My '95 F150 with almost 200k on it has been getting a little spongy in the brakes the last few months. Nothing too bad, and it goes away after about 10 minutes in the morning. However, I want to fix the problem before it gets bad.

I replaced the master cylinder a few months ago since it was leaking anyway, I'm looking at replacing the hydraulic booster next. My questions are:

1) Does this seem like the right solution?
2) How difficult is it?
3) Anyone have suggestions for other places to look for the source of the problem?

Thanks.

9/4/2007 8:31:06 AM

sounds like it could be moisture, i would try bleeding the brakes well, should take a quart or more, usually the pedal will start getting hard when the booster is fucking up on those

9/4/2007 8:36:25 AM

I bled them when I replaced the m/c, I could try it again.

9/4/2007 8:42:43 AM

The booster should not cause any sponginess. Unless it's leaking vacuum (you'd hear a hiss anytime you are holding the brake pedal), the booster is likely fine.

9/4/2007 10:11:01 AM

arent trucks brakes supposed to be spongy

i mean, you arent driving a sports car or something like that

9/4/2007 10:29:54 AM

^^ would I hear it inside, or would I have to be under the hood when the brake was depressed?

^ well yeah, but there is spongy and there is spongy. I guess the accurate term is spongier than it used to be, and the braking feels off. You'd expect this at 200k, but it fell off pretty quick. I'm a little paranoid when it comes to being able to stop.

Pads and rotors are fine, <5k on them.

[Edited on September 4, 2007 at 10:36 AM. Reason : .]

9/4/2007 10:34:06 AM

The hissing would be audible from the drivers seat. As long as pedal effort didn't increase, the booster is fine. It can't cause sponginess by itself.

When you bled the brakes, did you remember to bleed the RABS valve too?

9/4/2007 11:58:55 AM

ummmm . . .

I don't believe we did. As I recall, we just bled it at all four corners.

Does this look about right? http://www.asashop.org/autoinc/dec99/techtips.htm

9/4/2007 1:27:51 PM

make sure the rear brake star-wheel adjusters are not seized and brake shoes are adjusted correctly

9/4/2007 5:56:07 PM

yeah, thats not an issue . . . I'll check the RABS this weekend.

9/4/2007 6:34:13 PM

did you bench bleed the master or gravity bleed it or did you just install the master cylinder then bled the brakes

9/5/2007 3:04:11 AM

Installed the master cyl then bled the brakes, didn't bleed them prior to.

9/5/2007 6:32:53 AM

The RABS valve is on the driver side framerail right below the firewall. There's a small bleeder screw on that valve, which I would try bleeding there to see if that helps before trying to replace the RABS valve itself just yet. Was the old fluid really dirty? I suppose it's possible to have gotten some of that dirt lodged in there, but I'd try bleeding it first.

So did you bench bleed the master cylinder? If not, and bleeding the RABS valve doesn't help, that could be the problem.

9/5/2007 9:32:25 AM

should have bench bled the master first. take it off. pour fluid in it and put your fingers over the the holes push cylinder in with screw driver and cover holes with fingers on the "back stroke"
let fingers loose and depress again. cover holes on the back stroke. and repeat a few times.
good luck

9/5/2007 3:04:26 PM

fixed yet?

9/19/2007 9:29:46 PM

fixed. never did bleed the master cylinder, I realized that fluid was leaking out of the cruise control shutoff switch at the end of the MC and replaced it (there was a recall on this, but my truck didn't fall under it apparently). That stopped the leaking, brought the brakes back to where I expected them, and restored my cruise control.

Not bad for an $18 part.

10/25/2007 6:59:22 PM

^ = ab0ve-average tww garage usr

10/25/2007 8:14:53 PM

play by play repairing. i approve this thread

model thread for future reference. no flaming or anything. thread of the year

10/25/2007 10:16:16 PM