Temperamental Brakes When At A Stop?

[Curt]

Sitting at a red light for more than 1-2 minutes, the brake pedal goes from firm to mushy and the truck starts creeping forward. I push my foot on the brake pedal harder to stop. My foot almost reaches the floor before it stops the truck again. Then the brakes return to normal once driving resumes. It does this at almost every light. Sometimes when I press the brake pedal that far down it turns on the emergency brake light on the dash. I've checked for the pedal contacting any wires but haven't seen any. I'm at a loss. Any help is appreciated.

 

[Jay33089]

Sitting at a red light for more than 1-2 minutes, the brake pedal goes from firm to mushy and the truck starts creeping forward. I push my foot on the brake pedal harder to stop. My foot almost reaches the floor before it stops the truck again. Then the brakes return to normal once driving resumes. It does this at almost every light. Sometimes when I press the brake pedal that far down it turns on the emergency brake light on the dash. I've checked for the pedal contacting any wires but haven't seen any. I'm at a loss. Any help is appreciated.

Sounds like a bad master cylinder to me. Try it sitting in the driveway in park with the truck off. If the pedal goes down with steady pressure on it. Then more than likely the master is bad. But the braking systems on these trucks are mysterious in ways that can’t be explained! Lol! But that’s where I’d start!

 

[Curt]

Sounds like a bad master cylinder to me. Try it sitting in the driveway in park with the truck off. If the pedal goes down with steady pressure on it. Then more than likely the master is bad. But the braking systems on these trucks are mysterious in ways that can’t be explained! Lol! But that’s where I’d start!

Thanks for the tip! Just gave it a shot, and I'm confident you nailed it. The pedal went down with ease with constant pressure. Looks like it's time for a new master cylinder! Thanks for the help! Any recommendations of where to get a master cylinder?

 

[Robert l]

could be the power booster the thing the master cylinder is mounted to . It has a vacuum line that comes from a tee in the back of the intake . These have a known history of stopping up with carbon.

 

[Curt]

could be the power booster the thing the master cylinder is mounted to . It has a vacuum line that comes from a tee in the back of the intake . These have a known history of stopping up with carbon.

Oh, I'll check that out too. Do you know how to check it out?

 

[Jay33089]

Thanks for the tip! Just gave it a shot, and I'm confident you nailed it. The pedal went down with ease with constant pressure. Looks like it's time for a new master cylinder! Thanks for the help! Any recommendations of where to get a master cylinder?

Any parts house should have one in stock. Depending on how much money you wanna spend. I always opt for the new instead of a reman. They are generally not that much more. You could also go to the dealership, but get you pocket book out! Lol! Or you could do the gmt800 upgrade!

 

[Jay33089]

Oh, I'll check that out too. Do you know how to check it out?

The booster not working would just result in a extremely hard pedal. It would not cause the bleed off problem your having. They are not directly connected to the hydraulics of the braking system. It just assists in applying the necessary pressure to the master to stop the truck efficiently.

 

[Curt]

The booster not working would just result in a extremely hard pedal. It would not cause the bleed off problem your having. They are not directly connected to the hydraulics of the braking system. It just assists in applying the necessary pressure to the master to stop the truck efficiently.

Ah gotcha, that makes sense. I'm going to shop around for a new master cylinder. Most likely going to stick with OEM (if I can find it) as I never had any issue with my pedal feel prior to this issue (I was luckily only of the ones who never had a spongy pedal). Thanks for all the help!

 

[jsfrmsj]

Be sure whoever does the work has the computer that can interface with the GM ABS computer. Otherwise, they'll try bleeding it the traditional way and break the abs controller. Ask me how I know $$$$

 

[Curt]

Be sure whoever does the work has the computer that can interface with the GM ABS computer. Otherwise, they'll try bleeding it the traditional way and break the abs controller. Ask me how I know $$$$

Good point. I was planning on doing this myself, but never mind! I got a couple shops in mind. Thanks for the tip!