resetting a Brake Proportioning valve?

somerset · 04-13-2005, 06:42 PM

1991 4X4 C/K1500 5 Litre Cheyanne. Has anyone ever reset a brake proportioning valve before and if so how? I changed the master cylinder and bench bled that prior to installing. Then I pressure bled all the brakes (in the right order). My brakes feel good except I only use my front brakes now, as I cannot lock up the read ones. The brake light (DASH) stays on most of the time (not if I punch the peddle fast). I'm thinking the proportioning valve sensor got pushed to one side when I bled the system and now it can't reset? quite frankly i'm at a loss and I don't want to get a new valve if I don't have to. Any comments and help would be greatly appreciated.

Wheeler88 · 04-13-2005, 10:19 PM

Your brake light switch is on the break peddle. My break lights use to stay on. A friend of mine fixed it with a little screw driver or something, I couldn't see what exactly he did. So theres some kind of adjustment there.
It might be that your brake vacuum booster is broken letting the peddle go lower than it should be, thereby tripping the switch to on.

somerset · 04-13-2005, 11:10 PM

I checked the emergency break cable and switch and all was in a normal position. The light will go out if I push hard and fast on the peddle, with about three inches of movement. But as soon as I give a normal application (about 5 inches in length) the light goes back on. I disconnected the wires into the top of the porportioning valve and PRESTO the light problem ended completely. This tells me that the problem is in proportioning valve. Any ideas or old stories on how to reset this valve back to normal. I was told that you can reset them, I just don't know how.

Wheeler88 · 04-13-2005, 11:40 PM

Are you talking about a console brake light on the dash? Cause I thought you where asking about the rear break lights. I'm not sure but sometimes removing the battery ground for a few minutes will reset some sensors.
If that don't work you'll need some of the real mechanics on this board to comment. I'm still learning the basics.

2000CAYukon · 04-14-2005, 12:25 AM

I own a 90 K1500 5.7 that I bought new and I have a set of factory service manuals for it. First thing is that you probably have Rear Wheel AntiLock (RWAL)brakes so you should not be able to lock the rears up unless the RWAL system is not working.

According to the FSM. The brake warning light will come on for:
1. Air in the brakes
2. Malfunctioning Master Cylinder
3. Contaiminated or improper brake fluid.
4. Parking brake is on or not fully released.
5. Worn out brake linings.
6. incorrect wheel bearing adjustment (does not apply to 4wheel drive)
7. Malfunctioning self-adjusters
8. Brake assembly attachments missing or loose.
9. Improperly adjusted master cylinder push rod.
10. RWAL system malfunction.

Having worked at a tire shop many years ago and having done the brakes on my K1500 (a couple of times), it is really important to adjust the rear brakes by hand. The self adjusters do not cut it. I have found that adjusting them by hand every tire rotation really helps keep the pedal nice and firm. I also get much better wear out of the fronts when I do this.

The light will come on if the pedal travels too far. If the rears are not adjusted properly, this can cause your light to come on.

Also make sure you got all the air out. If the pedal pumps up when you push the pedal a few times in a row, then there is still air in the system.

//2000CAYukon

somerset · 04-14-2005, 12:46 AM

I thought about some of those points too, but what about the when I removed the wiring from the proportioning valve and the problem disapeared? Thank you for the information on why my back brakes didn't lock up...that answered that question. To use your check list:
1. bled the sytem under pressure three days in a row and went through about four litres of fluid;
2. New master cylinder and I bench bled it first too;
3. Napa brand brake fluid proper type brand new
4. checked many times not that
5.???? didn't check yet
6. I have 4X4
7. ?????? didn't check yet
8. looks normal
9. ?how do you check this (It was new)
10. ??? didn't check yet

It looks like I have some more work ahead of me, I was just hoping to get a start with that proportioning valve. I keep the vehicle VERY clean so I have been monitoring for any signs of leaks and have found none yet. Thanks for the help it is appreciated.

somerset · 04-14-2005, 12:48 AM

just to clairify I am talking about the dash warning light that stays on.

2000CAYukon · 04-14-2005, 04:18 PM

How does the pedal feel? Does it travel far to stop the truck? Does the emergency brake go all the way to the floor?

//2000CAYukon

localyokel · 04-14-2005, 11:15 PM

Hi,I am wondering if the light was on before you replaced the master cylinder.Brake warning light from the porportioning valve would be caused by a pressure difference that causes a stem to stick out of the end of the valve underneath the rubber boot.The stem is what trips the warning light.Remove the rubber cover and if the stem is sticking out force it back in and your light should go out. However this sounds to me like air in the master.(and no matter how much you bleed it from the wheels the master will still have air in it) Have someone hold down the brake pedal while you loosen the the lines(one at a time)just far enough for fluid to squirt out and tighten when the pedal bottoms out.repeat if necessary. Good luck!!

bigdaddy1832 · 04-15-2005, 06:28 AM

The last time I replaced a MAster cylinder I had to get three. The first two were just as bad as the one I origially had. I did finially get a good one though.

jveik · 04-15-2005, 08:30 AM

Quote:

Originally Posted by 2000CAYukon

How does the pedal feel? Does it travel far to stop the truck? Does the emergency brake go all the way to the floor?

//2000CAYukon

im confused. how would the e brake goin to the floor have anything to do with the power assist brake system? is there a new system for the ebrake now or what? i have an old truck with a cable goin to each rear brake drum, and i just assumed that they are all still cables, is there hydraulic ebrake systems now?

kenny-1907 · 04-15-2005, 12:17 PM

I do not know if it is the same for your truck or not , but a garage one time were my dad took his 80 1/2 ton in to for brake problems talked about "resetting" the proportioning valve and when asked how they do that their response was, and i quote " You take a 1 1/2 to 2 lb deadblow hammer and hit the brake pedal as hard as you can one time" Me personally i don't think i would want to try that, but if all else fails...........<shrugs>

2000CAYukon · 04-15-2005, 12:54 PM

Quote:

Originally Posted by jveik

im confused. how would the e brake goin to the floor have anything to do with the power assist brake system? is there a new system for the ebrake now or what? i have an old truck with a cable goin to each rear brake drum, and i just assumed that they are all still cables, is there hydraulic ebrake systems now?

If the rears are out of adjustment, the ebrake will not be tight and go all the way to the floor. The rears only self adjust while in reverse. If the rears are way out of adjustment, the brake light can come on when pressing the brake.

//2000CAYukon

somerset · 04-15-2005, 02:33 PM

Wow,
Thanks for all of this advice I shall try most (might not try the hammer method). I shall let you guys know what happens as I go along. Once again thanks for the good advice.

bobboinge · 04-15-2005, 03:30 PM

I have a '94 K1500 blazer and had a problem like yours. I've seen guys jab the brake peddle and think the power booster was going to fly off. What I found to work is: make sure the brakes are adjusted, then slowly push the break peddle about half way and release. You may have to do this a few times. Slowly roll the truck backwards and push the peddle half way again. See what happens!!!!

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