Bad Brake Booster??

As the title implies. I believe my vacuum booster has sprung a leak in the diaphragm, however from everything I have read, this should cause a harder brake pedal as the vacuum assist lessens.

I'm having the opposite effect, the hiss under the dash is audible next to the booster and it threw a p0174 code on the way home today (bank 2 running lean, telltale of a vacuum leak) but the pedal is just the same as before, in fact it feels softer at times, though that may just be a placebo effect. There are no fluid leaks that I can see and no evidence of leaking fluid on the MC anywhere. Also the brake fluid appears to be fine, about a quarter inch over the max line but otherwise fine.

I have tested the one way vacuum valve on the booster itself and the hose, both are fine, no leaks. I have also done the pedal pressure test, but instead of the pedal getting harder as the brakes are pumped, it remains at the same level irregardless and the hiss is consistent.

Any suggestions before I go by the stealership tomorrow to order a booster? I'd really like to sort and fix this as I am planning a 2000km trip over the weekend, I would rather not worry about the leak causing the truck to stall out in the middle of Rogers Pass

 

Have you pinched off or capped the booster vacuum line and ran the engine to confirm that the hiss stops? If it does, it sounds as though the booster may be at fault. Best internet diagnosis I can give.

 

Yep, truck runs fine when the line is capped, no hiss at all. More than anything I suppose I'm looking for an alternative to replacing the whole unit (like a seal or something).

 

I do not think there is an alternative to an internal booster leak. Many years ago they could rebuild these. Today they are just throw aways.

 

I suppose some of the good things are just lost over time, it's a cryin shame that roll of duct tape and can of WD40 have been relegated to the shelf now.

Anyways thanks for the input guys, fingers crossed I can find one in the next day or two here.