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Discussion Starter · #1 ·
I am struggling with a 95 astro. At one point a while ago the usual rear brake line blew, and it was driven for a while after, causing the front brake reservoir to drain dry, and the proportioning valve to close to front brakes only.

Ive gone through and replaced all the bad lines including rear wheel cylinders, and am now having an awful time trying to bleed the brakes. I cannot move any fluid through the lines at all with any amount of pumping.

Research finally clued me into the proportioning valve being closed and ive been attempting not so great youtube ideas to move the valve.

On this forum ive heard the special tool mentioned several times, and just wanted to confirm what this was. (to get my hands on one). From what i can tell its simply a solid plug which screws into the brake warning switch hole with a pin that forces the valve into an open position? Like basically a solid warning switch? Can you also use a 3rd helper to hold a piece of rounded pin sized wire down the hole to move the valve?

Any help is much appreciated
 

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Discussion Starter · #2 · (Edited)
Well to follow up i have no clue if this did anything, but i was able to bleed the brakes after doing 2 things.

One i made my own pin tool out of a coat hanger and attempted to center the valve. This from what i could tell didnt do anything obvious.

Then i hooked up a vacuum pump on a rear bleeder on the theory that i might be able to draw the valve open with sufficient vacuum on the brake line.

Not sure what worked here, but after that i was able to bleed normally with the pedal and everything is working properly now, so something did something even though nothing was obvious
 

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My brake line burst last year and in nursing the van home all the fluid in the reservoir spilled out. Could not bleed the system afterwards, not sure if it was the proportioning valve or air in the master cylinder. Was about to take it off to bench bleed, then remembered a video I had seen - dude disconnected one of the brake lines from the master and held his finger firmly over the hole while a helper pressed the brake pedal. Messy as hell but after several pumps (bubbles were coming up in the reservoir) I reattached the line and it bled just fine.
 

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Discussion Starter · #4 ·
Good tip, i may give that a try

Another follow up-
The brakes worked properly for about 2 hours, then i started to experience what is evidently a classic proportioning valve failure, the rear brakes are jammed on, fronts working fine.

I dont know if mucking about with the original introduced a problem, certainly possible. Or it could have been sitting so long jammed in one position that it was corroded. I did order a replacement valve since they arent too expensive, and the correct bleed tool, which i found on google by typing in 1995 GM brake proportioning valve bleed tool.
 

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The brakes worked properly for about 2 hours, then i started to experience what is evidently a classic proportioning valve failure, the rear brakes are jammed on, fronts working fine.
Are you sure the drum brakes are installed and adjusted properly? Primary and secondary shoes facing the correct direction, shoe contact points on the backing plate are lubed and don't have grooves worn in them, adjusters are installed on the proper side/direction/operating freely, and finally that they are adjusted properly?
 

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Discussion Starter · #6 ·
Pretty sure, i went back through them. They are both getting to the same level of heat jammed on. Everything recently serviced and lubed, new wheel cylinders and hardware kit.

We will see what happens when my new valve and tool arrive
 
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