92betsy

Ok I am not positive but am pretty sure my brake booster is dead. It is maybe 3 or 4 years since it was installed. I had a load of brick on my truck the other day and heard a pop and a slight his when towing. Then after I dropped off the trailer my pedal was pushing a little farther in than usual. The next morning on the way to work a girl in front of me pulled one of those to busy putting on makeup to realize she was passing her turn moments and locked up her brakes. Well when I hit my brakes the pedal hit the firewall and the truck kept going. I got it stopped before I hit her luckily and got my truck home. I had checked my fluid maybe 3 days before and it was fine but I noticed my fluid was very low now but can't find any leaking fluid. So I added more brake fluid and when bleeding the brakes laying under my truck I noticed a mist coming from the booster. I assume it is a vacuum leak but would like some opinions to make sure. If it is what kind of trucks would I be able to use a hydraulic system from and ditch the vacuum junk that is on there. Any help would be very appreciated it is my daily driver and my work truck so kinda in a bind right now. Thanks.

maybe368

The RWAL modulator valve that is in the frame rail behind the left rear axle, may be stuck open. Do a search on this forum and you will get many threads that try to deal with this very common problem. Good luck...Mark

92betsy

Ok so while messing with the RWAL modulator I got nowhere other than my anti-lock brake light now has come on. I got 2 flashes so according to what I have read my problem is (Open isolation valve wiring or bad control module). Any tips on how to troubleshoot that. I keep finding things on google for different vehicles but not my truck. I also noticed the RWAL diagnostic connector behind the glove box has a wire going into it but that there is no wire or male plug going into the plug side. I can't find any wires or anything that could plug into it either, is this normal or am I going to have to tear the whole dash apart to find a missing wire? I'm not a mechanic or anything but can usually figure things out with a little information so any would be great.

maybe368

Here and here are pretty good descriptions of the system. There is no anything connected to the diagnostic code wire. The control module is behind the glove box. There is also a proportioning/combination valve. Yhese brakes can be vexing Mark

92betsy

Ok so at this point I have put on a new master cylinder and booster. Bleed the whole system and nothing. So not having the money right now for a new RWAL I bypassed it and unplugged it behind the glove box. Still no pressure. It will build pressure in the system when bleeding the brakes and you can feel it in the peddle. As soon as I put it in reverse to back out all pressure was lost. Not really able to pay for a shop or a tow truck to get it to one right now. Suppose to start a new job in the morning and could really use any advice anyone can give. Thank you.

454 no more

Just went through the same problem. I bypassed the RWAL and still had a soft pedal. After putting in two rebuilt master cylinders, I finally put in a new, not rebuilt master and it fixed the problem. I have yet to reconnect the RWAL but I'm tempted to just leave it disconnected.

jogl

Try plugging off the rears and the fronts, one at a time, at the master or at the equalizer valve, and see if you can isolate the problem.

If not plug them both off at the master. If you do not then have a rock hard pedal then it is master, booster or vacuum.

JP.

92betsy

I will go try to plug them off and see thanks for the advice. Hope it works I told my wife to put a for sale sign in it I'm so mad at the beast. Good thing she knows me and explained how much I would miss the dang truck if I got rid of it. It has been in the family so long it has turned into a heirloom anymore.

92betsy

Ok just got done bleeding another master cylinder and same problem. This one built great pressure in the system but again after bleeding the lines same problem no pressure. I am starting to wonder if it is the "isolation valve", or "combination valve" not sure proper name the valve the lines go to straight from the master cylinder. Where can I get a new one of these? Can't seem to find one.

92betsy

I just started thinking my power steering pump has a leak and I know there is a vacuum hose going to it. Could that cause a issue also?

maybe368

It is called the combination valve and the only place I could find them is http://www.wermoparonline.com . This is a slippery slope, I am converting my rears to disk and then I am going to eliminate that valve, if the the system doesn't work..Good luck....Mark

92betsy

Any chance that a gassers valve would work?

jogl

If 'the "isolation valve", or "combination valve"' is your problem you should be able to isolate and verify that before you throw more parts at the problem.

On these trucks the power steering and brake systems are not interconnected, so the answer to your question is NO.

You still do not know if your problem can be isolated to fronts or rears. Put a plug in the out port of 'the "isolation valve", or "combination valve"' for the rear line and see what happens. If nothing then try the front. I always try the rear first because it is usually the POS ABS valve that is phucked.

A plug can be easily made by crimping and then soldering or brazing a short piece of brake line and then putting on a flare nut and flaring. Keep the piece of brake line as short as possible so that it holds the least amount of (compressible) air as possible.

Let us know.

JP.

dieselJon

I bet your truck has at LEAST a oil pan gasket leak, right?

If you do, I can also bet then you didn't check the hard line that runs under the engine, no?

Also, the front soft lines can leak internally. Check for bulging.

92betsy

I broke this can anyone tell me what it is? It connects from the fender to the brake booster check valve.

https://www.t-mobilepictures.com/mya...8707833000.jpg

https://www.t-mobilepictures.com/mya...8708325000.jpg