I have the RPO codes of MM5 and M39, the MM5 is a merchandised tranny, the M39 is a 2.95 Borg Warner. Is the MM5 just saying that it isn't a Chevy tranny. Eventually the engine will be replaced in my RS, will this tranny work with a 350 or larger. Thanks in advance for any help.

One other question. It's been awhile since driving a 5 spd. I am having problems down shifting for that extra added ummfff. It doesn't want to seem to go into any other gear until the speed goes down to around 45 or 50 mph.

[This message has been edited by 89RSProject (edited January 16, 2001).]

I'm not sure on the RPO codes, but mine is MK6 for a 2.75 first gear. I'm using it behind my 350, and it lasts for a little while. When I go racing it likes to act up on me.

I've noticed that too, that it wont go into lower gears. I think its a safety feature to keep you from over-revving it.


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Thanks Kevin. I wonder if there is a way to disconnect or over ride that feature if it is a safety, I'm sure there is. By the way isn't Lake Forest just South of Hunington Beach.

I think its the way the trans is designed, no way to defeat it. Why would you want to?

Lake Forest is about 15 mins southeast of Huntington Beach, where the 5 and 405 freeways meet in Orange County.

i know you have an RS, but on an 89' firebird
those two RPO codes describe the following.
RPO MM5 is manual tranny, and M39 is 5-speed manual tranny. Will this tranny work on a V-8, depends. If there is a v-8 currently under the hood i see no reason why it wouldn't. If it's a 6 under there it won't.
The 6 has a different bolt pattern than the 8.