Rear Brakes sticking

Out of the blue I drove 1 mile, stopped and when i let off the brakes both rear calipers would not release, i drove back home 1 mile and both rotors were red hot (not the ebrake) I had recently replaced all the pads front and rear, front is TRD BBK, I had problems with the front calipers that needed repair, so it was apart for a few days. extensive bleeding and still not 100% but working ok for weeks until the rears stuck. when I did the rears the pistons pushed in easily (only 56K on the truck) I changed all the brake fluid, the pads and had the rotors cut (touched up) so after they cooled off I pulled the calipers and tried to push the pistons in but they would not move, so I pushed the brake pedal a few times and pistons moved, then tried to push the pistons in and the went in with no resistance. I am sure it's not the calipers, can the ABS be the problem? can it be bled without a scan tool? or maybe the load sensing valve? please help!

 

On my 2010, I had soft brake problems for years. I replaced everything except the ABS module before I got rid of the truck, so I believe it can cause issues even though my issue was different. I think the proportioning valve is inside the ABS module.

On my 2018, my rear brakes were rusted and sticking after about 3 winters. I replaced the calipers from factory but still used OEM and never had a problem again.

You said at first the calipers wouldn’t move in, even if they worked later. I’d try replacing those next. They are or were about $70 a piece if I remember right.

 

when I replaced the pads the pistons went in easily, only after the rears would not release, I pulled the calipers and they would not go in until I pushed the brake pedal several times then they went fully in easily, I have never seen 2 calipers stick at the same exact time, thats why i'm thinking maybe air in the ABS, or rear load valve.

 

Maybe, but they could have been sticking for awhile. Just not bad enough to notice until the work you did. Did you completely flush your brake fluid? Maybe some contaminants got pushed in to the lines going to the rear.

 

Did you maintenance the pistons? Was there any boot damage to allow water in? Piston locking up is a big issue in wet areas. It will wear down one pad side much faster or possibly lock up.

Most likely your caliber is locking up.

 

I would be looking at the master cylinder. The ABS stops pressure from the pedal going to the pads. I guess it could fail in a way that wouldn't allow pressure to bleed off but that would be opposite of how it normally works. The proportioning valve only adjusts when the bed has weight in it. If you recently had a large load in the bed maybe it stuck. But in my mind the master is where I would look. It's main job is to keep pressure on the pads when stepping on the brake pedal and then removing the pressure from the brakes once you let off the pedal.

 

Took the rear calipers apart, no pitting, a little bit of grunge, cleaned and installed new seals and boots.Good solid pedal, Under light braking truck stops like normal, when you take your foot off the brake pedal, rear calipers release! under moderate to heavy braking when you let up on the pedal the rear calipers do not release, But if you push the brake pedal harder and let up on the pedal, the brakes release like normal. if I hit the brakes hard on grass or gravel and cause the antilock to activate, the pedal dives about 2 inches and the rear brakes don't disengage unless you again push the pedal hard a second time. my truck has no load sensing valve. I am beginning to think it's the ABS unit. Anyone have any input? Just traced the brake lines front to back, there is NO Proportioning valves anywhere. 2 lines from the master to the ABS, 4 lines out, 2 on top go all the way to the rear calipers, 2 on the side go to front brakes. the only cheap thing to try is the 4 rubber hoses at the rear axle, can't be the master because if the spool valve was stuck it would hold the fronts engaged also, that leaves the ABS unit to be the culprit.

 

The good news is that if you’re able to duplicate the issue predictably, you can do a couple of easy things to nail down the culprit before you fire up the parts cannon and shoot some new stuff at it.

Get the rear brakes to hold like you’re describing. First step I’d go with, is to loosen the front steel line at the master cylinder. Have something under to catch any drips, and wrap a rag around the fitting after you put your wrench on. Snug it back up, and see if the rear brakes release. If no, try the rear line, but I’m pretty sure it will be the front one for the rear brakes.

If they are still not releasing, loosen the lines to the rear calipers at the ABS module. I’m pretty sure they’re labeled on the modulator body, and you’ve said you traced them, so getting the right ones should be easy.

Have some water on hand to quickly rinse away any spilled brake fluid before it eats the paint from anything.

I’m pretty sure you’re going to find it to be the master cylinder if both rears are acting the same, as the “rear” inlet to ABS modulator is where the rear splits into two separate ABS channels. I’m thinking either the master cylinder return port is plugged up for the rear, or the master cylinder rear piston itself is sticking in the bore and the cup seal isn’t returning past the return port.

There’s two separate pistons in the master cylinder, so yes, it’s very possible that the piston for the front is working normally while the piston for the rear is sticking.


It’s not likely a booster / pedal / pushrod issue or adjustment problem if the front brakes aren’t dragging at all, but worth a quick check too.

 

I did not know the master had seperate spool valves, so what your saying makes sense. I will definatly try bleeding the pressure off between the master and the ABS unit. the rear valve sticking also makes sense that when I pump the pedal the extra back pressure pushes the valve into the open position. Thanks for the Input, so far I have only spent 25 Dollars on caliper seals and boots and a bottle of brake fluid. and my time. Not sure if or how far the pedal should drop when the ABS activates, but now that I got it to cycle in my driveway/yard i will bleed all 4 wheels again just incase it released some air into the system.

 

Master cylinder. For both to do the same thing. Has to be a fluid pressure issue.