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Old 09-16-2010, 04:00 PM
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Need help with adjusting height sensing prop valve

New here - need some advice. Had to replace the HSPV, but the rear brakes are still grabbing. How do I adjust this thing? What is the "sane" procedure?

Found out (on wet pavement no less) that it aint good to not have this working right...

1984 GMC 3/4 ton High Sierra.

Thanks.

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Old 09-18-2010, 06:45 PM
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GM has a tool for that. It slips on the shaft of the valve after you remove the actuating lever.I believe you need the black one (there are 3 colors, each for a different application ) Part number 14061395.
There is a "D" shaped hole in it that slides over the shaft of the valve under the actuactor arm, then it has a tang the posisitions the valve by lining up into the lower bolthole in the valve. It then calls for the actuator arm to be reinstalled and the tang cut off.
This is all fine but good luck finding a chevrolet parts guy who has a clue.
If they are too active pull the arm off and move the valve clockwise one tooth at a time untill desired operation.
looking at the valve, with your back to the driveshaft, turning valve clockwise and reassembling the arm to the valve decreases application pressure to the rear (decreasing pontential locking of brakes) . turning it counterclockwise and re-attaching arm increases pressure to rears (makes them lock up easier)
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Old 09-18-2010, 08:31 PM
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latech,

OK, I turned it clockwise - inch by inch, retesting each time - 3 full rotations - and no difference. Went so far each time in the adjustment and it feels like there is a spring in there that it "flips" over. When it flips over have I gone too far and is it just resetting? I am massively confused at this point.

This is a new part I got from Vintage parts, but didn't come with the tool.

Here is some more info, in case I am barking up the wrong tree: when the brakes are cold the back ones grab and skid - concrete,ashphalt, everything. When they heat up they dont grab so much, but it can still throw you through the windshield if you dont watch it.

I Just did a couple of panic brakes at 30mph and the fronts are grabbing - nose of the pickup dives, no skidding of brakes anywhere. BUT - apply the brakes normally and and the backs grab hard, but dont skid unless they are cold.

Frustrated? Oh yeah...what is going on here? Am I adjusting this thing too much, not ennough, or is it something else? I am just sliding under there and adjusting it clockwise -not putting the axle off the ground or anything to get a no-load type condition. Am I doing this right so far?

BTW, no kidding on getting anyone who knows about the tool.
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Old 09-18-2010, 09:01 PM
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I meant to say turn it to the next Notch or spline posisition,not turn it a whole turn. whoops my bad
I dont know about a reset condition on that valve,sounds like it goes so far and starts over like you are thinking.
At this point i would look at the rear brakes.
Check for
1 fluid leaking/contamination of shoe material
2 shoes installed correctley short shoe in front long shoe in rear (primary-secondary)
3 Broken hardware /return spring
4 look at RPO list For braking option and check for correct size wheel cylinders. brake options are listed on the Regular Production Option list
It is a sticker probably on the glovebox. It will have a bunch of letters and numbers grouped together on it. Brakes have the option starting with a "J"
Like JB5 or JB8 and such. check your brakes and see if there is a problem. If you cant figure out wheel cylinder size post the RPO for the brakes and I will look into it for you. check em out. Let me know.
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