I had one of our older trailers last year and couldn’t get the tandems to slide forward after I slid them back to get loaded. I ended up putting my coveralls on, and then I crawled up between the axles and soaked it with PB blaster. Then I sprayed inner slide lube on the rest of the rail. Once it broke loose I slid the tandems back and forth the whole length of the rail a few times. I ended up pulling that trailer for a couple more weeks and didn’t have any other issues sliding the tandems again.
1st of all, you'll never get stuck tandems to move with a load on, and 2nd, maybe the previous owner "fixed" the tandems so they don't move.
If I read your post right you tried another trailer under the same circumstance. And it wouldn't budge also?. If i read that wrong. I would say you have a warp.
I’ve hooked up a different truck to the same trailer thinking something is going on with my truck and the other truck couldn’t also shift them. I see other trucks with the same weight as me at warehouses move there’s without any problems.
@gentleroger probably has the answer. There was / is a problem with Great Danes. I had the same problem. I told my dispatcher that I couldn't get my tandems to slide. He said, "Is it a great Dane?"
Are the tandems currently all the way back? If so what's likely occurring is the slider rails weren't installed properly. I know we had issues with a string of trailers where the rails were not parallel so the tandem carriage gets wedged in when they are all the way back. The easiest solution is to find a curb and get lined up square to it, about 10 feet in front. Get the whole rig moving and as your trailer tires hit the curb, set the brakes. It's ugly and hard on the equipment, but effective.
Did I tell you the one about the brand new trailer that was being inprocessed by the shop with the abs light on? Shop dug DEEP into the abs system looking for the problem. Turns out the abs light was wired into the license plate light.