trying to bleed completly dry brake system on 68 with front discs
bleed front ok but cannot bleed back i have bleeders on the master cylinder can bleed them
it is origanal system
compersatin valve does not look like it moves but that only operates the front
brian

Why can't you bleed the rear brakes?

Conventional wisdom says to always start bleeding with the longest pipe first, which would be right rear, then left rear, then right front, and finally left front.

that right but i could not bleed rear and i read somewere on front disks start at closest on 68 firebird so i tryed it
brian

Again - why can you not bleed the rear brakes?

Your efforts will be worthless if you cannot bleed the entire system.

If the front has fluid and the rear is dry - the porportioning valve will "jam" toward the side with no pressure.

You said you're bleeding a completely dry system, right? Maybe the proportioning valve has the rear system blocked as a result of bleeding the front system first. Pressure on the front system with no pressure on the rear system results in the proportioning valve blocking off the "sensed" system with no pressure which, in this case, is the rear system.

Have you tried "re-setting" the proportioning valve to see if it's blocking off the rear brakes? That is; if you have a "proportioning valve" installed.

Or maybe the proportioning valve was blocking off the rear brakes before you started bleeding any of them.

Also, some service manuals will say to bleed the rear brakes first, while other manuals will say to bleed the front brakes first. As in this case.

The front brakes and rear brakes are basically two separate systems........meaning that the fluid from one side doesn't mix with the fluid from the other. So if one side has air trapped in it, the air won't contaminate the other side, either.

So in reality, it doesn't matter which side (front or rear) is bled first. Unless you want to believe one service manual over the other.

thanks brett that sounds like the problem but how do i reset the proportioning valve the manual say there is a plunger to hold closed but i cannot find it
brian

Yeah, I have read that the "plunger" is suppose to be clamped with a big C-clamp and a piece of wood to stop the proportioning valve from blocking out either the front or rear brakes during the bleeding process. I don't have a "plunger" on (what I think is) the original equipment proportioning valve.

When I bleed my brakes I use one of those "one man" vacuum bleeder kits from HARBOR FREIGHT. They're cheap but it works pretty good for me and I don't have to worry about the proportioning valve blocking out the front or rear brakes as during "traditional" bleeding by having someone pumping and holding the brakes while someone else cracks open the bleeder at the brake.

Any way here's a good way to "reset" your proportioning valve:

Set up one front wheel and one rear wheel for bleeding at the same time. Crack both bleeder screws and gently pump the pedal a few times.
The blocked side will trickle fluid out when the bleeder screw is cracked and the pedal pressed. An unblocked line will squirt fluid out the bleeder.
The lines that are clear must be left open and the blocked lines should have the bleeder screws tight to cause pressure to build up on that side. Be sure to use the standard bleeding procedures to prevent air from entering the system.
Slowly press the pedal with steady pressure a number of times; this will center the differential valve. You may also hear a pop come from the proportioning valve. This is the metering valve returning to its equalized position. Then close the bleeder.

Hope this helps. If it doesn't clear the problem then you might have a blocked brake line.

Nope never start at the closest brake. Always start the farthest first moving towards the next closest etc. when bleeding brakes. Usually what i do especially if it’s a new fill, fill reservoir OPEN all the bleeders and let gravity be your friend! . Place cap on reservoir pump a few times. Fill again, remove cover, go have a cold one and just sit and wait until all of the bleeders start a good flow, and make sure to keep res full. Now close bleeders from farthest to closest, rarely do I ever need anybody to help me bleed a system, been doing this for over 30 years it works fine. At times I do use myself bleeder cup if it’s being a PIA.

thanks again brett i will try that tomorrow sound like it will work
brian

thanks pci i have always done it that way but i think the proportioning valve is one way and a manual i read said start at nearest
brian

it worked fine on my disk brake conversion.

PM sent.

hi brett have not solved the problem yet pulled valve and it is ok
get good presser from front so i am going to use the front to bleed the back then reconnect everything and try again with all lines full
brian

managing to bleed right side only on back running the car for testing now get back to brack problem later brian

I started with a dry system. I could not gravity feed or pump the fluid through. I ended up getting a vacuum pump from Harbor frieght for $20. That did the trick.

Ditto on the HF tool. One of those tools you say to yourself, "Why didn't I buy that 10 years ago." Used it on my MC, daughter's clutch, several brake jobs, troubleshooting my FGF's AC controls, etc.