Jennings

Greetings,

I am looking for opinions on a replacing a 2 speed auto trans in a 1965 Corvette coupe possibly with a TH350/TH400 or modern overdrive unit.

I understand the transmission tunnel is narrow on C2's and do not want to modify the tunnel for fitment.

Please help, what are my options?

Jen

Bluestripe67

Have you used the "search" function for this subject? Several posts on this. Dennis

Nowhere Man

a 200R4 is a popular choice. Like Dennis said check the archives

Black_Magic

350/400 fairly easy swap...overdrive transmission require MORE work.

Here is my 200-4R install in a '66 ===>> Click Here

George

SI67

I don't think TH400 is an option without modifying the tunnel.

Westlotorn

I would look hard at the 200R4 option as others have advised.
Same length as the powerglide so no new driveshaft needed.
Smaller case than all other 4 speed automatics
Well spaced gears with overdrive included
lighter tranny but can be built to hold up behind strong engines.
Never talked to anyone that did not love this swap.

The Turbo 350 would be second choice if cost is an issue.

emccomas

I concur, the 2004R is a great option.

Look specifically for the transmission from a Buick Grand National of a Monte Carlo SS, or get one built to those specifications.

3JsVette

As the others have already said. Why go through the expense and work of replacing the transmission and not end up with an overdrive?

GearheadJoe

I am quite certain that the TH350, 700R4, and 2004R will all fit in the C2 transmission tunnel with no clearance issues. This may also be true of the TH400, since some sources say that the 700R4 was based on the TH400. However, as has been noted in other posts, a properly built TH350 will hold up fine for up to 400 HP (maybe more). So, unless you are planning to run a monster engine, I think you can reasonably limit your options to the TH350, 700R4, and 2004R.

Hopefully a search of the archives will turn up several prior threads where these three transmissions have been compared. In general, I think there are several characteristics that need to be compared in order to determine which transmission is the best match for your preferences:

1) Is it a bolt-in installation, or does the rear frame mount require modification?
2) Does it require a shortened drive shaft?
3) Does it use a mechanical throttle position sensor or use computer control?
4) Does it have a lock-up torque converter?
5) How well do the gear ratios match your goals?

I won't attempt to provide a complete comparison here, but here are some examples:

* The TH350 and the 700R4 are bolt-in solutions, while the 2004R requires some modification of the frame for the rear mount.

* The TH350, and possibly the 2004R can use the stock driveshaft, while the 700R4 uses a shorter drive shaft

* The TH350 is a very simple installation, but it lacks the overdrive 4th gear. However, first gear in the TH350 is WAY lower than first gear in the Powerglide, so for any given rear axle ratio, you get much better standing-start launch with the TH350 than with a Powerglide. If you pair the TH350 with a 3.36 rear end, the highway rpm might be sufficiently low for your goals.

* The nice thing about the 700R4 and the 2004R is that the overdrive 4th gear lets you run, say, a 3.70 rear axle ratio and still have low highway rpm. And, this combination has a stronger launch than the TH350 combined with a 3.36 rear axle.

* The gear ratios of the 7004R are spaced differently than the gear ratios of the 2004R (especially for the 1-2 shift). Most people think the 2004R gear spacings are preferable to the 700R4 spacings.

I hope the above summary helps you get started with selecting the transmission that's the best match for your goals. Any of these three transmissions will be a big improvement over the Powerglide in terms of how responsive the car feels. Keep in mind that there are several companies that sell specially-built performance versions of each of these transmissions. And, some companies offer complete kits with all the required parts.