Greetings! I have the TH400 in the car, and measured the driveshaft. Turns out I had the wrong yoke, apparently from a 4x4 or something. Driveline guy gave me a yoke, remeasured in my car. I slip in the yoke, then push HARD to get it all the way in, and it springs out about 3/4" or slightly more. This is new to me (what isn't?) so I'd like to ask. Do all TH400 have this? Mine's a long tail shaft unit, maybe all longs do? What vehicles would this be from?

advTHANKSance

What do you mean it springs out?

If it only goes in until about 3/4" of smooth outside diameter is left, this is normal.

There are several different lengths of slip yoke.

BUT...
If you have a truck trans that originally had a bolt on yoke, you either have to change or machine the output shaft, or buy a special counterbored yoke.

Tom's Differentials, denny's Driveshafts, or TCi has these I believe.

this could be a non vented yoke,very common.if so you need to drill a 040 "hole in the area behind the splines to vent out the air

What happens if it's not drilled? It's not a new yoke, so if this is the case then the trapped air hasn't been a problem in the past...