I have a 87 sr5 86k miles and about seven months ago my rear end would start to lock up and hop whenever i was coming to a stop(slow speeds). I bled my brakes and there was no change, after a little troubleshooting i concluded that it was my rear drivers side wheel cylinder that was causing the issue so i replaced it and it was fixed. now six or so months later the issue has resurfaced, i'm assuming that there is an outlying issue that i'm missing and its something else that is causing my wheel cylinder to defect. Any advice would be much appreciated.
Yeah there should b a proportioning valve. It controls how much breaking power is supplied to the rear wheels. The valve responds to load capacity, so if ur hauling of towing it will increase rear breaking power. It should be mounted on the frame rail the brake line from the front go into it before going to the rear cylinder also has a rod coming out if it connect to the rear end. It could b stuck or just needs replaced. Hope this helps
The proportioning valve is self adjusting based on the amount of weight in the rear so if you add drop blocks to the rear it will act as if you are carrying a heavy load.There is an easy fix just do some searching here and you should be able to find it.Search LSPV(load sensing proportioning valve)
I fought with a similar issue a couple summers ago. I'd completely rebuilt the rear brakes and the rears kept locking up. Everything was in great shape and installed correctly. Temp fix if happened while driving was to open and close the bleed screw and it would release the brakes. After I messed with/replaced everything else, including the proportioning valve and master cylinder, I concluded it was just a crappy replacement wheel cylinder. Went back and got a high quality part and haven't had a problem since. Those cheap auto parts store rebuild parts are crap. Always ask for the best they can get, and price compare with websites like rockauto.com