TH400 rebuild?

[Jcode]

This is the first truck I've ever had with a TH400. I've lost count how many vehicles I've had with a TH350 or TH700r4. Should the shifts in a 400 feel similar to a 350 or 700? I expected to be able to at least "feel" it shift. I don't feel anything. It's like it slips into gear (the only way I know it shifts is lower engine rpm's). Also, it seems like it goes from 1st to 3rd. Is it time for a rebuild? I plan to tow with the truck and this tranny has me concerned. Supposedly the tranny has low miles, but the previous owner towed ~10K lbs (and bragged about how hard he pushed the truck) on occasions with no external tranny cooler. Appreciate the help.

[Robyn]

The 400 in stock trim will shift fairly easy.

Now if the vacuum control valve on the Injector pump is not adjusted correctly the shifts can be very soft.

Yank the tranny pan and see whats in there ??? If the oil is pink and there is not any crap from fried clutches then the box is probably ok.

Try doing the shifting manually and checking to see if the thing is actually shifting from 1-2-3.

If it is shifting bu is a little soft, try adjusting the vacuum valve clockwise a little bit as you look at it from the RH side of the rig.
The valve is a little plastic device that bolts to the RH side of the injector pump.
This valve is held on with two (2) little bolts and just loosening them a little and rotating the valve CW about 1/16" and then give a try.

The shift from 1-2 is not a neck breaker and neither is the 2-3 but it should be noticeable.

If the oil smells burnt or the pan has flakes of clutch lining then its time to do a rebuild.

A 400 is an easy box to rebuild. Very straight forward and requires only a few special tools (That can be improvised)

Good luck

Robyn

[Jcode]

Great info! Thanks for the reply. Planning to drop the pan and change the fluid soon, will check for shavings/debris in the pan. If I don't find anything, will make an adjustment to the IP.