[pontiacman63383]

So this is my first time diving into old muscle cars. ive got a 69 gto im doing a full restore on. Im about to do the rear end. I want a set of gears that will give me a bunch of umph off the line for when i take it to the strip/ drive it around but ones that i could take in on the highway without peging the motor. Gas milage is not a concern as i wont drive it all that much. I just dont want a gear thats going to limit me to 60 on the highway. Ill be running a mild built 400 and a munci m22 4 speed with the 8.2 rear. with posi. Id love the idea of running 4.10 but eveyone ive talked to said there to much for any kind of street driving. Im not sure so im turning to your guys plethora of information

[Engo]

3.55 or 3.73 would be good for what you want. It also depends on the diameter of the rear tires. Personally, I would go with 3.73 combined with a M22.

[geeteeohguy]

For your application and what you're running, I recommend a 3.23 rear gear. Good off the line, good on the highway. I've driven/owned many GTO's over the years with all types of rear ends, from 2.56 to 4.88, and for a stick car that is street driven and goes on the highway, 3.23 is great. For an automatic, 3.08 or 2.93 is my favorite. 3.55 and steeper gears will suck gas and you'll be wound out at well below the speed limit with Hyundai's and Nissans blowing by you. The stock ratio in your '69 was/is probably a 3.36, which is also fine for what you want to do.

[Half-Inch Stud]

we drove a 70 GTO 400 stick for years and later found out it was a 2.54:1 posi.

I'd reco 3's like 3.23:1, 3.36:1, maybe 3.55:1 but must be posi.

[tom s]

Get rid of the m22 and get a 20.I would chose a 3.08 with the 2.52 low m20.I have a 69 with a m20 and a 3.55 and too many RPMs on the highway IMO.Your first gear will be 7.81 with the m22 and the 3.55 and will be 7.76 with the 3.08 and the m20.Tom

[Engo]

3.08 or 3.23 with a m22 is a DOG of the line. Just sayin...

Look what GM offered with the m22...

[rontiac]

Originally Posted by Engo

3.08 or 3.23 with a m22 is a DOG of the line. Just sayin...

Look what GM offered with the m22...

I agree....close ratio needs gear....wide ratio manual go with 3.23. I think with the M22 on the highway you'd at least have to have a 3.55. Though Engo nailed it.............4.10 would be more gear banging fun!
The compromise would be a 3.73....IMO.

[71SportRagtop]

My previous car was a 72 Challenger with a 440 6 pack, 4 speed, and a 4:10 rear. It was a beast. It drove SUPER strong but was a 100% street weekend car. Honestly it was a blast to drive with the 4:10's. My current car is a 68 Firebird with a mostly stock 68 400, an M-20 4 speed, and a 3:08 rear. Honestly, I HATE the 3:08 gears. It seems like my car takes forever to wind out through the gears.

I'm doing a gear swap very shortly and have decided to go with 3:55's as I feel like they will be better than the 4:10's for street driving but also have more pull off the line than the 3:08's. I've heard guys talk about how 3:55's aren't great for highway cruising but my car really doesn't see any long term highway runs anyway. Plus after running a big block Mopar with 4:10's, I still don't think that 3:55's will feel all that bad.

[pontiacman63383]

Ok, thanks for the info guys. As far as tires go im still torn on that. ive got a se of 14" rally II's that came with the car but i really like the new rally II's that you can get in 17" or 18" So i can get down with the 3.73. what about 3.90? Remember that i dont car about gas milage what so ever and that i wont be on the highway all that much. I just need to to be about to do about 75 or so withoug blowing up. It can be pretty high up in the rpms just not enought to hurt the motor. would the 3.90 be to much? Also the m22 is staying in the car.

[tom s]

I dont think the factory did gears taller than a 3.90 with the m22.There was a reason.Tom

[FrankieT/A]

My car has an M20 and 3.08. I started with an M21(M21 and M22 have the same gearing). I hated starting off from a light or a stop with the M21, so I switched out the input shaft and cluster, now it's an M20. It's much better but still sucks! Highway cruising is not bad though. I ordered an SS700, so I will change things around, but that's another story on another thread. If I were going to stay with my Muncie, I would go with minimum, I say minimum 3.23. And max 3.55. With previous cars I owned I find gears in the 3.42-3.55 range ideal. I have one car now with 4.10's that's miserable to drive on the highway, and use A/C on the highway? That's simply not happening. No A/C 60 MPH is 3000 RPM temp starts to creep, everybody is passing me, which even if I blast past them within a mile they just pass me cause I can't keep it up. I'm not comfortable unless I'm at no more than 2500. After that, its a scream. The 3.08 is much better with 70 at about 2750. Not bad, but the speed limit is 70. I like to go about 5 over. Guess what, back at 3000. In order to get in a chain of cars you have be able to sustain 80+. Ok, enough about me,back to where you wanna be, I would not go beyond 3.55. It's a great all around gear. 3.08 is hard on a clutch. If you go down to the 3.08 range, a Super T-10 would be a better choice because there is a wider selection for first gear options. Probably why Pontiac started going to them in the mid to late 70's. JMO trying to be helpful.

[Tom Vaught]

I ran around college for several years with a 4.33 rear axle that was originally installed in Jim Wanger's 64 Red GTO. Used that with a M-22 Muncie transmission. Average speed around town was 35 mph or the "Radar Love" boys would make an appearance.

On the highway we were buzzing along with the buses and the trucks, oh what fun!
(at 55 mph eating gas like a fiend. Burned 21 gallons of gas on a 150 mile trip one time. 7 mpg!!)

So then I installed a Ford 9" rear axle (got tired of blowing up the GM crap) and went with a 2.75 rear gear with a Doug Nash 5 speed (3.27 1st gear and 1 to 1 final drive).
A very nice street and highway set-up, in my opinion.

So I am happy with that deal. Some of the over-drive transmissions today with5 and 6 speeds seem to work well too.

Today if you don't run 80 on some of the freeways you get run over by the teenagers, trucks, buses, hockey moms, business women, and a few little old ladies. The men drive your speed and give you the Thumbs Up sign often.

Tom Vaught

[FrankieT/A]

In the old days Tom, there really wasn't an OD trans available in the after market(economically speaking). The Doug Nash only came with really deep gears 1,2,3,4 and 5th was 1:1 as you stated. So that was the only way to go pretty much. I realize you being an engineer and the math works out with gear multiplication, but, to me it seems like the stress to over come the dead gears in the rear would take its toll on the rear end and U joints upon hard acceleration. No? Please correct me if I'm wrong. Thanks

[David Jones]

So, let me sum this up. You want a good rear gear. All you need to do is swap the rear end for a 9" Ford. Get a 5-6 speed transmission. Rebuild your engine. Paint the car. Then move to a larger house.

Simple.

[b-man]

A set of 3.55 gears would be liveable on the freeway, this is the tallest gear you'd want to use with the close-ratio Muncie M22 and still have a decent launch.

If you were running a wide-ratio M20 I would go with 3.23 gears.

[FrankieT/A]

Originally Posted by b-man

A set of 3.55 gears would be liveable on the freeway, this is the tallest gear you'd want to use with the close-ratio Muncie M22 and still have a decent launch.

If you were running a wide-ratio M20 I would go with 3.23 gears.

X2!

[geeteeohguy]

I'm with b-man and Frankie. I didn't pick up that the OP was running a close ratio box. That said, I've run 3.55's a bunch on the highway. They worked MUCH better when the speed limit was 55 mph. These days, I hate 'em. I changed out the 3.55's in my '65 for a 3.36 gearset only because that's as tall as I could go. With 27.5" rear tires, it works out to about 3.23....just livable at 70 mph. My 2 cents based on a ton of driving in these cars.

[MG12692]

I know you probably love your 4-speed and I loved my super t-10 as well, however when I got my Tremec TKO 5-speed with a .64 over drive I had no problem breaking up with the 4-speed. Smoother shifts, shorter throws, no external linkage that could bind up from time to time, not screaming anymore on the highway. Just a better experience any way you look at it. Dump the munci get a tremec and run 3.73 you wont be disapointed. Just my opinion. Good luck.

[Tom Vaught]

Originally Posted by FrankieT/A

In the old days Tom, there really wasn't an OD trans available in the after market(economically speaking). The Doug Nash only came with really deep gears 1,2,3,4 and 5th was 1:1 as you stated. So that was the only way to go pretty much. I realize you being an engineer and the math works out with gear multiplication, but, to me it seems like the stress to over come the dead gears in the rear would take its toll on the rear end and U joints upon hard acceleration. No? Please correct me if I'm wrong. Thanks

Some things to consider Frankie:

The gears in a 9" ford are well supported by a rear pinion gear bearing.

The 2.75 Rear gears for a 9" ford have 16 teeth on the pinion gear and 44 teeth on the ring gear. There are multiple pinion teeth engaging the ring gear teeth to spread the load from the engine torque.

A typical 3.55 gear set will have 10 pinion teeth and 35 ring geat teeth. Typically you get one full tooth of mesh and possibly a partial mesh on a second tooth. The pinion gear size is much smaller vs the 2.75 gear size. Less size means less material = less strength.

A Doug Nash transmission has a fully supported counter-shaft vs the non supported counter-shaft (in the middle) of the GM Muncie Transmissions. Gm increased the counter shaft pin diameter to 1" but that actually gave little extra safety factor to the trans.

So that is why I like my Nash Trans with 5 forward gears and a 2.75 gear set vs a od type trans and 3.55 gears.

Tom Vaught

[FrankieT/A]

Yes, I know about the nine inch front pinion support, and I do realize that lower numerically rear gears are acually stronger because of the physically larger pinion gear. The numbers do not lie(as far as gear multiplication). It just seems counter intuitive.