Like everyone, I'd like to make better mileage, esp. with present fuel prices. I don't use my '78 Clipper (440) for towing, and am considering changing the 4.10 gears to 3.55 to get the revs down at cruising speed. (My present setup makes about 3000 rpm at 60 mph). Anyone had experience with this approach??
The chassis was probably the same as the one ton truck so there might be a 2 speed rear end available. There are also 3 speed gearboxes (made by brownlite for example) intended to go into the drive line that give you an underdrive, straight through, and overdrive. I just saw one of those on ebay for $250 within the last month. It's my impression that the stock transmission does not have a lock up torque converter. The same transmission was used in trucks, cars etc with a mechanical lock up (per one transmission expert I talked with) but not in the van as they were not required to meet mileage standards in the vans. There are also replacement transmissions that include overdrive and are much heavier duty. Keep in mind that if you kick the gear ratio up it will have to work harder getting away from the stop light. If I recall correctly a 727 transmission at Summit Racing designed to handle 500 horsepower was around $800 and one designed to replace the 727 and include an overdrive was around $1300 through one outfit in Canada and again rated for around 500 horsepower. If your transmission needs rebuilding it is not much extra to go one of those ways. Depends upon your budget and time. I think the 2 speed rear end approach wouldn't cost much more than what you would have in changing ring and pinion.
I would go with the lockup torque converter. Depending on the stall characteristics of the 727 torque converter (high stall or low stall) I would guess about a 50% improvement in fuel consumption. The only problem there is you might have to go to a lower geared rear end because of the overdrive gear in the lockup automatic. I would check with your local transmission repair man and see about getting a transmission core from a wrecking yard and rebuilding that. Unless you go with turbocharging on the engine, I think the stock unit would work.
Thanks for the response and suggestions. I've checked into a two-speed axle (according to my local Dodge parts dep't, none was ever offered for the 1 ton van), and a "Brownie" won't fit into the driveline with adequate clearance. I can get a set of gears (3.55) for under $50.00, but installation will be the catch there. No easy solution, but I do believe that a gear change would work OK - my current setup almost never shifts down on hills and maintains 60 mph with relative ease.
Did you switch your gears and get any better results? I'm thinking of doing the same change.