More then likely you have a cut seal in the reverse drum inside the transmission. This means when the vehicle is put in reverse pressure is applied to this drum and when it cannot hold the pressure due to a cut seal the clutch is no applied and it does not engage reverse.
The fact that sometimes it does just shows that there is a point in which it is able to seal enough to engage the clutch.
There is a small chance that this is just a solenoid but there should be a code with that. So let's start with checking for codes and see if there is anything pointing us in a different direction.
If not, we will most likely need to overhaul the unit but specifically the items that I attached.
Please let me know if you have questions and what you find with codes. If there are no codes then that would support a cut seal or other internal transmission issue with this drum and clutch set.
Images (Click to enlarge)
Mar 31, 2020 at 3:50 PM
