Rear brakes lock up

Hey I have a 1997 sr5 4runner and it will lock up the rear brakes on a hard stop. Regardless of weather conditions. I have replaced the wheel cylinders, front brake hoses and new brake fluid. Also have checked all my sensors and all are fine. What am I missing??? Anything helps!

 

Axle seals leaking?

 

Nope ran into that in past vehicles owned. Drums are nice and dry an nothing leaks

 

On my last rear brake job the brake material was starting to separate from the shoe. How do they look?

 

Shoes only have a few hundred miles on them, about 1/4 inch thick still. They're in good shape

 

We're all the springs put back correctly?

 

Yep all is put back together correctly. Brakes work and feel good. I can stop pretty quick but if I need to stand on them I spin out cause the back locks up

 

Seized caliper? Mine had a problem with the whole car shaking when stopping. Turned out one of the pistons on the front driver side was seized. Cost like 90 bucks to replace.

 

Mine pulls to the right when I stop but I believe my calipers are fine. It's the back that locks. Not the front

 

Does it stay locked after you've come to a stop and take your foot off the brake?

Are both rear brakes locking up or one side or the other?

 

So in the case of me needing to stop immediately. I push hard on the brake pedal and it's very hard. That's because I'm going straight from gas to brake pedal. As I push it is hard for a few seconds then the pedal feels as it normaly does. But as it goes back to being soft (soft as in not rock hard) the back drums lock up and until I take my foot off the brake. Once I take my foot off the brake all is normal again

 

Isn't a lack of engine vacuum to the brake booster indicative of a hard pedal? That may be what you want to investigate.

 

At the rate I'm going I'll probably just one day replace the brake booser/ master cylinder. As well as front calipers. Hopefully it's not the abs unit itself. The vehicle has 310,000 miles on it so I'm still breaking it in ya know