[jimn]

I'm finally in the planning stage of fixing-up/cleaning-up my 67 GTO convertable. The rear gears are 3:55's, the trans. is an
M-21 close ratio 4 spd, the motor has been rebuilt with 9.5:1 compression w/068 cam.
I don't think this trans./3:55 combo was an original option. Does anyone have opinions or experience with this combination. I'm wondering if it will have enough low end "grunt". I want it to be a daily driver, but I also want it to xxxx on the local chevy,s. Thanks

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[jimn]

I'm finally in the planning stage of fixing-up/cleaning-up my 67 GTO convertable. The rear gears are 3:55's, the trans. is an
M-21 close ratio 4 spd, the motor has been rebuilt with 9.5:1 compression w/068 cam.
I don't think this trans./3:55 combo was an original option. Does anyone have opinions or experience with this combination. I'm wondering if it will have enough low end "grunt". I want it to be a daily driver, but I also want it to xxxx on the local chevy,s. Thanks

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[Blackcat]

Having worked on several 67's. The years take a toll on 4-speeds/rearends/engines. Most likely the trans was replaced. Getting a build sheet will tell you exactly what the car came with. The 3:55 rear had the wide ratio trans.

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Gatomon
A car is cheaper than a girlfriend. Better than a wife. If it gives you trouble you can park it and for get about it!

[Ed Neasham]

To the best of my recollection the close-ratio (M21) came with a 3.90, 4.11 or 4.55 rear, with the 3.90 the standard and the other two were optional. The 3.55 will not give you as much pull in first (with the 2.20 gear instead of the 2.54 of the M-20), but will definitly give you a more cruisable highway rpm than the 3.90 or above.

Ed

[ghaines]

I bought a new GTO in 1970. I took what was on the lot. It had a M-22 and a Hurst competition plus 4 speed shifter with 3:55 open rear. Stock 400 / 350 HP. I knew 2 guys with 67's and neither had the M-21.

[ghaines]

My error. I believe the M-20 was the wide ratio.

[ghaines]

<BLOCKQUOTE class="ip-ubbcode-quote"><font size="-1">quote:</font><HR>Originally posted by ghaines:
My error. I believe the M-20 was the wide ratio.<HR></BLOCKQUOTE>
wasn't the M-22 the close ratio?

['ol Pinion head]

The M22 was only used by Pontiac in '71-72 A & F-body lines. It was the heavy duty close ratio Muncie & was used behind '71-72 455HO cars.

[This message has been edited by 'ol Pinion head (edited 10-25-2000).]

[old gto]

Right, but the M-22 was known as the "rock Crusher" wasn`t it? The M-21 was a sort of mid-range, and the M-20 was the standard, is this correct? Also, you say M-22 wasn`t in 60`s Pontiacs, but didn`t some Chevies get them.....specifically `Vettes? (How far off am I?)

[jimn]

Thankyou gentlemen. I think Blackcat hit it when he said "the trans has been replaced".
It sounds like 3:90's would be nice. How to I change 3:55's into 3:90's.
Thanks

['ol Pinion head]

The 3.55's & a wide ratio Muncie are a great combo with a moderate built 389 or 400 in an early GTO. The factory knew what they were doing with this combo. If you want 3.90's to go with the M21, Richmond Gear makes them & the rearend would have to be setup with them. Unfortunately, the rpms at 60-70 mph with the 3.90's will probably drive you crazy in a daily driver.

If you are considering swapping tranny's, usually M20's are easier to find than M21's & cheaper to boot. If the M21 tranny turns out to be #'s match to your car, I would not sell it. In that case, rearend was swapped out earlier.

[Ccass]

Moving topic to "Drivetrain Forums- Street"

Thanks for your contributions.

[Old Man Taylor]

Unless you want more of a racecar, you would be better off leaving the 3.55 and replacing the M-21 with an M-20. Your first three gears will be very much like having an M-21 with 4.10 gears. The down side is when you hit fourth gear, but you are doing about 90 when you do that. However, make sure you really have an M-21 first. I can’t tell you how many M-21’s and M-22’s I have looked at that have all turned out to be M-20’s.

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Jim

[Blackcat]

Leave the 3:55's in the car. You have a 90% chance that they are the original gears. Transmissions were more likely to get broken and replaced than the rear. You will be happy with the 3:55's with the combo you described in your post. It will give you good power and still have highway drivability with a Wide ratio 4-speed. 3:90's and the close ratio are for racing. It will cost you more to do the rear than to trade trans with someone. One way will cost maybe 200.00 the other may go as high as 1000.00 to get the rear Done Right!

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Gatomon
A car is cheaper than a girlfriend. Better than a wife. If it gives you trouble you can park it and forget about it!

[Half-Inch Stud]

OPH ; I always thought the M21-HD was in the 70s' Pontiac F-bodies. M21-HD identified by TH400 output shaft, 1"dia countershaft, fine-spline input shaft, with 2 cut-rings on that input shaft.

Maybe I never saw an M22 [that I'd use over an M21HD]. Because the M22s' in the 60's were mostly Chevy issue, had the smaller countershaft diameter, and couldn't hold a candle to 455 torque. I saw many stripped countershaft clustergears on top of shop counters, and would ask "dwatds that?" "er, ah that WAS an M22 clustergear...until the 2-3shift"

I v'e seen the "fatter gear teeth...so what. The larger 1" diameter support shaft is key, and found in the 70's muncie 4spd. I bet those 70s' M22s' are quite rare. So, I've only seen M21-HDs.

I'm under the impression that Close and wide ratio was avaliable in the M21-HD.
Possibly the M22 was only close ratio.

Am I right/close/wrong?

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"his peg-leg got woodworm , and broke into three"--G. Baker

[Half-Inch Stud]

My above post; nowhere did I address the regular M21.

455HO [L75] WG motor'd 70 Grand Prix car came with the M21 Trans 4SP HD.....That's the M21-HD for yaz...and a 3.31:1 12Bolt rear.

My brother's 70 [Orbit Orange] Judge came with the M20 4spd [L74 400ram Air] into a 4-pinion 3.55:1 gear 10bolt.

My 69OHC4BBL SprintBird got the Saginaw 4spd, into a 3.55:1 4-pinion 10Bolt..but now I really digres.

['ol Pinion head]

....1/2", For some reason the '70 GTO's with the 455 got there own code of Muncie, code WG, I believe. Have had two of these '70 factory 455 4speed GTO's, both with A/C, & both had lunched their original Muncies & been swapped out, so I can't say what was different with them from the M21's used behind close ratio equipped GTO's that year. This is a question I have wondered about for years. The 455 version may have been Pontiac's first use of the big output shaft fine spline input Muncie.

The big output shaft Muncies were 1st released in the '70 GM model year in LS6 & L78 Chevelles from all the all the # decyphering I have done on Muncies during the rebuilding process. Probably also used in the highest horse Vettes this year. For some reason, I believe they were not used in the '70 high horse L78 Nova's & Camaro's, instead they used small output shaft versions. The '70 T/A, I believe also used the small output shaft Muncie too.

For 1971 models, All Muncies used by all 4 divisions had the big output shaft & fine spline inputs. These were available in all 3 versions: wide ratio M20, close ratio M21, & M22(HD close ratio-rockcrusher). The 455 HO cars optioned with a 4 speed got the M22. Originally for '71, the 3.90 8.2 10 bolt gear set was planned for certain no a/c 400 4speed (close ratio) A-bodies. Believe this was a M21 not a M22. A very few early '71 A-bodies were even delivered 3.90's & M21's. The vast majority of these 400 4 speed cars had M20's & 3.55's or 3.23's.

For '72, the M22's continued behind the 455HO 4speed cars. I believe, as low ratioed as one could get behind a 400 Pontiac 4bbl A-body, was a 3.55 (3.23 with a/c), so I believe, no M21's. The '72 M21's I have built or bought came out of '72 Camaro's & Vettes.

For '73 the M22 was gone in the Pontiac line. If GM still used it was in a high horse (for '73, lol) BB Vette application. Don't know enough about the no a/c 4speed SD T/A's to say M-21 or M20. Do know, my '73 4speed A/C 455 D-port T/A has its original M20 & 3.42's. These big ouput shaft Muncies were used up until mid '74 & the '74 version's side covers will have 2 bosses for TCS switches.

Better stop, please excuse the length of this minature novel.

[This message has been edited by 'ol Pinion head (edited 10-26-2000).]

[This message has been edited by 'ol Pinion head (edited 10-27-2000).]

[Half-Inch Stud]

OPH,

Sounds fairly historical.
I figured the M20's lacked the TH400 output, and lacked the 1" countershaft, for all years.

While M21 and M21-HD follow your info. I would hang my hat on the 1971 info.

I figured Pontiac didn't ever use the M22 in the 70's. Would like to see a Build Sheet....

Didn't 73 use the T-10? [ST-10 not out yet??]

Overall, I would like to know that you're correct, and I've working under folklore information. Suppose my statements put me in the novice catagory for 4-speeds. You know I could never get a straight answer on close/wide ratio from anybody when pointing to a muncie on the ground..."count the input shaft rings...look at the first gear teeth...input shaft tooth count..." That's what happens when I grow-up in a cheby speedshop town; Holley carbs, Crane cams, and Mr Ga**** shifters.