Vacuum brake booster leak/replacement

About a month ago a faint hissing started under my dash, very quiet at first, but it got progressively louder the further I drove. Turns out my vacuum booster was leaking near the firewall gasket in the engine bay (more on this below). This sets off a regular stream of CEL's for p0171 and p0174 (left and right banks running lean) and occasionally bogs the RPM's down close to 500, wanting to stall the truck out.

Because a broken stud turned out to be the culprit, I figured a DIY would help anyone else by posting my methods and madness, should I not be alone

Supplies needed:
Replacement booster (wreckers, here in AB, dealer wants ~600$)
32-64oz [1-2L] brake fluid of choice (bleeding, always have more than you need)
Replacement firewall gasket (part #: 44785-04020)
Replacement Master Cylinder O-ring (part #: 90015-AH002)
Min. 18" clear plastic tubing for bleeding
2-4 hours of your time
A friend to pump the brakes

Tools needed:
10, 12, 14mm regular sockets
12mm deep socket
10, 12mm open/box wrenches
18" extension (I use 3/8 drive)
3/8 universal joint - HIGHLY ADVISED
Dremel w/metal cutoff wheel - optional
Hammer drill - optional

First to disconnect the battery, remove the sill, dead pedal, corner kick, and lower kick panels from the dash and disconnect all the switches, then pull the cotter pin, and disconnect the booster rod from the brake pedal.



Next to remove the brake master cylinder, disconnect the 2 bolts holding it to the booster, disconnect the 2 brake lines and the fluid level sensor connector.



Remove the 4 firewall bolts, this is where my leak came from. (the 18" extension and universal joint are particularly handy here) The upper-inside stud had broken loose somewhere inside the frame within the booster and the whole stud was spinning freely, prohibiting removal via conventional means. I used the Dremel to cut the nut off, the tool barely fit in behind the steering column with little room to spare (the brake pedal assembly is held to the firewall by these same 4 bolts, so no luck there either). This was by far the most tedious point of the whole replacement.

Before:



After:



I suspect the bolt had either been torqued down improperly at the factory, or had loosened during some form of inspection, there was a noticeable gap between the booster and gasket after removal.



Installation is reverse, I took the opportunity to do a brake fluid flush and upgrade to DOT 4 while I was in there, ergo the extra fluid advisory

All in all a pretty straightforward DIY, It certainly helps to set aside plenty of extra time though, I hit the broken stud, and didn't have enough brake fluid to complete the flush, turned a 3 hour project into a 2 day one.

 

Same problem here and got cel code 0171 1130 1135 sorry for bumping old thread but if that one bolt was tied do you think its still leaking?

 

Are all the studs at least hand tight from the inside of the firewall? I believe my issue came from the stud breaking loose and working its way into the booster.

 

What Tourque amount did you use for the two outer nuts at the MS and the four inner underneath the pedal?

TIA
Joe