Need Help/Advice MM6 5th gear ratio change?
 

I have a '99 coupe with a MM6 tranny and 3:73 rearend gears. I'm going to have the tranny rebuilt and would like to have the 5th gear ratio changed to be closer to 4th.
Can the MM6 5th gear .74:1 be swapped for the M12 5th gear .84:1?
Do any other parts need to be changed?
Or, is there a manufacture who makes different gear ratios for 5th that can be used without having to change other parts?

This car is 90% daily driver and 8 - 10 HPDE's per year. I would like to keep the .5:1 6th gear ratio for highway driving.

Yes.. It can be done. I just had my mm6 rebuilt and the .74 5th gear replaced with the zo6 .84 5th gear. Did not mess with 6th because I never use it. Have not had car on track yet and only one track that I use 5th is TWS..
G-force has custom ratios but pricey.
http://www.gforcetransmissions.com/

I know that RPM Transmissions http://www.rpmtransmissions.com/ offers a higher 5th and 6th with the M6, you may also check out Rockland Standard Gear http://www.rsgear.com/ they are in NY so they would be closer to you, they don't have it listed on there site but they do have other ratios, you'll just have to ask.

Thank You for the info. Who did the rebuild? Did they have to replace the counter shaft or anything else or was it just use the Z06 5th gear? Did they leave the original 6th gear?

The only places I have needed 5th are Watkins Glen and Pocono when they run Nascar turns 1 and 2. I need it going down the Long Pond into the tunnel turn.

Sixspeeds inc in houston did mine http://0174de9.netsolstores.com/
A simple swap on the gears.. no extra stuff.. I tried to get them to just leave 6th out to save a few lbs but it did not work out. So still has original 6th