Mark Allen

Hello everyone, I have a 2003 Chevrolet Silverado 1500 4D Ext Cab with 2WD, base 5.3L engine. I have been having issues with brake drag. After a few miles, the brake pedal feel gets very firm and the vehicle will struggle to maintain momentum. Letting off the gas, the front nose dives and the truck slows very quickly. Sometimes, though, the brakes seem to release and then begin working normally. I began checking the brakes frequently with an IR thermometer and found that temperatures of the rotors and brake components gets extremely high when this happens, especially on the front brakes.

So , far I have changed the front right caliper and the rubber brake lines to the front brakes. When that didn't solve the problem, I unplugged the ABS module to rule it out. That didn't change anything. I removed some of the fluid from the master cylinder reservoir as well, and that seemed to help, but only momentarily. I would still find that sometimes the pedal would get very firm and then the brakes would start dragging again.

Then, I unplugged the electric vacuum assist pump (for some strange reason, my truck has this. Is this normal for this model???). It seemed to clear up, but then re-appeared after a day or two. Now, I am driving with the vacuum line completely disconnected from the brake booster and it seems that the issue has cleared up. So, it leads me to believe that the brake booster is the culprit. Possibly the master cylinder too.

However, before I spend any more money on this, I was just curious if my conclusion is sound or if there is anything else I could be overlooking. Have any of you had this issue with this model?

Jay Byrd

Pull away the master cylinder from the brake booster and see if your master cylinder is leaking fluid into the booster. Also, take a listen inside the cabin for what sounds like a vacuum leak at the area of the brake pedal pushrod at the firewall.
Fld inside the booster = You'll need both the master cyl and booster assm.
Only Vac Leak at pedal = Booster assm.
If neither...I'd replace the booster first.

Mark Allen

Thanks, Jay! That's exactly what I did when I got home yesterday. No fluid appears to be leaking from the master cylinder. I'm pretty convinced it's just the brake booster. My thinking is that the internal valve is staying closed and causing it to push against the master cylinder. Another clue for this is because often when this has happened, the brake drag has been from immediate startup, really before the brakes have ever even been applied.

Thank you for your reply!

Also, I discovered yesterday that the brake assist pump apparently comes standard on the same year model GMC Sierra 1500, but not on the Chevy Silverado 1500. Kind of makes me scratch my head as to why there's one on my truck.

Jay Byrd

Mark,
There was one other observation you could do before replacing the booster and I blame myself because it's been a number of years I've been away from my wrenches, and I hate telling you to take another look....after pulling away the master cyl, I should have advised you to take a look at the master cyl's. plunger piston valve, to see if it's properly seated, not recessed or "hanging" up inside the master cylinder body. Even going so far as to pushing the plunger valve, making sure it re-seats when released or that it isn't binding. within the housing.

Mark Allen

You were on the money with this one!!!

I replaced the booster and it did help, but did not completely eliminate the brake drag. I then suspected the master cylinder wasn't allowing the fluid to return completely and then replaced it as well. The brakes are working like a champ now.

After replacing the master cylinder, I inspected the old one more closely. Although the plunger appeared to be working properly, I noticed there was a lot of sludge clinging to the bottom of the reservoir. I suspect that was somehow preventing the fluid to properly return and the calipers from releasing.

But, since replacing the master cylinder, it's been working very nicely. Thank you so much for your advice!