Manual Transmission T56 | T5 | MN12 | Clutches | Hydraulics | Shifters

MN12 in a 98 Firebird

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Old Sep 4, 2007 | 09:53 PM
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Default MN12 in a 98 Firebird

Can I replace the T56 with a MN12.
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Old Sep 4, 2007 | 10:56 PM
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Not without a huge conversion process. Two totally different transmissions.
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Old Sep 5, 2007 | 12:53 PM
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If you're referring to the GTO's transmission, it's not too difficult. You may need to change the tail-housing, but everything forward of that should bolt up just fine.
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Old Sep 5, 2007 | 02:01 PM
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Originally Posted by _JB_
Not without a huge conversion process. Two totally different transmissions.
Damn...now you tell me! I guess that since I just bolted mine up and have been driving it like that for over 10,000 miles I need to look into the "conversion process" to see what I had to have done wrong.

All you really have to do is swap out the shifter cup from your T56 into the M12 and it is a direct bolt in.

Galen
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Old Sep 6, 2007 | 01:58 AM
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Originally Posted by Galen
Damn...now you tell me! I guess that since I just bolted mine up and have been driving it like that for over 10,000 miles I need to look into the "conversion process" to see what I had to have done wrong.

All you really have to do is swap out the shifter cup from your T56 into the M12 and it is a direct bolt in.

Galen
I thought a MN12 tranny is out of a C5 Z06?

Last edited by _JB_; Sep 6, 2007 at 02:14 AM.
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Old Sep 6, 2007 | 02:08 AM
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Originally Posted by Galen
Damn...now you tell me! I guess that since I just bolted mine up and have been driving it like that for over 10,000 miles I need to look into the "conversion process" to see what I had to have done wrong.

All you really have to do is swap out the shifter cup from your T56 into the M12 and it is a direct bolt in.

Galen

i guess you did lol serious is it any better?
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Old Sep 6, 2007 | 08:22 AM
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Originally Posted by _JB_
I thought a MN12 tranny is out of a C5 Z06?
Think of the Mxx designations as indicators of the gear ratios. The C5Z, GTO, and CTS-V all used the M12, despite the differences in casing.
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Old Sep 6, 2007 | 08:53 AM
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it is a direct bolt in except for the shifter cup. You will have to take that off of you t56. I just ordered my mn12 and it will be going in next week. Cant wait
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Old Sep 6, 2007 | 09:56 AM
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I've got one too. I created a chart that shows the equivalent gear ratios that you would have if you have 3.42 or 4.10 gears.

https://ls1tech.com/forums/manual-transmission/776536-comparison-f-body-gto-t-56-a.html
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Old Sep 6, 2007 | 11:54 AM
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Originally Posted by itslow
Think of the Mxx designations as indicators of the gear ratios. The C5Z, GTO, and CTS-V all used the M12, despite the differences in casing.
Ah ok thanks!
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Old Oct 6, 2007 | 08:33 PM
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where can I get a shifter cup? and whats different? mine will be going into my RX7
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Old Oct 6, 2007 | 09:14 PM
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You can get one from me for $25 plus shipping. The GTO sits the shifter farther back and the GTO shifter is the only one you can use. With an F-Body shifter assembly you have more choice and all of my trans customers that have RX-7's use the F-Body shifters.

Thanks,
Amber
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Old Oct 6, 2007 | 10:46 PM
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what do MN12s usually run?
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Old Oct 8, 2007 | 12:04 AM
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Originally Posted by SPLATT
what do MN12s usually run?
ditto.
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Old Oct 8, 2007 | 12:33 AM
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needing a price on a built T56 or this mn12?...something to hold about 700rwhp...but i dont know squat about this GTO tranny...so far so good on this thread...but hows the price/warranty differ?
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Old Oct 8, 2007 | 08:25 AM
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The M12 (there's no 'N" in it's RPO) is a T56. It simply has different ratios and other improvements than the version found in the F-Body. It's price should be comparable to that of any other "non-built" T56.
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Old Oct 10, 2007 | 01:42 AM
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Originally Posted by itslow
Think of the Mxx designations as indicators of the gear ratios. The C5Z, GTO, and CTS-V all used the M12, despite the differences in casing.
Could a M12 from an of these cars fit in a F-body or would it have to be a M12 from a GTO?

How much does an M12 cost?

What are the advantages of having a M12 rather than a t-56?
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Old Oct 10, 2007 | 08:47 AM
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A GTO trans is $2250 built compaired to an FB at $1950. Due to the blocker rings being triple cone in the GTO that is what drives the price up. As for putting one in, all you have to change is the shifter assembly over to the FB and it is a direct bolt in. The GTO is a 2.97 1st gear which alot of the road racers prefer. Most of the time the GTO will shift better and be smoother.

The only issue is that the GTO is alot harder to get since they stopped production. It normally takes me 4-6 weeks on average to gather all of the parts for one. I just got a few mainshafts yesterday. Since the gears are the same as the Z06 that tends not to be an issue most of the time.

Thanks,
Amber
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Old Oct 11, 2007 | 06:06 PM
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Originally Posted by Six Speeds Inc.
A GTO trans is $2250 built compaired to an FB at $1950. Due to the blocker rings being triple cone in the GTO that is what drives the price up. As for putting one in, all you have to change is the shifter assembly over to the FB and it is a direct bolt in. The GTO is a 2.97 1st gear which alot of the road racers prefer. Most of the time the GTO will shift better and be smoother.

The only issue is that the GTO is alot harder to get since they stopped production. It normally takes me 4-6 weeks on average to gather all of the parts for one. I just got a few mainshafts yesterday. Since the gears are the same as the Z06 that tends not to be an issue most of the time.

Thanks,
Amber
Thanks for your reply. I wish that someone who has done the swap would comment on the benefits of doing the swap.
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Old Oct 11, 2007 | 06:23 PM
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Originally Posted by SSDude
Thanks for your reply. I wish that someone who has done the swap would comment on the benefits of doing the swap.
Driving the car you can physically feel the difference inthe transmissions, the m12 there is no dobt about when it is in gear, even with a stock shifter. The tension is more firm and 1-3 gears do react a lot better as far as the power band is concerned ( all of these are just observations i have made sicne my swap) i personally preffer the feel of the m12 as opposed to my old t56.
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