Brake failure

[sam0822]

I have a 98 gmc c1500. I’ve been have bad brake issues since I bought the truck about a year ago. Recently I found that my master cylinder was cracked and replaced it and all new stainless brake lines. It would stop alright for a little while then the other day I started hearing a hissing noise when braking and have been having to pump the pedal multiple times to stop. The brake fluid was black and small amounts of debris coming out of the bleeder valves when bleeding. Now I’m thinking my brake booster could have gone bad. Any other suggestions of what the issue could be? Also if anyone knows upgrades to prevent this from happening in the future?

 

[someotherguy]

Sounds like separate issues you're still battling.

The hissing noise is probably your booster gone bad, yes. You can confirm it by temporarily disconnecting the vacuum line to the booster and capping the line so you don't have a giant vacuum leak. Yard-drive the truck and beware of course that it will take much more pedal effort to get it to stop, but listen for the hissing noise. If it's gone with the booster unplugged, then it's time to replace the booster.

The black crumbs coming out when you bleed the system is dirty old brake fluid full of bits of the flex hoses and possibly seals from the old master cylinder and possibly your calipers and wheel cylinders. Most likely suspect though would be the flex hoses as they do go bad internally over time. If yours look old.. replace 'em; all three. They're cheap. Bleed the system thoroughly with a lot of fresh fluid.

Richard

 

[Schurkey]

Sounds like separate issues you're still battling.

Agreed.

Bleed the system thoroughly with a lot of fresh fluid.

It's a '98. He will have to have a scan tool to properly bleed the brakes. The ABS unit cannot be bled properly without one--doubly true since the brake fluid is known to have grit in it.