Not sure where to post this, since there is no forum for the TH400 transmission.

After four years I have my 1979 Jimmy converted over to diesel. The engine, TH400 transmission and transfer case came out of a 1984 CUCV Blazer with 15,247 on the drive train according to the National Guard service records. The original truck sat for several years in a National Guard depot before I got the drive train. Then the drive train sat in the Jimmy for roughly four years.

The issue that I'm having is that first thing in the morning, especially when it's cold, the truck will barely move with the throttle floored. After the transmission warms up, after about a quarter of a mile driving, it then acts fairly normal. I have no idea how well this was treated while it was with the National Guard. I pulled the transmission pan and everything looked OK with no metal fragments or band material. However, the NP208 transfer case went out the first week when a bearing failed between the input and output shafts. I've added some Lucas automatic transmission additive but no improvement when cold though the shifts became better once it warmed up. I've never worked on a TH400 and could use some guidance.

Did you change the filter when the pan was off? The cold fluid is thicker & harder to pull through the filter if slightly clogged. Also the filter o-ring can be bad allowing air to be drawn into the trans causing slippage.

Lonnie

Filter was changed and new fluid was added.

All trans seem a little sluggish when they're cold. Let it warm up a little, like 5-10miles before putting the throttle to the wall. Ever notice things break easier when cold? I do

True about the cold and automatice transmissions, but this is more than being sluggish. Floored and on level ground I can get out of the truck and walk faster than it will move.

is it trying to start out in 2nd instead of first? ie manually shifting it to 1 2 3