tfdcruiser

I have a 1998 12v 2500 with rwal only. I have done extensive searching and have not found the answer anywhere. The problem I am having is that my brakes feel like the M/C is going bad i.e. the pedal travels too far, feels soft and the ABS and Brake light come on. The problem initially (six months ago) seemed intermiten but now it is pretty regular and dangerous. I did replace the M/C and it still felt the same, I replaced all the brake hoses with DOT stainless braided, new front calipers with new pads, new rotors, the backs are disc with good rotors, good discs and lots of pads (aftermarket rear disc kit that has worked great for years prior to this prob). Thinking I may have gotten a bad M/C I returned it after six months and they gave me a new one, I believe they were remans but what are the chances of two in a row being bad. I removed the rear abs sensor and it looked good for what that is worth. The truck bleeds very easily with clear clean fluid coming out all the bleed screws are pointing up like they should and I pedal bleed until there are no bubbles.There are no fluid leaks anywhere. When bleeding with the truck not running everything seems fine, firm pedal good fluid exchange etc. It seems to be okay when I first start the truck but within the second pump of the brake the abs and brake light come on and the pedal goes back to feeling soft and travelling far. Could the Hydroboost be pushing too hard? Or could it be the electrical system to the ABS module is not on until I start the truck. Like I said when bleeding everything feels great, but the truck is not running then.

I am now suspect of the proportioning valve or the ABS module both under the hood near the fuse box. Does anyone know if the brass pin in the prop valve is supposed to go up and down with the pushing of the brake pedal. Does anyone also know if the ABS module with the two small metal canister soleniods can be tested?Has anyone bypassed the ABS module by making a small double female brake line to go around the module. The module is like $900 to replace and I am not even sure if that is the problem. How does this module work? I have put my scan tools on the truck and it is not showing any fault codes even with the AbS/brake lights on while reading. Sorry to write a novel but I wanted to give good detail because I am at my wits end on this and really need help I don't trust the brakes till this gets resolved. Please help. Thanks.

swordfish

Shootin' from the hip here because I just recently did my M/C...when you bled the system did you start at the M/C and work your way down through the brake lines and then to the bleeders on your calipers? I followed the Haynes manual when I did mine and that is what they instructed to do with M/C replacement. This way all the air gets out of the M/C, proportioning valve and the abs module. I also did mine with the engine off and everything on mine has worked great. I did buy a new one from Napa. The price difference between reman and new was like $15 so I went with piece of mind. Just my .05 (adjust for inflation)

swordfish

patdaly

Do you have 2wheel ABS or 4?

tfdcruiser

It is rear wheel anti lock only. I bled the system from the furthest (pass rear ) to the closest (dr. front) to the M/C. Like I said when I bled the system everything feels great but when I turn the truck on the pedal gets soft and the abs/brke light comes on soon after the first few pumps of the pedal.

rebal

sounds like you still have air or your RWAL valve is acting up

tfdcruiser

Yeah I know it is acting like there is air but why do I get a great firm pedal with no air ( and believe me I have been bleeding the heck out of it, friend pumping hard for several pumps, hold then crack open and shut the bleeder, repeat several times for each bleeder starting from the furthest) when it is not running but when you start the truck I get a soft pedal and lights. Could a malfunctioning ABS module (two little electrical soliniod cans near engine fuse box) allow the pedal to go down so far? This part is close to $1k and the proportioning valve is about $140 I would like to be able to get some insight on testing them or other peoples experience with these parts before I just try and buy them. I searched alot before I asked but found nothing, so I am really fearful that I am the only one having a problem with these parts. These are the only two hydraulic components left in the system.

esde

disconnect the lever for the rear load/ proportioning valve, and secure it as if the truck is fully loaded. You will then have full flow to the rear brakes. I use a pressure bleeder, essentially a small garden sprayer filled w brake fluid, hooked to the M/C. Also, rod from the booster to M/C is adjusted to the right length? Good luck!

patdaly

Ok, I went through this on both Brownie and Greenie. For whatever reason, the RWAL valve under the master cyl. is not closing off. If you look at it, the 2WAL systems do not have a return to the MC like the 4WABS systems do, so the method of operation is the valve is shut during normal operation, and when the rear is detected in a lockup, the solenoid lifts, allowing the rear brake pressure to accumulate in a pressurized reservoir on the valve. When the lockup is gone, the fluid is returned to the line. Mine went thru a period of sticking open, and one time you would have great brakes, and the very next time, you would swear you were going to die.

I ended up changing the valve, and never had another issue. The bad thing is they are no longer available from the factory, I could not find any dealerships that had remanned units either. The good thing is they used that same valve from 94-99 on 1/2-3/4 and 1 ton full sized trucks with 2WABS only. Every time my buddy at the junkyard gets one in, I scavenge it. So far, I am 1 ahead..........

tfdcruiser

Okay Pat so far you have described pretty accurately what I have experienced and what I am suspecting. I went to the junk yard today and found the rwal abs module (that's what I am calling it) BUT when I took it off the truck I noticed that the fittings although the same size wise but the ends on the steel lines were different. On my 1998 the ends actually bulge out at I am assuming a 45* flare that screw into the abs module with a recessed flare to match. On the junkyard truck (1996) the steel line ends have a more conventional 45* inverted flare (what most of us can make with a double flaring tool) that goes into the junk yard abs module that has a matching shape to fit. I felt me heart sink as I looked at these differences knowing that they wouldn't interchange without a lot of line reflaring. I didn't want to take the chance of re doing the lines only to not solve the problem. It is good to know( i guess) that you did have this module go bad on you and that replacing it fixed your problem. I am thinking that if I could fabricate a small 2-4" line that could bypass this module it should tell me for certain that this was the culprit and if it worked I think I would just keep it bypassed as I am not at all impressed with the rwal system. Has anyone else experieinced this and is there a way to electrically trick the solinoid into staying open or closed or whatever they need to not be in ABS mode. BTW I do have the rear height sensing rod removed and secured in the fully loaded position, it has been this way for a long time prior to this problem.

tfdcruiser

another question is this part also called the dump valve? I am refering to the proportioning valve looking device with two electrical solenoids on it under the hood next to the M/C, I have been calling an abs module. Getting the nomenclature right is half the battle when looking for answers it seems.

Polaraco

I haven't seen it said yet, but pull the fuse on the ABS and see how it is.

A bit of forensics. . . What were the events leading up to this? There may be a clue there.

Pulling the fuse deactivates the unit obviously, but it will give you normal braking without ABS. That is if the problem is actually there.

How much travel is in the pedal before the brakes get hard?

When you start the truck, put your foot on the brake as you start it. If it sinks then, you may have a hydro boost problem. I forget if they were Hydro on those or not. Brakes are brakes.

That would help me before I stick my foot in my mouth

tfdcruiser

I did try pullling the 40A Fuse in the engine compartment. I believe it still caused the light ot come on and the pedal still felt soft, but if the valves in the dump valve(?) are stuck in a certain position it could still present the same way even if they were not powered up, right?

I have another abs dump valve from another truck in my shed (but it actually has different type flares on it) but upon examining it I think that if I take the active valve bodies out of the solenoids and the spring out of the accumulator from the one on my truck wouldn't that effectively give me a hollow body, that would be just like making a bypass line around the abs dump valve. I am thinking of trying this tomorrow, ultimately I would like to just have a straight hydraulic braking system w/o the questionable performance of rwal. For those of you that understood what I just wrote please let me know what you think of this idea.

Polaraco

Heh
I drove without ABS for 35 years so I don't need it. Never hit anything but one snow bank in black ice years ago, Ohhh maybe 73.

I have cars i drive all the time from the 60's and 70's without them. Stop very well. ABS is for people who can't drive. (Boy there's plenty of them around.)

The throttle valves should center when inactive.

I'll ask again. What were the events that lead up to the problem?

You said you changed the master. Are you sure it's the right one? They look the same, but have different bores in the body. That can cause it too. I don't think a 1500 is the same. Lemme guess. . . Auto Zone

Take it on some dirt and lock them up. See if all 4 are locking. It's possible you have a bad master to start with. If it started later (I have to read back again) you may have a contaminated system. That can kill a master too. Crap get stuck in the check valves and it can cause bleed back. But usually, that will cause the brakes to lock and stay there after a few plunges

patdaly

The FSM calls it the rear wheel antilock valve, as well as referring to it as a HCU ( Hydraulic Control Unit ).

I am now somewhat confused, because when I was going through this, the reman part called for all from 94-99 1/2 ton to 1 ton as the same. Looking at my 98 parts cat, I do get a different number, 5003313AA versus my 97 number of 52008934AB.

Here is what MPA lists them as.


Part Number: 52008934AB List Price Core Price Your Price

Electrical Abs components Valve Proportioning Proportioning
$179.00 $0.00 $146.59

Part Number: 5003313AB List Price Core Price Your Price

Brakes - Hydraulic system - Pressure metering valve Pressure metering valve, full size vans, all 2000
$297.00 $0.00 $243.86
Part number 5003313AA was superceded by part number 5003313AB.

BTW, spending 35 bucks at Genos for a FSM on disc would be a very wise move.........

patdaly

Polarco, believe me, I am from the same era, and I went nuts changing M/C's. etc.

You can have PERFECT brakes 99 percent of the time, but when that dump valve gets PMS, you freak.

I am pretty sure that is what he has going on.............