Is there any real benefit to a 10+ speed trans in these trucks, other than cool factor?


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Feb 17, 2017
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Wittmann, AZ
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 :D 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 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".


Another old truck
Supporting Member
Mar 1, 2013
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If you were hauling for a living....yes.
One thing comes to mind on the regear idea is being under the torque curve and having no balls to pull top gears.
I'm all for gear selection, just unsure this will bump the mpg'$ much due to the extra weight for one.
But we have a couple multi gearset guys on here....

Here is some perspective.
I have 2 trucks with multiple gear sets,
One is an old willys flatfender v8,3sp trans,2 speed transfer case with a manual 2 speed od., Then an electric 2 speed od, and 4.88 ring\pinion.

This one would barley keep speed on the highway in top gear(3rd gear, high range, first od in hi, second od in Hi) forget passing anything.

Truck 2
Toyota with 4:10 axles.
4 cyl 5 speed doubled t case (2 speed range box in front of a regular 2speed case) this realizes 20 gears UNDER 5th High.
This one will do 80-90 as expected, but it's at 175:1 low gear, and will do 1.5 mph at redline in first under low Range.
This will walk up 3' rocks at idle speed.
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Full timer RVer
Oct 18, 2017
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Heck, I'd be happy to have 4 speeds in my RV


bilge rat
May 8, 2007
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The dual-range trans get heavy, and perhaps a little cumbersome for most folks daily driving.

There is the 7spd Spicer used in some International MDTs... should be sae2 pattern. Not sure what it takes to fit an IDI


Full Access Member
Oct 21, 2015
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Delta Junction AK
Lots of shifting keeps you close to the top of the torque curve, lets you keep RPMs up for horsepower. You'll still be at a walk when you reach the top of the hill, you'll just be able to cruise at a lower RPM on the flats. The full in-bed tank weighs as much as the big roadranger transmission, but the big transmission doesn't get lighter when you're running empty and don't need it.

I'm thinking that these engines are fairly flexible, have a decent power band, and it might be enough to use the wide range gears from a 460 ZF5 to get a little extra low end torque to handle a little less reduction in the rear end. The only way these old trucks are going to match the performance of a 400hp modern rig is if we hotrod them up to 400hp.

If I need a medium truck, I'll get a medium truck.


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Feb 21, 2008
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Campbell River, B.C.
I got by for a few years with nothing but a C6 and 3.08 gears. Basically, I traded 1st gear for an equivalent higher top gear. It worked well because 1st gear with 4.10s was pretty much useless with how l used the truck. I died and went to heaven when the E4OD went.

I don't really need more gears but a 10 speed would add a new level of cool factor.