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I bought my 70 Vette 3-4 years ago and it has just been sitting. I know it has new brakes/ lines/ master cylinder. I took the new master cylinder off and bench bled it till it had no bubbles at all. Now, when I go to bleed the brakes, I cannot get fluid to the rear no matter what I do. I've read about the proportioning valve and done everything I read to check it out and make sure it works. I couldn't make it work. Now, I have it out of the car. How can I know that it is good so I can fix it instead of spending bucks on a new one? Thanks.
At the risk of opening up another can-of-worms thread about proportioning blocks, I will post this picture of what should be in your car. The electrical switch is removed and inside you should just see a rod. What you can't see are two o-ring sealed pistons on either side of the rod that will move back and forth to provide a ground to the switch. If you can blow air through both MC input lines and feel it come out the output lines your distribution block should be allowing pressure and brake fluid to both front and back brakes. If you can't, that piston rod assembly is stuck somehow. I can't advise what is appropriate under those circumstances but I would just buy a new one. If your distribution block looks different some significant mods have probably been done to your car.
If your distribution block looks different internally or externally, please post a picture as this has been an ongoing topic.
Thanks for this great info. I'm not sure what is controversial, unless it is the discussion whether one should or should not use a proportioning block. I'm going to use one, so question answered. I have my block out of the car. I cannot seem to get the electrical switch out of the block. It seems stuck! However, I can blow though both sides and the air comes out with no problem. Perhaps my best bet is to buy a new one.
I think the controversy is that it is not really a proportioning valve. It is a distribution block. It has been discussed many times. I would replace it if at all questionable.
It doesn't proportion anything. The master cylinder has separate front and rear systems. If pushing the brake pedal creates more pressure in one system over the other, the plunger is moved off center. That creates a closed electrical circuit, which illuminates the brake warning light on the dash. Note: the brake warning light is also illuminated when the parking brake (what a joke) handle is lifted.
New everything else, sitting for 3 to 4 years since. Hmmm... how do you know the "new" master cylinder is working correctly?
Last edited by Faster Rat; Jun 11, 2017 at 11:06 AM.
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Proportioning valve question
