Converting a close ratio Muncie to a wide ratio

[Michael J.]

I am interested in knowing if anyone has had experience doing this, I have a '64 close ratio original, VIN stamped case I would like to convert to a wide ratio gearing inside. I have a 3.08 rear end ratio and think it would work better for drivability. Thanks for any help.

[Douglas L.]

Re: Converting a close ratio Muncie to a wide ratio

Hi Michael, how have you been? Although I've never done it I believe the only difference between the M20 and M21 is the input gear and the cluster(countershaft) gear(s). I believe everything else can be reused. As I understand it, the difference is the tooth count on the the input shaft gear and the most forward gear on the countershaft.

Doug

[Joe L.]

Re: Converting a close ratio Muncie to a wide ratio

Hi Michael, how have you been? Although I've never done it I believe the only difference between the M20 and M21 is the input gear and the cluster(countershaft) gear(s). I believe everything else can be reused. As I understand it, the difference is the tooth count on the the input shaft gear and the most forward gear on the countershaft.

Doug

Doug and Michael------

Yup, that's how it is. All that needs to be changed are the input gear and the countergear. These gears are long-since GM-discontinued but are available in the aftermarket as manufactured by Masiero S.A.

Of course, when doing this one should go through the transmission and replace other parts, as needed.

[Michael J.]

Re: Converting a close ratio Muncie to a wide ratio

Thanks Guys! Joe, we are going through it now to see what needs attention but wanted to make it a better driver in the process. And Doug I am doing well and hope to have this car to SoCal chapter judging before year end, if I and my helpers can get all the stuff sorted out that is, much to do, so hope to see you there.

[Chris B.]

Re: Converting a close ratio Muncie to a wide ratio

Michael, I had my M-21 tranny rebuilt as part of my 68 L68 project restoration. My guy suggested I replace the close ratio first gear with the wide ratio first gear. He said that with the 3:36 gear in back it would work much better for around town driveability. I had him do that as it made sense to me but I won't be on the road for some time so can't say for sure yet. Regards, Chris

[Loren L.]

Re: Converting a close ratio Muncie to a wide ratio

Is there a reason to not just go out and buy a '65 vintage wide ratio transmission and go through it with new brass and bearings?

[Michael J.]

Re: Converting a close ratio Muncie to a wide ratio

Well I prefer to keep the original '64 VIN stamped tranny in the car for many reasons.

[Tom P.]

Re: Converting a close ratio Muncie to a wide ratio

Michael, I had my M-21 tranny rebuilt as part of my 68 L68 project restoration. My guy suggested I replace the close ratio first gear with the wide ratio first gear. He said that with the 3:36 gear in back it would work much better for around town driveability. I had him do that as it made sense to me but I won't be on the road for some time so can't say for sure yet. Regards, Chris

First of all, in the past 50yrs that I've been rebuilding Muncies (and T-10s) I've done multiple gear ratio changes to Muncies. And as mentioned above, ALL that has to be done to change from wide to close, or close to wide, ratio is simply replacing the input and cluster gears. It's just that simple.
BUUUUUUUUUUUUUUUUT, next, There is no such thing as a wide or close ratio first gear in a Muncie-------------NONE!!! With the lone exception of the 63 first gear (same ratio, but totally different, one year only) in a Muncie, ALLLLLLLLLLLLLLLLLL 1st, 2nd, 3rd gears in ALLLLLLLLLLLL Muncies (except, of course, the M22) are the same. ONLY the input and cluster gears differ.
I hope I'm not being presumptuous, but I guess everyone knows that the 63-65 Muncies had the smaller 7/8in cluster gear shaft and the 66-later Muncies had the larger 1in shaft--------------------which is a nice upgrade that can be done to the 63-65 Muncies. Simply have the case bored out (BY AN EXPERIENCED, COMPETENT TRANSMISSION SHOP) to accept a 1in shaft and then install the input/cluster gears for a 66-74 Muncie. And if you really want to take it one step further, use the 26spline 71-74 input.

[Duke W.]

Re: Converting a close ratio Muncie to a wide ratio

I am interested in knowing if anyone has had experience doing this, I have a '64 close ratio original, VIN stamped case I would like to convert to a wide ratio gearing inside. I have a 3.08 rear end ratio and think it would work better for drivability. Thanks for any help.

The trouble with the way the WR is implemented by the simple expedient of a different clutch gear and countergear shaft with a steeper reduction ratio with the same other tooth counts on the meshing gears so both versions could use the same mainshart gears means the first three ratios are shorter with the same spacing as the CR, then there's a HUGE gap to fourth, and the engine just falls on it's face regardless of how low or high you rev it.

If this is your recently procured '64 FI, then performance with a CR trans/3.08 axle will be less than user friendly with the notoriously torque-shy 30-30 cam and further deteriorated by you high altitude.

Another choice, which might make more sense, and not cost much more is to buy and bolt in a Richmond Super T-10 wide ratio (2.64, 1.75, 1.34, 1.0:1), which has "progressive gear spacing", so the biggest gap is 1-2 and it gets closer with 2-3, and again with 3-4. Even better for your application might be the the 2.88, 1.91, 1.33, 1.00:1 progressive ratio gear set, which will give you a 31 PERCENT shorter first with only marginally more 3-4 spacing than the CR Muncie. (Given how picky I am about ratio spacing I would prefer a 1.88 second, but most probably couldn't detect the difference.)

The B-W Super T-10 was used on Corvettes beginning sometime in the seventies when GM stopped manufacturing four-speed manuals, and it should be pretty much a "bolt-in" other than maybe requiring a different spline count clutch disk and output yoke. Richmond bought the tooling and continued production sometime in the eighties.

Search for a recent thread started by me about a "gear chart". It's an Excel program that allows to you input gearing, tire, and shift point data to "design" your gear set, and if you can figure out how to plot the speed-rpm lines you get a gold star. I was able to do it once, but forgot how.

You can find out more on the Richmond website. Here's the link to the Super T-10 data.

http://www.richmondgear.com/pdf/RG25.pdf

Duke

[Michael J.]

Re: Converting a close ratio Muncie to a wide ratio

Thanks Duke, that is something else to consider. Yes, it is the fuelie and I have also considered putting in a 4.11 rear end, but really wanted something better suited for touring. Around town kind of stuff is not as important as touring at highway speeds, which is most of what I will be doing with it. My '64 L76 has the CR and a 3.70 rear, which seems about right too. But I also really wanted to retain the original 3.08 since it is such an unusual gear, so lots to consider.

[Duke W.]

Re: Converting a close ratio Muncie to a wide ratio

I've always said that a CR/3.08 drivetrain is like a five-speed with no first, and a CR/4.11 is like a five-speed with no fifth. If your primary application will be touring then maybe it's not worth the effort and expense to make any changes.

The 3.08 is a good cruise gear - about 3100 at 80, and a SHP/FI engine is just loafing while delivering about 20 MPG, and there is plenty of reserve power to accelerate briskly without downshifting.

The tall gear is only an issue in getting the car rolling from a dead stop, so hilly urban terrain or stop-and-go driving can be a chore, but above about 15 MPH tall gears are great.

Back in the day when I accepted most rolling start challenges, my strategy was to go from 40 MPH, and I was in first gear!

Duke

[Michael J.]

Re: Converting a close ratio Muncie to a wide ratio

Very true Duke, and with that MPG I can see the rationale for the original owner (a lady I believe) equipping it that way for the rally competitions she was contemplating. BTW, just drove my '64 L76 (with the 3.70 rear) on a long trip today and averaged 16 MPG, which I was pretty happy with too.