OH NO! Is my TH400 about to bite the dust???

[Chevy3+3]

First of all my truck is an 88' Crew dually 4x4 with 134K. My tranny fluid is at the correct level.

About 3 weeks ago I noticed that 1st gear felt like it was slipping some when pulling a heavier load. It would eventually shift and 2nd would pull fine and 3rd would as well. The last few times I drove it I noticed that now I'm getting slippage in 1st gear without a load. My 2nd & 3rd gear are still great.

Should I be prepping myself for a tranny rebuild? Or could it be something else?

I just wasn't sure what the warning signs were for a TH400.

On to my next question......Simplicity would be to go back with a TH400 but overdrive is something that would be nice. What would be the easiest overdrive tranny to swap in and would mate to my np205 tcase. I know a 4l80E would be an option but I would need a stand alone controller I believe. Im not sure how to do any of that.

I've also considered rebuilding the TH400 and putting a gear vendor on instead of an overdrive tranny. Just not sure what to do

I would also consider swapping in a nv4500. I think I have access to all the clutch components in a junk truck.

[turbosix]

First thing I would do is drop the pan. That will tell u a lot. If there is a lot of clutch material in the bottom that's not good. I'm not that familiar with the 400, but if it's like the 350 1st and reverse use the same clutch pack.
If it's not too bad you might try using a tranny additive, they soften the seals to help them seal better. I've had some luck with them fixing some issues.

[mud.man.rj]

x2, may just need filter serviced, they do plug up after time.

[Chevy3+3]

Okay thanks guys. I figured if it was a filter issue then I would have problems in every gear. 1st gear is my only problem.

[imjeff]

Different gears require different pressures so it's a bit of a crap shoot trying to predict failure. If the fluid isn't burnt and you don't have stuff in the pan, it may just need a fluid/filter change. The only things that kill automatics are heat (kills fluid, too) and contaminants (you'll find in the filter). If you haven't serviced it in a while it may just be a little gummed up in the valve body. If your fluid and filter look good when you service it consider a shift kit.

[Chevy3+3]

Okay. I will yank the pan and see what's going on.

[Chevy3+3]

I tried something different. If I shift the truck into 1st gear and take off it doesn't slip at all. If I put the shifter in drive then 1st gear slips bad. Kinda weird.

[imjeff]

Originally Posted by Chevy3+3

I tried something different. If I shift the truck into 1st gear and take off it doesn't slip at all. If I put the shifter in drive then 1st gear slips bad. Kinda weird.

It's been a while since I've rebuilt one, but it sounds like something sticking in your valve body versus a clutch/steel problem. How long has the fluid been in there?

[Chevy3+3]

Originally Posted by imjeff

It's been a while since I've rebuilt one, but it sounds like something sticking in your valve body versus a clutch/steel problem. How long has the fluid been in there?

Its been a while. The fluid looks good and red on dipstick. Doesn't smell burnt. I'm gonna change fluid & filter to start with