On the Ranger with RABS, there is no ABS on the front disk brakes. I'm waiting for a Ford tech to hopefully respond and confirm that the fluid just goes between the caliper and the master cylinder/resevior for the fronts and doesn't go to the ABS pump.
On newer cars with delicate, elaborate, 4 wheel ABS systems -- like that Prius -- it makes sense that there is a risk in sending brake fluid from the caliper back up into the fancy ABS pump. The fluid in the piston gets hot which can cause it to loose some of it's good properties. The seals are not perfect so it's possible for some dirt or other contaminents to get back into the fluid. With all that, it's not worth the risk.
To me a viable alternative is to pump some fresh fluid through the calipers with a pressure bleeder and the bleed screws open a bit. But, that's about as much work as doing a proper bleed during and after the piston pushback.
One thing I do know is that the Helm shop manual does not mention bleeding during the piston compression. Also, it does insist on using a pressure bleeder for bleeding (on my 94) when you have RABS if you're not using the fancy Ford special tool for bleeding the ABS pump.
Yes, with RABS...the fluid for the front brakes goes from the master to the front calipers. Only the rear line has the RABS valve in it.
Like I said...that escape hybrid is the only thing we have ever come across that got messed up from just pressing the calipers back when replacing pads/servicing brakes.
No need whatsoever to use a pressure bleeder for your truck, conventional brake bleeding works just fine. There really is never a need to complete an ABS service bleed on a vehicle unless you have replaced the HCU.
RABS and ABS are really quite different animals. You do not have a hydraulic control unit like the full 4wabs system does.
Edit:
Here is the description of operation of the RABS system:
The Rear Anti-Lock Brake System (RABS II) continually monitors rear wheel speed with a sensor mounted on the rear axle housing (4010) while the brakes are applied. When the teeth on the speed sensor ring, mounted on the ring gear, pass the sensor pole piece, an AC voltage is induced in the sensor circuit with a frequency proportional to the average rear wheel speed. In the event of an impending lockup condition during braking, the RABS II modulates hydraulic pressure to the rear brake drums (1126) . This inhibits rear wheel lockup.
When the brake pedal (2455) is applied, the anti-lock brake control module (2B373) senses the drop in rear wheel speed. If the rate of deceleration is too great, indicating that wheel lockup is going to occur, the anti-lock brake control module activates the electro-hydraulic valve causing the isolation valve to close. With the isolation valve closed, the rear wheel cylinders (2261) are isolated from the brake master cylinder (2140) and the rear brake pressure cannot increase. If the rate of deceleration is still too great, the anti-lock brake control 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 (1007) 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 rear brake tube (2267) and up to the brake master cylinder . Normal brake operation is resumed.
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