TH400 Shifting?

[kennyw]

I put a rebuilt TH400 in place of the 700R4 in my '83 K20 a few months ago. I never drive it that much except running errands on weekends or when my motorcycle is needing something and I can't take it to work.

When I first got it back the vacuum pump was dead so I change it for a good spare, then found the IP mounted vacuum switch was bad off my donor truck and bought a new one from the dealer ($125 ). I don't have the kick down switch hooked up on the gas pedal yet.

Now with everything but the kickdown switch hooked up my tranny shifts straight from 1st to 3rd (anywhere from 15-25mph depending on where I adjust the vacuum switch) and skips 2nd gear. Only way to get it to use 2nd is to pull the shifter down a notch then it shifts smoothly from 1st to 2nd around 15mph.

Anyone know what controls the 1-2 shift on a TH400? I need to know if I should bring it back for warranty work or if there is something simple I can adjust?

 

[85CUCV]

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[kennyw]

Just an update... took the truck back to the transmission rebuilder and found it was toast. Actually so bad I had to find another core to rebuild

 

[MaxPF]

Let me guess - the lugs inside the case were broken?

 

[kennyw]

All I know right now is the case was cracked and heavily oxidized. It got very hot even with very limited driving. It was probably the stop and go traffic on the couple days I did drive it to work that got it hot though.

I'll take a closer look at it when I get all the parts back and post pics of what I find.