I have a 3/4 ton 4/4 disk front drum rear abs and the brakes lock up at slow speed. The pads and shoes are in good shape and does not appear to be any leaks in the system. I have seen this discussion before just wondering if anyone had any new info.

 

Is it the front or the rears that are locking up?

 

Front for sure may be all.

 

In most cases the rear lock up. Its actually very rare for the front to lock up. Drums will lock up first drive due to moisture. Also pretty common to have weak springs or incorrectly adjusted shoes to cause a lockup.

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mysterync is correct, the rears are common to lock up the first couple of times after the truck as sat overnight or for any length of time when it hasn't been driven. However, the front can lock up, and in my experience, a new set of calipers is an inexpensive fix. The best way to check would be in loose gravel... just brake like you normally do and see which tires are skidding. If it is the front, the first thing I would check would be the calipers to make sure they're installed properly. If everything seems to be installed correctly, my only other question would be about the possibility that the pistons make be sticking.

If it ends up being the rear drums, remove the wheel and drum and check for any sign of brake fluid leaking from the wheel cylinder. Over time, the rubber seals can break down and form leaks that will cause some pretty violent grabbing. If you see brake fluid, wheel cylinder replacement may be in order. They can be rebuilt, but it's cheaper to replace them... and make sure you do them in pairs. If no brake fluid, check the wheel-cylinder-to-backplate mounting location and see if there's any possibility that water/debris could be entering the drum. If so, silicone is your best friend (it's actually recommended when replacing the wheel cylinder to seal the backplate...). Like mysterync said, check all the springs to see if they're abnormally loose or broken. A spring/hardware kit is something like $5.00 at your local parts store. If all your hardware seems fine and you see no leaks, I would replace the wheel and drum and do rear brake adjustments. Drive the truck forward. Brake to a complete stop. Drive the truck in reverse. Brake to a complete stop. Repeat the process 6-8 times. That should tighten them up if they're out of adjustment. You can actually spin the little star wheel yourself, but it's a PITA.

Hope this helps!

 

One point worth mentioning might be the bigger wheel cylinders in the rear if your working the truck.

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It's actually funny you mention that. That was my problem. Oversized wheel cylinders worked great when the previous owner of my truck hauled 27k lbs, but not so much for my everyday driving. So, yeah, mysterync, good point!

 

Empty they sure can be tricky

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You got that right! Downtown driving, eight lanes of traffic, and when I hit my brakes, I know my rear axle was hopping off the pavement a good inch or so. Bought me a new set of cylinders and a new pair of pants and that fixed both of my problems! Lol!

 

was having this same problem. turned out previous owner had them assembled wrong. I installed all new everything a few months ago, but can not figure out why the driver's side brake makes a "chirp, chirp, chirp" while driving forward, but not while in reverse. Its possible that the new cylinder I installed on that side is bad, or maybe the return springs.....with the drum off and someone else pushing the brakes everything appears to be fine. I thought maybe I installed the wheel bearings wrong or faulty ones, but while lightly pushing the brake and driving the chirping stops. guess ill silicon the backing plate and see if its moisture.....