the fronts work great. Could the master just be bad where it operates the rears??

 

[LouD500]

I mean the parts are relatively cheap....im about to just swap out the master and put a new brass prop valve and start from scratch.

 

[LouD500]

But the brakes worked great unless i was only running off the fronts and didnt know before and the prop valve is stuck. The master is crusty and so is the prop valve...so I thonk an R&R is in order anyway.

 

[TexasT]

I put a Cadillac plastic reservoir on my swap. Kirban has a prop valve for like $50. I think you have air in it if it is spongy. Or maybe the front lines are old and flexing.

 

[LouD500]

I ordered the prop valve from kirban and a new MC. Just gonna put clean parts on and bleed it all again from scratch. See what happens.

But I appreciate all the input from everyone.

 

[LouD500]

I suspect the good pedal I had was really only the front brakes working and prop valve was stuck somewhere in the middle and letting some fluid to the rears, but not enough to really engage them...but enough to bleed the lines and wheel cyls. The master is old and rusty, the cap is rusty and the gasket is torn...so a new MC wont hurt and I can bench bleed it off the car the right way. And the new brass prop valve will be nice an clean. So far all the lines and bleeders came off nice and easy so I dont forsee any trouble with removing the fittings on the block.

I will definitely use the block of wood you suggested in order to not overstroke the MC.

 

[LouD500]

Verdict:

Well fellas. I put a new master cylinder and brass proportioning valve (Kirban) on the T-Type. Bled all 4 wheels in the correct order. Thing stops on a dime now and brakes are working beautifully. I had the cast iron prop valve and that thing is stuck like Chuck.

Thanks for all the input and help. Greatly appreciated.

Lou

 

[TexasT]

Awesome! I know I love mine. Just not in the same league as the powermaster.