I have a rather strange, very disconcerting, problem with my truck that I've never seen before. The truck has disks on the front and drums on the rear. This has happened twice now and it's only a matter of time before I run it into someones rear end.

Here in the Dallas area, they're putting up these red light cameras everywhere and sending out fines if you're caught in the intersection when the light changes to red. A week ago, I was doing the speed limit, 55 mph, on a local highway and the light changed to yellow as I approached the intersection. I hit the brakes pretty hard to stop and it seemed the brakes engaged for one second, then let loose for about fifty feet, and then they re-engaged enough to skid the vehicle. However, even though I could hear the vehicle skidding, the vehicle wasn't braking nearly as much as it should be. I am not sure whether it was the fronts or the rears that engaged, but I'm guessingit was one or the other based on the braking behavior of the vehicle, but not both front and rear engaged. I wound up in the middle of the intersection and had to drive it on through the red light. I am waiting on the ticket since I know this particular intersection is monitored and active.

The strange thing is under normal braking, the truck is fine. This only happens when I have to hit the brakes hard. Like I said, I've experienced this twice now and I need to get it addressed.

 

Sounds like it could be several things. Since you said they locked up, I am assuming that you do not have an ABS system. You will want to check the pads for wear, and if they need to be replaced as well as the shoes in your rear drums. Also, bleeding the brake system couldn't hurt. An air bubble in your lines can really make things go bad, fast. Have you looked at your rotors lately? Do they vibrate when braking? Try taking the pads off of the front and slightly sand them to create a more aggressive contact patch. I would recommend replacing your pads with ceramic pads, along with bleeding your lines. Let us know what happens.

 

Thanks for the feedback. I bought this truck used about six months ago when the wifey's Expedition got rear-ended and totalled. I absolutely love this truck. When I bought the truck, I noticed the rotors were warped pretty badly. Then I had the first occurence mentioned in my original post, so I replaced the rotors with some Wagner rotors (mid-level quality, not the best but not the cheapest either) as a first step because it needed to be done anyway. Replacing the rotors made a big improvement in the braking behavior and I thought I had even fixed the problem. But it happened again at the aforementioned intersection.

When I replaced the rotors, I noticed the brake pads had a lot of goodie left on them so I left them on. I sanded them down, but that was it. Next steps for me is to bleed the brakes and replace the pads as you described. The brake fluid in the truck right now is a little dirty for sure - about the color of watery Coca Cola so it won't hurt to bleed the system really well and it'll be a cheap thing to try. I'll replace the pads while I'm at it. I'll keep everyone notified how it goes, thought it'll be a week or so before I get around to it since I'm out of town at the moment.

As far as ABS goes, I know ABS is standard on the rear drums on my model truck. I think the front brakes are not ABS, but I don't know for sure.

 

Well, at least it sounds like you know what you are doing! Unfortunately, the rear drums only account for about 20% of the overall braking power of our trucks. You are definately on the right track! Let us know how it turns out!

 

Sorry to bring up an almost month old topic, but has anyone figured out what is causing this? I too have a '00 QC 4x4 that does the same exact thing.. under heavy braking the pedal will shoot straight to the floor for about 2 seconds then I get about half of the normal braking power back... I've checked for any leaks, not losing any fluid at all, and the pedal does not get any stiffer if I pump the brakes, so I don't think my master cylinder is to blame... I haven't tried bleeding the brakes yet though as it has done this since I bought it used in '05.