7 Speed Mack Tranny

[bobcotkg]

I've got a 10 speed unishift in my B-61 with a 237 for power. I'm gonna eventually get around and put a tip turbine on it I have and have the pump turned up accordingly. I know the 10 speed will hold up IF I'm careful, but I like to get after it and am planning on using the truck to haul equipment and pull with. I found a guy who has a 7 speed Mack with overdrive (probably the 7s all are) in an old whipped out DM. Was hoping for higher highway speed, hence the OD, and it still has a good low gear for starting out. I know I'll have to change the clutch and linkage to fit the B model.

So after having said that, here comes the question. Are the 7 speeds a good tranny or should I find another OD tranny? What is the OD gear ratio? I'm hoping for 70 mph. I don't know my gear ratio in the rears. Where to look for the ratio or how to figure it out? They are Rockwells on Hendrickson suspension that I think came out of a White truck. I have drove it a little around home and figured it goes about 60 topped out the way it is. It had 10.00 20s on it and now its going to have 12R22.5 tires on it.

Any thoughts?

Bob