TH400 slipping... sort of

[Geektrucker]

Okay... Turbo400 in the truck, NOT the original tranny, original was a 4 speed. When the truck is cold, taking a LEFT turn only, low speed only, from a stop, (taking a left after a red light or leaving the driveway) it will shift from 1st to 2nd without problem, then often, will immediately shift back down to 1st almost like it's fluid starved until I let off, or straighten up.

Changed the rag and fluid last fall, nothing major in the pan, although the fluid smelled... nasty / foul, but NOT burnt. Refilled and checked level, all good there. If I let the truck warm up thoroughly (15 or more minutes) I DO NOT experience this, nor do I notice it on a right turn, only left.

Thoughts?

In every other aspect the tranny works / shifts / operates as it should, perfectly. Once warmed or after about 2 - 3 min of driving, I cannot replicate the problem, only when cold (as in overnight or sitting for several hours, and only from a dead stop.

 

[HotRodPC]

Sounding to me like it might have dropped the filter and it is doing exactly as you describe. It's starving for fluid cuz it can't pick it up due to the filter actually acts as the pick up. Do you have the deep pan or the shallow pan? It won't hurt to run a Th400 with a pint to much of fluid and even if it does, it will foam and come out the vent tube. So, for purpose of maybe trying to figure this out without dropping the pan first, maybe add the half quart of fluid and see if the problem disappears or gets better. I really only think this due to you mention it happens while turning left, so the fluid is going to the opposite side of the pan and the tube can't reach the fluid. After the fluid warms up, it likely swells a little making the fluid level higher. Hopefully by going a pint over, it will still have fluid there to pick up when cold too. That'll get you by until you can drop the pan and fix it, but keep in mind, you're fluid isn't being filtered before it's going through the valve body now if this is the case.

 

[Geektrucker]

As far as I know it's not a deep pan.. how do I confirm / measure?

 

[HotRodPC]

It's quite obvious. The standard passenger car pan is about 1.5 inches deep, the truck pan is at least double that or so. Say 3-4 inches deep.