I recently purchased a 1997 f150 4x4 with ABS. When I was driving it one day at about 10 MPH (thankfully) I went to slow down at a stop sign and my brake petal was ROCK SOLID. It didn't budge. I kinda freaked and tromped on the e brake. Well even at only 10 MPH I skid my rears for about 10 feet. Then the ABS light cam on and I THINK I heard a single clunk noise like a big relay or valve moving. I carefully drove it home but as I suspected because of the ABS light being on it drove fine. The light has not gone out since.

What would cause this? It seems dangerous to have a component in a brake system that could stop the brake pressure from being delivered to the calipers if there is an electronic failure.

Thank you

 

Maybe air in the brake lines. I would bleed them to be sure. And the ABS light prolly came on from having to lock 'em up so tight. It should go out after a few start cycles.

 

I think air would cause sponginess. The pedal would not depress. But thanks

 

I imagine you have it fixed by now... but just in case...

Its not air in the brake lines, that would indeed cause spongy brakes / long pedal travel.

This is very likely a vacuum booster problem. Hopefully just an issue with the vacuum hose and not the booster itself. Start by checking the hose for any holes/cuts. If you do not have any boost, the brake pedal will be very very hard.

To see what this feels like on a good system, shut off your engine and pump the brake pedal about 5 times to deplete the vacuum in the booster - you will barely be able to move the pedal. There are government regulations on un-boosted stopping distance that are taken into account when designing vehicles. This ensures that you have some degree of safety if the booster fails. But its still a big difference from the normal brake pedal feel.

 

good thing the e-brake was working. i dont understand these people that say dont be concerned with your e-brake when its not working correctly.