Will fluid leak from Brake Proportioning Valve when line disconnected?

[Jack O.]

Hi everyone. I'm replacing my front-to-rear brake line on my '69 non P/B car. I've cut the line off at the front below where it drops down to the side of the frame and let whatever fluid is in the line come out. My question is, if I now disconnect what remains of the front-to-rear line form the brake proportioning valve will the brake fluid in the master cylinder drain out or not? That is, will the valve keep the fluid from draining out due? I will probably siphon most of it out of the master cylinder anyway but like to know how much potential residual I may have to deal with.

Thanks!

Jack

[Edward J.]

Re: Will fluid leak from Brake Proportioning Valve when line disconnected?

Jack sometimes you can just use a rubber plug from like the caliper bleeder to plug off the proportioning valve or something similar. to keep the fluid from running empty in the master cylinder. This makes for a easier bleed process. once the master goes empty it takes much more time to bleed the air out of the system. Even if you can slow down the leaking process while installing the line that will help, or just keep the fluid in master up and check from time to time. changing out the fluid can be done at the bleeding process.

[Joe L.]

Re: Will fluid leak from Brake Proportioning Valve when line disconnected?

Hi everyone. I'm replacing my front-to-rear brake line on my '69 non P/B car. I've cut the line off at the front below where it drops down to the side of the frame and let whatever fluid is in the line come out. My question is, if I now disconnect what remains of the front-to-rear line form the brake proportioning valve will the brake fluid in the master cylinder drain out or not? That is, will the valve keep the fluid from draining out due? I will probably siphon most of it out of the master cylinder anyway but like to know how much potential residual I may have to deal with.

Thanks!

Jack

Jack------


No 1969 Corvette EVER originally used a brake proportioning valve. NONE. An adjustable proportioning valve was used on 1966-68 Corvettes equipped with J-56 HD brakes and a fixed rate COMBINATION valve was used on all 1978-82 Corvettes. A COMBINATION valve incorporates proportioning, brake fluid distribution, and pressure differential sensing in one device. The 1969 part to which you are referring is only a brake fluid distribution and pressure differential sensing device. And, yes, brake fluid will drip or flow from it if the outflow lines are loosened or disconnected.

In case anyone is wondering: why do 1978-82 Corvettes have a brake fluid distribution and pressure differential sensing device which also includes a proportioning function while 1967-77 Corvettes do not? It's like this: for 1965-77 Corvettes the front-to-rear proportioning was accomplished via the different size caliper pistons used front and rear. For 1978 the Corvette began to grow so heavy due to a variety of factors (e.g. bumper standards, safety standards, emissions standards, etc.) that the designed-in proportioning of the disc brake system was no longer adequate. So, rather than re-design the system, GM simply added a fixed rate proportioning function to the brake fluid distribution and pressure differential sensing block. The fixed rate proportioning function adjusted the designed-in function to suit the higher vehicle weights.

[Jack O.]

Re: Will fluid leak from Brake Proportioning Valve when line disconnected?

Thanks for the clarification Joe. Another case of me being "fast and loose" with terminology. I quickly looked up the part online at Paragon and that's what they call it. I just checked CC and they call it a brake line distribution block/proportioning valve switch. Based on the price (~$100), they probably want to make it sound more sophisticated .

[Joe L.]

Re: Will fluid leak from Brake Proportioning Valve when line disconnected?

Thanks for the clarification Joe. Another case of me being "fast and loose" with terminology. I quickly looked up the part online at Paragon and that's what they call it. I just checked CC and they call it a brake line distribution block/proportioning valve switch. Based on the price (~$100), they probably want to make it sound more sophisticated .

Jack------


I can absolutely guarantee you that anyone that calls the 1967-77 device (except for 66-68 J-56 valve which is used in conjunction with a brake fluid distribution block and pressure differential sensing switch) a proportioning valve is incorrect. I only bet on sure things and this one is a sure thing (so, I'd bet on it).

[Erich C.]

Re: Will fluid leak from Brake Proportioning Valve when line disconnected?

Years ago, I purchased inverted flare plugs for the express purpose of preventing fluid loss while doing maintenance on brake systems. I think I bought them at NAPA. I couldn't find them on their site but O'reilly's showed them ( photo ). I'm guessing there also available at other flaps. These are straight thread plugs not pipe plugs which have a tapered thread.