Upgrading the 3 speed automatic transmission

Has anyone replaced their 3 speed automatic transmission with a 4 or 5 speed automatic? If so what was the new trans and what was involved in the upgrade? I saw a listing for one car that claimed to have been upgraded to a GM 4 speed automatic. I used to own a 412A but did not like the transmission and would consider buying one again if I could replace the transmission with something more modern with more gears.

 

The easiest swap would be with a 700R4. It is a 4 speed O/D with a possibility of lock up torque. Many C3 Corvette have been done. I have plans to do it on both of mine, vette and 400i. The first gear has a better ratio for off the hole performance and you can also use a higher stall torque to better match the engine hp and torque rpm.

Look here http://www.proformancepowertrain.com/index.htm

 

Great resource

 

I don't the think a transmission swap has ever been done in one of these cars. There is a torque tube connecting the rear of the transmission to the front of the engine. If you look at the engine mounts there are just two, same with the rear diff. The torque tube keeps the engine and diff from rocking back and forth. Since there is a torque tube attached to the transmission there is a special tail shaft on the transmission. I'm not saying the swap hasn't been done or can't be done. It's just much more complicated then bolting in a new transmission and having a shop make a new drive shaft (our drive shaft is a metal rod with no universal joints on the end). A transmission swap would be a great mod but it's going to be a challenge.

 

I was involved in a plan on doing a swap to a 700R4. Very doable including fabricating the provision for the torque tube. To take advantage of the swap and get any real life performance improvement meant changing the differential gearing. A 5 speed ring and pinion was prohibitively expensive at the time and there was very few and no inexpensive alternatives to that problem back then. That expense is what killed the project.

 

I looked into it as well... Ended up redoing mine because there hasn't been a definitive swap that others can follow in with theirs. I recall the issue with the mounts, the diff, as well as the new drive shaft - quite a bit of engineering with some guesstimation, luck, time, etc!

 

Some calculation for fun. To compare. Using stock 240/55R415 TRX like my car.

The TRX if I'm right should have around 755 rev per miles.

Final drive is 3.4167, so the engine is reving 2580 per miles. At 60 mph it's 2580 RPM.

The 700R4 has a 4th(OD) gear ratio of 0.70 so the RPM at 60 mph should be around 1800 RPM. Which is low but common with most cars today.

You can always stay on 3rd if you want more RPM as it is 1:1 like the TH400 on 3rd.
You also have the possibility of locking up the torque and save some RPM on 3rd.
But in the swap if you replace the torque with a higher stall and don't use the lock-up you will have a higher RPM than 1800. Which will help.

Another big improvement is the 3.06 1st gear ratio of the 700R4 that will put the engine in a much better RPM range for him, if you add this to a high stall torque you just woke up the car a lot I think.

Brian what do you think?

 

The 4th gear ratio is exactly why we wanted a different ring and pinion. At 1800 rpm it will need to down shift just to go over an overpass and as a practical matter you will never need the cruising speed that will give you and it just does not have the HP to drive that big a gear. With a higher stall speed and shorter rear gears it would wake the car up and that really is the object of the entire exercise.

As far as the torque tube, that's easy. I do not recall the AOL of the 2 transmissions but lengthening or shortening a torque tube is easy. The TH400 tail shaft housing can be cut and grafted on the 700R4. Any difference in drive shaft length can be handled by fabricating a different length of sleeve coupling and or shortening the shaft.

 

What would the cost be of a set of gears made from scratch?

 

From what I know from the Testarossa, Newman can get new set made around $5000 cdn if I'm right.

 

Gears have actually become less costly to make. Back when we were working on this it was much more expensive. Seems to me it was around 12 or 13k and that was a lot of money in the early 90's.

 

Over the years there has been lots of talk but I've never been able to confirm an actual swap taking place.

 

I have never seen it done but historically because of the value of the cars people couldn't bring themselves to do an expensive experiment. The cars are getting to be worth more and oddly enough the price of the experiment has become easier to stomach.

They were a great car with a terrible mismatch of transmission. I'd like to see someone do it.

 

I can't remember where but I saw a car for sale that had it done. I'll try to find the ad on the web.

 

Didn't the silver twin turbo 400i have a 4-speed ?

 

Yes Arvid! Found it right away. It is the car for sale by IAG (foxyroxygirl). It has a twin turbo and also a overdrive automatic. No more info but this one has been modified.

The text in BAT talk about it. Under-Hyped: Twin Turbo 1984 Ferrari 400i | Bring a Trailer

 

Car was in Costa Mesa. That is near Rod Drew and FAI. I'd ask if he knew the car. He might have been involved.

 

Great, thanks Brian.

 

I remember coming across an advert on a 400i (I believe) that was hooked up to a Tremec 6-speed in the past year but didn't save any of the info.

 

Too bad it's the regular 400i set

Ferrari 400 GT Gearbox Crown Wheel and Pinion Set 117244 | eBay

 

Listing is somewhat confusing…the listing header states 400 GT Gearbox (which is the gears Brian was talking about using with an upgraded automatic) whereas in the description, it states 400 GTi / 400i Auto
When someone mentions 'gearbox', I generally think Manual (10/43 gears), not Automatic/slush box (12/41 gears).

The question is...which one is it

 

I counted the crown and came very close to 40 not 43 for sure. Also you see about half the pinion and my guess is 6 you can count so............

 

...it's from an Automatic car unfortunately

 

Dont know if this helps but there are 3 ratios available

DIFFERENTIAL AND AXEL SHAFTS - Ricambi America, Inc.

And for what its worth after going through the process of having gears made I learned that you want a minimum of 12 pinion teeth to get reliability - the gear shop educated me. Has to do with the amount of contact area with the crown gear teeth preventing them from breaking off which seems to be more of a problem in the 365 boxer until they numerically lowered the ratio finally ending up with the 3.21:1 in the BB512.

 

Has anyone attempted this again?

Do you have any drawings for the fabrication work needed to swap the 700R4?



Sent from my MAR-LX1M using Tapatalk