Update on Brake problem

accordingly.

get a piece of crap in it and stick "open". It is expensive so worth trying to clean. Being that you have one......I say swap er out. You might have to have someone press the pedal while you bleed to get the prop valve back centered when you are done(if its off). I cant remember if that one will go goofy or not.

accordingly.

Add to the list:

6) Replaced ABS hydraulic module (aka: isolation/dump valve). Still no pedal and the brake light remains on.

Doc

>

proportioning

I just replaced it with a reman from Advance Auto ($135, ouch). No effect. It's been awhile since I had to bleed an RWAL hydraulic module but as memeory served: open iso/dump bleeder, press pedal to floor letting air/fluid escape, tighten bleeder, release pedal, repeat till there are no more bubbles. It took awhile but I get her nice and air free, then re-bled all four corners again. F**kin' truck is about one more expensive part from the demoilition derby...................

Doc

pulled the codes yet?

Doc, Don't know if this applies to your vehicle but some ABS modules have to be cycled several times to get all the air out.

Dave

proportioning

out. If it goes out it isn't centered. If so, have someone press the shit out of the pedal while its running and bleed a front and a rear to see if you can get it centered. The light will go out if it does return to normal. If you cant get it that way, try and remove the sensor on the valve and carefully push it back. If removing the wire from the prop valve doesnt turn the light off , check contenuity from ground to the sensor, (with out wire on)should be none. If you have continuity you got two problems(if it had two lights, both would be on) did that make since? GL

The 3 ways of turning the light on, parking brake (dim), prop valve (dimmer) and abs ecm (dimmest). If the light gets brighter when you step on the parking brake, it isnt that. If it gets brighter when you ground the wire to the prop valve, that isnt it either and than your left with the ecm. Ground the aldl a-h and see what codes come up.

Pull the codes. jump A to H of aldl. Codes should flash after about 20 seconds. Count the short flashes after the long flash. Including the long flash in the count. The first count may short but subsequent counts will be accurate. To clear codes I believe the STOP/HAZARD fuse must be pulled. I have a factory service manual for my 92 but I believe its the same. If you need anything out of it let me know and I will send it to your E-mail Address. Good Luck JRE

Scott,

Brake light goes off when wire is unplugged. I figured that this was simply due to the fact that with the wire unplugged and the e-brake off, there isn't anything to make the light go on. You're telling me otherwise eh?

On the proportioning valve, there is a large, flat nut on the front of it with a nippley-lookin' thing in the middle that moves in and out with pedal operation. When this nippley-lookin' thing is depressed with a phillips screwdriver and the pedal is pushed the brake fluid comes squirting out pretty good.

Replacing the prop valve was my next step as it's the only damn thing I haven't replaced yet. Seeing as how my brakes were pretty shitty the day before I started tinkering I'm beginning to think that this guy was on his way out anyways, and when I adjusted the rears it helped it give up the ghost just a little bit quicker.

Doc

Bill,

It's not the ABS light that's on but the regular brake light. No way to pull codes AFAIK.

Doc

ground a-h, turn key on, and wait till it flashes. Very limited number of codes though. In 90 they changed to some soft codes that would be erased when you tried it and set a code though. my grandpas truck was an 88 and I pulled the codes on it. In another post I saw you wrote that the light went out when you disconnected the prop valve. The abs is disabled when that light is on, maybe if you unhooked it, turn the key on till the light went out, then tried bleeding everything again it would reset the dump/isolation valve to their proper position and mystically fix itself? The prop valve needs equal pressure on both sides to reset it self. and if you dump valve is open you would just be pumping fluid into the accumulator.

Bill,

Grounded A-H, turned key on, nothing. After the jumper wire was removed and key turned back on, I get a code 9. A quick internet search tells me that code 9 can be set when A-H are grounded for more than 20 seconds and there are no pre-existing codes. To sum it up, no codes.

IMO it's one of two things:

1) Prop valve is cooked (OE valve, 147k) 2) Iso/Dump is still open. I just replaced the RWAL hydraulic module this afternoon. I don't need to calibrate it or anything to make sure dump is closed do I? Isn't it's base state closed until the ABS computer tells it to open? I bled it out as per the instructions, but they didn't say anthing about calibration.

One last thing I've noticed, with MC resevoir cap off, when pedal is depressed, I get a geyser of fluid from the front brake side of the resevoir, but nothing from the rear brake side of the resevoir. This is what initially made me suspect the ABS hyrdaulic module was shot and the dump was stuck open, but after replacing the hydraulics the problem persists, still just squirting from the front brake resevoir, and brake light stays on (although now it;s flashing code 9's ).

Whaddya think, prop valve shot? R&R?

Doc

JR,

See my reply to William's post a few messages up from this one. In a nutshell, no stored codes. It's either the prop valve is cooked or the ABS dump is stuck open, even after replacing the ABS hydraulic module with a new one.

Doc

Good, my kh rwal manual says that the software changed to that in august 90, your abs ecm must be newer, Older number on ecm would start with 912349k, newer ecms 919220k. Some codes are soft in the newer one and have to be read with scan tool.

I just read the chapter on mc. If the pedal is depressed and released suddenly, i.e. slide foot off side of pedal, that the brake fluid should only shoot up about 3 inches or less, more than that indicates trapped air. I'll think more about this and if its not solved by tommow i'll come up with more ideas

""Doc"" wrote in message news:1wQbb.12415$ snipped-for-privacy@nwrddc03.gnilink.net...

safety thing, if you loose fluid/pressure from the front or rear it cuts out the offending side(front or rear. I dont remember exactly how to reset the little piston back to center in there, but that is what needs to be done. You should be able to remove to sendor and manually center it if need be. What happens is, when it goes off center it lets the wire ground turning your light on. If you remove the sendor or switch or whatever you want to call it you will see how it works, and you will see the little piston with a low or high spot in it that the tip of the switch rides on. Take a little screwdriver or something and push it back to center. You know its right if it turns the light out. The only other thing that will light the light is the ABS or the park brake. It doesnt have a ABS light on it does it? I think it just uses the red "brake" light on that year, no other light. Just FYI, you probably popped the valve off center when bleeding it. When you get it reset, make sure the rears are adjusted up, pump it a few times slowly, (mostly just for fun, and to get a feel of it)start bleeding from the rears first. If there is alot of air somewhere you risk popping the piston in the prop valve again when you stomp the pedal. It been a long time since I worked on this setup, I might have a book on it(actually took a class at the GM training center on this RWAL, but a very long time ago...:) I'll see if I can find the book and see if it say anything interesting :) GL and Ill let you know if I find it. Maybe theres a way to reset it with the little nipple you discribed. Ill look for the book.

I read this on the internet, it must be true! :) /Couldnt find the book......

It sounds as though at some point in time either the rear brakes failed, or more likely, that when they were bled, the valve wasn't held in position so that it wouldn't transfer all fluid to the fronts. The valve can't differentiate between bleeding and a catastrophic failure.

There's a pin that should stick out the front of the valve and must be held with a clamp, vise grips, whatever, while bleeding to keep this from happening. You may have to open the rear bleeders to allow the pin to be pulled out.

Bill,

Scott M may be on to something. I must have popped the valve off center when I was adjusting the rears. Here's why I think so.

Brakes were kinda goofy Friday. Felt like the rears weren't doing their thing. The way I adjust GM drums is as follows. I pull the drums off and visually inspect, then tighten up the adjuster a few clicks at a time until the drum slides on and off with some resistance. I put the drum back on and hold it in place with 2 lugs and pump the pedal a few times in between adjustments to make sure the brake assembley is centered and the shoes are nicely seated in the drums. After I'm done, I reverse-brake a few times to let the self-adjusters do their thing.

It was after doing this on both sides that my brakes were shot. No lines were cracked so no air got in there in-between when the brakes were working (albeit slightly diminished) and when they were shot.

So, how the f**k do I recenter the prop valve? If you read Scott's post below, he mentions holding the prop valve piston (which currently moves in and out with pedal action (piston pops out when pedal pressed, retreats when pedal is let up. Does your book on RWAL say anything about this at all?

Thanks a million, it's nice to have a few brains in on this one. I've done brakes on RWAL systems a bajillion times and never had this happen before................................

Doc

Scott,

The brakes went from slightly diminished to zero with no lines broken for bleeding. They were at about 65% of normal when I pulled the drums and tightened them up, and zero after I put the drums back on and fired her up. In the process of adjustment I pump the pedal a few times between adjustments to get the brake assembley centered and get the shoes seated in the drums. This must have popped the prop valve off center.

So what yer' saying is, get the pin (aka nippley-thing) pulled all the way out, hold it in place, then bleed the brakes again right?

The prop valve itself is dealer-only item and $206, so I'm going to try to get this one fixed before I spend more money on this damn thing.

Thanks so much for your input thus far,

Doc

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?