my6 trans

[muleys86]

Well, after replacing the glovebox plastic I found a rpo code for the trans in my 86 Scottsdale. This truck has the 4.3 v6 and the mm7 trans. I thought it was the my6. So what is the difference in these two trans?
I like this combo, just wish it got better mileage. Is the my6 an aluminum case and the mm7 cast iron or vice versa? Ive had this truck almost two years and would have sworn it was an my6. All info is greatly appreciated. Muley

 

[HotRodPC]

It could be. Is yours cast iron or aluminum? The 4x4's I've seen were MM7 and were cast iron.

 

[Keith Seymore]

Well, after replacing the glovebox plastic I found a rpo code for the trans in my 86 Scottsdale. This truck has the 4.3 v6 and the mm7 trans. I thought it was the my6. So what is the difference in these two trans?
I like this combo, just wish it got better mileage. Is the my6 an aluminum case and the mm7 cast iron or vice versa? Ive had this truck almost two years and would have sworn it was an my6. All info is greatly appreciated. Muley

MM7 is the "merchandised" RPO and "MY6" is the "non-merchandised" RPO.

Basically one is available to the customer to choose and then the powertrain charts/engineering specifications drive the correct detail.

It is perhaps easier explaned by using a different transmission as an example: the three on the tree Saginaw was available in the Squarebody with two different first gear ratios, a 2.54 and a 3.50 low gear.

The customer would say "I want a three on the tree" and choose the merchanised RPO MM3 (aka three speed manual trans). The engineering specifications would then drive the appropriate specific trans, non-merchandised RPO M62 or M64, depending on the rest of the desired powertrain (2wd vs 4wd, rear axle ratio, GVW, etc).

MM4 (merchandised RPO) => M20 (non merchandised) => SM465 four speed, including the creeper gear

Same thing happened with automatic trans (MX1 = non overdrive; MX0 = overdrive automatic).

It is perhaps overkill when only one transmission of a particular type is available, but the system was structured to handle the proliferation of truck drivelines, which were/are mind boggling.

K