DRR

I have a '98 vert 6sp with trans problems. I can replace my old MN6 with a new MN12, LS6 clutch kit, master and slave cyls. I will not be changing my 3.42 diff. How is the MN12 different from the MN6. Gear ratios? Beefier parts? S/S shift forks? Is the MN12 a better trans? Thanks, Doug

pburant

The M12 has lower gears (higher numeric ratio) than the M6 for gears 1-3. Fourth is the same as M6 at 1:1. I do believe the two overdrive gears are also lower on the M12, but I can't recall for sure. An M12 with a 3.42 rear end is roughly the equivalent of using a 3.8 rear end with an M6 trans (somewhere between a 3.73 and 3.90).

The other main difference is that the gears are spaced further apart on the M12 due to the LS6 having a wider bandwidth than the LS1.

I don't kno whether the M12 has any beefier parts. It really jwouldn't need to, as the rear end and output shafts seem to fail before any trans. parts (as a result of excess power, that is).

-Pete

RPOZ4Z

go for it, the MN12 has better gearing, but I believe the final drive ratio is the same.

Richin Chicago

The MN12 is lower in all gears except 4th.(1 to 1)
The MN12 is the equivalent of changing to a 3.90 differential and should be well worth it.

Madkarter

it depends on what your looking for. i think the m12 is better for drag racing, because of the low 1st gear, and i like the m6 for road racing because the gears are closer together. iv'e got both.

happa

Go for the M12!

nwdanner

Without a doubt!

msuc5vette

depends on cost difference...

DRR

Any one out there know the factual difference between M12 and MN6. I would like to do this right the first time. Doug

Richin Chicago

What do you mean by factual?
Ratios? Performance differences?

Here is some more information:

http://www.z06vette.com/forums/archi...ex.php/t-37054

John Shiels

m12

DRR

[QUOTE=Richin Chicago]What do you mean by factual?
Ratios? Performance differences?

I am looking at replacing my '98 MN6. It has several weak points, alum shift forks, stamped slider keys, and weak syncronizers. So, I am trying to find out if these problems are corrected on the new M12. I am not looking for opinions, only verifiable facts. Thanks, Doug

C54FUN

I just had the Vette Doctors change out my MN6 for a M12 which with my 4.10 rear provides awesome performance in the lower three gears. It is the lower three gears where the difference is. I waited until I had to change or repair my MN6 before I did this; I also went ahead at that time and changed out my Z06 clutch and slave to an Exedy. I haven't stopped smiling since these changes. Good luck with your choices.
Joe

ZO6vettepilot

MN6 MN12
1st 2.66 2.97
2nd 1.78 2.07
3rd 1.30 1.43

4th 1.00 1.00

5th 0.74 0.84
6th 0.50 0.57

The MN 12 transmission to the best of my knowledge does not have higher grade materials than the same year MN6 units. Any improvements incorporated into either were also incoporated into the other, things such as the improved shifter rod, blocker rings etc.
The MN12 is a wide ratio transmission, the ratios were selected to take advantage of the LS6 power curve and higher RPM capabilities.
However, the LS1 power curve is very close to the LS6 below 4500 RPM, so I think the LS1 will do very well with the new ratios throughout the RPM range. Your will notice your RPM will be about 300 higher in 6th when on the highway cruising, and that may improve your passing /acceleration potential.
The clutch was improved for the Z06 in 2002. I'm not absolutely certain if it was improved in the 2001 Z06 model or not. I'm assumming it was, then upgraded again when the LS6 went to the 405 HP in 2002.

So as others have already said... go for it.

zo6vettepilot

DRR

Thanks to all for the advise and info. The latest info I found today is from Tom @ Fitchners and he found a new part # for the M12. He says this means that it was changed/upgraded. In what way is unknown. The part # for this 2nd design is 12589534. Problem is that there are 10 of the old #12561852 left in Lansing and the new ones won't be available until the old one are gone. Meanwhile my search for info go on. Doug

0rodney@rpmtransmissions

The old part # 12561852 uses silicone to seal the tail housing to the main case,which is prone to leak eventually. The new part # 12589534 uses a gasket between the two halves and NO silicone. Othger than the gasket/silicone the units are the same.

DRR

Thanks Rodney. I was hoping there would be improvement in the weak spots. (alum shift forks, composite blocker rings, stamped slider keys, weak syncronizers) I am still undecided as to go with your rebuild or a new M12. Doug

Tino

Here is a different perspective from an old drag racer. My 04 vert is a stocker so this is not based on experience with my vette. I have found that for stock displacement/output motors, the MN12 gear ratio's (higher numeric numbers) work best as they help put the motor into the power band quicker and make use of the stock output better for quarter mile usage. When you start building stroker motors or just stock displacement engines with serious torque, I found that the MN6 type gear ratios (lower numeric numbers) worked best as they would allow the motor to grunt and work through the power band.

For a stocker go with the MN12, if you plan on putting some serious torque and hp into your ride ??? You may want to reconsider. Just a different perspective and my .02

Best of luck in your decision.

Tino

Dope

As I mentioned in my PM, definitely give Rodney a good consideration. In the end you'll have a stronger and more reliable transmission. And it'll cost less than a new M12 or M6. What's there to lose?

Dope

hflynn

Use Rodney. He took care of me and I've got a year, 5000 miles and three track events on the m12 no issues. If nervous go watch him work, very thorough and fast. Not to mention reasonable.