93TALT4A4

Engine off. I noticed when I leaned on the rear driver side VC, I heard a hissing coming out of valve cover. Stood up, no noise, leaned on it again heard the hiss.

Did I unproperly torque them down, is there a sequence or is there something else wrong? The hex nuts are getting pretty worn, I'd hate to strip them. Can the standard steel LT1 valve cover bolts be used?

Whaleman

With the engine off the only thing with pressure that could "hiss" is the fuel lines. Dan

Talfryyn

I’d take a listen at the brake booster check valve.

RUU

jmgtp

If this is lingering vacuum hiss with engine off, brake booster is def a good place to look. There is also a vacuum ball down low near the horn.

93TALT4A4

Seriously? Why brake booster?

Talfryyn

The booster has an inline check valve to retain vacuum. This is so you still have a few brake applications with power assist if the engine stops or at WOT.
If the grommet is leaking you would hear a hiss at the booster. If the check valve is leaking you would hear a hiss at the drivers side valve cover where the vacuum line connects to the intake manifold.

Talfryyn

Delete

93TALT4A4

Is the check valve hard to remove or do I need to get a new brake booster?

One time a month ago, braking at a green light was pretty scary. I had to stand on it and it finally screeched to a halt. Related I imagine now.

Talfryyn

A bad booster will often give a hissing sound inside the car by the brake pedal. No hiss with foot off the pedal, hiss when pushed.
the check valve is easy to replace. Pull the hose off. Pull the check valve out of the grommet on the booster.
Repo check valves and grommets can be had from Corvette part vendors. Universal replacements can be had at your local part stores. Just bring in the one from the car to compare.