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How did the early ABS systems work?

Pretty sure they read the rear wheel speed via the VSS on the end of the trans/t-case. My 89 S10 had rear ABS but the rear axle never had any speed sensors on it, nor did any of the front IFS stuff that I cut off. Suffice to say, when I ran new brake lines, none of the new ones ran through the ABS actuator. I just eliminated it from the truck.
 
Fords had a tone wheel on the rear ring gear. Don't know about GM. Easy to tell though. Look at the top of your rear housing. If you see a wire harness plugged in, thats it.
 
For GM's RWABS and early 4WABS systems the speed for the rear wheels was calculated using the VSS sensor, on the 4WABS systems they also had wheel speed sensors on each front wheel
 
Ditto what was said above. The RWAL used the VSS on the t-case or trans housing (2wd). My '90 K5 came with RWAL and there were no sensors or electric wires going to the rear axle.
 
6.2Blazer said:
Ditto what was said above. The RWAL used the VSS on the t-case or trans housing (2wd). My '90 K5 came with RWAL and there were no sensors or electric wires going to the rear axle.
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Interesting. What Im trying to chase down is a weird speed related gremin. When the truck reaches a certain speed (25-30) the brake light comes on. Goes off once the truck is off and powered back on again. Im guessing its the ABS sensor not reading correctly.

any thoughts?
 
Pookster said:
Interesting. What Im trying to chase down is a weird speed related gremin. When the truck reaches a certain speed (25-30) the brake light comes on. Goes off once the truck is off and powered back on again. Im guessing its the ABS sensor not reading correctly.

any thoughts?
Click to expand...

If your speedo is working the sensor is fine, they both use the same sensor, the difference in the signal comes from the VSS speed buffer, this is what takes the 40 pulse per drive shaft revolution and converts the signal to a digital signal for the various systems in the truck.

1st think you should do is check the brake codes to see if there are any. You should be able to check them in a similar manner as you would check engine codes, a qucik google search should show you what pin you need to ground out
 
Pookster said:
Interesting. What Im trying to chase down is a weird speed related gremin. When the truck reaches a certain speed (25-30) the brake light comes on. Goes off once the truck is off and powered back on again. Im guessing its the ABS sensor not reading correctly.

any thoughts?
Click to expand...

Check your brake light switch. Make sure the brake pedal engages the button on the switch when it is realeased. You will find the switch under your dash, on the right side of the brake pedal assembly. It is a small box with a button facing the brake pedal.
 
Keitha said:
Check your brake light switch. Make sure the brake pedal engages the button on the switch when it is realeased. You will find the switch under your dash, on the right side of the brake pedal assembly. It is a small box with a button facing the brake pedal.
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I checked it, appears fine. The light goes on and off, as its supposed to. I found rock auto listed this for my truck http://www.rockauto.com/catalog/moreinfo.php?pk=1113583 which looks pretty similiar to the usual tone ring type. I gotta look again.
 
Pookster said:
I checked it, appears fine. The light goes on and off, as its supposed to. I found rock auto listed this for my truck http://www.rockauto.com/catalog/moreinfo.php?pk=1113583 which looks pretty similiar to the usual tone ring type. I gotta look again.
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Don't just look at your brake light on the switch issue. Get under your dash and make sure the pedal is pushing in the switch. The switch also acts as your TCC lock-up switch - when you press your brake pedal, the TCC disengages. Without any pressure on your brake pedal, push the switch into the housing as far as it will go. You have to see it to understand what I am describing.
 
I have a similar issue, but the speedo and cruise dont work either? Does anyone know where the wires from the VSS go into the DRAC? I think they would be the purple/white green/black ones. i suspect a short. maybie your problem too?
 
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