Well you have multiple people telling you youre wrong in this thread. The Corvette Black Book says youre wrong. The console of the car says youre wrong. Go do a google search for "RPO MN6" and come back and tell us what you find.

If we all told you the sky was blue and you insisted it was green no matter how many people tell you, you still wouldn't believe them. Clearly you will not admit it, so at this point the conversation is moot.

 

Here's a shot of the underside of my console on my 1991. You can see both ML9 and MN6 posted right next to one another:



Here's a shot of the Helm/field/factory service manual for my 1991:



You can clearly see here that there is NO Production and Process code (otherwise known as Regular Production Option, or 'RPO') for designation MN6.

That means that in the truly, technical application of the question CFI-EFI is right. While the MN6 code could very well indicate a manual 6 speed transmission, General Motors has not printed anything that I can find to corroborate that story. Until someone comes up with something other than "There are lots of people telling you here, and it's widely accepted on the Internet that MN6 means 6 speed" I am siding with CFI-EFI. My service manual tells me that ML9 means ZF six speed, the manual doesn't contain any information on MN6. I have no choice but to choose to believe the information that I can verify.

I sort of think that most people think MN6 represents a 6 speed because it phonetically resembles 'manual six.' If that were the case, how did the common representation of A4 come to be? My service manual says an automatic equipped C4 should carry RPO code MD8, not A4. In fact, you won't find any reference to A4 in any manual.

I am puzzled as to why MN6 appears on RPO list under my console lid and not in my service manual, but ML9 DOES appear in my manual and it indicates ZF6. ML9, 100% assuredly, indicates ZF6 speed. Everything on MN6 that I have seen here or anywhere else is educated guess at best, Internet myth mostly, and CFI-EFI bashing at it's worst. He is giving you the information as it comes from GM, for his trouble he is lambasted and called thick headed. Instead of taking his word, admittedly sometimes delivered in a harsh manner, his word that is backed up by the GM service literature, you guys are perpetuating a myth. A myth, that no one can prove. While it may be true that MN6 indicates a manual transmission, there is no proof that I've been able to find.

I'll take the 100% proof over what a bunch of people 'think' any time.

Oh ya, and settle the Hell down when you get corrected by CFI-EFI. I've never once seen him correct someone who was right. If you were wrong and he blasts you for it, consider yourself lucky that some new guy didn't grenade an engine, wreck his car, or have some other incredible misfortune from listening to your wrong advice. You should bow down and thank whatever higher power you believe in that CFI-EFI was there to save that poor new guy's pride, ride, or possibly life depending on the inaccuracy of you erroneous post.

 

A4 is a nickname, just like M6.
MN6 is a RPO code.

 

I agree, it's on my RPO sticker.

The confusion is how the manual 6 speed became attached to that RPO code. I can't find anything from GM that even explains what the MN6 RPO code is. I think the only reason people spread the rumor that it indicated a manual 6 speed is because of it's phonetic resemblance. None of the other RPO codes bear any phonetic resemblance to what they indicate, why would MN6 be different?

More importantly, why would GM put 2 RPO codes on my car that both mean it's a manual 6 speed? It doesn't make sense to do something like that, there are no other duplicate RPO codes, why this one? Some think it's a parts issue, but there are no other RPO anomalies like this. No code for air conditioning, then another for R12 or R14. There aren't 2 codes for the rear end, one indicating axle ratio, the other for D44 or D36. It doesn't make sense for GM to tag the car ML9 to indicate ZF6 and then also MN6 to indicate manual 6 speed.

Can anyone find something from GM that explains what MN6 means? Something really from GM, not something from google, or wikipedia, something that general motors put out?

 

What does this all boil down to? GMs RPO coding structure is entirely too illogical and inconsistant to make any sense out of.

 

I don't know how else to perceive it. Apology accepted. I just wish you wouldn't jump to conclusions about my content.

 

I found it. MN6 is the GM RPO code for a merchandised transmission, and the 6 speed provisions. It appears that it indicated pedal arrangement, and the hydraulic components associated with the transmission; at least that is the way I am reading it. The transmission itself would be a different RPO code, ML9 in our case, MM6 would be the code for the earlier T56's that were made by Borg Warner. There is also a Borg Warner six speed listed under RPO M28 and M29, but I'm not sure of their application. There is a ZF6 with RPO ML6, however given it uses a 5.79 first gear I am assuming that it's the ZF6 used in the newer HD trucks. ML9 is also listed as an RPO for a 4 speed Muncie transmission. Whether that's the 4+3 I don't know, it could just be some of GM's re-using of RPO codes like ZO6 and 1LE.

The later model Tremec T56's are probably a different RPO, but I don't have any information on those.

Cliff notes: MN6 indicates merchandised transmission and 6 speed provisions.

 

Damnit and the thread was going so well until this point.


The parts manual is very clear that ML9 is the rpo for the zf. Whether or not the mn6 is redundant doesn't matter.

How do you know the sky is blue? Is it because someone told you so? Can you prove it? There's more B.S. than truth in this forum, so I can't fault CFI for being critical, in fact nothing he wrote was incorrect.

 

Here's another example:

All 4+3 cars came with rpo MM4 (4-spd, Manual Trans.)

But, there were two types of 4+3s used, depending on the overdrive ratio. A second rpo was used for this, MK2 or MH5 (Manual 4-speed Doug Nash transmission)


For the ZF6 it just happens those rpos are redundant since there was only one transmission choice, ML9 to put in the MN6 cars. The fact that MN6 was carried over to the C5 makes this clear.


I think GM used this method on rear gears also. One rpo to indicate a "performance ratio" and a second rpo to indicate what that ratio is.

 

Does it really even matter?

 

Desert

 

anyone have any opinions on this list of RPO's?

http://www.c2e.info/rpocodes/gmrpocodesGthroughM.html

Desert

 

Until now apparently

Thanks, this is what Ive been saying the whole thread.

I'll agree with the BS part but......Actually yes he was wrong when he wrote this....

Im sorry to ruin everyone's religion in proving their hero wrong.

Im guess I don't understand why so many people have their head up his azz, but it is kinda funny. Sure he's a smart guy, but a total azz even when the need is not there. People on this forum have stroked his ego to gigantic proportions.

 

Before you go throwing him a pity party...

Would you care to comment about what he wrote to Bogus? see Post 4 as well.

Not exactly what I would call nice comments.

 

Hmmmmm?

 

From the GM source book at the Corvette shop I worked at for a number of years, here's what I have;
ML9 = ZF-6 speed manual transmission
MN6 = provisions - manual transmission

You should read the threads about the "performance axles". Talk about two RPO codes confusing people.

A/C does have RPO codes. In C4s C60 was for manual A/C, and C68 was for electric A/C.

 

Z-07, who's the bitch in your avatar? She's damn hot, in the highest order

 

Hey, that's my sister!

 

your sister would be too old for me

 

So, you won't have ML9 without MN6. But ML9 /= MN6. Its probably there because of how assembly line production works, where the transmission would be put in at a different time then the pedals and lines. Trans goes in a frame, pedals/hydralics go in when the body is mostly completed.