trans went out, which 1 to replace?

I never heard of that myself, had a 18 in the cabover and did not see a difference in fuel mileage, too many factors to blame it on a 18 in my humble opinion.

 

Cowpie geared his truck with a standard 18, he just geared it to run in 16th (Direct) at normal speeds. 2.64 rears, or something.

I would think that in your case, any gain from going to a direct high gear would be more than offset by the loss from the higher rpm. Find a 13 if that Super 10 isn't any good. What you spend to redo driveline for a straight ten will likely pay the difference between a 10 and 13.

EDIT: Just went and looked, the FR series ten speeds are 3+ inches shorter than a super 10/13/18. A 15 is the same length, too; but only .79 ratio OD. The 8LL and 9LL are also options, as they're based on the same case .

 

If a 13 speed is available, get that instead. The 13 has a stronger torque rating than any 10 speed. The 13 speed has a 9 speed shift pattern, but you split the high side gears. I plan on going that route when my super 10 kicks the bucket.

 

So your sating that a RTO14613 is stronger than a FRO18210C, I think not, the 10spd in this case carries over 400 ft-lbs more torque capacity than the 13spd. Each transmission has its own torque rating, it does not matter how many gears it has.

 

You're right SmokinCAT. I am wrong. Any 13 speed should bolt up in place of the Super 10. FRO18210c or any other straight 10 will require driveline modifications.

 

And with his Super 10, a 13 is a bolt-in swap. It almost sounds as if his shop is pushing what they have on hand rather than what would be best.

 

Boss's truck had a super 10 and he switched it to a 13dot last year. Just needed a different shifter and some air line mods.