Hello C3 forum! I am new to C3's but not vettes. I have a C4 vert, 6 speed. I will soon be getting an 81 from the estate of a long time friend who passed recently. It is an automatic. I want to convert it to a manual!

A friend of my Dad has a fresh 1970 Muncie M22 rock crusher in his 72 Chevelle with a Hurst Comp shifter that he will give me if I swap back in his original automatic for him.

I have read a lot of threads about various swaps, but could not find a definitive answer. What would it take to swap this transmission into the 81? From what I have read, I guess that I will likely need to change rear end gears to maybe 3.73 or 4.11's for one thing.

The situation is the car has been sitting for probably 15 years, so it will need a lot of work ($$$) just to get it back on the road again, so budget is a concern with a transmission swap!!!

Thanks!
-Rick

 

are you certain its an 81? It says L82 by the photo which wasn't an option in 81... might be an 80? or badges just added to an 81

 

Good eye! GM didn't make any 1980 L82 4-speed cars at all, so this will be special once you are done.

The cross-flag emblems had chrome trim in 1980, and black trim in 1981. Check the VIN! There's a decoder here:
https://corvettec3.ca/vin.htm

Do you have a plan for adding the clutch pedal? Working under the dash is likely the most difficult part of this swap. If you decide you need new gears, consider a hybrid rear axle, using the 79 and earlier iron diff, with your aluminum batwing. The Dana rear end that came on 80-82 cars is a known weak point, and cars that came with automatics originally had the even weaker version of that. You may have to shorten the driveshaft for diff swap.

But by all means get the 4-speed in there!

 

Yes, I am sure it is an 81. My buddy's Dad bought it new. He blew up the original L81 many, many years ago before passing the car on to my buddy! It was replaced with an earlier L82 and the shop who did that added the badges.

 

Yes, I read that the pedals will be a PIA. I would guess I'd take the steering column out to give me some room. As for the rear end. That aluminum Dana 44 went on in the stick C4's. I understanding the aluminum is a weak point, but this car will just be a cruiser. I have my race car for power! If anything I will put a mild cam. If the C3 Dana 44 is close to as good as the C4 Dana 44's it would be good for 3-400 hp, no? I'd think the radial tires would break loose before the rear end broke. Not planning on sticky tires. LOL. BUT, didn't the manual C3's come with larger shaft on the Dana 44 installed in those? Perhaps that would make a difference.

 

If it is a real M22 it is only a 2.20 1st gear and has straight cut gears, so they really whine.
CR boxes need 373 to 411 rear gears to feel peppy.
It definately has some value, they are rare.
They mostly only came in SHP BBC cars.

My suggestion would be to swap that trans for a BW S-TI0 wide ratio with a ~2.72 1st gear. You'll be much happier, both with the gear and less noise.

I doubt a non-Corvette comp plus Hurst shifter will fit & work. But you could check.

The clutch pedals will be a pain.

But the above trans will help you with the rear gears, and may even prevent you from having to change it. See what it has now.

A stock 1981 had a 2.87 rear gear with an auto. Auto trans had a 2.52 1st gear.
so your auto overall gear is 2.87x2.52 = 7.23 (low)

If you go to a 2.20 1st gear you would have 6.3 overall (lower)
a 3.73 rear gives you 8.2 overall, a 411 gives you 9.0 overall *

with a 2.72 1st gear:
2.87 gives 7.8 overall
3.08 gives 8.4
3.36 gives 9.1 *
3.55 gives 9.6 *

I (*) 'd my advice

 

Thanks for the input Leigh. Sounds like I'm better off selling the M22 and getting something more suitable for the car. Orrrrrrr....just keep it an automatic.....which is certainly not ideal.

 

I'd strongly suggest a Tremec TKX from Silver Sport Transmission, shiftsst.com , if you decide to keep the car and make it worth driving.

Or a wide ratio B&W Super T-10 from the last few years of C3.

You likely have a 2.87 rear, which is not far off from my 80 4-speed's 3.07. Perhaps this spreadsheet is helpful. The extra wide TKX might be a good choice (3.27 first gear for a 9.38 total first ratio).

 

I'm in the middle of doing this conversion on my 80, to an M21 I bought at Carlisle. Just finished up the pedals which weren't as bad as I expected. Just pull the seat, column, and column mounting plates. Getting it all out took less than an hour. Getting it back in with the linkages and sizing things up took about 2-3. I ran into a bunch of missing bolts and messed up threads from the previous owner. If yours is in good shape and you're using original linkages, might be faster.

One thing I keep hearing is that the 80-82 removable cross member might cause interference with the Hurst trans mounted shifter. Finding the "right" shifter mount for an 80-82 seems impossible as they're discontinued from Hurst. So I'm planning to use a 69-79 shifter mount kit and chop and box weld the part of the cross member when I get there. But that's just from what I read....not from experience yet. Probably 2 weeks away from that.

I didn't go TKX after looking at the cost, even though that'd probably be much better having an overdrive. They quoted me 6700 plus shipping for a 5 speed full conversion kit with hydraulic clutch. My 4 speed conversion will end up costing me about 2700, granted I did some swap meet picking...but thats the fun part for me.

Good luck!

-mort

 

I'll throw in two cents. Think about how you will be driving it and if you can handle the gearing involved with the M22. You said you're on a budget so you can't beat free.

You'll have something unique when you're done. Later fastback Corvette with an L82 engine and M22 rock crusher trans. Sounds pretty cool to me.

 

cicch95
I'd throw in the M-22 for now. You can always go to an Overdrive later if you get tired of it and by then you'll have the clutch assembly installed.