Rafter B

The brake pedal on my 93 goes nearly to the floor. It will stop the truck, but not very safe and I'm not sure what the problem is. The ABS lite stays on. Can anyone walk me through the bleed or maybe give me a clue as to what could be the problem. We pull a trailer a lot and it makes me nervous wondering if I'm gonna get stopped or not. Thanx!

maybe368

Have you done any work to the truck's Brakes? the bleeding order is rwal MODULATOR VALVE (IN FRAME RAIL BEHIND LEFT REAR WHEEL), RRW, LRR, RFW and LFW. It sounds like a bad master cylinder or maladjusted actuator rod. If it is the master cylinder, I would highly recommend getting a mated MC and booster and replace them as a unit...Mark

Rafter B

Everything is nearly new.

sooty

if you havent done any work, and the pedal degraded quickly, the rwal valve will be suspect, make sure the rear drum shoes are properly adjusted, search forums to identify common abs problems, when mine went out, i bypassed the valve, with a jumper line, this is not in everybodys intrest, if you have an accident that contributes to lost control, you could be held accountable, ive got a camper on my rig, the xtra weight will prevent a lockup condition, in my personal intrest, i like the brakes without the troubles, of the abs system.

maybe368

This seems to be the common result when "everything" is new. Did you replace the mc and booster? If so. I believe that there is 1 or 2 things wrong, the push rod on the booster is not correctly adjusted for the mc or the mc has a different plunger cup than the original and is not compatible with the booster. There is an adjustment procedure, but that would not solve any compatibility problems. I think the easiest, while not the cheapest, is to put in a mated mc and booster unit that is compatible and adjusted correctly at the factory. That is what finally solved my problems...Mark

rebal

if it going to the floor its ether
air
out of adjusted rear shoes
bad m/c
bad rwal
I have real good brakes ...now that EVERY part is new
this system has no room for a weak link

BearKiller

Way back when these trucks were shiny-new, they were notorious for sorry brakes.

I believe all the blame should go to that RWAL mess.

I can well remember how, after driving various Fords and Chevys, we would head out somewhere in a shiny-new Dodge and the biggest concern would always be "where are the brakes".

Take them back to the dealer, because they were under warranty, and no better for the experience, because they couldn't figure out why they wouldn't stop either.

Now, these trucks are twenty-plus years old and most of us have just gotten used to them.

For a good example, just let someone who mostly drives a 1st Gen. Dodge get under the wheel of just about any other truck; they will almost throw themselves through the windshield the first time they need the brakes.

The only reason I haven't yet eliminated that RWAL mess from our fleet is on account of me having to lay on my back in the gravel for such adventures and I keep hoping a new administration will provide me with the means to finally get a concrete floor to roll around on, yet things just get worse and we just get poorer.

I am anxious to feel the difference in braking response.

brainfade

If the brakes were OK previously and given that the ABS light is on now, the RWAL malfunction is the most likely culprit. The RWAL functions by releasing the pressure from the rear brake system when it detects rear wheel lock. The fluid goes into a sort of accumulator that is part of the RWAL assembly in the left rear frame rail. Sometimes a malfunction will cause the computer to hold this valve open all the time, my guess is that's what's happened here since the light is on.

Possible causes and fixes: Sometimes the sensor in the rear axle will gather up a bunch shavings and such (it's magnetic) and cause it to read the speed wrong. The sensor is held into the top of the rear end housing with a little bolt, about 8 or 10 mm IIRC. Take it out, wipe it off, put it back and reset the ABS computer by unplugging the harness (it's behind the glove box) or just pulling the battery cable for a few minutes.

The other possibility is the wiring or computer going wonkers. Likely not the computer since it's showing the light but I have heard of the wiring going bad or the sensor going bad. Time to get out the old Ohm meter and start checking...The sensor should be about 1200 - 1700 Ohms I think. Someone with the FSM could verify that.

One thing I would urge you not to do is bypass the RWAL except for test purposes. When the rear brakes on these trucks are working correctly they will go to lock long before the fronts on an empty or lightly loaded truck. If the front wheels are on un-even surfaces (one on ice, one on asphalt) the truck will rotate around the wheel with traction much faster than you can catch it and of course it will be at the worst possible time.

BearKiller

I guess it may be a generation gap.

Myself, I absolutely abhor driving any kind of "anti-lock" braking system, be it car or truck, especially on icey or rain-slick pavement; I much prefer the simple system like that on my 1985 Ford and 1978 Chevy = they will stop and stop straight.

We safely got by with plain old brakes for generations, and anyone that half-way knew how to drive never had a problem.

Now, we are letting electronics and computers do our thinking for us and the news has several fatal accidents every night.

brainfade

Hey B/K,
I've got a lot of respect for you bud and I generally agree with what you post and completly agree that people should be taught to drive properly and be held responsible for they're own stupidity...but...I spent 18 years at the proving grounds for a major tier 1 supplier of brakes to all the OEMs and have performed hundreds of FMVSS certification tests for pass car and light truck, done development work on brake systems of every kind and I can show you the data...no human foot can out-brake the computer in a straight line, turn or slalom on dry, wet or ice surfaces. On gravel or certain types of snow a locked wheel is better for distance (still can't steer) than ABS.

That being said, the issue with the Dodges is one of design rather than driver skill. The engineers at Dodge put a really powerful brake on the rear axle so that the truck could meet stopping distance and fade requirements at a greater GVW. The problem then becomes controling the output of the brake at LLVW. The Ford and Chevy trucks use a proportioning valve to reduce pressure to the rear brakes under light load, Dodge chose to use the ABS as the proportioning device. Therfore, when the ABS is disabled or removed from the system, the rear brakes recieve full pressure at all times and the spin-out scenario becomes possible. The issue is system balance, not driver skill.

I've tested some new cars with all the super-duper ABS and stability controls etc., that are seriously good with everything working correctly but nearly unmanagable with the system turned off. As a measure of this I would note that the stopping distance requirement for ABS off is more than double that for ABS on for pass car/light truck in the FNVSS 135.

This explanation is certainly not intended as anything but food for discussion so I hope we don't set off any flame wars. As for the increase in crashes, I'd chalk most of that up to poor driver training and cell phones...but that's another post.

maybe368

Dodge also has a proportioning valve...Mark PS Also, while I agree with what you say, where Dodge dropped the ball was that in a fault situation on the ABS, you can completely lose ALL braking. IMHO, THIS SHOULD NEVER BE ALLOWED TO HAPPEN. It is a failsafe failure.

rebal

thats not just dodges fault chevy used the same rwal for a few years too its a kellsey hays issue . that said , my rwal worked fine up until this year so I just installed a reman mand its working fine

maybe368

You are absolutely right, Ford also and others no doubt, but, as I recall. when antilock brakes were first being sold to the public, it was PROMISED that any failure in the ABS would not result in loss of brakes. I cannot believe that corporations did not keep their promise . Seriously it is a lousy feeling when you hit the binders and no binding happens ...Mark

SOOT4BRAINS

So from what I am understanding from this is that there is a lot of braking potential in the back brakes. Then the abs system can reduce this pressure as needed to keep the rear brakes from locking up. More load = more traction and abs should allow more pressure to the back as needed as long as it does not sense it locking up. Correct? I know a couple guys on here have bypassed the anti lock and say the brakes work much better. What about bypassing the anti lock and putting in a aftermarket style proportioning valve? This way you can fine tune it a bit. It would not prevent lock up, but it could improve braking while reducing the chance of them locking up over just bypassing the anti lock. I typically do not like the feel of antilock brakes on this vintage of vehicle. I do like the feel of the abs system in my dads 05 dodge. And as B/K suggests, every time I get in it I hit the pedal too hard and am pinned by the seat belt. This may be more of an issue of vacuum assist vs. hydro assist. But I have dad to stand on them on water before and it stopped great with out locking up. His truck also weighs a lot more than mine too. I will not argue that a computer can do a better job. I like the idea of anti lock brakes, but I feel like my rear brakes on my truck do very little stopping. I just redid my rears due to a bad wheel seal getting one side wet. The shoes were the original ones and had 160,00 on them but had very little wear. And they were adjusted properly. Is this a bad antilock system or is this pretty typical? My theory is if they are not wearing, they aren't doing much work. I know the back end is light but I feel that more braking could be done in the rear without locking it up.

brainfade

Some more info: When the RWAL enters this failure mode and it's dumping fluid to it's internal reservor it feels the same as a 1/2 system failure, IE a broken rear line. The front brakes are still active as the systems are isolated from each other but the pedal requires much more travel to make the fronts work. Just gotta push that puppy through the firewall and the truck should still stop if the fronts are in good shape. One way to tell if this is the type of failure you have is that a couple of quick pumps will fill the RWAL reservor and the pedal will come back up and be firm and the truck will stop like normal. However, after a little time off the brakes the RWAL pushes the fluid back into the M/C and you're back to the long pedal again.

For Soot,
You've got it! The rears don't do a lot of work in an un-loaded truck. If all those miles were empty it's possible the rears could last that long. I'll agree it's a crappy, cheap ABS sustem, but it's what we're stuck with and it's safer to spend the effort to make it work right.
Yes, an adjustable prop valve will work well for this but takes a little fooling around with. You'll need a wet or gravel road and an empty truck. From a low speed make a stop that locks the front wheels. Check the rears and adjust the valve so that the rears keep rolling after the fronts lock. Once you've found this point then you should be able to lock the fronts and then with additional force on the pedal lock the rears. Mark the valve postion and do it again with the truck loaded. Now you just have to remember to adjust the valve when you change weights. Bottom line: You always want the fronts to lock first under all conditions.