Need Help Transmission Swap

[Howell1988]

So I have a 1968 3/4 ton Custom Camper GMC with a 350 small block rebuilt and a turbo 400. Problem is Turbo won't shift into drive or at least I'm pretty dang sure its staying in second when it does shift up and also is now slipping when going into second it jumps back down. I need some professional advice from you guys on what to put in it that will be the least modification. I have a guy with a 700R4 who just pulled it earlier this month with less than 100,000 miles for 350.00 but I'm thinking even after changing the yoke on the driveshaft (also being a two piece)it may not be the right length. Haven't looked at it yet but was hoping someone may have done this swap before and have some advice. Thanks all.

[LockDoc]

Originally Posted by Howell1988

So I have a 1968 3/4 ton Custom Camper GMC with a 350 small block rebuilt and a turbo 400. Problem is Turbo won't shift into drive or at least I'm pretty dang sure its staying in second when it does shift up and also is now slipping when going into second it jumps back down. I need some professional advice from you guys on what to put in it that will be the least modification. I have a guy with a 700R4 who just pulled it earlier this month with less than 100,000 miles for 350.00 but I'm thinking even after changing the yoke on the driveshaft (also being a two piece)it may not be the right length. Haven't looked at it yet but was hoping someone may have done this swap before and have some advice. Thanks all.

I don't know how much this will help you but it's a start,,,,,

LockDoc

[Howell1988]

Originally Posted by LockDoc

I don't know how much this will help you but it's a start,,,,,

LockDoc

Hey that is a cool diagram thank you

[Sheepdip]

Yes you will have to shorten your driveline, if it doesn't already have a after market converter lock up kit it will need one, that's roughly $200, that's assuming it comes with the lockup converter. And if no throttle position cable (TPC) you'll need that too, roughly $40. It will also be very important that the TPC is properly adjusted or you will burn that tranny up real quick. with 100,000 mi on it.... it would be even quicker to burn up.

[kwmech]

Personally I wouldn't go backwards on strength and reliability. With what you'll end up spending converting and swapping everything, plus the hassle getting the TV cable correct so it doesn't burn up you could have the 400 rebuilt and not worry about the trans for another 20 years

[MARKDTN]

Originally Posted by kwmech

Personally I wouldn't go backwards on strength and reliability. With what you'll end up spending converting and swapping everything, plus the hassle getting the TV cable correct so it doesn't burn up you could have the 400 rebuilt and not worry about the trans for another 20 years

If you are not worried about rpms/mileage then a TH400 is the way to stay. Get it rebuilt and it will probably last a lifetime. No mods needed.

You might change the fluid and make sure the modulator is working and getting vacuum first.

I love a 700R4, but you do need shorter driveshaft, different yoke, and TV cable bracket at the carb at a minimum to swap. I think $350 is high for a 100k mile transmission. I would call that more of a core.

And just for the record, I would do a 700R4 long before a 200R4 especially in a truck.

[Howell1988]

Wierd. Drive to work this morning never missed a beat right at 2800 rpm shifted and never missed a shift now I never get over 45 and so not sure about the going into drive but I'll say it never even at 55 has seemed to even feel or sound like it goes into drive. A rebuild is sounding like the best plan and thank you all for the advice once again.

[BigBird05]

Turbo 400 was the best trans that GM ever made. Just rebuild it.