I just bought a Kellison J6 with a Chevy 350 with the TH350 automatic. I would like to put in a manual 4 speed. What would be the best choice, a M20 or M21 I guess the M20 has a wider ratio. Which is the best choice for this car? Not planing on racing the car but some serious spirited driving is what I am hoping for. Any suggestions are appreciated. Thanks, Martin
I'll get the ratio tomorrow, has a Currie Ford 9 inch. Not sure on the weight but its got to be about 600lbs less than a 1958 Vette.
The intended environment the car is to be used in plays a big role but my suggestion is to base your choice on a number of factors, vehicle weight, rear tire diameter and the rearend gear ratio planned. A 2.56 first gear Muncie (M-20) will allow a lower numerically (3.07 for instance) geared car to move easier from a dead stop compared to the M-21 (2.20) 4 speed. I don't know the weight of a J6 body/chassis but that could equally dictate your choice of transmissions.
I would do an Muncie M22 Rock crusher. Nice close ratio gears, and a little gear whine. Put a Hurst Competition Plus shifter on it. There's a guy on ebay that builds the transmissions, and he's really good. Have one behind a 502 Chevy and it's really nice.
If you got it before the big musclecar collector boom, good for you, maybe they were still reachable pricewise for the working man. For what I see some of them going for on "the bay" you can buy two brand new Richmond Super T-10's. You are right about that whine though, I drove a brand new LS-6 Chevelle in 1970 and I still remember it.
If you're keeping the Auto ratio rear end! Go for a wide ratio BW Super T10 from 1979 to 1982 [a bit more modern and still tough as nails] 1st 2.88:1 2nd 1.91:1 3rd 1.33:1 4rd 1.00:1 The BW has a better stacked ratio spread [It is wider down low where torque multiplication is greatest] Apart from spline differences the BW is a direct bolt in swap with the Muncie , The BW has the same splines as the M22 rockcrusher
This is an Autogear Super 22. I ordered it with a 2.56 1st gear ratio, lower is available now I hear. Much stronger than the Muncie.
The Auto Gear is the way to go. The last Muncie was made in 1973 or so. I run a M20 in my Ford that weighs around 3500. It had a 2.56 1st gear until I broke it in 2018, now it has a later 2.52 1st gear. The rear is a 3.89 posi.
Believe I ran the original M-20 in my '31 A coupe. Having the low first, and spread between gears worked. Top gear felt like overdrive, w/a 3:08 rear.
Always liked Kellisons and almost bought one (wish I had). I suppose it depends on what you consider spirited driving. As you know they used a number of solid axle Corvette chassis under some of the Kellisons and if had a Kellison I would go with a M20 with the better 2.56 first gear. I lean more towards the drag racing end so 3.07 gears are not in my vocabulary. I have a 327/365 in my black 62 Corvette with a 3.70 gear and few years ago I switched from the Muncie M21 to a M22 wide ratio with a 2.56 first and I would never go back to the close ratio. With that advantage in first gear it really is noticeable running through that 1st to 2nd gear. There may be a bit of a drop off in the higher gears but by that time I already have a smile on my face.
The tall tires I used on my car really took a lot of the gear out of it. I started with a 3:55 and then went to a 3:70 gear. Still, around town I did not like the way the car "took off" from a stop sign. I just changed the input and cluster in my Muncie from a 2.2 to a 2.5 setup and like it a whole bunch better for the type of driving I do most of the time. Since I don't race the car, the drop between first and second is really not that noticeable. D
My car came with a 3.56 rear and the car with the cam lugged badly around town, so the 3.89 was perfect when I went posi. I have close to a 29" tire on the car, it would be a screamer at 26". Mine sees a little abuse now and then.
I LOVE Kellisons, got any pictures? As for the transmission I’ve ran both The Close ratios are fun once the car is rolling but the higher first gear isn’t great for taking off. In a lightweight car like a J6 with a decent small block I bet it would work. The Auto gear stuff is really nice, but I’ve heard parts are hard to get right now. If tunnel room is available may a close ratio TKO would be better with a rear gear in the 3.50-3.70 range. Let’s see that Kellison!!!
The ebay seller we bought the rebuilt M22 from is naz130. I don't see a complete tranny on his for sale items today, but ask him if he'll build you one.
I would suggest that no matter which one you choose, make sure it is 1966 or later. GM had trouble with the 63 - 65 7/8 countetshaft transmissions. The last three numbers on the top line on the right side of the case end in 325 I was warned, but didn't listen to a friend that ran the early 325 and had breath problems. It took 4 rebuilds and finally exploded as I drove very slowly across railroad tracks and destroyed the input and cluster. I went back to the 66 up trans and ran it for many trouble free years 010 and 660 are two of those case numbers. That extra 8th inch in diameter Countetshaft seemed to cure lots of dependability problems. Of course you could spring for the new reproduction MUNCIE mentioned here. I haven't heard any complaints form any person that used it.
Much appreciated. I was just interested because I know of a couple on eBay that I wouldn’t trust with anyone’s daughter , if you know what I mean.
Sounds familiar.... the countershaft on mine went blooey what I broke it. The rebuilder also machined the case for the 1" pin. Mine spun in the case, like a big lathe bit and destroyed the mid plate. He showed me a drawer full of used pins, both sizes. My 7/8" went in the drawer, he said they almost never go bad.
We put the M22 behind a very healthy 502 Big Block in an off topic 69 Camaro. It's not babied by any means, and we haven't had any trouble with the transmission. It runs low 12's in street trim, and I know it would go into the 11's with very little effort.
Right now my Coupe has a Muncie M21, close ratio trans. The only difference in the M22 is the angle of the teeth. I would go with the M20 in a sports car. Especially if you aren't gonna race it. Much quieter also. The 22 and 21 are really loud!
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