Newbie here. Both to the forum and automotive DIY.

I have a 1996 GMC Suburban with a 5.7L Vortec V8 with 180k miles. I bought it cheap and plan to do as much work on it myself to learn.

But I am stumped. I have a major brake fluid leak and I can't figure out where exactly it is coming from.

The basic issue is that when I hit the brakes, it creates a geyser of brake fluid up the side of the booster. I'm not sure if the leak is from between the master and booster or in the booster itself.

I took a video of it and put it up on youtube. Please take a look at it and let me know what you think. It seems like there is a lot of air coming out of the bottom of the booster, but I'm not positive.


At this point, I'm thinking of replacing both the master cylinder and the booster, just to be safe.

 

To start, there is no fluid in the booster, and it's not coming from the master cylinder. Looks to me like its coming from the brake line just below the booster. Put a piece of paper under the steering column and the booster and repeat the test. My bet is that it's one of those lines that drop down on top of the frame rail.

 

I know that there is not supposed to be any fluid in the booster. That's kind of what I am worried about. It looks like there is.

As far as I can tell, there is no brake line running under the booster. There are a couple wire bundles covered in the corrugated plastic tube. If you look at 1:25 in the video, you can see them. Later in the video (at 1:49) you can see most of the brake fluid gets shot up the side of the booster, but some comes down on the steering column. But no brake lines between the two.

At 1:59 you can see the two lines coming out of the master cylinder and into the Electronic Brake Control Module and you can see lines heading out of there and going much deeper into the compartment than the master cylinder. I know I traced the brake lines coming out of the EBCM but I can't remember where exactly they go. I'll look tonight to make sure.

 

As rotted as the booster is, I would suspect the master cylinder has also started leaking at the rear seal and is running into the booster...I replace the whole unit...