I am experiencing an intermittent softness in my pedal. The truck always stops fine, but occasionally the pedal sinks to the floor.
Any ideas on what is wrong?

Thanks,

Richie

1989 F-150 XLT Lariat 4x4

 

A faulty R.A.B.S. valve will sometimes cause a sinking brake pedal

 

What does R.A.B.S stands for and where is its location?

 

I've read many FAQs and I have been encountering many MC failing and they call it "bottoming out" when most technician bench bled the MC and that's when the MC becomes defective and then when the MC installed and the technician thinks the MC they got is defective but majority was because it "bottom out".

However, I'm still not sure what they mean by "bottoming out". I would think they meant something along the o-ring, etc. If anyone has an explanation about this "bottoming out", let us hear about it.

When I bled my brakes, I usually use a one man bleeder kit. It contains a plastic bottle with a hose and different size rubber connector that goes in the bleeder valve on 4 brakes.

Don't use a regular wrench to loosen then bleeder valve, instead get those bleeder kit wrench that fits the bleeder valve properly. Those ordinary wrench will strip the heads of the bleeder valve.

I usually get two large brake fluid bottle when bleeding. First, I use the bleeder wrench to loosen the bleeder valve a little bit(making sure no brake fluid comes out). I then put the rubber connector of my one man bleeder kit and the turn the bleeder valve slowly a bit more.
If you have a helper, it will speed things up as you just tell your helper to pump the brakes slowly many times until the bubbles coming out of the clear hose is gone. If you don't have a helper then just pump the brake pedal yourself slowly but a couple of times and then check the bleeder kit clear hose and once there are no bubbles then you can tighten the bleeder valve and go to the next wheel.
Just fill the MC of brake fluid before you go to the next wheel.

Note: Brake fluid needs to be changed every two years to prevent rust build up or corrosion that might slowly fail your brake calipers, MC, etc.

 

well the bottoming out means what it says, you push the plunger until it hits the back of the MC. As for the wrench the flare nut wrench grips the nut and keeps it from turning. R.A.B.S. (rear anilock brake sensor. on f-150 til '91? transfer case mounted. then 1 year both then after that rear diff top mount. I had a problem with my proportionate valve with ABS connected. I tried changing fluid, bleed brakes about 4 times. when ever coming to a quick stop, brake would "hop and skip" feel then suddenly lock up. it would be intermittantly. Almost likea SLOW abs pump, like lateral runout then lock up. disconnected my abs line to the valve and no problem after that. running 33" swampers w/stock sixe brakes so no problem ....... good luck.

 

I recently bought a 1989 F-150 XLT Lariat 4x4. Was RABS standard on a 1989 F-150 XLT Lariat 4x4? The reason I am asking is, I don't think I have it because I didn't see any sensors on the back wheels nor have I ever seen the RABS light on the dash.

That being said, the MC looks brand new, but the booster does not. Would a bad booster cause the pedal to sometimes sink to the floor? I never actually lose my brakes.

Thoughts?

-Richie

 

let me rephrase that, wheel speed sensor. sorry about that.
and the way to check if you don't have a manual is to turn key on and when the gauges all light up there should be a light that
indicates abs. I have a donor 89' and it was equipped with a rear
abs and the speed sensor was on the transfer case. so They guy swapped in a 9" rear. check your proportionate valve also for a
connector......