I believe I've got a bad brake booster. Hard pedal, very hard to stop, and hissing sound from under the dash. Truck stumbles with pedal depressed at stoplights. Vacuum is good from the intake, although I'm thinking that a bad brake booster w/a slow vacuum leak may have been causing my high idle.

I just had the truck wired for a brake controller the other day, and halfway through our road trip I noticed the problem with the brakes. Thankfully, there's not a lot of traffic out here in the middle of South Dakota, and I've got a good brake controller & trailer brakes so it's more of a convenience issue.

Isn't there a check valve I can take a look at? I read something about it but I'm not sure where to look.

I've found this thread:
http://www.automotiveforums.com/vbulletin/showthread.php?t=499453&highlight=brake+booster

It's a good explanation of how to fix it.

Is there anything else I should check before doing a swapout? I'm probably going to do this myself as I'm guessing it's a $500+ job in a shop but sub-$200 if I do it myself.

Thanks in advance...

There is a plastic 90 degree check valve on the outside where engine vacuum line goes to booster.

If it is leaking inside booster or out the back of it when you step on brakes the booster is bad inside.

Not hard to change.

Parts places have rebuilt boosters.
Wagner is a good trusted brand for brake parts.
Leave your brake master cylinders brake lines and other stuff on the brake master cylinder.
Just unbolt brake master cylinder from brake booster and move it over out of the road.

You will have to unbolt brake pedal apply rod from under dash.
Then unbolt booster mounting bolts to dash.

Good luck and let us know how it goes.
MT

There is a plastic 90 degree check valve on the outside where engine vacuum line goes to booster.

If it is leaking inside booster or out the back of it when you step on brakes the booster is bad inside.

Not hard to change.

Parts places have rebuilt boosters.
Wagner is a good trusted brand for brake parts.
Leave your brake master cylinders brake lines and other stuff on the brake master cylinder.
Just unbolt brake master cylinder from brake booster and move it over out of the road.

You will have to unbolt brake pedal apply rod from under dash.
Then unbolt booster mounting bolts to dash.

Good luck and let us know how it goes.
MT

Great words, thanks. Between that thread and your description I think it's enough info to complete the job. The brake pedal apply rod clip was a little bugger, I bought a set of angled long pliers and spread the outer clip apart (the one that clips around the shaft) with a flathead screwdriver. Removing that outer clip allows the flat retaining clip to slide off (that's underneath, next to what seems to be the switch body). I'm not sure if it's the approved solution or not but it worked in my case, once I figured out the clip was in two pieces, and it reinstalled well.

After that, the only hard part is the fact my ratchets only moved a few degrees and it made the job of removing the four retaining nuts inside the firewall a very long process.

I had to go to Autozone as it was the only one open late enough on the Saturday of the long weekend, and the part was about $90 plus $23 core, apparently a rebuilt OEM unit. For my truck, a beater at 130k miles, it should be fine as it's got a lifetime warranty. I had to buy a single deep-drive 15mm socket, but when I checked back in with the core I had a big credit on my Autozone account so I bought the rest of the sizes to have a complete set of 1/4" drive deep metric sockets.

I'm sure the hotel was thrilled with a guy upside down under his dashboard swapping out a brake booster but it had to be done before we finished our trip. I was of the mindset that if I screwed it up, I'd have a garage fix it because the truck wouldn't have been fun to drive the rest of the way.

Thanks again, hopefully this will help someone else swap out the brake booster. Not a terrible job once you get the clip off, definitely in the realm of a do-it-yourselfer.

You are welcome and thanks for posting back how it went.
I am sure the holtel has had a few people under the hood or dash before.
Just do not leave a bunch of grease on driveway or keep them up all night and all will be good.
Good luck
MT