Brake problems

[Brad Buchanan]

Hey folks. Been a while since I posted last.

I have a problem with my 1971 Chev c-30 dual rear. I had a rotted 1/4" brake line that extended to the rear and someone had but compression fittings in it to patch it.

I replaced the line and could not get fluid to the rear where it splits to 3/16 line. I replaced the master cylinder, bench bled it and still cannot get fluid. I am considering fabricating a power bleeder.

Is this a good plan or should I consider the proportioning valve that is plumbed to the master cylinder?

Thanks in advance, Brad

 

[glennster]

brad ifyou want an in expensive power bleeder check out the link to amazon. i have a similiar one i use on my 72 corvette. its a pain to bleed
but this works good. if you an crack the line at the proportioning valve and check for fluid, that would be good but judging from the age of
the truck it may break in trying. is it possible the rubber brake line over the differential collapsed? heres a link
poke here

 

[Brad Buchanan]

Hey Glenn. I tried to crack the 1/4 line on the valve but it is stuck hard but not corroded. I was thinking about putting some heat on it but don't know if it would affect the valve.

That rig you posted looks good but the cheap Scot in me wants to take the old cover fom the master cylinder and braze a milton air fitting to it and poke a hole in the rubber insert.

Brad

 

[Janicholson]

Rubber hoses from the rear bleeders into a small cup of fluid, can allow air to escape well enough to purge. Jim

 

[Papaw8]

Probable the rubber hose that allows the rear end suspension to flex. Those cause a lot of problems on the front too. The hole is small and the rubber
swells and closes off the line. See if you can get pressure before the rubber hose.

 

[glennster]

i wouldnt heat it with a torch. maybe a heat gun, but no more. if you have an old master cyl cover, just braze a barb hose fitting in and use a
cheap plastic 1 gallon pump sprayer. release the pressure at the pump handle before removing the master cover, otherwise.brake fluid
bath!

 

[guido]

Janicholson,

And, you will see when the ugly stuff stops coming. Giving the system a good flush.

Been doing it that way, with a clear jar for years! Usually by my self and a long hose,

Guido.

 

[sms]

Been a long time. When you relieve
pressure on one side of the proportioning
valve doesn't it shift over and block
that line until that line is pressurized
again? Can it be stuck now?

 

[Brad Buchanan]

I think you may have solved my problem. I ordered a tool to assist bleeding by keeping the valve from moving. That is unless it is really stuck.
Thanks, Brad

 

[wsmm]

What I use on my vehicles is a mightyvac vacuum pump. Take the cap off of the master cylinder, and use a mightyvac attached to the bleeder valve. Crack the bleeder open and apply vacuum. Usually does the job to bleed the system.

 

[Hobo,NC]

More than likely the proportioning valve has the rear blocked off like it was designed to do.

Open a front bleeder jam the brake pedal as hard as you can to the floor this is an attempt to get the valve to move to center.

Those rear rubber flex hoses will eat your lunch that's why I replace all of them every chance I get. Its the proportioning valve are the rear hose is swelled shut... Pick your poison both can be eliminated. A pressure bleeder is not the answer. BTDT

 

[Steve@Advance]

If you have a high hard pedal and no pressure at the rear brakes, the system is
blead to the restriction, be it the proportioning valve or a collapsed hose.

If the pedal is soft and low, and you get a continuing fountain of fluid inside
the master cylinder when the pedal is released, then there is still air in the
system.

 

[kencombs]

Be really careful with that approach. It's really easy to empty the master. And if you do, that method fills the lines withair, instantly. Better to use a pump up sprayer with brake fluid.

 

[Sprint 6]

Fluid is probably congealed in the rear
frame to axle hose.

 

[ASEguy]

If you lost a lot of fluid the pressure differential valve has floated to the rear blocking off the rear brakes. You probably have a hard as
a rock pedal, but no fluid coming out. You can either take out the grounding switch and physically move it with a pick, Stomp on the pedal
until the pedal softens or open up a front bleeder causing the front brakes to have a pressure loss and the valve will go back to center.

 

[ASEguy]

The pressure differential valve is either right by the master cylinder or on the frame rail by the driver. The valve pointing towards the front is the metering valve, middle valve is the pressure diff. and the rearmost valve is the proportioning valve.