2nd Gen Non-Engine/Transmission occasional brake problem

[raxley]

This has happened 3 times and it's worrisome each time. I will be stopped or very close to being stopped and my brakes will not work. I mean they go to the floor and the truck keeps going even if it's only idling. The first two times I was really worried about how I was going to get back home to work on it without brakes, but when it happened yesterday I had thought about it and I took it out of gear and revved it up a little and it went away. It seems to have something to do with the vacuum or maybe it's because of the low speed, but it goes away when it's revved up. I've checked the vacuum lines going to the brake booster and they seemed fine, but I have a vacuum gauge tester someplace around here, if I can find it.
Do you think it's something to do with vacuum or a vacuum leak or something? It goes all the way to the floor and the brakes do NOTHING, but goes away.
Another similar thing is that I don't have a emergency brake, it goes to the floor and has no effect. I have heard something to the effect that the 'automatic' rear brake adjusters don't work well on the earlier trucks and don't adjust.
Do you get what you pay for in brake linings? I've seen linings from less than $20 up to $100.I mostly (always) use my truck for really light work, I have construction tools I carry and sometimes some plywood or sheet rock so I don't really need the fade resistance that some people need when hauling heavy and down hills, etc. Is there anything to the carbon linings or the expensive things like Kevlar? I assume that they need metal or some type of metal powder that's mixed up in the lining, but I think most cars have that too.
I was planning on putting the one ton cylinders in the back drum brakes-I heard about that here I think.

Edit: This is for a 1994 reg. cab automatic, 2WD 100% stock. I wrecked the 2005 in my signature-but is there brake parts (like brake booster or calipers) that I can take off the 2005 for the 1994, or is everything (brake-wise) entirely different?

 

[JR]

I would think a vacuum loss would cause your pedal to become very stiff rather than just go to the floor.
Does your truck have ABS?

 

[GAmes]

You adjust the travel of the parking brake by adjusting the rear shoes. The automatic adjustment on our trucks rarely work. Even when mine was new I had to manually adjust the rear shoes. See if your problem goes away after you have adjusted the brakes. I think that adapting the rear brakes from the '05 to the '94 would be difficult.

 

[NGuzik]

My truck did that afew times over the last months. I checked to make sure all vacuum lines were connected and weren't cracked. You'd know if it's a vacuum leak if you don't have hvac control. I then rebuilt my vacuum pump with new seals and cleaned up the compression fins with no chance. I also haven't had a true speedometer reading since I got the truck. This made me think the rear end or speed sensor weren't working. I replaced both when I got the truck to solve my speedometer problems but after a year I didn't have a speedometer agin. I chalked it up to bad wiring from the op, my truck was all hacked up with bad connections. At this point I had no light on abs light or any codes thrown. Just to test my idea I unplugged my rear end sensor and the problem has gone away, but now I have an abs light. I've been driving around the last few weeks this way and found my speedometer has become intermittent and only goes up to 30 or 40 mph. This weekend I am replacing the rend sensor to see if this all goes away. So basically I believe the system is trying to read the abs and can't find any info, causing the breaks to go soft and not complete an abs cycle.

 

[raxley]

The truck does have abs. when I start it up, it takes about 5-10 seconds but the brake lights come on, that is the warning light in the dash 'brakes' stays lit.
I looked under the rear wheels for a adjustment window to stick a screwdriver in to turn the 'star' wheel thing (assuming it's like my old VW, but I thought there was just one window-a vw has two 'windows for 2 star wheels) but I can't find any hole.
That makes sense that without vacuum the brakes might get harder rather than going to floor, but I just don't know what's going on or not going on with them.

 

[seafish]

While I have never experiecned it, I HAVE heard about ABS malfunctions causing just the type of symptom that you are having.
There are people who 4wd in rough country and they actually UNPLUG the fuse for the ABS controller in order to PREVENT just the type of problem that you are having, which in a rough country situation could spell instant disaster.

Perhaps you could troubleshoot your truck by unplugging the ABS fuse and seeing if the problem repeats or not...that wouyld tell you if it was the ABS causinf your issue.

 

[GAmes]

. I also haven't had a true speedometer reading since I got the truck. This made me think the rear end or speed sensor weren't working.

'97s and earlier vehicle speed sensor (VSS) is located on the tailshaft of 2WD transmissions and on the transfer case on 4X4s. It wasn't until '98 that the ABS sensor had a duel role. The factory service manual has full a trouble shooting guide for the ABS. It costs less than throwing parts.

 

[JR]

Find your ABS fuse and pull it and see if the problem goes away. We recently sold a Tahoe that I experienced the same problem with, I was coming up to an intersection and went to hit the brakes and the pedal went right to the floor board. Not a good feeling. Pulling the fuse will disable the ABS system and essentially give you a standard brake system. I can't really help you beyond that and it's not the right way to fix it, but at least you will know which direction to head

 

[raxley]

If the ABS is the problem (which can be checked by removing the fuse for it) then is it fixed by a part that plugs into the transmission?
I have a shop manual (actually have 2 versions including the Bishko which is supposed to be offical-they are on CD) I will have to look for that section.
The main thing is that it's very rarely that it happens, I've had the truck for a month, maybe 6 weeks and it's only done it 3 times. All of the times the truck was only going 2-3 miles per hour, always in a parking lot-but even then it's frightening-brakes don't work at all (And emergency is out of adjustment-it's no help)
Maybe I will just take the fuse out and see if it returns, and look for that troubleshooting section hopefully in my CD's.
It would be nice if I could adjust the rear brakes-I don't see a hole in the backing plates to do it though.

 

[JR]

If that is whats causing it then the problem would be in the abs module near the master cylinder. I could not tell you if there are any repairs that could be made or if the entire module would have to be swapped out. Or you deal with standard brakes (no abs) and a light on in your dash.....I know the module for my Tahoe would have run me over $400.

 

[raxley]

Wow, $400-was that the dealer and/or without install?
That's a heck of a engineering job on the abs for design, the whole brake system doesn't work if/when it goes out. Only the government (I thought) could design something as 'smart' as that.

 

[JR]

$400 was a steal, that price was through a friend that owns a garage. The next cheapest price I found was on the internet at around $550. I don't understand the logistics of the modules myself, one would assume parts like that would have a failsafe erring on the side of safety. According to my friend its not all that uncommon with the GMs.

 

[raxley]

If it's part of the transmission-I'm planning on putting my 2005 engine and transmission into the 1994. I was getting to the point where I was going to have to take all of my performance stuff of of the 2005 so that I could continue to register it. When I did all the high performance work, they didn't have a law in Cal for smog inspection. Years later they changed that, and a lot of performance shops for diesels went out of business because so much work was done on the basis of people thinking that they'd be able to legally drive their pickups and that changed. In some ways it's good that I wrecked the 2005 because it would have cost a lot to get it back in smog shape .
So I guess the plan is to pull the fuse and not worry about the abs, and it will eventually get fixed when I get the money to change the engine and trans over.
I still need to adjust the back brakes though. Do you think that they changed the backing plates for the brakes in the belief that the manual adjustments weren't needed because of the 'automatic' feature? It's that or there is some other way to adjust or I'm somehow missing where the adjustment window is (possible).

 

[fest3er]

It's been many years since I looked at this. Basically, when the CAB (Controller, Antilock Brake) thinks the rear wheels have locked up, it essentially removes most of the front braking as well as the rear braking. (I think it's a dangerous Dodge design flaw that should've been fixed.) When the truck was new, it happened all the time when braking on rough road. Dumping the OEM shocks and installing KYBs solved *that* problem.

The next time I had problems, I would be slowing down easily to a stop. At about 6 MPH, the brakes would essentially cut out; only then did I correlate the loss of braking with the speedo dropping to zero at that very speed. (Mine's a '98; rear sensor is dual purpose.) Again, it was the CAB thinking the rear brakes locked up. This time though, it was the VSS signal that was dropping out. For some reason*, the voltage was dropping below about 400mV at around 6MPH, below the CAB's detection sensitivity, and causing ABS to engage. Under normal conditions, the voltage drops under the low threshold at around 3MPH; thus the reason ABS doesn't work under about 4MPH.

In your case, find out what causes the signal to drop below the lower threshold at too high of a speed. Maybe there's dirt or something between the sensor and the toothed wheel. Or it's misaligned. Or the wheel has broken loose. Or there's a failure in the twisted pair wiring between the sensor and the CAB. Or corrosion in connectors along the way.


* I was using an Abbott speedo corrector at the time. It had worked for a while, but then started acting up. I fixed the splice connectors which helped, but not enough or long enough. I finally paid the money for a TruSpeed and haven't had a bit of trouble since. I connected a sillyscope to the sensor to see just what it was doing and discovered the electrical 'characteristics' around 400mV at 4MPH, rising to around 2.5V at around 25MPH and above.

 

[GAmes]

I still need to adjust the back brakes though. Do you think that they changed the backing plates for the brakes in the belief that the manual adjustments weren't needed because of the 'automatic' feature? It's that or there is some other way to adjust or I'm somehow missing where the adjustment window is (possible).

I can't imagine the backing plate not having a rubber plug over the adjustment wheel. The D80 I have has two. Not only can I adjust the wheel, I can inspect the thickness of both shoe liners.