Allison Flush in Park or Neutral

[BozDMAX]

Ready to take on a flush myself, but after reading the thread 56Nomad posted with the procedure I see him say to have the trans in Neutral. DmaxMaverick says leave it in Park when flushing the cooler lines.

Which is it?

[DmaxMaverick]

Other than the engagement of the parking pawl, and the TCM signal, there is no functional difference between P and N (unlike Chryslers of old). I suggest leaving it in P for safety reasons, but it does not matter when you do a flush. When in P, brake pedal pressure and movement of the shift lever (with a pull toward the driver) is necessary to get it into gear. If in N, all it takes is a "bump" of the shifter to get into gear. Not safe, IMO, even with the E-brake engaged.

[BozDMAX]

Thanks, figured I could count on ya!

[SoTxPollock]

Any thoughts on this? If you are up on a lift with the engine ideling doing the flush, would it flush better in gear with the gears turning or be about the same as in park?

[DmaxMaverick]

Any thoughts on this? If you are up on a lift with the engine ideling doing the flush, would it flush better in gear with the gears turning or be about the same as in park?

The fluid exchange through the clutch pressure pistons is very minimal, less than a couple oz's. I do as you suggest, but omit it from the instruction process because of the huge safety factor. It will probably gain very little, if any, advantage, but I do it anyway. I don't suggest anyone else do it, but old habits die hard.

[SoTxPollock]

Yeah, I agree about the old habits and safety is the most important of all especially when rotating parts are concerned. I don't even like the idea of having the engine running if it's on the ground and your underneath, even with the wheels chocked. I was in my old truck one day and reached for something on the dash and had the engine at a fast idle, elbow bumped it into reverse and it blasted out of the shop and accross half the back lot before I could get to the brake, you just can't imagine how fast something can happen. After its all over you start to think about what if anyone or anything had been behind me, what if I would have had the door open, what if I had bumped it into drive and wiped out my old firebird, what if the front wheels had been turned, what if..................