Want to upgrade TH350 to 700R4 in a 79'

[thedoctorisin]

I've got a TH350 in my cutlass... not computer controlled.

what would I have to get to parts wise to get a 700R4 working properly in there? I'm not quite sure the difference between lock-up converters and non-lock-up, I'm just pretty sure I'll need some sort trigger switch so it would know when I was getting off and on the freeway?

if there are any threads out there about this very thing point me in that direction but I hadn't found exactly what i was looking for yet.

 

[othtim]

Lock-up converter just means that at a certain point the converter will mechanically clamp together. That way you don't lose power from slippage in the torque converter. Saves fuel economy. Personally I don't like lockup converters in the TH-250s because I haven't had much luck with them (the th-250 I had would randomly engage). The 4l60 lockups seem to be much better.

The 700r4 is longer than a TH350. So you'll need a shorter driveshaft. Unless you have a th350 with a long nose.
The Th350 has a mechanical speedo. The 700r4 can have a mechanical OR electronic speedo. You need to check your donor 700r4 and see what type it has.
You may need to move the crossmember back.
You'll need a 700r4 torque converter, and a lockup switch (i dont know what is involved with this since I dont have lockup)
Your oil cooler lines won't be long enough
Plus the 7004r is bigger. You might have to hammer out the trans tunnel a bit. I'm not sure. I've only done this swap on a pickup truck! Didn't have to hammer anything out 🙂

A shift kit will make it feel better - factory shift points are strange, imo. 1st is too short, second is too long. Get a shift kit to help with that.

Check out this site:http://www.700r4.com/faq/faq.shtml
Everything you need to know is on that site! Great resource.

 

[patmckinneyracing]

Here are all the threads I started and went through to do the research on the swap:

viewtopic.php?f=14&t=16626

viewtopic.php?f=14&t=17362

viewtopic.php?f=14&t=17607

viewtopic.php?f=14&t=18656

 

[JBreu]

I recently went with a 700-r4 in my baby.........no mods were needed to the transmission hump. You will need to get your driveshaft shortened 3" assuming you have a 7.5 rear.........49.5" from center of U joint to center of u joint...As for me I went with the non lock up converter, lock up only saves you about 300 rpm's or so....Just get a decent transmission cooler and you'll be fine....You migt as well get a new crossmember as well from Iceman racing and you will be good to go.You will LOVE the O/D 4th gear!!!

 

[thedoctorisin]

Thanks for the info everyone, I just wanted to start the ball rolling for my next project and this will work out great. My LT1 swap is in its final stages and the TH350 can barely keep on the freeway. I just feel I'm losing power across the board by only having 3 speeds and the whole point with the LT1 was to get major power gains... not that I didn't get it, I just want more hahaha.

But yeah its a 7.5... Posi at least, short tail shaft, and stock crossmember... I can do dual exhaust at least at the same time as the transmission.

 

[patmckinneyracing]

I have yet to try out my 700r4 since my car is getting a lot of mods done and another overhaul. I kept mine a lockup because I heard that these transmissions almost require a lockup in fourth gear to prevent overheating. I'm putting in a heavy duty trans cooler as well just for safety sake. IMO all OD transmissions need a transmission cool. I can't wait to try out first gear with my 3.73's in the back. Should definately launch real good...I hope lol.