zf5 problem

we put a used zf5 into a customers truck. we couldnt find a transmission with the exact same model, but we got one that had a similar production date and out of a 7.3. The only thing ive been able to determine being different is teh low gear ratio... It works as it should in 1-5, but about half the time you try and go into reverse it goes in about half way and grinds. The other half of the time it drops right into reverse as it should. What should i be looking for or should i dump the trans and find another? I can see anything wrong in the shift tower and just dont know why it would only have problems going into reverse about half the time. any ideas

My zf6 recently started doing that. But only when the truck is rolling forward, and Im trying to put it in reverse. If stopped it will drop in without issue. I believe thats the synchronizer for reverse failing.

Yeah thats what we have narrowed it down to! looks like used trans #3 is fixing on going in, this guy could have bought a ford reman at this point lol.

Or they could just basically come to a complete stop before putting it in reverse haha. Thats what I do!

synchronizer is gone on Reverse. Really common, happens due to people will roll forward and pop it in Reverse making it work harder.

Or a worn out dual mass clutch and flywheel.

The syncro is going out. My zf5 does the same thing too. I put a new clutch and single mass fly wheel in thinking it would fix it, shifts better in all other gears but still grinds sometimes going into reverse. Syncros it is

1994.5 CCLB zf5