As the title says. When I shift into reverse, I don’t hear it engage a the engine just revs. I’ve called around a few transmission places to get an idea of the issue and cost, they’re all saying it’s a full rebuild and quoting close to 6k. Disaster!

I believe the transmission was rebuild a few years ago. I also have the front differential and transfer case replaced last year, at that point the mech said the transmission was in good condition, so seems strange that it suddenly needs a rebuild.

Anyone have any ideas?

 

I think you've been around your Disco for a while now and I don't want to appear like I know what's going on, but I'll give my thoughts.
The two most common causes of transmission faults on our ZF units are incorrect fluid levels and bad electrical power.
I'm sure you know the correct procedure for checking trans fluid level so I won't explain it here.
A weak alternator or battery, or dirty electrical connections can cause issues. The transmission ECU is very picky about the power it gets.

 

Well power seems to be fine, all other gears have had no issues shifting and I just refilled trans fluid a few months back, but will double check that incase there’s a leak. I haven’t seen any evidence of that though. I fear it might be a lot worse.

 

Although Harvlr might be right about most common problems, that is not most common issue with no movement. That is usually a bad clutch pack. You can rebuild it, do the forward clutch while you are in there along with the pump sealing ring upgrade, or just source another one and put it in. Pretty rare occurence but it does happen.

 

Thanks for the clarification Extinct.