Need diagnosis - braking while backing

Boardmember · May 23, 2017

Hey guys, I've experienced this no more than 3-4 times. I have 27k miles on the truck.

When slowly backing in reverse, my brakes become tremendously squishy (the technical term, I think) and letting off to re-pump doesn't work. I barely have any stopping ability. Today I was attempting to back into a parking spot in a very crowded parking lot and it happened.

When I try to replicate it, I can't. I had tires rotated by a tire shop a couple weeks ago and asked them to do a visual (as did I). Everything looked fine.

What's going on here? Thanks in advance.

Boardmember · May 23, 2017

No brake-perts reading tonight?

XSKIER · May 23, 2017

Engine cold or warm?

Sent from my SM-G930V using Tapatalk

Boardmember · May 23, 2017

Warm.

XSKIER · May 23, 2017

After a warm restart, or after a drive, then successful fwd brake?

Sent from my SM-G930V using Tapatalk

Boardmember · May 23, 2017

Drive from my office to pick up wife at her work. Drive to a funeral home for a visitation. I'd say fully operationally warm. 20 miles. All fwd braking good. It happened at funeral home park lot. Left, drove wife back to her work to pick up her car, tried to make it happen again. Nope. Worked as designed.

But when it happens, it's unnerving.

XSKIER · May 23, 2017

Must be something with your vacuum power brake assist system. The sudden loss of vacuum in the system will allow the pedal to fall to the floor, while decreasing the effective hydraulic pressure seen by the brake calipers. You probably won't get a MIL code for this intermittent problem until it gets much worse, like happens all of the time. Maybe a wiggle test on the vacuum lines? Also, pay close attention to your idle speed when it happens. Sometimes these electric throttles can get a little goofy as carbon starts to build up. The idle speed is controlled by airflow in lbs/hr, not by a certain throttle plate angle. So, as carbon builds up (not perfectly round with the throttle body) the throttle plate will open to maintain the airflow rate. It doesn't take too many rpms over the base 600 to make the truck feel like it is hard to stop.

Sent from my SM-G930V using Tapatalk

Boardmember · May 23, 2017

Thanks. Will copy this and present it to the dealer. Appreciate it.

Boardmember · May 26, 2017

Returned truck today. Couldn't replicate brake failure. Even after I screen printed Xskier's suggestion and handed it to them.

Donstar · May 26, 2017

Returned truck today. Couldn't replicate brake failure. Even after I screen printed Xskier's suggestion and handed it to them.

"Couldn't replicate brake failure" is not an acceptable response, imo. You are not complaining about a squeak or a rattle! I would definitely express concerns about my personal safety and insist that they service your braking system in the same manner as if they could replicate the problem.

dasimmon · May 26, 2017

"Couldn't replicate brake failure" is not an acceptable response, imo. You are not complaining about a squeak or a rattle! I would definitely express concerns about my personal safety and insist that they service your braking system in the same manner as if they could replicate the problem.

+1