If it is locked in reverse, that is an internal failure.
Most likely you will need the transmission to be removed and inspected. It most likely will result in replacement with either a rebuilt unit or a used unit.
Roy
Feb 23, 2020 at 2:52 PM
CARADIODOC
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Hi guys. I thought this too, but wouldn't the torque converter still do its thing and let the engine idle? The torque converter would have to be locked up to snub the engine.
The van runs and shifts when in drive.
When you select reverse it attempts to back up then it locks up and stalls the engine.
Could it be the torque converter locking.
Feb 23, 2020 at 4:09 PM
ASEMASTER6371
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It could be but if the converter was bad, it would also do it in the drive.
I still think you have something internal locking up in reverse. The forward clutch pack may be the issue.