5/6 gear swap
#1
On The Tree
Thread Starter
iTrader: (2)
Join Date: Jul 2008
Posts: 181
Likes: 0
Received 0 Likes
on
0 Posts
![](https://ls1tech.com/forums/images/ranks/ls1tech10year.png)
![Default](https://ls1tech.com/forums/images/icons/icon1.gif)
Does anyone know if you can swap out the 5/6 gear parts from a 2.66 1st gear tranny to a 2.97 1st gear tranny? It looks like you could swap out the 5/6 driven and drive gears and related parts and be good. I'm just curious.
#2
Teching In
Join Date: Dec 2008
Location: NEAR MAPLE GROVE 1/4 MILE
Posts: 10
Likes: 0
Received 0 Likes
on
0 Posts
![Default](https://ls1tech.com/forums/images/icons/icon1.gif)
You can as long as both units are using the same type of driven gears. Some are one piece some are two. The two piece have a full spline mainshaft. Also some use single cone rings, some use three piece rings.
#3
Banned
iTrader: (60)
Join Date: Mar 2005
Location: Adkins - Tx
Posts: 2,693
Likes: 0
Received 0 Likes
on
0 Posts
![Default](https://ls1tech.com/forums/images/icons/icon1.gif)
As long as you use the complete setup , it will work fine . All of the GM and Viper stuff uses a 1 piece main shaft gear . The Terminator Ford and Aston Martins use a two piece main shaft gear and those are fully splined .
#4
Teching In
Join Date: Mar 2008
Location: Kennewick, WA
Posts: 5
Likes: 0
Received 0 Likes
on
0 Posts
![Default](https://ls1tech.com/forums/images/icons/icon1.gif)
Don't quote me on this, I'm not sure of it myself, but I believe that the big difference between 2.66 and 2.97 trannys is the tooth count on the input shaft gear and it's driven gear on the countershaft. All ratios (except fourth, your direct drive) are affected by this initial reduction, even your overdrives.
What this boils down to (and again, I'm not certain, it's just a theory) is that I think the overdrive gears are the same between the 2.97 and 2.66 trannys. The initial reduction at the input to the countershaft is what changes your overdrive ratios.
But to answer your question, I don't believe there would be any issue changing the overdrive gears out between the two transmission.
What this boils down to (and again, I'm not certain, it's just a theory) is that I think the overdrive gears are the same between the 2.97 and 2.66 trannys. The initial reduction at the input to the countershaft is what changes your overdrive ratios.
But to answer your question, I don't believe there would be any issue changing the overdrive gears out between the two transmission.
Last edited by Uncle Skeletor; 02-17-2009 at 08:16 PM.
#6
TECH Addict
iTrader: (9)
![Default](https://ls1tech.com/forums/images/icons/icon1.gif)
The GM MM6 and MN12 5th and 6th gears are the same tooth counts, and the the 5/6 driven gear is the same on both. As mentioned, all early MM6 versions are single cone synchros, while the later MM6 and MN12s have double cones, so to use them, you'll have to use the extension shaft with them also.
The MN12 differs in the input shaft, mainshaft gears and the countershaft gear it meshes with.
This is a little sanity check I did a few years ago, on the MM6 and MN12 when I first started working on T56s:
MM6
----------------------------------------------------------------------------------
The gear on the input shaft is 31 teeth, it drives the counter shaft gear with 36 teeth, for a constant .86 reduction in countershaft speed.
The 1st gear counter gear is 17t, mainshaft 39t = 2.294 / .86 = 2.66
The 2nd gear counter gear is 28t, mainshaft 43t = 1.536/ .86 = 1.78
The 3rd gear counter gear is 33t, mainshaft 37t = 1.121/ .86 = 1.30
4th gear is just locking the mainshaft to the input shaft = 1.0000000
The 5th gear ext. gear is 58t, mainshaft 37t = 0.638/ .86 = 0.740
The 6th gear ext. gear is 67t, mainshaft 29t = 0.433/ .86 = 0.503
Rev gear counter is 14t, mainshaft 35t, case 23t = 2.5 / .86 = 2.90
--------------------------------------------------------------------------
MN12
----------------------------------------------------------------------------------
The gear on the input shaft is 29 teeth, it drives the counter shaft gear with 38 teeth, for a constant .76 reduction in countershaft speed.
The 1st gear counter gear is 19t, mainshaft 43t = 2.263 / .76 = 2.97
The 2nd gear counter gear is 26t, mainshaft 41t = 1.577/ .76 = 2.07
The 3rd gear counter gear is 34t, mainshaft 37t = 1.088/ .76 = 1.43
4th gear is just locking the mainshaft to the input shaft = 1.0000000
The 5th gear ext. gear is 58t, mainshaft 37t = 0.638/ .76 = 0.84
The 6th gear ext. gear is 67t, mainshaft 29t = 0.433/ .76 = 0.56
Rev gear counter is 14t, mainshaft 35t, case 23t = 2.5 / .76 = 3.28
The MN12 differs in the input shaft, mainshaft gears and the countershaft gear it meshes with.
This is a little sanity check I did a few years ago, on the MM6 and MN12 when I first started working on T56s:
MM6
----------------------------------------------------------------------------------
The gear on the input shaft is 31 teeth, it drives the counter shaft gear with 36 teeth, for a constant .86 reduction in countershaft speed.
The 1st gear counter gear is 17t, mainshaft 39t = 2.294 / .86 = 2.66
The 2nd gear counter gear is 28t, mainshaft 43t = 1.536/ .86 = 1.78
The 3rd gear counter gear is 33t, mainshaft 37t = 1.121/ .86 = 1.30
4th gear is just locking the mainshaft to the input shaft = 1.0000000
The 5th gear ext. gear is 58t, mainshaft 37t = 0.638/ .86 = 0.740
The 6th gear ext. gear is 67t, mainshaft 29t = 0.433/ .86 = 0.503
Rev gear counter is 14t, mainshaft 35t, case 23t = 2.5 / .86 = 2.90
--------------------------------------------------------------------------
MN12
----------------------------------------------------------------------------------
The gear on the input shaft is 29 teeth, it drives the counter shaft gear with 38 teeth, for a constant .76 reduction in countershaft speed.
The 1st gear counter gear is 19t, mainshaft 43t = 2.263 / .76 = 2.97
The 2nd gear counter gear is 26t, mainshaft 41t = 1.577/ .76 = 2.07
The 3rd gear counter gear is 34t, mainshaft 37t = 1.088/ .76 = 1.43
4th gear is just locking the mainshaft to the input shaft = 1.0000000
The 5th gear ext. gear is 58t, mainshaft 37t = 0.638/ .76 = 0.84
The 6th gear ext. gear is 67t, mainshaft 29t = 0.433/ .76 = 0.56
Rev gear counter is 14t, mainshaft 35t, case 23t = 2.5 / .76 = 3.28
Last edited by 85MikeTPI; 02-18-2009 at 07:24 AM.
#7
On The Tree
Thread Starter
iTrader: (2)
Join Date: Jul 2008
Posts: 181
Likes: 0
Received 0 Likes
on
0 Posts
![](https://ls1tech.com/forums/images/ranks/ls1tech10year.png)
![Default](https://ls1tech.com/forums/images/icons/icon1.gif)
Interesting. Since the tooth count between the two transmissions is the same for the 5th and 6th gears, their final drive ratios would not change if you swapped them, i.e. the MN12 would still have a .56 final drive ratio with the MM6 gears!
Trending Topics
#10
TECH Addict
iTrader: (9)
![Default](https://ls1tech.com/forums/images/icons/icon1.gif)
I don't have the tooth ratio's handy to do the math, but I do have 2 sets
of them at home, I'll try to remember to grab the tooth counts and post back.
(My feeble brain seems to remember that a M29 5/6 set in a MM6 will move the .74/.50 ratio to .82/.58, but don't hold me to it..)
#11
TECH Addict
iTrader: (9)
![Default](https://ls1tech.com/forums/images/icons/icon1.gif)
The '93 M29 5/6 gears are:
The 5th gear ext. gear is 59t, mainshaft 36t = 0.610/ .76 = 0.80
The 6th gear ext. gear is 65t, mainshaft 31t = 0.477/ .76 = 0.62
The input/counter reduction ratio is the same as the M12, so putting the '93 5/6 driven and drive gears in one would give the same .80 and .62 ODs.
Putting them in the .86 ratio MM6, would give 0.710 5th gear, and a 0.555 6th gear.
The 5th gear ext. gear is 59t, mainshaft 36t = 0.610/ .76 = 0.80
The 6th gear ext. gear is 65t, mainshaft 31t = 0.477/ .76 = 0.62
The input/counter reduction ratio is the same as the M12, so putting the '93 5/6 driven and drive gears in one would give the same .80 and .62 ODs.
Putting them in the .86 ratio MM6, would give 0.710 5th gear, and a 0.555 6th gear.
#13
![Default](https://ls1tech.com/forums/images/icons/icon1.gif)
This has been a fantastic resource for me whilst trying to work out what to change on my GM MM6.
I want to bring 5th and 6th closer to a ratio of 0.84 and 0.70. As a complete novice to this, is it just a case of changing the 5th and 6th ext gear? With all other things remaining the same?
This gives a tooth count of 51 for 5th and 48 for 6th
Can anyone confirm I have this right? Do such gears exist?
Cheers
I want to bring 5th and 6th closer to a ratio of 0.84 and 0.70. As a complete novice to this, is it just a case of changing the 5th and 6th ext gear? With all other things remaining the same?
This gives a tooth count of 51 for 5th and 48 for 6th
Can anyone confirm I have this right? Do such gears exist?
Cheers
#14
TECH Addict
iTrader: (9)
![Default](https://ls1tech.com/forums/images/icons/icon1.gif)
Not that I'm aware of.. There was only one new ratio set added to the GM T56, and that was the MZ6 (Z51 vette) in 2006 and it would appear to take the gears in the opposite direction as you're trying to obtain.
__GEAR______Model__or__Option
____________Z06___Std_6-spd___Z51_6-spd____M12
__1st_______2.66____2.66________2.97________2.97
__2nd_______1.78____1.78________2.07_______2.07
__3rd_______1.30____1.30________1.43________1.43
__4th_______1.00____1.00________1.00________1.00
__5th_______0.74____0.74________0.71________0.84
__6th_______0.50____0.50________0.57________0.57
Reverse_____2.90____2.90________3.28________2.90
__GEAR______Model__or__Option
____________Z06___Std_6-spd___Z51_6-spd____M12
__1st_______2.66____2.66________2.97________2.97
__2nd_______1.78____1.78________2.07_______2.07
__3rd_______1.30____1.30________1.43________1.43
__4th_______1.00____1.00________1.00________1.00
__5th_______0.74____0.74________0.71________0.84
__6th_______0.50____0.50________0.57________0.57
Reverse_____2.90____2.90________3.28________2.90
#15
Launching!
Join Date: Mar 2006
Location: Indianapolis, IN
Posts: 285
Likes: 0
Received 0 Likes
on
0 Posts
![](https://ls1tech.com/forums/images/ranks/ls1tech10year.png)
![Default](https://ls1tech.com/forums/images/icons/icon1.gif)
The GM MM6 and MN12 5th and 6th gears are the same tooth counts, and the the 5/6 driven gear is the same on both. As mentioned, all early MM6 versions are single cone synchros, while the later MM6 and MN12s have double cones, so to use them, you'll have to use the extension shaft with them also.
The MN12 differs in the input shaft, mainshaft gears and the countershaft gear it meshes with.
This is a little sanity check I did a few years ago, on the MM6 and MN12 when I first started working on T56s:
MM6
----------------------------------------------------------------------------------
The gear on the input shaft is 31 teeth, it drives the counter shaft gear with 36 teeth, for a constant .86 reduction in countershaft speed.
The 1st gear counter gear is 17t, mainshaft 39t = 2.294 / .86 = 2.66
The 2nd gear counter gear is 28t, mainshaft 43t = 1.536/ .86 = 1.78
The 3rd gear counter gear is 33t, mainshaft 37t = 1.121/ .86 = 1.30
4th gear is just locking the mainshaft to the input shaft = 1.0000000
The 5th gear ext. gear is 58t, mainshaft 37t = 0.638/ .86 = 0.740
The 6th gear ext. gear is 67t, mainshaft 29t = 0.433/ .86 = 0.503
Rev gear counter is 14t, mainshaft 35t, case 23t = 2.5 / .86 = 2.90
--------------------------------------------------------------------------
MN12
----------------------------------------------------------------------------------
The gear on the input shaft is 29 teeth, it drives the counter shaft gear with 38 teeth, for a constant .76 reduction in countershaft speed.
The 1st gear counter gear is 19t, mainshaft 43t = 2.263 / .76 = 2.97
The 2nd gear counter gear is 26t, mainshaft 41t = 1.577/ .76 = 2.07
The 3rd gear counter gear is 34t, mainshaft 37t = 1.088/ .76 = 1.43
4th gear is just locking the mainshaft to the input shaft = 1.0000000
The 5th gear ext. gear is 58t, mainshaft 37t = 0.638/ .76 = 0.84
The 6th gear ext. gear is 67t, mainshaft 29t = 0.433/ .76 = 0.56
Rev gear counter is 14t, mainshaft 35t, case 23t = 2.5 / .76 = 3.28
The MN12 differs in the input shaft, mainshaft gears and the countershaft gear it meshes with.
This is a little sanity check I did a few years ago, on the MM6 and MN12 when I first started working on T56s:
MM6
----------------------------------------------------------------------------------
The gear on the input shaft is 31 teeth, it drives the counter shaft gear with 36 teeth, for a constant .86 reduction in countershaft speed.
The 1st gear counter gear is 17t, mainshaft 39t = 2.294 / .86 = 2.66
The 2nd gear counter gear is 28t, mainshaft 43t = 1.536/ .86 = 1.78
The 3rd gear counter gear is 33t, mainshaft 37t = 1.121/ .86 = 1.30
4th gear is just locking the mainshaft to the input shaft = 1.0000000
The 5th gear ext. gear is 58t, mainshaft 37t = 0.638/ .86 = 0.740
The 6th gear ext. gear is 67t, mainshaft 29t = 0.433/ .86 = 0.503
Rev gear counter is 14t, mainshaft 35t, case 23t = 2.5 / .86 = 2.90
--------------------------------------------------------------------------
MN12
----------------------------------------------------------------------------------
The gear on the input shaft is 29 teeth, it drives the counter shaft gear with 38 teeth, for a constant .76 reduction in countershaft speed.
The 1st gear counter gear is 19t, mainshaft 43t = 2.263 / .76 = 2.97
The 2nd gear counter gear is 26t, mainshaft 41t = 1.577/ .76 = 2.07
The 3rd gear counter gear is 34t, mainshaft 37t = 1.088/ .76 = 1.43
4th gear is just locking the mainshaft to the input shaft = 1.0000000
The 5th gear ext. gear is 58t, mainshaft 37t = 0.638/ .76 = 0.84
The 6th gear ext. gear is 67t, mainshaft 29t = 0.433/ .76 = 0.56
Rev gear counter is 14t, mainshaft 35t, case 23t = 2.5 / .76 = 3.28
#16
TECH Addict
iTrader: (9)
![Default](https://ls1tech.com/forums/images/icons/icon1.gif)
Ummm No.. Have you ever opened up a T56 ? You can't just arbitrarily change around gears. Also, the GM units have a 1 piece 5-6 driven gear on the mainshaft, so you can't change 5 and 6th ratios independently. You'd have to find a complete 5/6 extension (drive gear cluster) and the matching 5/6 driven gear and install them as a set. As this thread shows, the 5-6 tooth ratios between the MM6 and MN12 are exactly the same, so you can't change ratios by swapping parts between them.
#17
TECH Addict
iTrader: (4)
![Post](https://ls1tech.com/forums/images/icons/icon1.gif)
Take note of some German cars built for autobahn use. 5th or 6th tends to be closer to 1.00:1 and the rear gears tend to be in the 2.xx range. This is for lower driveline speed at 100mph+ speeds.
As well,
Super wide spreads between gears make the car less enjoyable and tractable to drive. Going from a .68 fifth to a .37 sixth would suck. Being forced to hold a gear longer because you can't yet use the next highest gear hurts mileage. Being able to use a .75 5th around town in the T56 helps mileage compared to not being able to use a .62 5th until higher mph, as an example.
Notice the MN12 spread between gears is a very similar % drop between 1-2 and 2-3 and 3-4. The time and expense put into the available ratios in the production T56s was not wasted.
Last edited by jmd; 07-22-2010 at 04:56 PM.
#18
![Default](https://ls1tech.com/forums/images/icons/icon1.gif)
forgive me for resurrecting such an old thread but its very relevant to my question.
According to 85MikeTPI's #6 post, would it be possible to swap MM6 counter/ext gears into an M12 T56?
this would result in a strange gear spread (by my tard-math 1st-3.32, 2nd-1.92, 3rd-1.47 4th-1 5th-.84 6th-.56 respectively) but this would be better suited to a theoretical project of mine.
Really im just trying to increase my understanding of hybrid t56 options.
According to 85MikeTPI's #6 post, would it be possible to swap MM6 counter/ext gears into an M12 T56?
this would result in a strange gear spread (by my tard-math 1st-3.32, 2nd-1.92, 3rd-1.47 4th-1 5th-.84 6th-.56 respectively) but this would be better suited to a theoretical project of mine.
Really im just trying to increase my understanding of hybrid t56 options.
#19
TECH Addict
iTrader: (9)
![Default](https://ls1tech.com/forums/images/icons/icon1.gif)
forgive me for resurrecting such an old thread but its very relevant to my question.
According to 85MikeTPI's #6 post, would it be possible to swap MM6 counter/ext gears into an M12 T56?
this would result in a strange gear spread (by my tard-math 1st-3.32, 2nd-1.92, 3rd-1.47 4th-1 5th-.84 6th-.56 respectively) but this would be better suited to a theoretical project of mine.
Really im just trying to increase my understanding of hybrid t56 options.
According to 85MikeTPI's #6 post, would it be possible to swap MM6 counter/ext gears into an M12 T56?
this would result in a strange gear spread (by my tard-math 1st-3.32, 2nd-1.92, 3rd-1.47 4th-1 5th-.84 6th-.56 respectively) but this would be better suited to a theoretical project of mine.
Really im just trying to increase my understanding of hybrid t56 options.
#20
![Default](https://ls1tech.com/forums/images/icons/icon1.gif)
For anyone interested in some research on the Vanquish v MM6 T56 gearboxes, see here
http://www.pistonheads.co.uk/gassing...20Monaro%20T56
http://www.pistonheads.co.uk/gassing...20Monaro%20T56