mazdaverx7

I'm considering swapping a 4+3 trans into my 84 and replacing the 700R4. I know mechanically what needs to be done as I have assisted in converting a couple early track only C4's to a 4+3 and bypassing the overdrive unit all together. However, this one is my personal 84 and my question is what wiring needs to be done, converted or added and does the swap require an ecu from a 4+3 car? I want the trans and the overdrive unit to function as intended.

HlhnEast

With all the better trannys out there, why would you consider the 4+3? When my OD unit tanks I am definitely not going back with the 4+3. This being said, I have had zero problem with my Doug Nash, but the cost of rebuild is about equal to an upgrade to a six speed or a T350/700/4L60.

If you have an auto now, yes, you will have to get a 4+3 ECM and associated wiring, pedal assembly, console, etc.

Good luck with it no matter which way you go!

vetteoz

Depends what you want;
many 4+3 owners have installed a switch to give full manual control of the O/d unit completely bypassing the ECM control ;
in which case you only need a relay, some wire and a switch instead of swapping in a whole manual harness

If you went with factory wiring /relay , would only need the 84 manual memcal installed in your ECM

mazdaverx7

The reason I want the 4+3 is that its available to me for free from a friend. I like odd 80's techno stuff and the DN trans is what was in my very first Vette. I would simply buy another 84 with the 4+3 if I were able to find one at a reasonable cost. I already have the 84 and some of the parts to do the swap..my auto trans is acting up and the only reason that I got an auto Vette was the price and my love for restoring cars that are in need. I do realize that there are better manual transmisions available but cost is a concern to me as some of the transmissions cost more than what I paid for my 84.

I think the best approach is to install the original switch and console plate but bypass the ECM control of the OD unit and use the switch as an on or off function. When I had my first 84, which was an original 4+3, I drove it like a regular 4spd and when I wanted a lower rpm in 4th, say for highway cruising or speeds over 45mph, I would push in the clutch, switch on the OD and release the clutch and it was as if I had a "5th" gear. Perfect for how I like to drive.

c4cruiser

You may want to check the tunnel under the console to make sure you can install the shifter. The 4+3 shifter bolts to the tunnel not the trans, and there is a pocket formed there for it. Turns out there's a shifter for sale in the C4 Parts For Sale section!

Finding the clutch pedal assembly and installing it can be a whole project in itself. The bellhousing, clutch setup with flywheel, throwout bearing and the fork should be easy to find. The clutch master and slave should be available as will be the hydraulic line.

mazdaverx7

The floor that houses the auto trans shifter assembly needs to be cut out and a new floor section from a manual trans 84 or later 4+3 car needs grafted in to allow the manual shifter to be bolted in place and for the shift rods to make contact with the shifter itself. This I feel will be the hardest part to acquire. I agree that the clutch and brake pedal assembly may also be a challange to find. I have the trans, bellhousing, and flywheel. I will purchase the hydraulic components as well as a driveshaft, shifter, floor section, clutch kit, and wiring to bypass the ECM.

vetteoz

You don' need a drive shaft unless you are also doing a diff swap

How are your engineering skills?
This is what a member on another forum did to mount the shifter in his auto - 4+3 swap
Shown mocked up ; the C-Beam bolts hold the plate in place when installed

mazdaverx7

My engineering skills are good. That's something that I can make and if possible attempt to improve on. Do you have a link to the thread where person made the brace?

mazdaverx7

Another question that I thought of.. Does the harmonic balancer need replaced when swapping over to a 4+3? For some reason I was thinking that they maybe different from the auto to manual trans.

WVZR-1

Balancer does NOT require change.

mazdaverx7

That's good news!