1997 Pathfinder - grinding shifting out of 4 low

[AlwaysWrenching]

Between 2HI and 4HI the transfer shifts smoothly and appears to work fine. However I can shift into 4LO but when shifting out of 4LO I have to shut the truck off otherwise the transfer case will shift from 4LO in to neutral but will not shift out of neutral without shutting off the engine. If I attempt to shift the transfer case out of neutral with the vehicle running the transfer case will grind. I had the transmission in neutral per owners manual. The fluid is brand new in the front diff, trans and t-case. 

Edited March 3, 2020 by AlwaysWrenching

[onespiritbrain]

They all do that if you’re not fast enough going from hi to lo and vice versa. The output shaft on the transmission spins even in neutral if there’s no resistance (ie the transfer case disconnects the rest of the drive train behind the transmission completely when you go from hi/lo to lo/hi). You have to be quick with the movement. Why doesn’t it say that in the manual...?

I bet someone smarter could explain exactly why the output shaft spins in neutral.


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[AlwaysWrenching]

Thanks a bunch. It seemed really odd. Well I guess it gave me an excuse to change the fluid in the front diff, t-case and transmission. 

[Slartibartfast]

Yep, OSB nailed it. The auto trans works with clutches, which I assume have a slight drag to them when they're not engaged. That drag isn't enough to move the truck, but it's enough to spin up the output shaft when the transfer's in neutral and there's nothing holding it back. Then you go to finish the shift and you're trying to couple a spinning part to a stationary part with no synchros in between, and it just grinds. Make the shift in one fluid motion and it won't have time to spin up. I fumbled mine and had to shut it off to finish a shift just yesterday, so don't feel like it's just you! It's not usually an issue once you're used to it, but it can be a pain at times.

 

Changing the transfer fluid in my '95 actually cleared up a different issue I'd been having, where it wasn't reliably disengaging from 4x. It's a fun box to get fluid into, isn't it?