Has anyone else had this issue? Brakes work fine and no leaks but a Hissing noise has started in the dash sounds like it is coming from the booster. when the steering wheel is turned or brake pedal is pressed it stops.

 

Just throwing out a wild guess here, but could it be possible that the lining in one of the hoses is coming loose?

 

I'm certain it is your vacuum assist brake booster starting to leak. My 1992 has done the same and is now in need of replacement. I'm gathering pieces for a hydra boost conversion.

 

That would be my guess also...It was not uncommon in GM products of previous generations...The symptoms were the same...To test, pull a vacuum on the booster and see if it holds with pedal released...If not, repeat with pedal pushed in slightly......Ben

 

It is the power brake booster system making the noise but the 3rd Gen trucks use the power steering pump for hydraulic power brake boost assist.

They do not have a vacuum assist power brake system.

 

Thanks.. I am going to check the lining today and go from there..