Update on Brake problem

Page 2 of 2  


YES, but.....I dont know if it will center the piston in there or not by doing this. Remember, your brake light will not be on if it is right.(must be plugged in). Try to remove the switch or take the whole thing apart if need be to center it. Then bleed while keeping the pin out. Do you understand the piston part? do you get LOTS of fluid from all the corners?
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way
Whenever work on the brake system is done it is possible that the brake warning light will come on and refuse to go off when the work is finished. In this event, the switch must be centered.
1.. Raise and support the truck. 2.. Attach a bleeder hose to the rear brake bleed screw and immerse the other end of the hose in a jar of clean brake fluid. 3.. Be sure that the master cylinder is full. 4.. When bleeding the brakes, the pin in the end of the metering portion of the combination valve must be held in the open position (with the tool described in the brake bleeding section installed under the pin mounting bolt). Be sure to tighten the bolt after removing the tool. 5.. Turn the ignition key ON. Open the bleed screw while an assistant applies heavy pressure on the brake pedal. The warning lamp should light. Close the bleed screw before the helper releases the pedal. 6.. To reset the switch, apply heavy pressure to the pedal. This will apply hydraulic pressure to the switch which will re-center it. 7.. Repeat Step 5 for the front bleed screw. 8.. Turn the ignition OFF and lower the truck. Are there bleed screws on the valve? If not bleed at the lines on the valve. What you are trying to do here is use pressure to center the valve's piston. Dont confuse rear brake bleed screw (in #2) with the rear wheels, we are talking on the valve here. Just watch the light for confirmation on reset.
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right.(must
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valve.
piston.
Allright! Now we're talkin'.....................
No, there aren't any bleed screws on the valve that I remember seeing. I'll take a closer look when I get home from work; maybe they're located in the back somewhere out of sight. If there aren't bleeders on the valve, it's gunna be impossible to rig up a hose! Maybe I can just crack the lines at the valve and use a shop rag to catch all the fluid.
Number 4 is kinda fuzzy too. Do I need to loosen the bolt on the prop valve before I give the pin a tug or can I just pull her right out with the bolt nice and snug? I don't have the tool described and have NO idea where to find one...........
Hey, what about nozel's advice? Seems to contradict yours...................
Thanks so much,
Doc

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Doc The combination / proportioning valve 'pin' should move out with pedal force applied and more importantly retract when pedal is released. This indicates front brake is pressurised. To recenter light, block the pin from extending (gm or snap on or Mack probably have such a fixture) then push hard on pedal to re seat switch. Be careful though for you could set the switch to rears failed position. The pin protruding from front side of valve is not the switch trigger: Trigger is buried deep inside the assembly. Proportion/ combiation valve is probably toasted due to its age Respectfully Rolf
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force
Ok Rolf, that's the exact opposite of what others have told me (hold pin IN not OUT). So what shall I do.................I think I'm gunna try both............
Doc

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way
Yes, I get lots of fluid from all four corners when bleeding with key off. Haven't tried with key on though.
Doc
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right.(must
if
corners?
I'm reading this thread with great interest. I have to replace the flex lines at the front of my 90 Sierra1/2ton. And possibly calipers depending on the bleeder screws. I'm not going to dive into it yet till I see how this one goes, heh. B
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Don't hold pin out, rather prevent pin from popping out whilst bleeding Gm manuals have a tool number but snap on or Mack may be able to supply fixture and is recommended if power bleeding your system. Rolf
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Hey, you all want to bet on how many gallons of brake fluid Doc has gone threw so far? I bet 1 and a 1/2 :)
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That pin is the metering valve bypass for the front brakes. It holds off the pressure to the front until the rear brakes have a chance to start working (have to overcome all the return springs in the drum brakes before you get any braking). If you can see the pin, it needs to be pulled out. If its covered with a rubber nipple, It needs to be pushed in. It should be bypassed to bleed the brakes properly.
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