I have an 85 4runner and whenever i put it in reverse the rear seems like it's locked up. What could be causing that?

 

Help us help you, what engine and tranny do you have?
is it 4 wheel drive?
Does it go forward without any funny noises? all the way up to highway speeds?
Jack up the rear end and see if you can turn the wheels with the vehicle in neutral.
Could be transmission, could be rear differential, could be brakes.

 

I'm not sure the engine size but it's a 5 speed. We jacked it up and took the rear wheels off and they turn in neutral. It wouldn't back up in reverse and we did figure out the ebrake wouldn't disengage fixed that but it still locks up in first gear.

 

You're just confusing the issue even more, reverse and first are two different gears so....
disconnect the driveshaft and see if it is a transmission issue or a rear diff issue. or remove the rear driveshaft altogether and see if you can drive around forward and reverse in 4wd.