I am interested in swapping my M6 for an M12. I need some specific details such as special tools required or any other pertinent information that might help me accomplish this task.
Thanks

 

The details of the trans remove and replace are more involved than can be posted here. If you are going to do this yourself, the $100 or so it will cost you for the GM service books will be money well spent. There was a thread a couple weeks ago about this swap. Someone said the M12 was around $2600, if I remember right.


[Modified by Terry Humiston, 4:52 PM 3/27/2002]

 

Whats a M12?

 

Z06 6-speed trans with the lower gear ratio set.

 

I would like to see that thread, you can pick up M12's between $1500-2600 depending on whether they are used or brand new. If anybody has seen that thread I would appreciate the help thanks.

 

WickedC5 in the C5Parts ForSale section has a ZO6 tranny for sale, $1800.
or:
I found two price listings for the M12:
$2750 at http://www.sdpc2000.com/cart.asp?act...d=875&pid=8176
$2495 at http://www.gmpartsdirect.com/
I can get the latter price from Chris@TeamChevrolet with extremely low shipping.





[Modified by C5Noir, 7:08 PM 3/27/2002]

 

I want to install Wicked's M12 in my friends car, I have dropped the whole rearend before. I just have never separated the Tq tube from the tranny, or the tranny from the differential. The manuals state you need special tools, well the manual also states that you need a spring compressor to take out the springs, I replaced both of mine with no spring compressor. So I am wondering if and what is needed to swap the tranny. If it was on my car I would just go for it, but I don't want to get stuck in the middle of the job on my friends car. I have seen quite a few M12's from various vendors for less than $1800, to me its better than doing a differential swap.
Thanks

 

FWIW It would be far cheaper just to guy and swap out the gears than buy a whole new tranny. FWIW Atlanta Chassis Dyno down here in Georgia did a total rebuild for my Trans Am LS1 for less than $1,000 in and out of the car. It would likely be a little more for a C5. Also, if memory serves you can also replace the first gear ratio with one out of a '93 F-Body

Year Model/Optn 1st 2nd 3rd 4th 5th 6th Final
---- ------------- ---- ---- ---- ---- ---- ---- -----
1993 Manual/M28 3.36 2.07 1.35 1.00 0.80 0.62 2.73 (GU2)
1993 Manual/M29 2.97 2.07 1.43 1.00 0.80 0.62 3.23 (GU4)
1994 Manual/MN6 2.66 1.78 1.30 1.00 0.74 0.50 3.42 (GU6)

The '97+ C5 uses the same gear ratios as the '94+ F-Body with the exception of the Z06. I don't have the M12 Gear Ratios handy...

-Adam

 

I dont think you can do that Adam, I believe the input shaft is different, and it is an integral part of first gear. You must change gear ratios in sets. 1-4 and 5-6. This is due to the design of the 1-4 countershaft and the 5-6 driven gear.

I added the Z06 gear ratios to the table:

Year Model/Optn 1st 2nd 3rd 4th 5th 6th Final
---- ------------- ---- ---- ---- ---- ---- ---- -----
1993 Manual/M28 3.36 2.07 1.35 1.00 0.80 0.62 2.73 (GU2)
1993 Manual/M29 2.97 2.07 1.43 1.00 0.80 0.62 3.23 (GU4)
1994 Manual/MN6 2.66 1.78 1.30 1.00 0.74 0.50 3.42 (GU6)
2001 Manual/M12 2.97 2.07 1.43 1.00 0.84 0.56 3.42 (GU6)

Personally, I want to put the Z06 5th/6th gears in my regular MN6 with a 3.73 rear end. So I would get 2.66 1.78 1.30 1.00 0.84 0.56. Here is the final drive ratio's compared to the Z06:

M12: 10.15 7.08 4.89 3.42 2.87 1.91 (3.42)
MN6: 9.10 6.09 4.44 3.42 2.53 1.71 (3.42)
Me: 9.92 6.63 4.84 3.73 3.13 2.09 (3.73)

This gives me the higher RPM's that I want in 4-6 without creating traction problems in 1-3. When I get around to it I will do the 5th/6th gear change myself. I rebuilt a T56 in my 94 Trans Am and the C5's transmissions are not drastically different.

Sorry if I strayed from the subject. I completely understand if someone wishes to buy a new transmission rather than rebuild with a different gear set.

Eric

 

66ImpalaLT1, I'll be getting the parts list in the next few days to do it! I'll keep you updated, man!

 

A possible option... The 3.90 rearend on a stock MN6 , will put you virutally identical to an M12-3.42 setup.


[Modified by kewlbrz, 11:33 AM 3/28/2002]

 

Let's see if this will post. Here are the final drives at Gear depending on rear diff.

--------------------1st-------2nd------3rd-------4th-------5th--------6th

M28--------------3.36-----2.07-----1.35-----1.00-----0.80------0.62
Final@2.73----9.17-----5.65-----3.68-----2.73-----2.18-----1.69
Final@3.73----12.53----7.72-----5.03----3.73-----2.98-----2.31

M29--------------2.97-----2.07-----1.43----1.00------0.8-------0.62
Final@3.42----9.59-----6.68-----4.61----3.23-----2.58------2.00
Final@3.73----11.07-----7.72----5.33----3.73-----2.98------2.31

MN6--------------2.66-----1.78-----1.30-----1.00-----0.74------0.5
Final@3.42----9.09-----6.08-----4.44-----3.42-----2.53------1.71
Final@3.73----9.92-----6.63-----4.84-----3.73------2.76-----1.86
Final@3.90---10.37----6.942----5.07-----3.90-----2.88-----1.95

M12--------------2.97-----2.07-----1.43-----1.00-----0.84------0.56
Final@3.42----10.15----7.07----4.89-----3.42-----2.87------1.91
Final@3.73----11.07----7.72----5.33-----3.73-----3.13------2.08
Final@3.90----11.58----8.07----5.57-----3.90-----3.27------2.18

 

The higher the gear ratio the quicker the acceleration? I'd appreciate it if someone could clarify what they mean ;)

 

You get quicker acceleration, but you may also have to deal with traction problems, especially on the street. Its also important to look at how this applys to the speeds you cruise at on the street. On the drag strip you want to make sure that the gears you select will let you get close to redline in 4th at the end of the track, without forcing you to shift into 5th.

For road course or autocross, I dont know.

Eric

 

The higher the OVERALL Ratio the higher your Torque Multiplication will be. However, the higher the overall ratio the higher your RPM will be at the same given speed. Example, a C5 with a MN6 and 3.90 Rear end in First gear has an overall ratio of 10.37. While a Z06 with the M12 has an overall first gear ratio stock of 10.15. So the Car with the 3.90 would have higher torque multiplication in first gear. This does not mean that a stock C5 with the simple addition of 3.90 gears would have faster acceleration as the torque being multiplied (LS1 in the C5 vs Ls6 in the Z06) is different. FWIW this is one reason why a Bone Stock M3 runs the same Qtr miles as a Bone stock C5 despite having less power and weighing more. First off the M3's 1:1 ratio is 5th gear, not 4th gear in an LS1. The T56 we use is a double overdrive 4 speed (which equals 6 gears), the 6 speed used in the M3 , S2000 and some others is a single overdrive 5 speed. What does this mean? you have more gears to keep you at peak power in the M3. The purpose of a transmission is to increase power under the curve over time. Since, as you accelerate you sweep in and out of the peak power point in your dyno curve, your transmission keeps you in that sweet spot. An M3 with only one overdrive gear vs two in our cars gives them more gears to keep the engine in the RPM sweet spot. I don't have the M3 gear ratios and final drive handy, but I seam to recall that overall first gear was something scarey like 13 or 14.

-Adam


[Modified by Adam Bruce, 1:41 PM 3/28/2002]

 

Oh, one more important note, this is overall ratio to the Tires, from there the heigth of the tires you have will further increase or decrease your overall ratio. If you go from a 26" tall tire to a 25" tall tire, you have INCREASED your overall ratio.