TexasSeabee

I am seeking your opinion on the pros/cons of installing either a rebuilt Muncie M22 4-speed OR a new Tremec TKX 5-speed into my '72 Olds.

The current drivetrain is the factory original 350 with 3-speed AT, however both the engine and transmission are tired and in need of a rebuild. My plan is to replace/upgrade both the engine and transmission to create a street cruiser. (and will keep the numbers matching engine/transmission for the future owner)

I have a 1970 455 (was mated to 4-speed, crank is drilled for pilot bearing) with a mild build and a Muncie M22 4-speed sitting in the garage. So I am ready to proceed; but after reading other posts I am wondering if the Tremec TKX 5-speed would be a better long-term solution for cruising at lower RPM's? Seems logical that modern engineering of the Tremec would be more dependable than the 50-year old Muncie....however the M22 did earn the nickname 'rock crusher' for a reason.

This forum has so many experienced members and I am looking forward to your comments. Thanks in advance.

Blue442

In my experience the Muncie transmissions in any form (M20, 21, or 22) hold up well on the street. However, for highway driving I’ve always wished for an overdrive. How well does the TKX fit in the tunnel and how much of a pain is it to integrate with the steering lockout and reverse light. You’ll need to covert over to new pedals and linkage anyway and cut a hole in the tunnel, so perhaps any further tunnel mods for a TKX may not be a concern. The driveshaft is another factor to consider.

My brother has run his ‘70 Vette with 3.73 and M20 for years on the street. I’ve run both 3.42 and 3.91 rear gears on my ‘70 442. The 3.42 gears were fine on the street with my M21. The 3.91s really limited highway speeds with my M21.

I think it really comes down to what your goals are. Either transmission should work fine.

VC455

I went through this same evaluation when I changed to a Tremec 6-speed 20 years ago.

Using my metrics from that time, here's how your matchup would work out...

RPM drop through first four gears.
M-22: 25% drop to second, 23% drop to third, 21% drop to fourth. Those are ideal road racing gears. Overall ratio is too narrow to do well on the street or at the strip.
TKX5: 34% drop to second, 32% drop to third, 22% drop to fourth. This would do well on the street and OK at the strip because of the deep first gear. The rpm drops to second and third are excessive compared to the M-22, but the 60 ft time would make up for it--and the important drop to fourth is nearly ideal--it would pull hard at the end of the 1/4.

Comparison in first gear (stoplight acceleration) and top gear (fuel economy) using a 3.23 axle ratio, for example.
M-22 in first gear has a 7.11 overall ratio. This will be a dog off the line.
TKX5 in first gear has a 9.27 overall ratio. This is much better, and enough to overpower big street tires on a light-rear car. You'll need some care in launching. You can see how that would blast away from a stop.

Comparison in top gear (fuel economy) using a 3.23 axle ratio.
M-22 in top gear has 3.23 overall ratio. This is decent.
TKX5 in top gear (with the 0.64 ratio) has 2.07 overall ratio. Imagine the better fuel economy.

Mass (weight)
M-22: about 150 pounds
TKX5: about 100 pounds

I had problems with stick location in the console.
I've read that this problem is solved in the TKX5 by enabling alternate shifter positions--but you will still need some guidance (or good measurements) to get the location correct.
This is a non-issue with the M-22.

Fit
I've read that banging on the tunnel enables the TKX5 to fit. Kits are available to add sealing boots.
M-22 is a drop-in with stock parts, and it requires the above-floor sheet metal adapter tower to be added.

Wiring
Reverse lockout is electrical on TKX5. I powered this by tapping into the brake light circuit. Reverse unlocks every time I apply the brakes. There are probably kit solutions now.
M-22 does not have an electrical lock out.
The TKX5 switch for reversing lights is different from the M-22--but you are changing from automatic, so the problem will be the same with both transmissions. Again, a kit will probably solve this for the TKX5.

Durability
Both are adequate.

BangScreech4-4-2

The fact that you're considering the Tremec and the engine swap indicates that you're not too concerned about authenticity, so that brings it down to a simple case of 1) practicality and 2) practicability.

1) The Tremec with its overdrive capability is probably more useful in a daily-driver type build, especially if you do a lot of highway driving. Also, the deeper first gear will be more fun.

2) The Muncie is the hands-down winner here, in no small part due to the fact that you have one in close proximity Also it would be pretty much of a bolt-in, while I imagine there would be some jiggering around necessitated by use of a Tremec. Further, there's the cost: the Tremec's gonna be $3-5K just for the box and associated hardware and that's if you can handle the whole installation on your own. True, some (much?) of that money can be recouped by the sale of the M-22 (I haven't priced these in a long time, but imagine they still fetch a good buck) but I think you'll still be out of pocket more with the Tremec.

Bottom line is, what kind of driving do you do, what do you want/need, and how much are you willing to spend?

fleming442

There are a bunch of variables afoot here. First of all, the 2.20 M22 1st gear just plain sucks. Then, it depends on what you can tolerate as a cruise rpm and speed. I run mine at 33-3500 on the highway with a 3.70 rear gear. I also haven't seen anyone beat on a 5 speed with Olds torque successfully. If'n I were to go for OD, I'd be doing tunnel surgery for a T6060 or better.
Autogear has 22s with steeper 1st gear and the wider M20 gear spread- the M22W with a 2.56 and the M22Z with a 2.99 1st. I have a 22W that I will sell if you're interested. I currently have a 22Z for better strip performance.

Blue442

x2 on the Autogear/Muncie Super Case transmissions. They will take abuse.

BangScreech4-4-2

Just for my own amazement, what's a ballpark price on one of these?

Lonnies Performance

The TKX has overdrive which is great, but the M20 wide ratio Muncie has a much better gear spread.
To me the TKX has too low of a first gear.
If you have 2.73 or 3.08 you may like the TKX in the lower gears, but the OD will be less useful.

The close ratio T56 Magnum is much bigger in size & has good gear ratios, but the factory T56 has terrible OD spreads.
The Magnum is way better with closer gear spreads plus OD than the TKX.
A close ratio T56 Magnum with 3.42 or 3.73 is about perfect overall.

fleming442

That's a tricky question. The aftermarket main cases have been out of production for about 2 years now. They keep telling me "check back in 3 months". I think I paid about $2k for my 22Z kit, but had to provide my own case andbuild it myself. Figure about $2500-3k for a new one. They have M23s in stock; not sure of the price.

66_Jetstar

I have a complete m22w gearset that I would sell. 10k street miles, probably 100 passes or so. I upgraded to the m23z stuff this summer.

joe_padavano

If you are talking about a stock M22 with 2.20:1 first gear, that is a horrible trans for the street. I would always use at least a wide ratio M20 and preferably a five or six speed trans.

olds 307 and 403

The TKX has two first gear options and 3 OD ratio options and a supposed 600 ft-lbs rating. As said, a 2.20, without the right rear gear, it will be not so great around town. What rear gear are you planning?