Yet another bleeding brake post

[Subourbon]

Hello all!
82 suburban K20 3/4 4x4 6.2 diesel.
History: going to help friend move, all of a sudden pedal goes to floor, truck stops but really gotta lean into it. I mean my leg was cramping by the time I got home.

This was really in the middle of covid shutdowns, so I just got the move done and went home. Didnt wanna mess around looking for shops or parts.

I pop the lid off the Master cylinder (mc) and when depressing the brake pedal, front chamber goes right down to the point of that I can see the bottom of forward chamber of mc. So, air is introduced. Yay.
Thing is, there are no leaks, none that I can see anyway. It also pulled slightly to the right when breaking, this was when the brakes worked mind you.

Got new calipers, pads, drum shoes and wheel cylinders n springs etc. And got some dot 3, so I'm geared up.
(Got calipers coz I suspect seized caliper causing the aforementioned pulling when braking)
So questions are as follows, forward chamber pf the MC is for front or rear brakes?

I was told it's better to gravity bleed the back and front so as not to trigger the proportioning valve, as having a bleeder open in the rear and pedal depressed would trip it

And the proportioning valve. Oh man. It's probably tripped, like I said I drove back from buddy's move on backroads to avoid main roads, back roads were hilly. So how do I go about bleeding, resetting and just how the hell. Still dont even know what caused the mystery lack of brakes. But anyway

Your help and knowledge is greatly welcomed and appreciated folks, I got a haynes chevy GMC 67 to 87 manual. There is no mention of proportioning valve, so I'm turning to you!

 

[WebMonkey]

https://www.gmsquarebody.com/thread...-your-square-lately.3435/page-664#post-579420

that's what i did after rebuilding the back brakes w/tripped p-valve.

good luck

 

[Jarrett Melvin]

https://www.gmsquarebody.com/thread...-your-square-lately.3435/page-664#post-579420

that's what i did after rebuilding the back brakes w/tripped p-valve.

good luck

Okay so read the post in the link. So if I figured it right. Of you blow a brake line, and trip the proportion valve. You can then open a bleeder on the working side of the brakes. To simulate a leak I'm guessing and then causing the proportion valve to trip back? Am I correct in thinking that?

Right now I have an 86 C30 and the rubber hose to the driver side caliper broke off, I have no fluid and zero brakes. There's no cracks or leaks in the lines anywhere I can see but there but I got no bake brakes either.

My question is, could I fill the master cylinder, bleed my back brakes and trip the the proportion valves back, then bleed my front brakes?

 

[Doc_Ellis]

For some reason the link isn’t taking me to the post you’re referring to, but I think I know the technique you’re talking about.

If none of that works for you, I can tell you what I ended up having to do. I took the warning light switch out, went in with a pick and moved the valve back to center manually.

Picture a rod with a notch in the middle, the notch should be centered, that’s where the plunger of the switch normally sits.

Toughest part is just seeing down there. Took me some alternating looking with a mirror and moving with the pick to get it right.

 

[Jarrett Melvin]

Yes I've also heard of that technique to

 

[WebMonkey]

Okay so read the post in the link. So if I figured it right. Of you blow a brake line, and trip the proportion valve. You can then open a bleeder on the working side of the brakes. To simulate a leak I'm guessing and then causing the proportion valve to trip back? Am I correct in thinking that?

Right now I have an 86 C30 and the rubber hose to the driver side caliper broke off, I have no fluid and zero brakes. There's no cracks or leaks in the lines anywhere I can see but there but I got no bake brakes either.

My question is, could I fill the master cylinder, bleed my back brakes and trip the the proportion valves back, then bleed my front brakes?

i'm not sure i'm understanding what you're trying to accomplish.
(that's my fault not yours).

the p-valve is a path of least resistance kind of thing.
so if the valve is shutting off the back brakes, i 'caused' the fluid to 'flow rapidly' out the opposite side of the valve (front brakes) which let the valve move/flow/float from one side to the other and find its way to center.

anyway, are you saying you've replaced/repaired all the lines and are wanting to regain back brakes (even though it was the front that broke off) ?

in my case, the valve had to be centered to get ANY fluid to flow to the back brakes.
that was what my stomping into a 'leak' method accomplished.

after 'stopping that leak' the back brakes were ready to accept fluid.

THE ISSUE is that if you push the pedal too fast, it'll appear as a leak if there wasn't any fluid in the rear (or front) lines. (air will move faster than brake fluid through the lines).

so i had to push the pedal super slow until fluid starting coming out the bleeder.
(the p-valve bleeding 'tool' forces the moving part to stay centered. i didn't have one)

sorry i'm probably not answering your question correctly but the goal is to center the valve (so all lines are 'exposed' to master cylinder) then bleed whatever needs bleeding SLOWLY as to not force the valve to shift one way or the other.