bb5401000

iTrader: (2)

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.

Bangin Bob

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.

thesource

iTrader: (60)

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 .

Uncle Skeletor

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.

thesource

iTrader: (60)

The input shaft and head gear tooth count effects all of the gear rations but there are two different tooth counts for both the 5th & 6th gears .

85MikeTPI

iTrader: (9)

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

bb5401000

iTrader: (2)

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!

98TADRIVER

iTrader: (36)

thatd be pretty sweet, 5th gear would pull harder and maybe 6th gear might actually pull at higher speeds lol

LSGunZ28

iTrader: (8)

Id want a .68 5th, instead of .74... and .37 6th.. a higher top speed and insane gas mileage with 6th gear

85MikeTPI

iTrader: (9)

Yes.. I thought you were asking if you could exchange parts, not trying to change ratios. If you wanted different ratios, the best bet would be to get some '93 5/6 gears (M28/M29) which did have different tooth counts.

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..)

85MikeTPI

iTrader: (9)

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.

bearcatt

iTrader: (41)

Wow this is very good information here.
So good I had to book mark it.


.

Harryoz

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

85MikeTPI

iTrader: (9)

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

vtirocz

Excellent info!! If I had a M12, could I change the 6th gear mainshaft to 26t (this is the gear that's also on the 2nd counter gear), which would result in a 0.511 6th gear? i.e. The 6th gear ext. gear is 67t, mainshaft 26t = 0.388/ .76 = 0.56.

85MikeTPI

iTrader: (9)

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.

jmd

iTrader: (4)

That you couldn't pull due to rpm that was too low unless you went to rear gears like 4.56. This would in turn create a higher driveline rpm speed and critical driveshaft speeds at extremely low mph.

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.

smurray

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.

85MikeTPI

iTrader: (9)

No.. Read down further to post# 16.. You can only swap out 5&6 gears between units, the 1-4 gears are exact fit and must remain paired between driven cluster and mainshaft drive gears.

Harryoz

For anyone interested in some research on the Vanquish v MM6 T56 gearboxes, see here

http://www.pistonheads.co.uk/gassing...20Monaro%20T56