All Big Six Extra over drive?

Relates to all big sixes
I need a bigger truck than my 4cyl ranger, I'm moving and gonna be doing work to my new place.
Anyway I found an f150 with a 300 in it for cheap, it's ugly and beat but who cares I'm just hauling crap with it. Gonna go check it out prolly this Saturday.

So I'm curious if anyone has come up with a better OD gear for an auto truck. As in a torque splitter behind the trans and divorced from the trans. This one is a 93 so I'm guessing it's got an e4od. But with fuel prices on the rise I'm spit balling ideas to get rpm down. On the highway


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Another idea is to put different gears in the axle, 3.08 would get your RPM down, I'm not sure if there's any higher available. If you get in the 2.xx it might not be great for hauling
Thought about regearing it too. Also had a wild idea of putting a divorced t case backwards in it ha ha like have the low range as some hoopty OD. But man that would get hot at 70 you'd need a cooler of some kind


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Keep it as is.

There is nothing to be gained from trying to stick tall gears in a work truck unless it's a truck that's dead heading all the time in Florida or somewhere with no hills.

I suspect that your truck has 308 or 355 gears since these were very common in F150s (gotta pump up that CAFE). If you are moving anything heavier than furniture you are doing to want deeper gears than that.


A stock 4R70w has .70:1 OD. A stock ZF has .76:1 OD. A stock E4OD has .71:1 OD. All pretty aggressive OD ratios, especially for a heavy truck. There are some manuals that get the OD ratios down in the .50:1 range, but OD's that deep become weak. Better (and cheaper) to run a steep diff gear and a tall tire. That will get RPM down below 2000 RPM on the freeway. The only F150's I've owned that broke 18 MPG on the freeway had 3.00 and 3.08 gears...


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How 'bout an Allison tranny? 5th and 6th are overdrive; 3.09, 1.81, 1.42, 1.0, .71, .61 all in a time proven package and no doubt available used at a competitive price.

Big six Farmer

Well-known member
If your going for gas mileage, wind drag at speed will work against you the most. In most any Pickup Truck, anything faster than 55-60 Fuel mileage starts to drop off hard. Overdrive on the Transmission really doesnt come into play til 50 or so... Most F150s have either a 3.08 0r 3.55 Rear axle ratio. If your Truck does not have an overdrive already, i would opt for taller rear tires, ( like others have suggested here) ... Be happy with 15- 19 mpg @ 60 mph, you wont do better than that, ( on average )... Way back in the day, i had a new 1985 F150 2wd 302 Fuel Injection, AOD Trans., 3.55 axle ratio. I got 23 mpg once on a trip, ( at a steady 55-60 ), For years after that it would pull 19-20 mpg, at best... So, drive slow with a light foot


allison.....the sae bellhousing on the industrial , has a 2 or 3, i do not recall which. in either case an allison is a fairly easy swap....but costly.
and fun.
and the transfer case drops same as ford.
stand alones are expensive.
transmission fits under cab
and i can use the bellhousing as a mounting point.
double o.d. is hard to acomplish im told.

would the parasitic drag of the 1000 or 2000 be too much fir the six?


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You can definitly get a repeatable 20 with the more aerodynamic 90s body assuming OD, stockish tires and a gear ratio in the bottom half of the 3's. But that requires long highway drives at ~60mph which is a really crappy way to spend your time. For the extra ~$10/wk that flooring it everywhere and getting 14mpg costs it's well worth it.


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I spoke with gearvendors about a similar thing and they said unless my rear end was close to the 4.xx gears or a big block v8, it would be useless... that even if i go against their advisement and got their double over drive anyways that the best i would see is .5 mile increase per gallon since i already have an e4od and 3.08 gears on my truck... there are other ways to get better fuel milage... i got 18 mpg with a different 94 4.9 on the highway doing 70mph after seafoam fogging the intake... the cleaner your engine is the better, and double check it for any vacuum leaks... tune up helps, there is precision auto injectors also who their injectors sprays more of a fog than a straight stream (gonna be trying them out myseld) and for the injectors they got for the 4.9 are only $150 for the set. Anyhow good luck with your trip.


Well-known member
Oh another thing to consider would be a shift kit... less slippage at the transmission would help for hauling and in theory be less parasitic loss