Original Muncie with new overdrive gearing?
12-16-2011, 02:47 PM
#1
Le Mans Master
Thread Starter
Original Muncie with new overdrive gearing?
Ok, I am game to listen to lowering my rpms on my L79 66 with a M-20 wide ratio and a 3.70 rear.
I do not want to give up using the orignal tranny, as it is a original engine drive train car that I have owned for 42 years.
I have read about the 3rd and 4th gear change, and on the T6 tread I asked about it but did not want to HI Jack .
Has anyone done the conversion? I know you put a new gear set in. I think AutoGear (they make new Muncies ?) has the gear set ?
I love my present set up, but after 35,000 miles in the last 18 months, and a possible new long adventure coming up, I would like to lose some rpms at 75 or 80 mph. I am at 3200 at 70 ish.
I may want to do it over the winter. So let me know of any experience with the change and if you would do it again.
Thanks for the help
Jack
I do not want to give up using the orignal tranny, as it is a original engine drive train car that I have owned for 42 years.
I have read about the 3rd and 4th gear change, and on the T6 tread I asked about it but did not want to HI Jack .
Has anyone done the conversion? I know you put a new gear set in. I think AutoGear (they make new Muncies ?) has the gear set ?
I love my present set up, but after 35,000 miles in the last 18 months, and a possible new long adventure coming up, I would like to lose some rpms at 75 or 80 mph. I am at 3200 at 70 ish.
I may want to do it over the winter. So let me know of any experience with the change and if you would do it again.
Thanks for the help
Jack
12-16-2011, 02:56 PM
#2
Le Mans Master
jack, i could be wrong on the ratio's but i think there is a 3-4 gearset that drops 4th to a .80??.....that would drop your cruise rpm by 20%
you can do the math, if you are cruising at 3500, then it would drop to approx. 700 less
why not just baggie the original 4 way and buy a tko??....the reason i say this is by converting your original, you may not like the gear spread from 2nd to 3rd, the tko does not have that issue because of the 5 speeds......i heard hogan called your top guy and changed the color??.......
ps....you should shoot for around a .70 or so with the 370
you can do the math, if you are cruising at 3500, then it would drop to approx. 700 less
why not just baggie the original 4 way and buy a tko??....the reason i say this is by converting your original, you may not like the gear spread from 2nd to 3rd, the tko does not have that issue because of the 5 speeds......i heard hogan called your top guy and changed the color??.......
ps....you should shoot for around a .70 or so with the 370
Last edited by midyearvette; 12-16-2011 at 03:03 PM.
12-16-2011, 03:20 PM
#3
Race Director
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St. Jude Donor '07
OK, here's what i posted in the T5 thread:
the gears in the MY6 trans are: 3.09 1st, 1.68 2nd, 1:1 3rd, and .73 4th. Also note that this is practically identical to the gearing in the 700R4 GM automatic trans.
the ratios on the M21Y (overdrive) 4 speed
2.199 1.506 1.000 0.859
the muncie OD gears would probably be better for your 3.70 rer as 1st gear would be a bit steep with the my6. i use the MY6 with a 3.36 rer. the downside in your case is that you now have a 2.54 1st that with your 3.70 = 9.4. the M21Y would give you 2.2 x 3.70 = 8.14 which is ok if you have the lowend torque but might take some getting used to for launch in everyday driving (although that should be the standard OEM close ratio/rearend gear combo.)...
1st with MY6: 3.09 x 3.36 = 10.38
1st with M21Y: 2.199 x 3.70 = 8.136
OD with MY6: .73 x 3.36 = 2.45
OD with M21Y: .859 x 3.70 = 3.18
the M21Y would give an effective rer somewhere between a 3.08 and a 3.36. better for cruising than you have now.
3rd gear becomes 1 to 1 and then 4th becomes OD. this is done by making a new cluster gear that reverses the positions of what would normally be the 3 & 4 gears on the cluster gear and then the 3/4 linkage arm on the side of the transmission is flipped to reverse the gear selection. your normal H-pattern or shifting is not changed, 4th position just becomes OD.
a google search for M21Y says the gear set is about $800 and a complete transmission about $1900. i don't see much sense to you taking apart your #s matching (unless it could use rebuilding...), so the common sense thing would to be to find a used muncie and build it, or find a MY6 (they come up on ebay every once in a while..) or go the tremec route.
as you can see from the info i gave on the gear ratios for the MY6 (above), there is quite a spread between gears compared to a tremec or even a non OD muncie, but i have found no problem with the gear spacing in everyday driving, so except for a slightly higher OD ratio, i don't see the M21Y muncie would be a problem either.
Bill
the gears in the MY6 trans are: 3.09 1st, 1.68 2nd, 1:1 3rd, and .73 4th. Also note that this is practically identical to the gearing in the 700R4 GM automatic trans.
the ratios on the M21Y (overdrive) 4 speed
2.199 1.506 1.000 0.859
the muncie OD gears would probably be better for your 3.70 rer as 1st gear would be a bit steep with the my6. i use the MY6 with a 3.36 rer. the downside in your case is that you now have a 2.54 1st that with your 3.70 = 9.4. the M21Y would give you 2.2 x 3.70 = 8.14 which is ok if you have the lowend torque but might take some getting used to for launch in everyday driving (although that should be the standard OEM close ratio/rearend gear combo.)...
1st with MY6: 3.09 x 3.36 = 10.38
1st with M21Y: 2.199 x 3.70 = 8.136
OD with MY6: .73 x 3.36 = 2.45
OD with M21Y: .859 x 3.70 = 3.18
the M21Y would give an effective rer somewhere between a 3.08 and a 3.36. better for cruising than you have now.
3rd gear becomes 1 to 1 and then 4th becomes OD. this is done by making a new cluster gear that reverses the positions of what would normally be the 3 & 4 gears on the cluster gear and then the 3/4 linkage arm on the side of the transmission is flipped to reverse the gear selection. your normal H-pattern or shifting is not changed, 4th position just becomes OD.
a google search for M21Y says the gear set is about $800 and a complete transmission about $1900. i don't see much sense to you taking apart your #s matching (unless it could use rebuilding...), so the common sense thing would to be to find a used muncie and build it, or find a MY6 (they come up on ebay every once in a while..) or go the tremec route.
as you can see from the info i gave on the gear ratios for the MY6 (above), there is quite a spread between gears compared to a tremec or even a non OD muncie, but i have found no problem with the gear spacing in everyday driving, so except for a slightly higher OD ratio, i don't see the M21Y muncie would be a problem either.
Bill
12-16-2011, 03:24 PM
#4
Ok, I am game to listen to lowering my rpms on my L79 66 with a M-20 wide ratio and a 3.70 rear.
I do not want to give up using the orignal tranny, as it is a original engine drive train car that I have owned for 42 years.
I have read about the 3rd and 4th gear change, and on the T6 tread I asked about it but did not want to HI Jack .
Has anyone done the conversion? I know you put a new gear set in. I think AutoGear (they make new Muncies ?) has the gear set ?
I love my present set up, but after 35,000 miles in the last 18 months, and a possible new long adventure coming up, I would like to lose some rpms at 75 or 80 mph. I am at 3200 at 70 ish.
I may want to do it over the winter. So let me know of any experience with the change and if you would do it again.
Thanks for the help
Jack
I do not want to give up using the orignal tranny, as it is a original engine drive train car that I have owned for 42 years.
I have read about the 3rd and 4th gear change, and on the T6 tread I asked about it but did not want to HI Jack .
Has anyone done the conversion? I know you put a new gear set in. I think AutoGear (they make new Muncies ?) has the gear set ?
I love my present set up, but after 35,000 miles in the last 18 months, and a possible new long adventure coming up, I would like to lose some rpms at 75 or 80 mph. I am at 3200 at 70 ish.
I may want to do it over the winter. So let me know of any experience with the change and if you would do it again.
Thanks for the help
Jack
The most effective thing you can do without all the bother (craziness)of a 5 or 6 speed is to change the rear end ratio.
You don't have frig around with mounts, ashtrays, shifters , driveshafts, yanking motors to change clutches etc etc and end up with a Volkswagen 1st gear !
You already have the perfect gear spreads in your Muncie - none of these aftermarket boxes have the nice (perfect) gear spreads that Muncies do
Seeing you already have an M-20 ; I would just change the rearend to 3.36's or if you don't mind slipping the clutch a bit, when starting off, then go for the 3.08's.
I am intending to install the same combo (M20 3.08) in my M21 3.70 equiped '59
First three gears give you ole time performance and then at 100 mph you shift into 4th for overdrive
Jerry
12-16-2011, 03:43 PM
#6
Le Mans Master
Thread Starter
I know I know
The overdrive reduction on that gearset is negligble - not worth the bother and expense - it is barely 10% if I recall correctly
The most effective thing you can do without all the bother (craziness)of a 5 or 6 speed is to change the rear end ratio.
You don't have frig around with mounts, ashtrays, shifters , driveshafts, yanking motors to change clutches etc etc and end up with a Volkswagen 1st gear !
You already have the perfect gear spreads in your Muncie - none of these aftermarket boxes have the nice (perfect) gear spreads that Muncies do
Seeing you already have an M-20 ; I would just change the rearend to 3.36's or if you don't mind slipping the clutch a bit, when starting off, then go for the 3.08's.
I am intending to install the same combo (M20 3.08) in my M21 3.70 equiped '59
First three gears give you ole time performance and then at 100 mph you shift into 4th for overdrive
Jerry
The most effective thing you can do without all the bother (craziness)of a 5 or 6 speed is to change the rear end ratio.
You don't have frig around with mounts, ashtrays, shifters , driveshafts, yanking motors to change clutches etc etc and end up with a Volkswagen 1st gear !
You already have the perfect gear spreads in your Muncie - none of these aftermarket boxes have the nice (perfect) gear spreads that Muncies do
Seeing you already have an M-20 ; I would just change the rearend to 3.36's or if you don't mind slipping the clutch a bit, when starting off, then go for the 3.08's.
I am intending to install the same combo (M20 3.08) in my M21 3.70 equiped '59
First three gears give you ole time performance and then at 100 mph you shift into 4th for overdrive
Jerry
I did not realize it was a 3.70 until last year when I brushed off the rust and read the numbers on the rear.
I should have felt the difference, but when you are 23 and going fast all the time, I just thought it was the new set of plugs that made the car zipper. The speedo never worked so I never knew how fast I was going. Silly isn't it , it was great being young.
I just look at the rear carrier bolts and the cross member and it says " no way am I coming apart easy ".
My son and I did the numbers gas use wise and it is not economical to change the rear to save on gas mileage.
somehow taking the tranny out seems less work and I know all the bolts are new.
Thanks for the info, it's the corvette thing,,,,,, nothing is broken so lets break something so we can fix it.
Jack
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Dan Hampton (03-09-2022)
12-16-2011, 05:06 PM
#8
Le Mans Master
Thread Starter
12-16-2011, 05:34 PM
#9
Le Mans Master
The overdrive reduction on that gearset is negligble - not worth the bother and expense - it is barely 10% if I recall correctly
The most effective thing you can do without all the bother (craziness)of a 5 or 6 speed is to change the rear end ratio.
You don't have frig around with mounts, ashtrays, shifters , driveshafts, yanking motors to change clutches etc etc and end up with a Volkswagen 1st gear !
You already have the perfect gear spreads in your Muncie - none of these aftermarket boxes have the nice (perfect) gear spreads that Muncies do
Seeing you already have an M-20 ; I would just change the rearend to 3.36's or if you don't mind slipping the clutch a bit, when starting off, then go for the 3.08's.
I am intending to install the same combo (M20 3.08) in my M21 3.70 equiped '59
First three gears give you ole time performance and then at 100 mph you shift into 4th for overdrive
Jerry
The most effective thing you can do without all the bother (craziness)of a 5 or 6 speed is to change the rear end ratio.
You don't have frig around with mounts, ashtrays, shifters , driveshafts, yanking motors to change clutches etc etc and end up with a Volkswagen 1st gear !
You already have the perfect gear spreads in your Muncie - none of these aftermarket boxes have the nice (perfect) gear spreads that Muncies do
Seeing you already have an M-20 ; I would just change the rearend to 3.36's or if you don't mind slipping the clutch a bit, when starting off, then go for the 3.08's.
I am intending to install the same combo (M20 3.08) in my M21 3.70 equiped '59
First three gears give you ole time performance and then at 100 mph you shift into 4th for overdrive
Jerry
Yes I concur. BUT............have you considered just mounting a much TALLER rear tire. I don't think you are tracking your car now (right?) so I sould just try a 78 series rear tire (Do the math) and get the biggest tire that will fit. It will be the cheapest (or most efficient) change you can make for gas mileage. Best of luck
12-16-2011, 06:24 PM
#10
Le Mans Master
Thread Starter
Ok
Yes I concur. BUT............have you considered just mounting a much TALLER rear tire. I don't think you are tracking your car now (right?) so I sould just try a 78 series rear tire (Do the math) and get the biggest tire that will fit. It will be the cheapest (or most efficient) change you can make for gas mileage. Best of luckSo, same engine rpm, more distance covered per rear tire revolution,,,, right? or less rpms for same distance covered .... yes
My current tires are about 26-27 inches 215 7015
Without changing rims, stock springs etc. what is that tire
215 78 15?
Sorry to sound so dumb, tracking ? No I am not I think ?
what brand tire with a white wall would you suggest and size
I have worn out the new tires I put on for the 48 state trip
So the fronts stays the same and the rear tires can be ?
Jack
12-16-2011, 06:37 PM
#11
Team Owner
Member Since: Mar 2003
Location: Greenville, Indiana
Posts: 26,118
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Merry Christmas, thanks for the card,
So, same engine rpm, more distance covered per rear tire revolution,,,, right? or less rpms for same distance covered .... yes
My current tires are about 26-27 inches 215 7015
Without changing rims, stock springs etc. what is that tire
215 78 15?
Sorry to sound so dumb, tracking ? No I am not I think ?
what brand tire with a white wall would you suggest and size
I have worn out the new tires I put on for the 48 state trip
So the fronts stays the same and the rear tires can be ?
Jack
So, same engine rpm, more distance covered per rear tire revolution,,,, right? or less rpms for same distance covered .... yes
My current tires are about 26-27 inches 215 7015
Without changing rims, stock springs etc. what is that tire
215 78 15?
Sorry to sound so dumb, tracking ? No I am not I think ?
what brand tire with a white wall would you suggest and size
I have worn out the new tires I put on for the 48 state trip
So the fronts stays the same and the rear tires can be ?
Jack
If you need a gear, I have a 3.36 or 3.08 posi out of a '76 model I'll trade you for your 3.70 if it's a posi. No real money to pay back on gas mileage except shipping.
If you figure time and money though, I wouldn't change either one for the samll, temporary benefit.
Last edited by MikeM; 12-16-2011 at 06:40 PM.
12-16-2011, 07:38 PM
#12
Le Mans Master
Rather than make my car look like a jacked up junker refugee from the '60's by putting oversize rear tires on it, I'd change the rear gear. They're not hard to change and you're not messing with your transmission ratios. Probably less trouble than a transmission.
If you need a gear, I have a 3.36 or 3.08 posi out of a '76 model I'll trade you for your 3.70 if it's a posi. No real money to pay back on gas mileage except shipping.
If you figure time and money though, I wouldn't change either one for the samll, temporary benefit.
If you need a gear, I have a 3.36 or 3.08 posi out of a '76 model I'll trade you for your 3.70 if it's a posi. No real money to pay back on gas mileage except shipping.
If you figure time and money though, I wouldn't change either one for the samll, temporary benefit.
Jack, forget the tires. This is a great deal. I recommend that you jump on it
12-16-2011, 08:17 PM
#13
Safety Car
Jack I know it's not the same as your car but i just swapped out a 4:11 rearend for a 3:08 set in my '65 P/G and what a difference, instead of 4500 RPM at 70 MPH it's now 2900 RPM well worth the effort! And the bonus is you get to clean up and repaint everything back there! 
By rob1album at 2011-12-16
By rob1album at 2011-12-16
By rob1album at 2011-12-16
By rob1album at 2011-12-16
By rob1album at 2011-12-16
By rob1album at 2011-12-16
By rob1album at 2011-12-16
By rob1album at 2011-12-16
Last edited by vt65; 12-16-2011 at 08:25 PM.
and i'm 2450 at 80...
12-17-2011, 09:51 AM
#16
Safety Car
12-17-2011, 10:28 AM
#17
12-17-2011, 03:30 PM
#19
OK, here's what i posted in the T5 thread:
the gears in the MY6 trans are: 3.09 1st, 1.68 2nd, 1:1 3rd, and .73 4th. Also note that this is practically identical to the gearing in the 700R4 GM automatic trans.
the ratios on the M21Y (overdrive) 4 speed
2.199 1.506 1.000 0.859
the muncie OD gears would probably be better for your 3.70 rer as 1st gear would be a bit steep with the my6. i use the MY6 with a 3.36 rer. the downside in your case is that you now have a 2.54 1st that with your 3.70 = 9.4. the M21Y would give you 2.2 x 3.70 = 8.14 which is ok if you have the lowend torque but might take some getting used to for launch in everyday driving (although that should be the standard OEM close ratio/rearend gear combo.)...
1st with MY6: 3.09 x 3.36 = 10.38
1st with M21Y: 2.199 x 3.70 = 8.136
OD with MY6: .73 x 3.36 = 2.45
OD with M21Y: .859 x 3.70 = 3.18
the M21Y would give an effective rer somewhere between a 3.08 and a 3.36. better for cruising than you have now.
3rd gear becomes 1 to 1 and then 4th becomes OD. this is done by making a new cluster gear that reverses the positions of what would normally be the 3 & 4 gears on the cluster gear and then the 3/4 linkage arm on the side of the transmission is flipped to reverse the gear selection. your normal H-pattern or shifting is not changed, 4th position just becomes OD.
a google search for M21Y says the gear set is about $800 and a complete transmission about $1900. i don't see much sense to you taking apart your #s matching (unless it could use rebuilding...), so the common sense thing would to be to find a used muncie and build it, or find a MY6 (they come up on ebay every once in a while..) or go the tremec route.
as you can see from the info i gave on the gear ratios for the MY6 (above), there is quite a spread between gears compared to a tremec or even a non OD muncie, but i have found no problem with the gear spacing in everyday driving, so except for a slightly higher OD ratio, i don't see the M21Y muncie would be a problem either.
Bill
the gears in the MY6 trans are: 3.09 1st, 1.68 2nd, 1:1 3rd, and .73 4th. Also note that this is practically identical to the gearing in the 700R4 GM automatic trans.
the ratios on the M21Y (overdrive) 4 speed
2.199 1.506 1.000 0.859
the muncie OD gears would probably be better for your 3.70 rer as 1st gear would be a bit steep with the my6. i use the MY6 with a 3.36 rer. the downside in your case is that you now have a 2.54 1st that with your 3.70 = 9.4. the M21Y would give you 2.2 x 3.70 = 8.14 which is ok if you have the lowend torque but might take some getting used to for launch in everyday driving (although that should be the standard OEM close ratio/rearend gear combo.)...
1st with MY6: 3.09 x 3.36 = 10.38
1st with M21Y: 2.199 x 3.70 = 8.136
OD with MY6: .73 x 3.36 = 2.45
OD with M21Y: .859 x 3.70 = 3.18
the M21Y would give an effective rer somewhere between a 3.08 and a 3.36. better for cruising than you have now.
3rd gear becomes 1 to 1 and then 4th becomes OD. this is done by making a new cluster gear that reverses the positions of what would normally be the 3 & 4 gears on the cluster gear and then the 3/4 linkage arm on the side of the transmission is flipped to reverse the gear selection. your normal H-pattern or shifting is not changed, 4th position just becomes OD.
a google search for M21Y says the gear set is about $800 and a complete transmission about $1900. i don't see much sense to you taking apart your #s matching (unless it could use rebuilding...), so the common sense thing would to be to find a used muncie and build it, or find a MY6 (they come up on ebay every once in a while..) or go the tremec route.
as you can see from the info i gave on the gear ratios for the MY6 (above), there is quite a spread between gears compared to a tremec or even a non OD muncie, but i have found no problem with the gear spacing in everyday driving, so except for a slightly higher OD ratio, i don't see the M21Y muncie would be a problem either.
Bill
Okay so to accomodate the MY6 ratio spread you have to change your rear end or else you run the risk of lugging in overdrive, so you end up with a half donkeyed 1st gear ratio of 10.38 which is the equivalent of a CR 1st with almost 4.88 gears or a WR with 4.11's.
In between you have two gears with 2nd not being too bad but 3rd is now your rear end ratio (of 3.36) !!
So after a tranny change plus a rear end swap what do you end up with : a granny 1st, an okay 2nd, a 3rd that is most peoples high gear and then your overdrive 4th.
The MY6 ratio's are spread out way to far : 1st is to low , 4th is to high.
If they reduced the spread they might have something !
If you just want to get your Vette from A to B with not much exhiliration in between then that could be the way to go.
The M21Y isn't as out to lunch on ratio's as the MY6 : 1st is the usual CR/3.70 1st, 2nd is a dragged 2nd halfway between a normal CR 2nd and 3rd, 3rd is your 3.70 normal high gear and then you have an overdrive ratio of 3.18.
WHY BOTHER ?! just put 3.36's in it and keep your perfect 1st, 2nd and 3rd ratio spread and then have your 4th gear of 3.36 which really isn't much lower than the 3.18 "overdrive" 4th of the M21Y.
Amen
Last edited by QIK59; 12-17-2011 at 03:49 PM.
12-17-2011, 04:01 PM
#20
Le Mans Master
Thread Starter
So what you are all saying.....
I was really silly to lose my 3:36 rear 40 years ago......
That for the last 40 years of fast acceleration, burning rubber....... and keeping it under 115 mph has not been worth it......
I should have stayed with the 3:36 so that I would be happy at my age now........
Life a bitch,,,,,,,,, I am going out and burn some rubber
jack
That for the last 40 years of fast acceleration, burning rubber....... and keeping it under 115 mph has not been worth it......
I should have stayed with the 3:36 so that I would be happy at my age now........
Life a bitch,,,,,,,,, I am going out and burn some rubber
jack
