Hi,
Since we are not slipping in reverse, it sounds like the clutch pack is good. If the clutches were bad, it would likely slip in reverse. The planetary low gear clutch is a one-way clutch. Either it is failing or there is a lack of pressure for engagement.
I'm going to try explaining how this works and what leads me to my theory.
See Pic 1
The (A) reverse clutch couples the (B) input shaft to the (C) reverse sun gear. It is applied in reverse range only.
See Pic 2
The (A) planetary (low) one-way clutch is a roller clutch that holds the (B) planetary gearset in first gear, (OD), and D ranges. During automatic coasting downshifts into first gear (OD) and D ranges), it freewheels so that there is no engine braking.
The only other thing I can think of is if the reverse servo is leaking. That can happen due to wear, and they have been known to leak. However, the servo may not fix it if the band and drum are worn or damaged.
I hope that made sense. Here is what I would suggest. First, service the transmission and the filter. Additionally, flush the converter and the transmission oil cooler.
Let me know if this helps or if you have other questions.
Take care,
Joe
See pics below.
Images (Click to make bigger)
Friday, April 15th, 2022 AT 6:37 PM