best 4 speed muncie for 3.55 gears? - Pontiac GTO Forum
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post #1 of 10 (permalink) Old 05-06-2018, 10:09 PM Thread Starter
 
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best 4 speed muncie for 3.55 gears?

Hey guys. I would like another gear but don't know what that will accomplish. Currently have a 400 stock engine w/ 067 heads 3 speed manual tranny and 355 rear gears. rear wheels are 24" tall.It is mostly for in town crusin. Twice a year its a fifteen mile cruise to a local car show.I like how it gets up and goes in 3rd or 2nd but!!! crusin in 3rd gets loud and old. Anyone have a decent suggestion on a close or wide ratio 4 speed? I dont have a clue.
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post #2 of 10 (permalink) Old 05-06-2018, 11:15 PM
 
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The three speed manual trans and both 4 speeds all have the same final drive ratio (1:1). So they all will behave the same at cruising speeds. You would need an overdrive trans if you want to lower the engine RPM at cruising speeds. Alternatively, you could also change the rear gear ratio.

We have a 61 Bel Air with a 348 and 3 speed manual and a 73 LeMans with the 3 speed manual. i prefer the 3 speeds for just cruising around town since there is less shifting.
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post #3 of 10 (permalink) Old 05-07-2018, 06:07 AM
 
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IMO, I think those 3.55 gears are the best all around gear. I had them in my '67 GTO-4 speed-not sure which ratio it had-and made the mistake and changed them to 3.73. Should have left them alone. I'm presently running the 3.55's in my '71 GTO-TH400 trans.- and love them. Like you, I make a few trips a year on an interstate highway. Going 60-65 mph, so that I don't get run over, the engine is certainly working a little extra and it can get a little loud. But it's only 2-3 times a year and I can take secondary roads if I wanted. Those 3.55 gears, get you up and going and it's a nice tradeoff, at least for me, Carmine.
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post #4 of 10 (permalink) Old 05-07-2018, 05:58 PM
 
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Originally Posted by RMTZ67 View Post
Hey guys. I would like another gear but don't know what that will accomplish. Currently have a 400 stock engine w/ 067 heads 3 speed manual tranny and 355 rear gears. rear wheels are 24" tall.It is mostly for in town crusin. Twice a year its a fifteen mile cruise to a local car show.I like how it gets up and goes in 3rd or 2nd but!!! crusin in 3rd gets loud and old. Anyone have a decent suggestion on a close or wide ratio 4 speed? I dont have a clue.

I too like the 3-speed manual - should be the Ford Dearborn 3-speed which is the heavy duty version adapted to be used by Pontiac, and why the bellhousing has 2 bolt patterns as the main case attachment "ears" are different than the Muncie. The dis-advantage is that you don't have that extra gear to drop down into if you are rolling along and are challenged. From a dead stop, the 3-speed can take advantage of Pontiac's torque and you'll never miss the extra gear.

With 3.55's, you can use any of the Muncie transmission, M-20, M-21, or M-22. The M-20 is considered a "wide ratio" transmission with a 2.52 first gear. These work OK with as low as a 3.23 gear in the rear, although you can certainly go lower, but it takes a little more slip of the clutch to get rolling. The M-21 is considered a "close ratio" transmission with a 2.20 first gear. The M-22 was used in big HP/torque applications and is a "close ratio" transmission like the M-21. It has straighter cut gears so it has an iconic whine that many like to hear being inside the car and is easily identified just by its sound alone.

M-20 gear ratio - 2.52 -first, 1.88 -second, 1.46 -third, 1.0 -fourth
M-21 & M-22 - 2.20 -first, 1.64 -second, 1.28 -third, 1.0 -fourth
Grooves on the spline of the input shaft can identify all three of these units.
1963-65 M20 2.56 ratio 10-spline 7/8-in. shaft - no grooves- 27-spline output shaft
1966-70 M20 2.52 ratio 10-spline 1-in. shaft - 2 grooves - 27-spline output shaft
1971-74 M20 2.52 ratio 26-spline 1-in. shaft - 2 grooves - 32-spline output shaft
1963-65 M21 2.20 ratio 10-spline 7/8-in. shaft - 1 groove - 27-spline output shaft
1966-70 M21 2.20 ratio 10-spline 1-in. shaft - 1 groove - 27-spline output shaft
1971-74 M21 2.20 ratio 26-spline 1-in. shaft - 1 groove - 32-spline output shaft
1965-70 M22 2.20 ratio 10-spline 1-in. shaft - no groove - 27-spline output shaft
1971-74 M22 2.20 ratio 26-spline 1-in. shaft - no groove - 32-spline output shaft

GM made it a little easier to identify these transmissions when they started using a letter designation on the end of the build code on 1969 models:

A- M20 2.52 ratio (wide)
B- M21 2.20 ratio (close)
C- M22 2.20 ratio HD (close)

The M-20 would be the more plentiful to find/purchase, the M-21 harder to find/purchase, and M-22 very rare. They do make an aftermarket M-22 with improvements, but not inexpensive and not really needed unless you have some serious HP/torque and like to race with it.

So best application for your car would be the M-20 unless you simply want a close ratio M-21. I had a factory M-21 in my '67 GTO which had the factory 3.90 rear. The close ratio keeps the RPM's higher up in the power band with each shift and there is little spread between the gears - thus the "close ratio" designation.
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post #5 of 10 (permalink) Old 05-07-2018, 09:26 PM Thread Starter
 
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3 speed or 4 speed???

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Originally Posted by Shake-N-Bake View Post
The three speed manual trans and both 4 speeds all have the same final drive ratio (1:1). So they all will behave the same at cruising speeds. You would need an overdrive trans if you want to lower the engine RPM at cruising speeds. Alternatively, you could also change the rear gear ratio.

We have a 61 Bel Air with a 348 and 3 speed manual and a 73 LeMans with the 3 speed manual. i prefer the 3 speeds for just cruising around town since there is less shifting.
Ya Shake-n-Bake the 3 speeds have certain advantages thats for sure. Thanks for your input. Art
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post #6 of 10 (permalink) Old 05-07-2018, 09:37 PM Thread Starter
 
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60/65 mph

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Originally Posted by Nicholas View Post
IMO, I think those 3.55 gears are the best all around gear. I had them in my '67 GTO-4 speed-not sure which ratio it had-and made the mistake and changed them to 3.73. Should have left them alone. I'm presently running the 3.55's in my '71 GTO-TH400 trans.- and love them. Like you, I make a few trips a year on an interstate highway. Going 60-65 mph, so that I don't get run over, the engine is certainly working a little extra and it can get a little loud. But it's only 2-3 times a year and I can take secondary roads if I wanted. Those 3.55 gears, get you up and going and it's a nice tradeoff, at least for me, Carmine.
60/65 You got that right. Told my wife one time that 55 highway speed limit was about right for this car. BUT get it on the qtr mile thats another story. 400 w/dearborn 3 speed, post car with no power robbing xtras. Well time to grow up now and get back to reality. Just trying to find a happy medium. Art
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post #7 of 10 (permalink) Old 05-07-2018, 09:55 PM Thread Starter
 
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M20 or m21

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Originally Posted by PontiacJim View Post
I too like the 3-speed manual - should be the Ford Dearborn 3-speed which is the heavy duty version adapted to be used by Pontiac, and why the bellhousing has 2 bolt patterns as the main case attachment "ears" are different than the Muncie. The dis-advantage is that you don't have that extra gear to drop down into if you are rolling along and are challenged. From a dead stop, the 3-speed can take advantage of Pontiac's torque and you'll never miss the extra gear.

With 3.55's, you can use any of the Muncie transmission, M-20, M-21, or M-22. The M-20 is considered a "wide ratio" transmission with a 2.52 first gear. These work OK with as low as a 3.23 gear in the rear, although you can certainly go lower, but it takes a little more slip of the clutch to get rolling. The M-21 is considered a "close ratio" transmission with a 2.20 first gear. The M-22 was used in big HP/torque applications and is a "close ratio" transmission like the M-21. It has straighter cut gears so it has an iconic whine that many like to hear being inside the car and is easily identified just by its sound alone.

M-20 gear ratio - 2.52 -first, 1.88 -second, 1.46 -third, 1.0 -fourth
M-21 & M-22 - 2.20 -first, 1.64 -second, 1.28 -third, 1.0 -fourth
Grooves on the spline of the input shaft can identify all three of these units.
1963-65 M20 2.56 ratio 10-spline 7/8-in. shaft - no grooves- 27-spline output shaft
1966-70 M20 2.52 ratio 10-spline 1-in. shaft - 2 grooves - 27-spline output shaft
1971-74 M20 2.52 ratio 26-spline 1-in. shaft - 2 grooves - 32-spline output shaft
1963-65 M21 2.20 ratio 10-spline 7/8-in. shaft - 1 groove - 27-spline output shaft
1966-70 M21 2.20 ratio 10-spline 1-in. shaft - 1 groove - 27-spline output shaft
1971-74 M21 2.20 ratio 26-spline 1-in. shaft - 1 groove - 32-spline output shaft
1965-70 M22 2.20 ratio 10-spline 1-in. shaft - no groove - 27-spline output shaft
1971-74 M22 2.20 ratio 26-spline 1-in. shaft - no groove - 32-spline output shaft

GM made it a little easier to identify these transmissions when they started using a letter designation on the end of the build code on 1969 models:

A- M20 2.52 ratio (wide)
B- M21 2.20 ratio (close)
C- M22 2.20 ratio HD (close)

The M-20 would be the more plentiful to find/purchase, the M-21 harder to find/purchase, and M-22 very rare. They do make an aftermarket M-22 with improvements, but not inexpensive and not really needed unless you have some serious HP/torque and like to race with it.

So best application for your car would be the M-20 unless you simply want a close ratio M-21. I had a factory M-21 in my '67 GTO which had the factory 3.90 rear. The close ratio keeps the RPM's higher up in the power band with each shift and there is little spread between the gears - thus the "close ratio" designation.
PontiacJim Thanks for all the info. The reason I have been trying to acquire info is a friend has a 66-70 1 groove 10 spline m21 with bell housing shifter/linkages pressure plate and a few other things. $800 for all. But it seems like that won't gain me much as the last gears are equal as stated above. or am wrong in that assumption?
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post #8 of 10 (permalink) Old 05-07-2018, 10:32 PM
 
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A good M20 and a 3.23 rear gear set and mid ratio Pontiac 8.2 carrier would work much better for your expectations.

Have had a ton of Muncie 4 speeds go through my hands. The publicized grooves in in the input shaft are all fine and good, but it's always smart to remove the side cover and examine and count the gear teeth on the cluster. So far I"ve owned three fine spline input shaft big output shaft M21's that had no cut (or groove) in the input shaft. One of these '70's replacement input shafts had been installed, along with an M21 gearset & cluster gear in a '71 application M22 case! Not sure what the idea behind that was... An old friend and I had several '64 & '65 "325" M20 casting cases about 15 years ago with stretched pin holes & had each cases pin hole properly remachined to accept the later 1" diam pin, then we rebuilt them with nice used 2.52 ratio M20 gearsets. Made for stronger M20's for several '64 and '65 owners, and we got rid of all but two of our "325" cases. Always pull the cover and verify.
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post #9 of 10 (permalink) Old 05-09-2018, 06:13 PM
 
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Originally Posted by RMTZ67 View Post
PontiacJim Thanks for all the info. The reason I have been trying to acquire info is a friend has a 66-70 1 groove 10 spline m21 with bell housing shifter/linkages pressure plate and a few other things. $800 for all. But it seems like that won't gain me much as the last gears are equal as stated above. or am wrong in that assumption?
Well, your buddies pricing is fair and about what to expect to pay, but I would bring it to a trans shop for inspection & a rebuild. Remember, these parts are old and likely worn, so $costs may go up from the $800 investment.

The final ratio of the 3-speed/4-speed are both 1-to-1 so no, you will not gain anything. You will still experience the same engine RPM's on the highway as you do now. As Pinion head stated, you could drop down to 3.23 gearing which is what I had with my 3-speed. You will gain a little lower RPM's, but in my opinion, not enough to justify the expense of the swap. You can use one of the online calculators where you can input the car's tire height, gear ratio, and final gear to give you your RPM's at 60/65 MPH and then input 3.23 instead of your 3.55's.

You can also go with a taller rear tire which will effectively drop the rear gear ratio a few hundred RPM's - from a 26" tire to a taller 28" tire will drop your RPM's just a little over 200 RPM's. So not much, but still a little better.

A transmission with overdrive is really the only way to get what you desire. The 5th gear is an overdrive which will drop your RPM's for highway cruising. Not an inexpensive venture. The TKO line of transmissions typically require modifying (cutting) the trans tunnel. Richmond makes a 5-speed OD that I believe fits without cutting, but is high dollar. McLeod also makes a 5-speed OD that states it will fit without cutting - again, costly.

So, no easy way to get what you desire and have the best of both worlds short of a 5-speed with overdrive.
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post #10 of 10 (permalink) Old 06-21-2018, 06:26 PM
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Having owned several early GTO's with 3.23, 3.36, and 3.55 gears, and 4 speed transmissions, my experience has been that the difference between a 3.23 and a 3.55 is huge on the open road. The cruising speed goes from 55 mph to 70. I loved the 3.55's in my youth when the speed limit was 55, but I changed the 3.55's out in my '65 to 3.36's when I blew up the rear end in 1990. Even the change to 3.36's made a big difference. With 29" tall rear tires and my 2.56 first gear M-20 Muncie, the car gets out from a stop just fine and cruises at 70-75 mph all day long. The best solution for the O.P. would be to find and simply install a 3.23 rear axle assembly and keep his three speed, or install a 3.23 rear axle assembly and upgrade to an M-20 Muncie. A friend recently restored his '67 with the 3.55's and the M-20, and his car is brutal at 60mph....we have to shout to have a conversation. Of course, he hardly ever drives it, and never leaves town. Not my cup of tea........
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  Pontiac GTO Forum > The 1964-1974 Pontiac Tempest, Lemans & GTO > 1964-1974 Tempest, Lemans & GTO Undercarriage, Frame, Transmission and Differential Discussions.

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