# 2006 GTO shift grinding



## GTOgrinder (Mar 12, 2011)

I have a 06 GTO with an M12. Replaced clutch. p.plate, throwout bearing, master cylinder, slave cylinder, and used GM super dot 4 fluid. Pedal feels like new. Bled all of the system twice. Also replaced the flywheel. Grinds when shifting. Any ideas?


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## GuatoLT1 (Jul 22, 2009)

what is an M12?


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## Poncho Dan (Jun 30, 2009)

RPO for the T56.

OP, try changing the actual trans fluid out to some Synth, preferably AMSoil ATF.


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## 740tank (Mar 23, 2009)

well does it grind on every single shift or just one specific gear? if it grinds on one gear every time, I would check the synchronizers in the tranny.


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## GTOgrinder (Mar 12, 2011)

*M12 and grinding.*

There are 2 types of transmissions in a 06 GTO. M6 and M12. The M12 is geared more like the Z06 Vette.

If shifts fine when cold but after a little warmup, it grinds trying to put it in 1st and also when shifting to 2nd.


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## HP11 (Apr 11, 2009)

GTOgrinder said:


> There are 2 types of transmissions in a 06 GTO. M6 and M12. The M12 is geared more like the Z06 Vette.


Where did you get that notion from? You may or may not be right about the gear ratios as I don't know what gear the Z06 Vette has but all GTOs, 04-06, that have a 6 speed, have the same trans.


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## GTOgrinder (Mar 12, 2011)

To hp11, Well, I guess you need to tell GM they made a mistake because on the front ID plate, it denotes an M12 transmission. Also head to head on stock 06 GTO's an M12 will bust an M6 every time. Sorry!


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## GTOgrinder (Mar 12, 2011)

HP11, Here is something else,fyi.

GTO's M12 T56
Just talked to a shop that specializes in T56 transmissions, the gtos trans is highly underrated, first its Z06 gearing (we already knew that) it has carbon fiber blocker rings and steel shift forks factory; now what i'm not 100% on is if 1-2 gear use triple cone syncronziers. I've heard the corvette designation T56 gets triple cone syncronizers and with the GTOs trans comming from a vette its quite possible.


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## HP11 (Apr 11, 2009)

GTOgrinder said:


> To hp11, Well, I guess you need to tell GM they made a mistake because on the front ID plate, it denotes an M12 transmission. Also head to head on stock 06 GTO's an M12 will bust an M6 every time. Sorry!


My 05 also says 'M12' on the ID plate as would an 04 if it had a manual trans. In your attempt to 'school' me, you missed my point. I don't think you and I are on the same page here so I'll just drop it. Someone help me out here because I really wasn't trying to argue.....


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## 68OldGoat (Nov 23, 2009)

HP11 said:


> My 05 also says 'M12' on the ID plate as would an 04 if it had a manual trans. In your attempt to 'school' me, you missed my point. I don't think you and I are on the same page here so I'll just drop it. Someone help me out here because I really wasn't trying to argue.....


There is some confusion on the difference between an M12 and M6 with our GTO's. Here is an excerpt from the other forum LS1.com. "On this forum I hear the six speed Tremec T56 refered to as the M6. On the Corvette forums the standard Tremec T56 is listed as the *MN6*. The GTO shares the Tremec T56 M12 close ratio six speed with the 01-04 ZO6s. It would be correct to call our six speeds Tremec M12s? So where did the M6 come from? Most 04-06 GTO owners on this forum refer to a manual transmission as the M6 ..... There never has been that designation as an RPO ...see below!

MN6 is the RPO code for the T-56 in the 93-02 F-body and base 97-05 Vette.
M12 is the RPO code for the T-56 in the GTO, 01-04 Z06, and 05 Z51 Vette.

The difference is in the gearing.

MN6 gearing is 1st 2.66, 2nd 1.78, 3rd 1.30, 4th 1.00, 5th .74, 6th .50
M12 gearing is 1st 2.97, 2nd 2.07, 3rd 1.43, 5th 1.00, 5th .84, 6th .57

HP11 is correct that there was only one manual transmission offered with the 04-06 GTO the M12 T56. Let's not get hung up on silly bickering and stick to helping each other with member questions. arty:

You still don't have an answer of why your transmission is grinding when you shift. Seems like you spent some time and money to get your transmission working properly with a new clutch package. Was the transmission shifting OK before you did the clutch work? Did you check out the shifter installation as the problem (the GTO stock shifter isn't the best because of sloppy gates) or take it back to the person who did all of the other work on the clutch to see if that could be the problem.


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## jpalamar (Jul 22, 2008)

Try a thicker fluid in the trans. Sometihng with GM Syncomesh would do nicely. I like it in mine. It was a little grindy if you didn't let the car warm up but after that it held up really nice.


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## LS2 MN6 (Jul 14, 2010)

68OldGoat said:


> There is some confusion on the difference between an M12 and M6 with our GTO's. Here is an excerpt from the other forum LS1.com. "On this forum I hear the six speed Tremec T56 refered to as the M6. On the Corvette forums the standard Tremec T56 is listed as the *MN6*. The GTO shares the Tremec T56 M12 close ratio six speed with the 01-04 ZO6s. It would be correct to call our six speeds Tremec M12s? So where did the M6 come from? Most 04-06 GTO owners on this forum refer to a manual transmission as the M6 ..... There never has been that designation as an RPO ...see below!
> 
> MN6 is the RPO code for the T-56 in the 93-02 F-body and base 97-05 Vette.
> M12 is the RPO code for the T-56 in the GTO, 01-04 Z06, and 05 Z51 Vette.
> ...


You are only half right.

MN6 isn't a gearing its the generic code for 6-Speed Manual Transmission (T56 or TR6060) Check the RPO sticker in your trunk (it's on the bottom of the floor facing down looking at the spare tire) you will see both MN6 and M12.

Current Corvette uses MM6 (base\Z06), MZ6 (Z51\GS), and MH3 (ZR1).
Current Camaro uses M10
Current CTS-V uses MG9

GM Media Online: English

GTO's all used M12
Older CTS-V's used M12 as well
C5 Corvettes used the M12 (Z06), and MM6 (base)
SSR used M10
Old Camaro used MM6 - http://archives.media.gm.com/division/chevrolet/products/cars/02chevrolet/camaro.html#information

M6 is a shorthand way of saying Manual 6, like A6 is for Automatic 6. 6-speed was common before autos got that high as a name for manuals as well.


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## HP11 (Apr 11, 2009)

LS2 MN6 said:


> GTO's all used M12.


I guess it's my fault that all of this got started but the above quoute is all I was saying........did we ever find out if the grinding was there before the clutch job?


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## Poncho Dan (Jun 30, 2009)

http://www.gtoforum.com/f2/2006-gto-shift-grinding-31751/#post261631

Seems to be a lot of people who missed post #3.

It's right there on the placard under the hood, right next to the "LS1" or LS2" RPO. Why are we arguing..?


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## LS2 MN6 (Jul 14, 2010)

Poncho Dan said:


> Why are we arguing..?


Not arguing! Discussing, learning, etc... (this is the internet after all!)

arty:


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## 68OldGoat (Nov 23, 2009)

Funny that GTOgrinder never came back to the discussion and didn't get an answer to his question.


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## HP11 (Apr 11, 2009)

Not really, he seemed to have all the answers to everything else........


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## pocketmaster (Feb 26, 2010)

HP11 said:


> Not really, he seemed to have all the answers to everything else........


I really didnt understand his "head to head" comment about M6 to M12 if we all have M12's......just sayin. I must admit I did learn something though. Kinda like takin a LONG walk around the bar for a drink of water!


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## GM4life (Mar 18, 2007)

68OldGoat said:


> Funny that GTOgrinder never came back to the discussion and didn't get an answer to his question.





HP11 said:


> Not really, he seemed to have all the answers to everything else........


I wouldn't have came back nither seeing that people were bickering about the type of trans that was in the car. Everybody was saying the same damn thing, someone just had to be more right 

Whats the solution to the problem?

Sycros, not enough fluid, fluid change, master cylinder is all you got left.


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## HP11 (Apr 11, 2009)

Good riddance then. When he said:


> There are 2 types of transmissions in a 06 GTO. M6 and M12. The M12 is geared more like the Z06 Vette


all I tried to do was set him straight. He jumped on me and tried to 'school' me. I didn't argue with him. Everyone else chimed in after that. I even tried to help by asking if the problem existed before or after the clutch job. Lock this crap. It's pretty lame anyway....


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## Poncho Dan (Jun 30, 2009)

You want a quick fix? Rev match the gears. I had to do that in my '64GP with a muncie 22. Give the throttle a squirt between gears. I got so good at it that I didn't grind any gears when being forced to dog shift it when a clutch linkage broke. It still sucked tho, because I had to stop at a stoplight... :lol:


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## GM4life (Mar 18, 2007)

HP11 said:


> Good riddance then. When he said:
> 
> all I tried to do was set him straight. He jumped on me and tried to 'school' me. I didn't argue with him. Everyone else chimed in after that. I even tried to help by asking if the problem existed before or after the clutch job. Lock this crap. It's pretty lame anyway....


I know HP11, I wasn't jumping on you.:cheers

I know he was alittle confused. M6 is the M12, T56, six speed, whatever or a BMW M6. M6 is just what people use to say they have a six speed manual.


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## HP11 (Apr 11, 2009)

I know. At the point where I made my comment, it I had just let it go, maybe everyone else would have too. I just don't care for anecdotal information, misinformation, etc. Stuff like that seem to become it's own brand of 'truth' or 'fact' if it's repeated often enough.


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## LS2 MN6 (Jul 14, 2010)

My Bad. I was just correcting the dude who was trying to correct HP11.

If you're going to correct someone get it right, misinformation gets to me (as my service manual escapade today illustrates)!


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## Jamie2525 (Aug 22, 2011)

OK..So I dont want to argue and I need an answer please...I have a 2005 GTO /6 Speed...Just went in for a LS7 Clutch/Flywheel/Slave Cylinder and throwout bearing...ALL fluids were drained and refilled including tranny lube and DOT4 for clutch. Before the clutch swap I NEVER had an issue with griding now if I dont stop between every gear I will get a slight grind or a "chunk" sound when it goes into gear...I have driven the car about 600 miles since the LS7 Clutch upgrade and as everyone said the clutch adjusted itself out and has a good pedal feel...BTW I Still have the factory shifter could it be out of adjustment?


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## GTO JUDGE (May 14, 2005)

Jamie2525 said:


> OK..So I dont want to argue and I need an answer please...I have a 2005 GTO /6 Speed...Just went in for a LS7 Clutch/Flywheel/Slave Cylinder and throwout bearing...ALL fluids were drained and refilled including tranny lube and DOT4 for clutch. Before the clutch swap I NEVER had an issue with griding now if I dont stop between every gear I will get a slight grind or a "chunk" sound when it goes into gear...I have driven the car about 600 miles since the LS7 Clutch upgrade and as everyone said the clutch adjusted itself out and has a good pedal feel...BTW I Still have the factory shifter could it be out of adjustment?


The factory shifter may be the culprit I know when I still had mine in often times it felt when shifting: Like it would hit a very slight obstruction and then guide into position almost like you describe "out of adjustment" feeling. It was like this from new. That issue stopped with the GMM rip shifter installation. That stock shifter is the weak link in the manual tranny. It's a shame you didn't have this replaced when you had clutch work done on it. It is definitely worth the money.


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