Skruball73

I replaced the break pads and tried to bleed the back breaks, but nothing ever cam out of the bleeder valves on either side...took the valves completely out and the back side of both were dry...switch to the front and they bled fine...anybody got any ideas? could there be blockage somewhere or could it be with the valves and plungers in the master cylinder ? :confused:

norvalwilhelm

I had a similiar problem, alot of pressure on the pedal to bleed the back brakes on both my 75 vet and 89 mustang. Talked to the local garage mechanic and he told me they have nothing but problems with the proportioning valve, that brass block under the steering column attached to the frame. On recommendations from my local CANSCAR racer I remove it. Best think I did for my brakes. I do NOT drive in rain or snow but I can lock up the 4 wheels if I try. My brakes felt alot strong once it was removed.
If your fronts bleed fine and the back are really stiff it must be this proportioning block. Also if you loose brakes in one end your pedal goes almost to the floor. With my completely seperate systems, no connection between the front and back the pedal even if one system fails feels fine. It does not go to the floor. Bleeding brakes is alot simpler and the brakes release alot faster.
I have had it remove in both cars for at least 3 years and like it. Remember I don't drive in the rain every.

Rockn-Roll

no fluid coming out the back is usually due to a clogged m/c. Remove the master cylinder and bench bleed it. Don't attempt to bleed the m/c while it's still in the car or you run the high risk of getting paint eating and everything staining brake fluid on your precious Stingray.

I must keep in mind that Norval is a seasoned driver and mechanic or I would be posting a polite "Ok if I disagree". Norval, please indicate exactly what you did in case Skruball73 wants to remove it. Like did you use a straight two into one junction or a two into four?

I don't recommend running without a distribution/proportioning valve in a brake system which has seperate front and back systems cause the valve will provide more consistent braking between front and back while providing reasonable insurance that you won't be without some brakes if one section fails. If you use a two into four junction or a two into one junction then 3 one into two junctions to join both systems, or just use one system with a one into four with the other system plugged then if the brakes fail then they will fail completely and you won't be able to lock up the system that is still good like you can with the original system.

The following advice is just for racing: a single brake system which provides equal pressure to all 4 wheels is the best for a cheap way to get the front and back balanced; however, seperate front and back systems that have a balance adjustment (like with the original proportioning valve) so you can apply more pressure to the front would help prevent the rear wheels from premature skidding under hard braking. The optimum of course is anti-lock brakes (though Merlin would argue that larger rotors are better) with a seperate system for each wheel so the pressure could be adjusted for each wheel individually.

gerry72

A '73 doesn't have a proportioning valve. '76 (I think) was first year for p-valve.

Brian Madderom

OK, lets clear up this subject! I am (ASE) certified in brakes, work in the tech department at Vette Brakes and Products and have (hands-on) done more than my share of C-3 brakes. The problem is very common on the '65-82' vette's. First, you (should never) take the distribution/proportioning valve out of the system (unless your racing) due to safety reasons. The rear and the front need to be seperate in case one or the other fails in which you need backup. The common misconception on the C-3's is that it's a proportioning valve. The pressure from the master to each wheel is equal and the Proportioning from front to rear is actually controlled by the size of the pistons in the calipers. There is a slider piston inside which balances the pressure and if the pressure is greater in the front it will move all the way to the rear and sometimes get stuck. The cure is to open the bleeders on the front (keeping the rear closed) and hit the pedal fairly quick to reset the slider piston to the front and let the pressure build in the rear again. After you hit the pedal a couple of times close the front bleeders and bleed the rear in a slow fashion so the piston doesn't return to block the pressure to the rear. I recommend one pump each time you open the bleeder. Have someone open the bleeder and the other person pushes the pedal (with a slow constant motion) to the floor once and hold. Then close the bleeder and have the other person let the pedal up fairly slow to ensure that the fluid is being replaced in the master. After the first couple of rounds you should have fluid. As soon as you get fluid move to the next one in this sequence: (outer RR, inner RR, outer LR, inner LR, RF, LF). When you get fluid to all the bleeders then you go around the car one more time to make sure the air is completely out. It may take a little more time but it sure beats pumping on air. :yesnod:


[Modified by Brian Madderom, 10:12 PM 12/7/2001]

Skruball73

Thanx for the info will try it out and see how it goes. :cheers:

73 Teach's Pet

As a tip
To prevent brake fluid from being squirted everywhere ( BE AWARE - brake fluid does remove paint - which makes it great for removing paint from plastic that other paint removers would eat) place a piece of tubing over the bleeder and direct the fluid into a container.
If you first add some fluid to the container, when you crack open the bleeder and have your friend push the brake peddle down, with the end of the tube in the fluid in the bottom of your container, then you don't have to worry about air being accidentally sucked back into the system. Only brake fluid can be be sucked back in preventing more air from entering your system which is exactly what you are trying to remove
I also had the same problem on my 73, but used my vacuum pump to help suck the fluid through the lines by attaching a tube to the bleeder and creating a vacuum at the furtherest bleeder from the master


[Modified by 73 Teach's Pet, 6:19 PM 12/7/2001]