My 1991 F-150 sometimes makes a "hissing" sound that comes from down by the brake pedal when I depress it. This doesn't happen all of the time, but just "sometimes". Sometimes it only hisses as I depress the brake, and sometimes it hisses all the while I have my foot on the pedal. Sometimes it doesn't do it at all.

Through all of this my brakes appear to work normally, with no increase in pedal pressure. If this is the power brake vacuum booster, approximately what does this run, parts and labor to have replaced? Has anyone had this problem in their truck?

 

Sounds like your brake booster has developed a leak. It can be replaced without disconnecting the master cylinder lines. When you get the booster off check it for signs of brake fluid.
regards
rikard

 

You can replace it with an F350 booster with no mods, it's a direct bolt in.

 

I've never attempted anything like this, and don't have anyone to help me other than my wife. Is this something I should look into doing myself, or would I be better off hiring the whole thing out? If you guys had to guess on labor, about how many hours would I be looking at? I can get a parts price on the phone.

 

Also, if this were to fail completely, would I lose all brakes, or just the power assist?

 

You would only loose the assist. Its actually a pretty easy job, and self explanatory. Once you get the new one you can apply the "take that one out and put this one in" technique. Lemme see if I can find a walk through to help ya.

 

http://www.fullsizebronco.com/forum/...d.php?t=156457

 

Thanks! That is very helpful, especially with the photos.

 

I took it in and sure enough the booster was bad. I drove it to and from work over the weekend and by Sunday night when I got home it was hissing like a freshly disturbed tom cat, and the pedal pressure was very heavy.

It also needed new front brakes, and they readjusted the rear brakes, flushed the old brake fluid out and repacked the front wheel bearings. They showed me the old pads and they were gone. So all total out the door, including a new booster installed was $650.00. What a difference. I almost put myself through the windshield when I first hit the brakes!

 

I'm glad you got it fixed, but that price just seems expensive, the rear brakes are self adjusting, and the rest of the parts were maybe $200.00.