Help a Buddy with Anti Lock problem

[Grim-Reaper]

This is a Buddy from the club I run with. Truck is a mid 90's Burb.

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The antilock problem is back and worse than before. After a little more investigation, I do have antilock sensors on each of the front wheels and no sensors on the rear wheels that I can find. There are no HAL effect pick-ups on the rear backing plates or inside the drums anywhere. I can find no wiring into the rear chunk for a tone wheel pick-up there either. Since I have antilock on the front and presumably on the back, I would like to keep it working. This was apparently an option on the 3/4 ton models - I was under the impression that it was only offered on the rear wheels as a single channel in '93.

Anyway...the light is coming on and I get some exciting braking when "trying" to come to a stop - the system will start dumping pressure when I am braking on asphalt and all four wheels are turning the same speed! The only difference, is that the speedo doesn't start registering until the truck is rolling at about 25mph. It also uses a tone ring on the output shaft of the TX case. It was nicked fairly bad when I had the TX case apart to rebuild - but it still worked! Is it possible that the speed sensor that reads that tone ring is screwed up and that affects the antilock system? The warning light does not activate until the truck has been rolling for about 10 seconds.

I tried driving down the insterstate while the speedo was registering, put the tranny in neutral, shut off the engine, and let it coast for a minute. I restarted the motor and put it back in OD and the light stayed off the rest of the trip.

What do you guys think??

[/ QUOTE ]
I think it's that sensor. Sounds to me like it is also used with the Anti Lock since he can't find a sensor on the axle.
Any thoughts or anybody know thses mid 90's trucks with Anti lock better?

 

[big83chevy4x4]

all i know the rear speed sensor reads from the drive shaft so it could be the speedo sensor and yes that would affect it. you could take it to a repair shop and have them do a test on the antilock system. im not sure how much it costs but they should test everything. they would be able to find the problem alot faster than you or me.
TJ /forums/images/graemlins/truck.gif

 

[wayne]

The antilock system when malfunctioning should revert back to normal locking brakes. At least that is what it is supposed to do. If there are no sensors on the axle then that speed sensor should be controlling it. I would ask him if the problem only started after he nicked that sensor ring and if that's the case then he will need to replace it. I had a problem with the abs on Donna's Sunbird that I spent hours tracking down the problem, and it turned out being a cap full low on brake fluid because of a wheel cylinder was starting to go bad. Every time the light came on though all it did was not allow the antilock to work but the brake's still worked fine.

 

[dyeager535]

Yeah, with the speedo not working correctly, I'd sure lean towards the VSS. If he can hook a scanner up to it, most of them will display vehicle speed AFAIK, if its showing no vehicle speed while he's moving, either the sensor is bad, or the reluctor ring (?) that it reads off of is screwed.

As to the ABS, not really the focus of the post, but I'm pretty sure that on some of the RWD cars, the ABS used a reluctor ring (I'm thinking thats what those are called) on the differential carrier, so that might be where the wiring for ABS sensors are.

 

[slider]

Like Wayne said if the system starts acting up(Hard Codes) it will shut off and you will have normal system braking. I would also say if the exciter ring is dammaged (missing teeth) it will never work right and you should get a hard code in the computer. If the antilock system is that screwed up it really sounds like the service brake system is also screwed up. You have to look over the service brake system then look at the antilock system. Biggest problem with these systems is wiring, grounds, connectors and wheel speed sensors. I hate to say this but bite the bullet on this one and go to a shop or find someone who has a scanner and the correct test information for this rig. It is the only way to troubleshoot some of these systems. Brake systems are nothing to screw around with if you don't know whats going on. Bad brakes can kill

 

[imiceman44]

That is what I know. It should be in the carrier.
I don't think it can be on the drive shaft since you can read a diferential of speed between sides, but in the carrier you can.

 

[95 Silverado]

I have seen ABS sensors on rear end housings that read off of the diff. carrier next to the ring gear and also from the pinion shaft, if a reading can be taken from either one of those, the driveshaft should work as well, it sounds like the VSS is causing both problems.

 

[K10ANDYKHAMNIC]

easy , pull the stupid fuse(S)