'89 with RABS not working?!?

[bryanb]

Got some snow today. I can't for the life of me get the RABS to activate; when I stomp on the pedal, it pretty much just locks the front.

I get the RABS light when the ignition is at run, but it goes off right after I start the Ranger. And I never see it again.

The pedal is quite spongy, indicating air in the lines, and I really need to get the front rotors and pads replaced. haven't looked at the rear drums yet. As I said, it just snowed, and I have no heated garage!

 

[ForOffRoadDriving]

if only the fronts are locking then your abs is working, since the rears didnt lock. have you tried driving in reverse while applying light brake pressure and then increasing the pressure until the truck almost stops? my truck needs an adjustment like this (this is the way the back brakes are supposed to automatically adjust) at least once a month or whenever my predal seems to be traveling farther than normal.

 

[srteach]

Everything you have written indicates a properly operating RABS system.
The light should run a diagnostic and then go out when you start the truck. If the light stays on with the engine running, or blinks a code, the RABS is faulty, and is not working.
The RABS system is designed to activate during panic or low traction situations. The Rear Anti-lock Braking System is supposed to keep the rear wheels from locking up. The front brakes aren't part of the RABS system, and can lock up with hard breaking even when the rear brakes don't lock up. The spongy pedal is because the RABS valve is releasing the rear brakes like it is supposed to, it is unlikely that there is air in the system if the front brakes lock up. Rapidly pump the brakes a few times when it activates, and it will shut off the RABS until the next time you attempt to stop.

 

[bryanb]

Not sure that I've noticed the rear brakes locking up. I do know that I don't get the buzzing, and pedal modulation feedback that I'd normally get in my Thunderbird, that had 4 wheel ABS.

Is rear ABS that different? Do they just not lock up? or is there some feedback when the system is activated? (the light comes on, or something similar to 4 wheel ABS?)

 

[Original_Ranger84]

well in a RAB system only the rears lock up as stated... And brakes generally have bias meaning most of the braking power travels to the front brakes instead of the rears. with less weight and less braking pressure then the front you wont feel it if they need to activate. because it takes so little for them to pulse off and spin again. Now if you had alot of weight inthe back... say a camper or trailer you would probably feel it alittle bit. I don't believe the light would come on as it doesn't on my 99 with 4 wheel abs or my diesel with RABS.

 

[locovaca]

I had the same symptoms and my modulator was corroded to all hell. Despite the fact it was working it never triggered an ABS error code. I found a practically new one at a JY one day, swapped it in, and could immediately tell the difference doing an "oh shit" stop. Despite it only being the rears, you will get feedback at the pedal if it's working properly (and your system is properly bled), but not as much as a 4 wheel ABS system.

I would get someone to stand out on the sidewalk and watch you slam on the brakes to see if the rears are still turning. It's very common for the ABS Modulator to go bad in Gen 2/3s... just do a search. And, it's not a cheap part, either.

 

[bryanb]

Where does this modulator live? So that I might give it a look over...

 

[modelageek]

the modulator on my 99 is on the fender wall 1 foot from the master cylinder. spongy brakes can be caused by improperly adjusted drum brakes. if your ebrake does not work well that could be caused by improperly adjusted drum brakes