If you have the G8o locking diff it may be the problem, look in the glove
box RPO tag see if G80 appears. If so try flushing the fluid in the diff,
look for any metal, add new fluid reg or syn. 75-90 and keep your fingers
crossed, the locking diffs were problematic.

    A buddy has a 88 or 89 K-1500 with a brake problem. When the truck sits
for a few weeks to a few months (its been in stages of body repair for a
few years now), the rear brake on the right side will lock up.

    If your brakes get hot enough, it is possible they could lock. Having
the run out checked on the drums couldn't hurt, nor would inspecting the
shoes & adjusters.
Charles

have you used your emerengcy brake any, it may have not released all the
way and is causing your brakes to lock up

Dave

I can only think of a few things. My first guess is that you have a
G80 gov loc that is binding and not releasing and when you start out
in a turn it binds. The second thing is the brakes are sticking. I
doubt it is the bearing in the rear axle because it they where that
tight the rear end would have toasted by now. Another thing is that
you may be getting tranny shudder/chatter because if you are back a
trailer up a incline and you have a fairly tall axle ratio the tranny
will get very hot quickly because rev is not as low as first in the
4L80 that you likely have. How big a trailer are you pulling, what is
your axle ratio  and do you have a aux tranny coolers too?

Thanks, everyone for the replies.
I didn't find G80 on the RPO label.
I know brakes can freeze up after sitting for extended periods, but it only
sat about 2 hours the last time this happened. Just long enough to load it.
Another thing, it seemed like I could back up, just couldn't go forward.
I'll let you know what we find when we pull the rear drums.

Dave

I have a G80 locker in the back of my '86 K5 Blazer...I've had the same
problem in the past.  Now the G80 is wasted, and I'm waiting on my new
axle to arrive.

You want to get that taken care of immediately.  I'm driving a borrowed
Suburban until I can get my new axle installed.

Don't end up stuck on the side of the road like me!

~JP