Driveshaft shortening...help

[72LoBurb]

I'm in the midst of swapping a 700r4 into my '72, but after removing the TH350 (short tailshaft) I have found the driveshaft will have to be shortened. My question is how much will it have to be shortened?
From what I can tell it will need to be shortened 2-2.5 inches, but I was hoping someone here has done this and can enlighten me.

The PO said he had a 700 in the 'burb for a short time without shortening the shaft (probably the reason for it being in a short time,LOL), but after seeing the difference in the length of the trannies I have a hard time believing it.

[5150]

There is no way he could have had the 700 in without shortening the driveshaft. Now he might have had another already shortened driveshaft, but not that one. I had mine shortened 3 inches and the yoke could go in a little farther if needed, but I made a 650 mile round trip to Maggie Valley in it at the beginning of May and it gave me no problems.

[72LoBurb]

Thanks for the reply yellow69.
Another question that I have is about the wiring for the lock-up converter. My 700 is out of my old '90 burb and has a plug with 3 wires coming out of it, and I understand that I have to wire in a switch for the lock-up. Any ideas on how this is done? Or is there other ways or having the lock-up operable?

[Long Roof]

Check Summit or Jegs, they sell a small stand alone controller for the tranny lockup.

Aaron

[N2TRUX]

Check this site- http://bowtieoverdrives.com/index.shtml. They have TONS of info on the 700r4.

[72LoBurb]

Thanks for the replies guys, I ended up using the Painless Wiring kit, getting the driveshaft shortened 3 inches, and doing it's first trip in it's new configuration...all went better than expected.
I also had replaced the cast GM 4bbl manifold and worn out Q-et with an Edelbrock Performer EPS and 600cfm carb.

With these changes the same cruise last year used 3 tanks of fuel; this year was under a 1 and 1/2. A rough guesstimate would be 16-17 mpg(imperial gal) without any major tuning on the carb.
Overall it's maiden voyage was around 540 km round trip, doing 105-110km/h,with a couple of 140+ km/h bursts, and I'm quite pleased.

A big thanks to all the members(alot of old posts inspired the work), but it's far from being completely done...

[5150]

Glad to help!

Have fun with it. I do mine. One more tip on the gas mpg thing. Get you an electric fan and that will help also. I haven't done it yet but I'm going to.