Hello guys,

I recently drove a 70’ with the M20 box and after that my 71’ with the 3spd auto hasn’t felt the same. I’ve been putting together a parts list and guide for swapping my th400 for an M20.

I was considering just swapping the whole car but since mine has 48k original miles and good bones I’d rather keep it but who knows. It’s only a base model convertible so I’m not too worried abt losing the originality plus that won’t even cross my mind with a 3rd pedal and a 4 speed.

Looks like a pretty straightforward process I just need to make sure I have all the parts so I can hammer it all out in one weekend. If anyone has done this in the past and can help me out or has seen other threads on here with all the details feel free to share.

Engine will be resealed while we’re at it. Engine looks brand new internally per bore scope and has plenty of power but if anyone recommends some other bolt ons that would be great. I want to keep the qjet as I spent a lot of money to source one with a matching serial number for the car. I’ve got the base 270hp with 2 bolt mains so there’s a power cap.

I don’t plan on keeping the original transmission so if anyone wants a perfect TH400 I’d be more than happy to arrange a sale or trade for an M20.

I’m looking for a parts car to pull everything out together. If anyone has parts collecting dust I’ll gladly take them off your hands. I do everything myself so as long as the parts don’t look like they’ve been sitting at the bottom of the ocean I can handle the work.

thank you guys!

 

Gabriel Vianna
My 2 cents:
If you're going Manual then find a Tranny with Overdrive. A 5 or 6 speed. Might as well if you're going to all that trouble.

 

Gabriel, what is your cars differential ratio? Will it work with the M20 ratios?

My original intent was a 5 speed swap, then it became obvious that I needed to spend time and money on the engine as well, I cheaped out and found a used wide ratio Saginaw 4 speed that luckily matched my differential ratio. I bought a new flywheel, bellhousing and clutch. I found used clutch linkage, pedal assembly and console shift plate on the classifieds here. You may consider posting a WTB ad here and start shopping Ebay.

It may be more than a weekend project, I took my time and with the engine swap it was 3 or 4 months over the winter.
Remove the transmission, console, steering column, gauge cluster, pedal assembly.
Install new pedal assembly, flywheel/clutch/bellhousing and clutch linkage, so you can determine where to weld the clutch cross shaft bracket on the frame.
Then install the transmission and build a mount to the cross member and have the drive shaft modified.
I got lucky, the mount and drive shaft from the TH350 fit the Saginaw.

It's worth it, the car is completely different to drive. Some of that may be a bit more HP out of the engine I installed at the same time.

 

it'll be original only once !
If ya keep it long enough, your age may grow to appreciate the AT.

 

I wish I could help with parts, as I fully support manual-swapping all C3s. But I'm already hoarding parts to do this to my 82.

If you can't source a pedal set, Silver Sport Transmission does sell new pedals. shiftsst.com

Good luck! Your car will be a million times more fun to drive after the conversion (as you've already discovered).

 

Here's a Facebook listing with pedals. Finely curated, and elegantly displayed on gravel. I have no connection to the seller.

https://www.facebook.com/commerce/li...0100537555602/

 

I don't care about originality but I understand folks wanting manuals.
I had a muncie m21 with my 4:11s...that sucked. So I went to a Richmond 6-speed with 0.62 overdrive. It was wonderful but I got tired of dealing with hills, and shifting, and stoplights so I went to a .67 overdrive 200-4R. I'm liking having an automatic.