Converting from TH400 to 700R4

[Jolly Green]

Hi guys. Trying to find a 700R4 to drop into my 68 442 with a 455. Got a TH400 right now. Will a 86 short shaft 700R4 out of a 4x4 Suburban work? Is a short shaft more desireable than a long shaft? Any differences? Gimme some advice fellas!

[J-(Chicago)]

You can't do that swap without changing your driveshaft yoke.
Th400 uses 32 splines and a 700r4 uses 27 or 30 depending on the year.

[88 coupe]

Originally Posted by Jolly Green

........ Will a 86 short shaft 700R4 out of a 4x4 Suburban work? ........

'85 and '86 are the strongest (and most desirable) of the, non computer, 700 series transmissions. You will need an adapter to make a Chev trans mate to Olds engines, as opposed to a 2004R which will bolt up to any BOP engine.

How long either might survive behind a 455, would depend on your driving habits.

Originally Posted by Jolly Green

........ Is a short shaft more desirable than a long shaft? ........

I am not aware of two different shaft lengths in the 700, although a different one might have been used with the "transfer case" in 4 wheel applications.

As stated above, you will need to make the driveshaft fit whatever trans you use.

I was considering a 4L80E (computer controlled 400 with a 4th gear added) because it is nearly as durable as the 400, and the ratios are close to ideal for use with high torque street engines.

Nixed it. for two reasons: Use of the computer would have violated my "no electronics" policy and, typically, my engines are "happiest" at higher RPM.

Norm

[Steve O]

The 4x4 trans wont work. There is no extension housing for it, the transfer case adapter takes it's place. The output shaft is too short to use with a 2WD extension housing and there is no provision for a speedo gear...

As far as I know the 2WD transmissions are all the same length...

You will need a BOP to Chevy adapter, 27 spline TH350 style slip yoke, TV cable and a bracket to mount it on the intake... You will also need a carb with a nipple on it to connect the cable. That nipple must have the right geometry or the trans wont shift right and it wont last long.

You also have to shorten the driveshaft and move the transmission cross member back...

After that's done you gotta wire up the lock up torque converter...

The best transmissions were the 85 and up, the earlier ones have a smaller input shaft and use the same converter as the TH200R4. They were used in Chevy 2WD trucks up to 93. The later the trans the better. The late trans has an electronic speed sensor where the speedo gear goes. That can be swapped out for a regular speedo gear...

A 200R4 will bolt right in without the adapter but you still need to swap slip yokes to 27 spline, TV cable, lock up converter ect...

Either way a stock one wont live long behind a big block and a lead foot...

They both can be built to take the abuse but it's not a cheap swap when it's all said and done...