jankyrre

I put fluid in the brake system today,but the rear brakes are still dry.
It is a 68 442,drums all around,no PB.
New master and wheel cylinders.
What do you guys think is causing this?

joe_padavano

You may still have air in the M/C. If not, the next most likely candidate is that the piston for the differential pressure switch in the distribution block as moved all the way to one side. You may need to remove the outlet line on the rear brakes and physically push the piston back into position. If this is the original distribution block, crud can build up and cause the piston to stick. If that's not it, check the rubber hose from the frame to the rear axle. The inner liner can collapse, sealing the hose.

jankyrre

Bleeded the MC after it was installed in the car.Plugged the outlets and pumped slowly until all the air was out.I'll give it another try.
All brakelines have been off the car,cleaned and replaced where nessesary.
Hoses have been replaced.
The distribution block;didn't even know it was a piston in it.
Can you explain the function ?
Don't know if the block is original to the car or not.I have not replaced it though.

joe_padavano

The distribution block has a differential pressure switch that turns on the BRAKE light on the dash if you loose pressure in one half of the brake system. This diagram is not the dist block you have, but the internal functions are the same.



This article shows the disassembly of a 1970 GM dist block.

jankyrre

Thanks.
Does this mean that the warning light should be lit before I put fluid in the system.
If the piston is stuck blocking the rear circuit

joe_padavano

Yes, if the piston is pushed all the way to one side, the light should be on if the wire is connected to the terminal on the dist block.

jankyrre

Solved. At least partial.
Yesterday the car was standing on the front wheels and the rear was on jack stands.I lowered the rear end until the MC was horisontal and was able to get out more air.This solved the problem.
I do have a leak in the rear,wheelcyl-brakeline connection.I'll sort that out later,had to run.Sunday coffee at my inlaws.

redoldsman

It sounds like you did not bench bleed the master cylinder before you installed it on the car. If you don't bench bleed it you will never get all the air out.

jankyrre

Correct.But does it make any difference?
Of cause it's easier to level the MC on the bench than in the car and you can do it without a helper.
Seems to be ok now,no leaks and a firm pedal.
The aft camber in the MC was the hardest to bleed,my helper(son) was about to loose his patient.

young olds

ive got a similar situation. i just did a 4 wheel disk brake conversion and im not getting much fluid to the rear. the master cylinder, dist block and calipers were all previously used but said to not have been much. anyways the fronts appeared to have bled fine and working properly. the rear calipers dribble fluid while trying to bleed instead of a stream and they arent trying to clamp at all.

jankyrre

I will suggest that you loosen up the coupling to the rear circuit on the MC a little,get somebody to press the pedal and look for leaks.
No fluid -something wrong with the MC,a severe spray-MC most likely OK.You can start looking elsewhere.
If you dont want more air drawn into the system,thighten up the connection before your helper releases the pedal.
You dont want brakefluid all over,so cover up.

young olds

I cleaned out the bleeders and gravity bled it and got fluid to the rear. Now when I get a helper I'll do the normal bleeding procedure