Detroit80
Full Access Member
Truck is a 1990 F350 CCLB 4x4 DRW, 7.3 w/Banks Sidewinder, 5 speed ZF trans. Currently seeing around 13-14mpg empty, with 80%+ freeway driving. Been a long time since I've had a heavy trailer hitched up, but I seem to recall getting 8-10 towing. Planning on ordering a new set of injectors here soon with fingers crossed that number will go up a bit.
Slowly refreshing the truck, and as I fix things here and there, this old pig is really starting to grow on me The 3rd & 5th gear synchros are on their way out. Not really a HUGE deal to me, as my other "big" truck, a '59 International B-160, has a T-30 5 speed non synchro trans & 2 speed rear end..so I'm quite familiar with RPM matching shifting. But I also know that any trans with synchros was never intended to be shifted via RPM matching or double clutching, and doing so is a poor band-aid "fix" at best.
As I live in Arizona, and travel around the southwest, I occasionally pull some decent grades, and have found myself wishing for a few more gears here and there. I would also LOVE to have some additional range in the truck. I already have factory dual tanks, and the easy solution of "add another aux tank" occurred to me, but tossing another 100 gallons of diesel in the bed means another 700lbs of weight I'm hauling (though obviously, the weight will go down as the fuel is burned off).
I've thought about putting a 2 speed rear end in, though that obviously will complicate things with the 4x4, which I absolutely want to keep. It's easy enough to just leave the rear in low range when going 4x4, but finding a 2 speed rear with a gear ratio that will match what I can put in a D60 front might not happen. Thought about a brownie box, or other aux trans, and going to a divorced transfer case. Twin sticks don't bother me in the slightest either.
Then the 10+ speed trans occurred to me...I've read over some swap threads, so I know it CAN be done. I could regear the axles to much higher ratio to bring RPMs down on the freeway while having much deeper low gears from the trans to make up for it. Adding on board air is a trivial matter for me to run air shifters if needed. Yes, they're heavy, but so is another 100 gallons of diesel in an aux tank. But is there really a benefit to going that route, other than the cool factor of being able to say I have a 10/13/18/whatever speed trans?
Will lowering RPMs this way really make much of a difference? I know I won't likely see any overall savings via more MPGs once the cost of the trans swap and axle regearing comes in factored in, but my real intent for doing this is extending the time between fuel stops on long drives, and _hopefully_ being able to bring RPMs down a bit on the freeway for less noise/more comfortable driving. I'm not looking at this as a money saving venture at all - otherwise I'd just go buy a newer truck with a more efficient engine to begin with, lol. Though honestly, even if I won the lottery, I just don't see myself buying a new truck...there's just nothing that even interests me any more. I'd just as soon drop the '59 off at some shop with a blank check, and say "rebuild it for me with all modern drivetrain stuff".
Slowly refreshing the truck, and as I fix things here and there, this old pig is really starting to grow on me The 3rd & 5th gear synchros are on their way out. Not really a HUGE deal to me, as my other "big" truck, a '59 International B-160, has a T-30 5 speed non synchro trans & 2 speed rear end..so I'm quite familiar with RPM matching shifting. But I also know that any trans with synchros was never intended to be shifted via RPM matching or double clutching, and doing so is a poor band-aid "fix" at best.
As I live in Arizona, and travel around the southwest, I occasionally pull some decent grades, and have found myself wishing for a few more gears here and there. I would also LOVE to have some additional range in the truck. I already have factory dual tanks, and the easy solution of "add another aux tank" occurred to me, but tossing another 100 gallons of diesel in the bed means another 700lbs of weight I'm hauling (though obviously, the weight will go down as the fuel is burned off).
I've thought about putting a 2 speed rear end in, though that obviously will complicate things with the 4x4, which I absolutely want to keep. It's easy enough to just leave the rear in low range when going 4x4, but finding a 2 speed rear with a gear ratio that will match what I can put in a D60 front might not happen. Thought about a brownie box, or other aux trans, and going to a divorced transfer case. Twin sticks don't bother me in the slightest either.
Then the 10+ speed trans occurred to me...I've read over some swap threads, so I know it CAN be done. I could regear the axles to much higher ratio to bring RPMs down on the freeway while having much deeper low gears from the trans to make up for it. Adding on board air is a trivial matter for me to run air shifters if needed. Yes, they're heavy, but so is another 100 gallons of diesel in an aux tank. But is there really a benefit to going that route, other than the cool factor of being able to say I have a 10/13/18/whatever speed trans?
Will lowering RPMs this way really make much of a difference? I know I won't likely see any overall savings via more MPGs once the cost of the trans swap and axle regearing comes in factored in, but my real intent for doing this is extending the time between fuel stops on long drives, and _hopefully_ being able to bring RPMs down a bit on the freeway for less noise/more comfortable driving. I'm not looking at this as a money saving venture at all - otherwise I'd just go buy a newer truck with a more efficient engine to begin with, lol. Though honestly, even if I won the lottery, I just don't see myself buying a new truck...there's just nothing that even interests me any more. I'd just as soon drop the '59 off at some shop with a blank check, and say "rebuild it for me with all modern drivetrain stuff".