# How tell close ratio 4speed from a wide ratio.



## Chris Holabaugh (Jan 18, 2009)

The transmission is out of my 1965 GTO and I want to find out which ratio it is.
I have all the numbers off of the case and also was told to look at the spline.


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## Too Many Projects (Nov 15, 2008)

Hard to say if it has the original input shaft but if it has grooved rings around it, 1 ring is M21 (close ratio) and 2 rings is an M20 (wide ratio). Otherwise, you need to remove the side cover and count the teeth on the 1st gear. The case numbers will get you a ballpark application year but many were used for 2-3 models at the same time.

Edit; I just went to the site below to provide the link but I see the 65 model M20 is different still than the 66-up models with NO rings on the input shaft and a lower gear ratio at 2:56 rather than 2.52. Please post the case numbers you have and look at the link below to determine what you have. If it is the original trans, it is a rarity.....:cool

Muncie 4 Speed Transmissions


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## Chris Holabaugh (Jan 18, 2009)

*Case numbers*

Thanks for the information. Here are the case numbers.

1. Top side 5K43832
2. Side driver 335308
3. Side passenger 3851325
4. Back Side passenger P0619

Also we could not see any rings on the input shaft.


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## Too Many Projects (Nov 15, 2008)

Chris Holabaugh said:


> Thanks for the information. Here are the case numbers.
> 
> 1. Top side 5K43832
> 2. Side driver 335308
> ...


You have a 65 transmission, most likely an M20, since the M21 was supposed to have 1 ring, but you need to pull the side cover and count the teeth on the input shaft to know for sure. M20=24 teeth, M21=26. 
The first number you list is a VIN # and if the last 5 digits match the last 5 of your cars VIN then it is the original !!!! 
The last number is a date code for when it was assembled. P just indicates Muncie 4 speed, 06=June, 19= 19th day. If this date is within a few weeks of the cars build date it would support the trans as original. 
The down side to all this is the countershaft is 7/8ths " instead of the 66 and up 1". Together with the lower gear ratio set, parts may be harder to come by. If it is the original and you plan to run the car hard, I would shelve it and get a newer trans. Having the original is very rare even if the engine is a numbers matching, since many transmissions got beat up and swapped out.


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## Rukee (Feb 8, 2007)

I don't think any part of the vin # was on the engine or tranny in `65.


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## Chris Holabaugh (Jan 18, 2009)

*Transmission*

It sounds like this is the original transmission because the date I got form PHS, on the build date are within a few weeks, but unfortunately the original engine is long gone, even the driveshaft and rear end are not origianal. When restoring the car we found evidence that the car had been changed to race.


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## Too Many Projects (Nov 15, 2008)

Chris Holabaugh said:


> It sounds like this is the original transmission because the date I got form PHS, on the build date are within a few weeks, but unfortunately the original engine is long gone, even the driveshaft and rear end are not origianal. When restoring the car we found evidence that the car had been changed to race.


Bummer on the rest of the drivetrain missing. Funny the trans survived, unless it was removed during the race career.


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## geeteeohguy (Feb 2, 2008)

My '65 has the original M-20 in place. It is also the only original part of the drivetrain (along with the driveshaft). I blew out the front bearing retainer in '82 or '83, and rebuilt it then. It's still fine. My original WS 389 got blown up at Baylands Raceway in Fremont, CA, around 1978 (A few miles from where the car was built on 4/29/65!). The car had a tired 428 in it when I got it in '82, along with an open 3.23 rear end. My PHS says 3.55 posi. So, the engine got lunched, the rear end got thrashed, and only the poor, small shaft Muncie remained!!! I was able to get a '65 WT389 out of a roached '65 GTO, and I rebuilt that. The rear end came out of a '66 GTO that was given to me as a parts car. It was a 3.90 posi, but I changed the gears to 3.36. I agree, though. These early Muncies are usually not as durable as the rest of the powertrain. I guess it's luck of the draw. An M20 is more desirable than an M21 if you're running a streetable (3.55 or numerically lower) gear. M21's came in the 3.90 and 4.33 geared cars. If you're going to run it hard, a later and stronger unit is the way to go.


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## Chris Holabaugh (Jan 18, 2009)

*Thanks again for all of the info..*

The rear is a 12 bolt and had 410's, but have lowered them to 373's. The engine is a 455 that is 30 over and makes around 500+ horsepower. The car will just be driven to the shows, so I think the transmission should be okay. At present all that needs to be done is to have the engine put back together. The first engine builder made many errors and what is funny is that they build motors for circle track. Once it is finished I will post pictures.


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## 66tempestGT (Nov 28, 2009)

why wait till its finished? :cheers


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## Bobbyg (Jul 22, 2009)

Did someone mention pictures???


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## Too Many Projects (Nov 15, 2008)

Chris Holabaugh said:


> The rear is a 12 bolt and had 410's, but have lowered them to 373's. The engine is a 455 that is 30 over and makes around 500+ horsepower. The car will just be driven to the shows, so I think the transmission should be okay. At present all that needs to be done is to have the engine put back together. The first engine builder made many errors and what is funny is that they build motors for circle track. Once it is finished I will post pictures.





66tempestGT said:


> why wait till its finished? :cheers


Made the motion



Bobbyg said:


> Did someone mention pictures???


Seconded it


All those in favor say ay....AY
Motion carries, pics needed now...........:rofl:


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