I’d like to upgrade the transmission on my ‘71 350 Automatic. There are times when I need to hit the highway and three gears forces me to cruise at 3000rpm while only hitting 65-70mph tops.

Where would I even begin to look for a compatible transmission? Anyone else have experience with this upgrade? Looking for at least a 4-speed automatic, possibly may go 5-speed automatic if it can be done.

She’s not matching numbers so I’m looking to make her as comfortable to drive regularly as possible.

Thanks in advance!

 

700R4 is your answer and was used on the late C3s so parts are available.

 

Here’s another option

 

You will never regret adding a third pedal. Silver State Transmission sells complete kits.

 

Im going with a 2004r myself since its the same length as the original th400 in my 74.. Also swapping the rear gears from 3.08 to 3.55 so I can have a better first gear and more usable overdrive ratio. the 700r4 has a lower first gear so you wouldnt need to do the rear end but you need to shorten the driveshaft and a possible custom crossmember setup.

 

Also consider the 4L60(non-electric)......4 speeds with no need to purchase an aftermarket transmission computer to make the trans shift coŕectly. Some mods will have to be made.

 

I did the 200-4r swap in my 76 because of the direct swap from TH350.I also have an 84 w/the 700r-4 and prefer the tighter 2-3 200-4r gear spacing.

 

..........

 

I am in the middle of installing a 200-4R right now. Just doing it for entertainment. I have 4.11s. I removed the Richmond 6-speed(ROD) with 0.62 overdrive.
The 200-4R supposedly has 0.67 overdrive so that will be about the same, highway wise, as the ROD. Overdrive is wonderful.

 

I looked into the 200R4 and 700R4/4L60 for my 1980 L82 , 1980 Corvettes are already set up for lock up converter from the Turbo350C transmission so easy switch for either transmission choices
As a person that has a lot transmission experience and well aware of the short comings of the 200R4 my quest for the 200R4 ended when my transmission suppliers had ZERO parts or cores available for the 200R4 which to me meant Art Car 200R4 and I just didn't want to drop that kind of money on a driver , otherwise the 200R4 is a direct bolt in from a T350 minus the TV Cable and the easiest to swap of the two do to the shortening the drive shaft and possible cross member issue with the 700/4L60
Now onto the 700R4 4L60 which I had two cores available for me to build one so I choose this route . Now the transmission itself is 3 inches longer than the T350 and will require the drive shaft to be shortened by 3 inches , the Transmission mount however is only roughly 1.5 inches further but I still went with the G Force cross member because it opens up different exhaust system options such as the 1974 style duals verses the Y pipe style of the original system on my car but the original cross member also looks like it has room to be drilled for the 700R4 mount but I never looked at it that hard and your 71 is different than my 80 so hard for me to say there

TV cables need set up on both transmissions as they control the transmission Line/pump pressure , on mine I'm still using the Turbo350's kickdown cable hook up on the carb with a adjustable TV cable and have it set to where it shifts fine and I don't see anymore need to change anything , shifter detent will need modified for either transmission to be able to shift manually into low 1

 

I used a 700R4 in my car with a lock up style converter...
it worked great and was a vast improvement over the stock 400 turbo.
mardyn

 

here's a post i made back in 2015 when i swapped out my TH400 for the 700R4 in my '72,
covers all the things / problems not usually mentioned, or the "Fiddly Bits"
covered things like the drive shaft shortening, x member mount, lock-up connections etc

 

where is the richmond going?

 

Haven't decided......

 

 

Zip Corvette did a 6 speed auto swap in their 76 Vette. I beleive the kit is in their catalog. You might try giving them a call and talk to them about it. That being said, I cruise my 79 down the highway at 3500 to 4000 rpm for hours on end each year on the way to and from Carlisle, and dont worry about it. Mine's a 4 speed, but yes, I'd love to have a tremec 5 speed conversion though

 

how long is the line to buy the richmond setup you are pulling out?

 

Thank you for the mention!

Our A41 package is based on the GM 4L60E (4L65E on Stage III) and comes as a complete kit. The Compushift controller allows for a Bluetooth connection to your smartphone where you will make your tuning adjustments via their app. It's pretty slick!

TREMEC TKX, TREMEC Magnum, & SST A41 Conversion Kits for 1968-1982 Corvette C3 (shiftsst.com)

This conversion will drop your cruising rpms by 30% making for a nice highway cruise and they start at $4,199.00 + shipping. As an added bonus, the 3.06 first gear will provide some extra snap off the line compared to a 2.52 low gear (TH350) or a 2.48 low gear (TH400).