Brake Porportioning Valve

[Justin Fleming]

Hello

I have a 86 k5 blazer and one of the line blew near the valve. My understanding is that that piston in the valve should have shuttled one direction and allow the part of the brake system to still work. In my case the pedal went right to the floor and I had zero brakes. The idea is I want to replace this valve and all the line, the problem is the local shops say this is a dealer item only and the dealer says gm discontinued this part and they show none in the system. What do you guys reccommend??

thanks

 

[rjfguitar]

LMC carries proportioning valves. And no, I don't believe that the valve would allow either the front or back to continue working if a line broke completely off. I might be wrong though.

A wrecking yard after an used one isn't a bad idea either.

 

[diesel4me]

I beleive the whole idea of having a dual master cylinder was to provide at least front or rear brakes when a failure occours in the plumbing!...and the proportioning valve does part of that,it also limits pressure to the rear wheels and creates a delay in activating them ,so they wont lock up the rear wheels or get full pressure to them till the front calipers have started applying pressure..

Many GM trucks and full sized cars from the 70's and 80's used the same proportioning valves,though internally they might be calibrated for each specific vehicle..I have swapped one off a 70's Impala onto one of my 80's pickups before and didn't notice any real differences though..

 

[Justin Fleming]

what I find on lmc is a upgrade kit which it appears it is for 4 wheel disc brake....

LMC carries proportioning valves. And no, I don't believe that the valve would allow either the front or back to continue working if a line broke completely off. I might be wrong though.

A wrecking yard after an used one isn't a bad idea either.

 

[Fordum]

Which line blew? If you have disk front and drum rear, its not uncommon for the rear brakes to not be working without your knowing it.
So, if the front line blows, you lose all brakes since the dual master cylinder sends all the remaining pressure to the rear and they cannot reach the drums.

You should have fluid in one side of the MC. If not, then something went wrong. And it could be the Prop. valve.

Usually you can get some brakes by pumping the pedal if the rear is out of adjustment.
If you did not lose all the fluid, I would consider just replacing the lines, since the Prop valve is probably good.