MM7 4 Speed overdrive transmission

[AJHack]

Does anyone know where to find a Chevy MM7 manual transmission? That is the 4 wheel drive version cast iron case. The 2 wheel drive aluminum case version is the MY6. They came in Chevy trucks from 81-88 I think. It is really a Mopar A-833 transmission with a Chevy bellhousing.

[wesmigletz]

I have a 2wd version in my 57 Vette and ran one in my son's 68 Camaro.

I think the transmissions were only used through 87, not 88. If you go to car-part.com and search for a 83 silverado - manual transmission - 4 speed, it will be identified as "with side shifter". The top shifters were the cast iron granny gear transmissions. If I remember correctly the iron trans have a unique bolt pattern for where the trans bolts to the bell housing. make sure you get the bell housing. The gear ratios are similar to a 700R4, with a .73 OD for 4th gear.

We used a cast iron trans in the camaro that was converted to 2wd prior to us getting it, or, maybe it was always 2wd. The bell housing was hard to track down.



This is my spare MY6/ A833 transmission. 2wd uses a TH350 yolk. The 2wd trans is the same length as a TH350 short tailshaft, or a M20/M21 transmission.


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[Keith Seymore]

Originally Posted by AJHack

Does anyone know where to find a Chevy MM7 manual transmission? That is the 4 wheel drive version cast iron case. The 2 wheel drive aluminum case version is the MY6. They came in Chevy trucks from 81-88 I think. It is really a Mopar A-833 transmission with a Chevy bellhousing.

Just to be clear - the MM7 and the MY6 are the same thing.

MM7 is the "merchandised RPO" that the dealer would chose for a floor shifted manual overdrive trans. MY6 is the "non-merchandised" option code that the engineering charts would choose based on GVW and powertrain considerations. Since there is only one offering they are the same.

The difference between 2wd and 4wd would be taken into account at the part number level.

And I agree that 1987 was the last year.

Contact site member "D13". He had two or three but may have just gotten rid of them.

K

[D13]

The cast iron case versions are less common than aluminum, at least in our truck applications. I have never really looked to see if standard A833 Mopar cases are a direct swap. I have a 2wd and a 4wd, both are aluminum case. My 2wd is GM vin stamped and my 4wd case appears to have come from a Mopar, with GM input and oputput shafts.
The output shafts are different 2wd/4wd. There is one shaft that is different between aluminum and iron cases and the aluminum case version is no longer available new.
If you buy one be sure to get the shifter, it's a Hurst Competition Plus but the plates and links are unique to GM. Oh, and the van version is slightly different, mounts and shifter package and links.

Most applications are 6.2 diesels, 4.3 V-6, occasionally a 305. Dodge did some in 318 and 6 cylinder trucks. I'm not sure what would trigger an iron case versus aluminum, I'm thinking heavy 1/2 or light 3/4 4wd might have gotten cast.

Run a search, we had a pretty good thread about these a few years ago. Use A-833 as the key word.