1970 Chevelle TH400 to TH700r4... easy?
Thread Starter
Staging Lane
Joined: Aug 2004
Posts: 55
Likes: 0
From: Flint, Michigan (Yeah, the little "F" you might find on your VIN)
1970 Chevelle TH400 to TH700r4... easy? 
So I've spent a few years playing with my Chevelle and it's TH400... it's alright, but obviously I lose a lot of gas mileage if I just want to cruise around... I picked up a 700r4 about two years ago, but haven't gotten around to installing it. I've looked around for conversion kits and found bowtieoverdrives.com has the kits to convert the shifters from the 3 to the 4 speed, and they have the crossmember, as well. My question is... how easy of a project is this going to be? Few weeks? Months? Also, what else am I going to need? From what I understand, I'm going to have to get my driveshaft chopped slightly, so I'm prepared for that as well...
With not a lot of experience in this area, should I take this to a shop and have it done, or is it worth the satisfaction of doing it yourself? I'd rather do it myself, but I'd also rather it be done right... I suppose the question is... what has to be done to do it right?
Thanks in advance, guys.
-Dave Foster
You will need a way to make the torque convertor lock. There are two ways to do it. You can have a good shop fix the transmission so that the lockup is hydraulic, meaning it will always lock up shortly after going into overdrive with no wiring needed at all. The other way is to get an aftermarket lockup kit. I have used two different types and the speed controlled type seems to be the best. They are a little more expensive than vacuum controlled units but never "hunt" for lockup like the vacuum setups sometimes do. Overdrive is the only way to go if you enjoy cruising in the car.
I think a 4L80E and a TCI controller box is what you
want for a big block. What size hammer do plan to
pound that skinny little transmission with?
For lockup on the 700R4 let me throw a concept at
you; I used to have a ST400 switch-pitch converter
(Buick) and for this they had a long slider switch
hung off the throttle cable that put it into high stall
at idle, low stall at low-mid throttle and high again at
WOT. You could rig something similar with a couple
of microswitches at the gas pedal. Latching relay
logic with a brake light cut-out if you wanted to
get even more sophisticated. I bet there are cheap
boxes that do this on the aftermarket already though.
Maybe even with some sort of RPM sense.
Might check the Conversions subforum for more ideas
on this kind of thing.
want for a big block. What size hammer do plan to
pound that skinny little transmission with?
For lockup on the 700R4 let me throw a concept at
you; I used to have a ST400 switch-pitch converter
(Buick) and for this they had a long slider switch
hung off the throttle cable that put it into high stall
at idle, low stall at low-mid throttle and high again at
WOT. You could rig something similar with a couple
of microswitches at the gas pedal. Latching relay
logic with a brake light cut-out if you wanted to
get even more sophisticated. I bet there are cheap
boxes that do this on the aftermarket already though.
Maybe even with some sort of RPM sense.
Might check the Conversions subforum for more ideas
on this kind of thing.
Thread Starter
Staging Lane
Joined: Aug 2004
Posts: 55
Likes: 0
From: Flint, Michigan (Yeah, the little "F" you might find on your VIN)
Thanks for the suggestions guys...
I dig the idea of the hydraulic lockup... I'll have to find a good transmission shop around here somewheres and see what they can do for me.
Also, the car isn't a big-block car... it's currently a 350 built to 1970 Corvette LT1 specs... but I'm planning on going LS2 / 6-Speed when I finish up the interior... I recall seeing a 70 SS in the GM tent at the Indy 500 time-trials a few years back that had the new LS6 and the intake was rigged up to ductwork under the hood to keep the flapper hood functional, which was pretty freakin' sweet... so I'll probably try to do something along those lines.
Anyways, thanks for taking the time to toss out some knowledge, guys!
I dig the idea of the hydraulic lockup... I'll have to find a good transmission shop around here somewheres and see what they can do for me.
Also, the car isn't a big-block car... it's currently a 350 built to 1970 Corvette LT1 specs... but I'm planning on going LS2 / 6-Speed when I finish up the interior... I recall seeing a 70 SS in the GM tent at the Indy 500 time-trials a few years back that had the new LS6 and the intake was rigged up to ductwork under the hood to keep the flapper hood functional, which was pretty freakin' sweet... so I'll probably try to do something along those lines.
Anyways, thanks for taking the time to toss out some knowledge, guys!
