I've made the swap from 2 speed auto to M21. It is 1965 model....what shifter linkage will work? Are there a specific model numbers I should be looking for? Will any and all years work?

Also trying to figure out rear end ratio. Car will be cruiser, not racer and will be on highway quite often, so need to keep RPMs down best I can. 350 engine with mild cam and intake/carb upgrades. I've got 308 gears today, but thinking that's not going to work....maybe 3.30s or 3.55? Would I burn clutch up using 3.08?

Thanks in advance!

If you are doing after market here is the shifter and rods.


Correct shifter and handle
https://www.npdlink.com/store/products/firebird_shift_lever_muncie_4_speed_chrome-144145-8007.html
correct Rods
https://www.npdlink.com/store/products/firebird_rod_set_transmission_shift_muncie_4-115360-8009.html

To mount the shifter to the Muncie you will need a bracket. This is better then the hurst adapter with the ubolt over the tail piece.
http://www.heartbeatcitycamaro.com/store/product/17883/Camaro-Shifter-mounting-bracket-SB-1969/


Finally, you will have to think about the backup switch. 68 backup parts is almost near impossible to find. You may go with a generic Muncie backup switch but there are a couple option to think about.

I have 2 original factory Hurst 3138 shifter, 5325 handle, bolts, linkage and mounting bracket...one is restored and one is not.

These are the correct as installed on the line, not reproductions. The linkage also has the correct levers.

If you are going M-21, 3.73 and higher, IMO.

I went from a 350 2bbl, 2.73 to 350 4bbl 3.42 and it worked out well. 3000 rpms at 6-65mph Save gas with your carb not your gears.

I think the m21 is a close ratio with a 2.20 first gear. You have to have at least a 3.70 to get the car moving.

I am not sure how high you can go and still have enough final gear to get the car going. The wide ratio suggest no less the 3.31 and my 3.36 with my m20 is high enough. I would not want to go higher or it starts making it hard to pull out. I bet you may need at least 3.73. To be happy.

Here is some reading on it. http://www.5speeds.com/ratios.html

The M-21 is meant for high RPM's. Harold is right that you need a numerically high rear end. Unfortunately that means the motor will be revving high on the highway.

It's a combination of tranny gears, rear gears and tire diameter. Yes I think you would be hard on your clutch starting with 3.08 gears and an M21.

Your M21 with your 3.08 gears would be the same as an M20 with 2.68 rear if the tire diameter is constant. But that's just the first gear, In fourth they are both direct and the engine rpm will be the same with the same gear. You don't want to be any higher than a 3.55 if you're going to drive on the highway. I would suggest a compromise between first gear launch and highway driving of something around a 3.36 rear. If you really can't live with the launch using a 3.36 maybe you can change the gears in your tranny, I don't know.
Before I rebuilt my engine and replaced the gearbox I started from red lights in second all the time, hardly used first gear with the 3.73 rear.

Not sure an m21 is a good choice for our cars. Think of a first gen Z28 with a high revving 302 meant for the race track. That's the ideal application.

Agreed...

M21 in our cars with the RPM and torque band peak/usable 1000 to 1500 rpm lower than a Chevy. M21 was 3.90 or 4.33 only. Pontiac engineers knew far better than Chevy what they were doing and were leaps and bounds ahead...

I put a BW T10 from a 80 Camero. 3.? first gear. I'd be in 2nd gear very quick!

This is some great info guys, just wished I had done more research prior to this investment. Too late now, I'm all in with M21! With 3.55 gears, it looks like I'll be turning somewhere around 2900 rpms @65mph with a 26.7" diameter tire. Does that sound correct?

Just for giggles....what if I decided to go a different route. What's a good 5 speed option for these cars?

Five speed options an ongoing subject, look down three posts from this one.

Have you checked out Gear Vendor Overdrive? If I had a Muncie instead of the Saginaw I'd go with the auxiliary overdrive. They aren't cheap but neither are the 5 speed conversions.

Bob S. found a more affordable 5 speed from McLeod Racing that requires a lot less modification.

Tremec TKO600 is option that will work excellent with rear gears 3.55 and numerically up.

I found an 8.5 '72 Nova rear with 3.42 gears for $250. Very minimal rust with everything in tact. Just needs Posi unit. We shall see.....

I run about 2900@65 with 3.23 gears and Nitto NT555 235/45/17( I forget the diameter but they were a bit shorter than the 235/60/14s I had before).