Brake Booster Hissing

[Aussie81]

Hi everyone. I'm based in Brisbane, Australia and have an 81 El Camino. I've recent completed an LS1 swap and she's running like a dream.

After the engine swap I noticed the brake booster made a hissing noise when depressing the brake pedal. The brakes worked fine and the engine idle changed slightly. It was the original booster single diaphragm so I got my mechanic to replace it with a new dual diaphragm booster from Rockauto, unfortunately the noise was still there with the new booster. The mechanic seemed to think it might just be a "thing" with these boosters.

I've since looked to upgrade the brakes to the blazer spindle/caliper setup and had investigated the b-body booster and master cylinder upgrade to support extra braking. This combined with the noisey/vacuum booster in the car I purchased again a new b-body booster and went to another mechanic for a second opinion and to complete the swap. I've just got the car back and this third booster is making the hissing noise when depressing the pedal. This mechanic thinks the booster is faulty and to try swap it.

Firstly, is it likely I'm having a bad run of boosters or is this normal noise/behaviour? This seems unlikely

Secondly, is there a trick or common issue with my setup that may be causing this to occur? Anything I should look at?

Finally, could the LS swap cause this? Is the vacuum too strong or have any impact?

Thanks,
Christian

 

[83StreetMachine]

Welcome! Love to see some pics of your ride when you have a chance!

During any of these booster swaps has the check valve and grommet been replaced?

It's the little white or black plastic barb that the vacuum hose attached to at the booster?

What about the vacuum hose itself? Is it the thick wall rubber hose? Not just some cheap fuel hose....

Where are you pulling vacuum from for the booster off the engine?

 

[64nailhead]

Sounds like the check valve is bad. But I find it highly unlikely that a number of mechanics haven't checked it out.

You have a vacuum leak somewhere, are you sure it's from the booster and the booster vacuum supply hose at the intake?

 

[Texas82GP]

Test the booster for leaking vacuum. Check manifold vacuum with the booster connected and with it disconnected. Try it both ways with the pedal both at rest and depressed. If the booster is leaking vacuum, it should show up on a vacuum gauge or by looking at the MAP sensor reading.

 

[565bbchevy]

could the LS swap cause this? Is the vacuum too strong or have any impact?

I am pulling 28 lbs of vacuum on my original booster so it's not that, my first thought is a faulty check valve or cracked or loose vacuum line.

 

[MYFINE79]

I had this on my 79 Grandprix & it was the rubber seal & check valve on the booster. It did the exact same thing, hissing noise. After changing the seal & check valve all was normal.