Brake issue 2019 Colorado

[LargestAl]

Looking for opinions. My 2019 Colorado Crew Cab, 3.6l, with about 8000 miles has an issue which has been going on a while, even after a dealership visit.

When stopped, and putting moderate to heavy pressure on the brake pedal, it the pedal creeps slowly to the floor. I can let off, which lets the truck move, and pump it to get the pedal position back up to normal. If I sit there long enough, it does it again. Dealership said they tested the 3 other Colorados on the lot and said they did the same thing so it must be normal. I have started a claim with GM, but with COVID-19 shutting everything down, I haven't taken it to another dealership

I any of the vehicles I have owned over the past 37 years had shown this issue, I would inspect each brake location, the vacuum hoses, brake lines and the master cylinder. One, or a few, were bad. Solid pedal after repair and changing fluid.

That being said, has anyone noticed anything like this in the newer GMs?

Thanks in advance.

 

[chemman]

Sounds like what my 1973 Chevy Impala used to do when the power brake booster developed a vacuum leak. Solution was to replace the booster unit and result was a non-sinking brake pedal one again.

Since they are telling you that other Colorados are the same way, I would ask them let you drive them to see for yourself.

 

[jhs914]

I have a GMC Canyon 3.6 CC (2017) and it has firm brakes after 54,000 miles. Definitely not normal. I hate when dealers try to skate with the "they all do it" excuse. Well if they all do it then they all need to be fixed. Sounds like air in the brake lines and they should be bled using a machine that can activate the ABS to clear all air from the system.

 

[oldhp]

Sounds like the master cylinder is bypassing internally.

 

[montero1]

Nothing like that on my GMC Canyon.

 

[Lou_Boyle]

Quote
Sounds like the master cylinder is bypassing internally.


This.^ I've had one that would do it every time and one that would only do it randomly.

 

[eljefino]

Had this happen on a 97-ish GMC 3/4 ton diesel. It felt "right", though, like it was going somewhere in the ABS plumbing.

But I could keep it from creeping in drive with normal 5 lbs on the pedal without it ever sinking.

 

[MrHorspwer]

Your Colorado has a vacuum pump to supplement the engine vacuum at idle. It uses a pressure sensor at the booster and if pressure drops below a certain threshold, it runs the pump, adding vacuum to the system. If you stand on the brake pedal at idle, you will deplete vacuum at the booster and the pump will turn on. When this happens, additional assist will come from the booster, causing the pedal to "sink". Once you're off the brake, the pump does it's thing, vacuum levels at the booster return to normal, and the pedal feels fine again.

The mention of the diesel full size is actually a good parallel. Those use hydroboost, which uses a hydraulic assist instead of vacuum. The operation is different, but the result is the same. On a hydroboost system, standing on the brake pedal will cause the system to respond with more assist, which is turn causes the pedal to travel down further.

 

[ARCOgraphite]

Originally Posted by LargestAl
Looking for opinions. My 2019 Colorado Crew Cab, 3.6l, with about 8000 miles has an issue which has been going on a while, even after a dealership visit.

When stopped, and putting moderate to heavy pressure on the brake pedal, it the pedal creeps slowly to the floor. .....

Thanks in advance.



It the pedal is going down, the ONLY way that is going to happen is with air in the system or dirt in the MC..( first assuming you don't have a caliper leak) A bit of sponginess is a combination of rubber brake hose ballooning and caliper distortion.

I've had issues trying to bleed ABS systems and they need to be activated to purge properly.
It's all in the shop manual.

A proper bleed with ABS activation should improve the brake pedal

Now good luck getting someone competent to do this.

 

[mk378]

If you used that same "moderate to heavy" pressure on the pedal when moving, the brakes would slam on and you'd realize you're using a lot more pressure than normally needed to stop and/or hold still.

This is kind of common when testing the brakes on a car that is not moving. The pedal seems "soft" just because there is a lot of power assist going on.

 

[ragtoplvr]

If the vacuum pump kicks on a vacuum booster petal should rise. Hydroboost will also never fall unless MC or ABS is failing or you have a leak.

follow up with dealer, if they lie call zone rep. If they all do it ask to check every one they have in stock. then follow up with NTSB
because it is a defect.

Rod