2018 Silverado 2500HD "long" brake pedal problem - easy (but strange) fix

[azyxzer]

I've got a 2018 Silverado 2500HD 4x4 gas truck, and a few weeks ago the brake pedal started feeling like a vehicle with drum brakes that were out of adjustment, i.e. long travel on the initial press of the pedal and then it would get high and solid with a second pump. I thought this was strange because it only has 65K on it and my brakes usually last a long time, there was no noise or any other symptoms, and no warning lights. The truck still stopped OK, but it was not confidence inspiring. I was just about to pull all the wheels and start checking things out, bleeding, etc. when I decided to do a little 'Net surfing and came across the following on a Duramax site https://www.duramaxforum.com/threads/brake-pedal-effort.1023066/:

I had the same soft pedal feeling and after researching, I found this fix on another forum. I followed this advice and soft pedal went away.
Go out and start your truck but leave it in park, push the pedal to the floor hard, all the way then remove your foot and let the pedal come all the way back up, two or three times.

It sounded pretty hokey but worth a try, and it worked! Several others on that site said the same thing. There must be something in the ABS software that lets the driver push the pedal all the way to the floor when stopped in park, and it feels really strange doing so, but you can do it. The pedal feel was back to normal immediately and it has stayed like that through multiple braking and power cycles. 

Whatever the deal is, mine only started doing it after five years, but apparently some new trucks have had the same issue, and I guess it can happen to both gas and diesel trucks. Maybe this can keep someone else from doing a lot of unnecessary work, like I was just about to do.

 

[ROBERT L]

That’s great information. Thanks for sharing. 

 

[L.R.S.]

Very interesting. My son's 2006 LBZ Duramax had 100% new brakes and the pedal is soft AF. Going to try this.

 

[Bobalos]

Go out and start your truck but leave it in park, push the pedal to the floor hard, all the way then remove your foot and let the pedal come all the way back up, two or three times.

Im curious about this.  what exactly does this mean?  "push slowly on the peddle down, but when it starts getting firm just keep driving the peddle into the floor as hard as you can" or "grab the steering wheel & stomp on the peddle with both feet in almost a violent manner"?

By "let the peddle come all the way back up".  does it matter?  I could "slowly pull my foot up to the stop" or "slip my foot off of the side of the peddle & let it pop up as fast as it can"

I wonder what this is doing?  is it screwing with the ABS valve manifold in some way? 

Do these ABS cars have a "normal proportioning valve" in them any more or is that done in the ABS manifold? 

thanks

Bob

 

[azyxzer]

I just put really firm (but not ridiculous, like stomping) pressure on the pedal and it slowly went all the way to the floor. I've been doing brake jobs for 40+ years and this felt totally wrong, but it did it nonetheless.  If it was on a non-ABS rig it would be a bad master cylinder. Now it has normal pedal feel like it used to before whatever changed. I really don't know what is going on with the system but I'm guessing that the ABS knows you are stopped and in Park and lets it happen somehow. More high-tech than I really like, but I guess that's how it is nowadays.

 

[Bobalos]

intersting, thanks.  I will give that a go on my Dodge & see if there is any change. 

 

[KLC]

You can normally push the pedal to the floor on any truck equipped with a hydraulic booster. There is a specification for brake pedal travel that is easily measured after the accumulator has been discharged, I don't have that number in my head right now though. Pumping the pedal with the engine shut off discharges the accumulator in the booster, the pedal will get very firm when this occurs. You can only evaluate the performance of the brake hydraulic system after discharging the booster's accumulator. If your pedal is still low after doing this, there are some other diagnostic tests you will need to perform to determine why the pedal is low, that's why there is a specification for pedal travel with the booster discharged. Keep in mind there are a lot of things that will cause a lower than normal pedal feel, air in the hydraulic system, worn master cylinder and worn brake linings are just a few of them.

There are accumulators inside of the ABS unit that could theoretically be allowing brake fluid to enter upon pedal application but in 30+ years as a dealer tech I can count on one hand how many I've replaced to correct a low pedal, none of which were on trucks, and none since the mid 90s. Performing a stop in which the ABS unit becomes active will sometimes reseat all of the valves internal to the unit as well as recharge the accumulators with fluid, get on an isolated stretch of road and stomp on the brake pedal from about 40 mph and allow the vehicle to stop completely, you will hear/feel the unit cycling. Do this a few times and then re-evaluate before you replace any parts. 

 

[azyxzer]

Very good information, thanks. A quick update - it's been about ten days now since I tried the "fix", and the pedal  feel is still just fine, whatever it actually did.