PEERPSI

I've noticed these abbreviations used in a number of threads and I'm wondering what the refer too Anyone have the answer?

cdkcorvette7

The MN12 was offered in the Z06 and the MN6 came in all other C5's. As far as I know, the gear ratio is biggest difference.

0tom01ss

mn6 is stronger m12 is for road racing, mn6 is suited for drag racing.

ZZOOM06

There is no difference in strength between the 2. The MN12 has lower gearing in 1st, 2nd, 3rd, 5th and 6th gears. The Z06 with the M12 and the stock 3.42 rear end feels like a regular C5 with the M6 and 3.90 or 4.10 rear gears. Either one will work well on the road course with the stock 3.42 rear gears. Alot of drag racers favor the M6 with 4.10's behind it. Personally, I like the M12 in my car with the 3.42 rear, but I have ALOT more torque than a stock car.

Jimbo

Mark C5

MN6 is the RPO code for a vehicle equipped with a manual transmission. There is no such thing as a MN12. In a C5 Corvette the Z06 got a M12 transmission. All other models with a manual transmission (Coupe, Vert, and Hardtop) received the MM6.

The main difference between the two is the gear ratios:

MM6
2.66, 1.78, 1.3, 1.0, .74, .50,

M12
2.97, 2.07, 1.43, 1.0, .084, .56,

The close ratios of the M12 are generally considered advantageous in a drag racing environment while the wider ratios are usually preferred in a road course event.

dgrant3830

I'll toss in a variable...the MZ6 transmission but its in the C-6's with the Z51 option and also there's a m6060 I think too or some numbering like that.

0tom01ss

well i havea z with 3.73 and its wicked, but i also im making 550hp and 495trq so prb a lower gear would be nicer

AU N EGL

Other way around.

0tom01ss

the 2.66 is a stronger gear b/c it has more(meat) metal between teeth

bumble-z

I believe AU N EGL was pointing out that the M12 was designed specifcally for twisty racing, as proven by how many championships they have accumulated since development?

Mark C5

Not quite right. Road racers prefer the ratios available in the MM6 as AU N EGL pointed out.

bumble-z

It doesn't take much to get me turned around.LOL.

Russ K

The M12 trans is rated for 450 ft lbs, and the MM6 is rated for 400 ft lbs.

Russ Kemp

Mark C5

Could you list your source for that information? Everything I can find shows all T56 transmissions from '98 and up rated at 450 ft/lbs. Thanks

http://www.mackstrans.com/TremecID.html for instance

sammy burks

How can you tall the M12 & MM6 apart

Russ K

GM service manual. That site lists the 1998 & up, the M12 didn't come till the 2001 ZO6.

Russ Kemp

Mark C5

I am aware of when the Z06 and the MM12 came out. The site lists the T56 at 450 ft/lbs for '98 and up which would be the MM6. You said the MM6 was rated at 400 ft/lbs.

I have looked all through my manual and can't find the section that lists the torque rating. Could you tell me the section? Thanks

PEERPSI

This should settle the torque questions.

Manual Transmission Description and Operation




Manual transmissions are identified by the number of forward gears and the measured distance between the centerline of the output shaft and the counter gear.

The 6-speed manual transmission (RPO MM6/M12), used in Corvettes, incorporates the following features:

An aluminum case
Fully synchronized gearing with an enhanced synchronizer cone arrangement:
Triple-cone: FIRST, SECOND
Double-cone: THIRD, FOURTH, FIFTH, SIXTH
Single-cone: REVERSE
An internal shift rail mechanism
A remote transmission shift control mounted forward of the transmission
An external transmission shift rod enabling the forward mount location of the transmission shift control
An extended-length transmission output shaft mating directly to the rear axle drive pinion, in the rear of the differential housing
Tapered roller bearings supporting the mainshaft and countershaft
Caged roller bearings under all speed gears
Solenoid inhibit of SECOND and THIRD gears
Solenoid inhibit of REVERSE gear during predefined forward motion
These features combine to yield a rugged, reliable system capable of handling input torques of up to 610 N·m (450 lb ft) for the MM6 and 540 N·m (400 lb ft) for the M12.

The gear ratios are as follows:

Gear
MM6 Ratio (:1)
M12 Ratio (:1)

FIRST
2.66
2.97

SECOND
1.78
2.07

THIRD
1.30
1.43

FOURTH
1.00
1.00

FIFTH
0.74
0.84

SIXTH
0.50
0.57

REVERSE
2.90
3.28


Shift Control and Shift Rod




To allow the rear-of-vehicle transmission location, the transmission shift shaft has been relocated to the front of the transmission. The shift shaft is connected to a transmission shift rod (2) which contains two sealed universal-style joints, enabling the range of motion necessary in order to shift gears. The shift rod (2) is connected to the transmission shift control (1) which is a lubricated and sealed unit, mounted to the driveline support assembly. The mounting system utilized for the shift control (1) incorporates rubber insulators. The cockpit of the vehicle is isolated from the driveline through the use of a shift control closeout boot which seals off the shift control and the driveline tunnel shift control opening.

Gear Select - Skip Shift
To ensure good fuel economy and compliance with federal fuel economy standards, SECOND and THIRD gears are inhibited when shifting out of FIRST gear under the following conditions:

Coolant temperature is above 76°C (169°F).
Vehicle speed is 24-31 km/h (15-19 mph).
Throttle is opened 21 percent or less.
Reverse Lockout
A reverse lockout system, consisting of a reverse lockout solenoid which operates a reverse lockout mechanism, is utilized to prevent shifting into REVERSE gear when the vehicle is moving forward at a speed of 5 km/h (3 mph) or more.

PEERPSI

It would seem the MM6 should be in the Z06 as it has the higher torque rating?

Mark C5

Thanks , that's what I was looking for. The MM6 is actually the stronger of the two.

Russ K had it backwards.