Originally Posted by aerocolorado

Only once or twice have I felt the RABS come on during slick roads or panic stop. The panic stop elicited a large, strong, intermittent pedal sensation quite unlike the rapid, small pulsations on newer vehicles.

Originally Posted by asavage

We haven't had enough ice/snow here yet for me to functionally test the RABS on my "new" '93, but looking at the manual, there's no speed sensor for the front wheels, so the RABS is looking at the decel rate of the VSS signal at the rear diff only, which seems like a poor way to figure out if the RABS should be activated or not. Or am I missing something?

Originally Posted by aerocolorado

That's correct, rear only. RABS = Rear Antilock Brake System. The RABS system was Ford's attempt to account for the difference between an empty and full loaded truck. Chevy and others use an adjustable proportioning valve to distribute braking forces.

Originally Posted by Aeroman59

So what triggers the RABS? must be a combination of
VSS=0 (or too rapid deceleration) & ......BOO switch= On

Originally Posted by Ford CD

[ . . . ]When the brake pedal is applied, the RABS II module senses the drop in rear wheel speed. If the rate of deceleration is too great, indicating that wheel lockup is going to occur, the RABS II module activates the electro-hydraulic valve causing the isolation valve to close. With the isolation valve closed, the rear wheel cylinders are isolated from the master cylinder and the rear brake pressure cannot increase. If the rate of deceleration is still too great, the RABS II module will energize the dump solenoid with a series of rapid pulses to bleed off rear wheel cylinder fluid into an accumulator built into the RABS valve. This will reduce the rear wheel cylinder pressure and allow the rear wheels to spin back up to vehicle speed. Continuing under RABS II module control, the dump and isolation solenoids will be pulsed in a manner that will keep the rear wheels rotating while still maintaining high levels of deceleration during braking.

At the end of the stop, when the operator releases the brake pedal, the isolation valve de-energizes and any fluid in the accumulator is returned to the master cylinder. Normal brake operation is resumed.

[ . . . ]The red BRAKE warning light is constantly monitored by the RABS II module. If the red light illuminates, the module will disable the RABS II system. For this reason, diagnosing and resolving any base brake concerns illuminating the red BRAKE warning light will, in most cases, resolve a perceived RABS II concern.

Originally Posted by Aeroman59

I'm having a bit of a problem with the way it works since, there is only one master cylinder & it looks like there should be independant hydraulic control of the front/rear brake lines!