Lost brakes, then returned and gone again....
 

Hey all!

I just recently bought this 1990 GMC Suburban, got it for a killer deal and it's in need of some things.

Today I was coming up to the stop light and went to hit the brakes, nothing.... Kinda panicked.... pumped a few times all the while lookin at the curb and this guys front lawn, hahaha. Then they reacted, they were fine till I just got to my street and started acting up, again no brakes. So into the driveway and under the hood I went. No leaks, traced lines to and from pump and cylinder. Rubber lines to and from calipers and everything visibly seems fine.

Engine off, brakes build pressure and pedal snaps back fine. Once I turn the engine on, pedal is soft and returns slowly. What are my options here? Anything I can do to determine if it's the Master Cylinder or the Brake Booster??

Thanks in advance for the help and info!

Sounds like a bad master cylinder to me.......

I guess this goes without saying.. but I will say it anyways. As a retired truck driver your truck should be considered UN-ROAD WORTHY until your braking issue is corrected.
As I understand your post, your brakes come and go. (intermittent) I would say your brake booster is on is way out.

Well, it turned out to be a broken brake line on the drivers side that was causing the issue all along.... hahahaha! Wow.... Oh well! I still replaced the master cylinder, rotors, pads, hard lines and rubber lines. This beauty stops on a dime now!