TH400 question...

[CTX-SLPR]

Re: TH400 question...

I don't believe so. TH350, Powerglide, and TH200-4R are the same length, the TH400 short tail is another length, and the TH700R4 is even longer but still shorter than a TH400 long tail.

[squirrel]

Re: TH400 question...

The short tailshaft TH350 and TH400 transmissions are very close to the same length, within an inch I think. The yokes are different though...sometimes you have to play with the driveshaft length if it's tight already.

see for yourself..the 400 is a skosh longer

[70.5CAMARO]

Re: TH400 question...

the yoke isnt an issue, and i think that less than an inch wont be either

[IndyShiftman]

Re: TH400 question...

Some 400's use a "O" ring on the output shaft. If you use a 400 yoke that wasn't made for the "O" ring, the yoke will bottom out on the "O" ring land on the output shaft. Making it appear that the drive shaft is too long. If you force it to fit, it will beat the crap out of the inside of the transmission.

Some people will then cut a section off the end of the yoke so the shaft will install. But what happens is, the yoke isn't supported as well in the rear bushing in the extention housing. this can cause vibrations and severe damage. I have seen it happen.

Bottom line is, make sure you know if the output shaft uses a "O" ring or not by removing the extension housing. If it has the O ring land, then find a yoke that was made for the O ring. The yoke will not have splines on the very end so it will slide over the O ring.

How I measure for drive shaft length is, slide the yoke all the way in the trans till it bottoms out. Then pull it back out about a inch. Then measure from the center of the u-joint cap location on the yoke, to the center of the u-joint cap location on the pinion flange. That will tell you what your drive shaft length needs to be. If you have someone shorten the shaft, be sure you tell them how you got the measurement.

[CTX-SLPR]

Re: TH400 question...

How would you suggest measuring a new driveshaft length for an application where you have a 2 piece drive shaft on a carrier bearing enclosed in an X-frame tunnel? I had to move my TH400 about 3.5in forward with the new engine, so I need a new forward driveshaft. I was thinking that if I measure the distance between the stock yoke and the end of the output shaft I could calculate how much longer of a shaft I needed.

[squirrel]

Re: TH400 question...

Still you'd be better off doing it just like IndyShiftman says...at least as a double-check.

Also on the TH400 o ring deal...yokes that are designed to work with the O ring usually have a hole in the plug in the end. The O ring seals the transmission fluid from entering the splines, so you have to grease the splines, and the hole vents the air that is trapped in the yoke. It's pretty common to not have the O ring in place and get a nice big leak out that hole.

[70.5CAMARO]

Re: TH400 question...

is the o-ring issue, related to year range? the trans i have is a original 69 out of my old chevelle, found out we changed the output shaft and houseing to fit the truck its currently in. I now have the chore of looking through every box bin and dusty area to see if i can locate the origonal.

[Robert1320]

Re: TH400 question...

Transmission Overall Length Rear Trans Mount Position
TH-350 27" 19.5"
TH-400 28" 26.25"
TH-200-4R 27" 26"
TH-700-R4 30" 21.25"

[70.5CAMARO]

Re: TH400 question...

ok I just tonight ripped out the big block and trans now this looks like a short shaft 400 to me but it tlooks like it has the wrong yoke. its a bolt style truck yoke that has a bolt going into the output shaft.

[Robert1320]

Re: TH400 question...

Take the bolt out....

[70.5CAMARO]

Re: TH400 question...

lol ok, that was a givin, I just didnt feel like it tonight

[IndyShiftman]

Re: TH400 question...

It is a short tail. You can still use a regular slip yoke with that output shaft.

[70.5CAMARO]

Re: TH400 question...

thats what i was wondering, thank you

[Robert1320]

Re: TH400 question...

Like I siad take the bolt out........ lol

[70.5CAMARO]

Re: TH400 question...

well i didnt know that you could just take the bolt out and put a slip on in place of it. thinkin, you know common sence that if a bolt is there a bolt goes there.