3.55 gears
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3.55 gears
I was playing around on the Ford Vehicle site last night and noticed that you can get 3.55 gears on the new SD with the 6.4 diesel. I don't think they were available last year on the 6.0 when I was doing the same "build your dream truck" thing. Do the new diesels make that much more torque or is this just to try to boost their abysmal mileage? Would 3.55 gears be OK for a 6.0 that isn't used for towing?
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Joined: Sep 2000
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From: Stephensville WI
Yes, it would work OK for a 6.0L that doesn't tow. The 6.0L makes enough low end torque that a 3.55 could be used.
HOWEVER
Your mileage won't go up that much, if any. Figuring $2000 for the modification, what is your payback? How many miles do you have to drive to break even?
HOWEVER
Your mileage won't go up that much, if any. Figuring $2000 for the modification, what is your payback? How many miles do you have to drive to break even?
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Redford, I'm not planning on changing my gears, just was curious because the 3.73 was the "highway gearing" option last year. Now there's a new engine and taller gearing to go with it. If I do anything with the diffs I'll get a pair of TrueTrac LS units and junk the worthless OEM un"Limited Slip" it came with.... It's much easier to get taller tires when the time comes to change the effective gearing, the biggest rub is in finding something taller without going wider. So far the best option seems to be the Rickson 19.5" wheels and 265(34.5") or 285(35.4") tires, but at $3500-4000 for a set of five it's pretty pricey even if you do get twice(+20% with a 5 tire rotation) the miles out of the set of tires. I wish the tire makers would come out with something like a 265/85R16E...
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From: Corvallis, OR
From all the reading I've done, the general conclusion is that for stock tires on a 6.0L you'll get better mileage with 4.10s than 3.73s if you keep it under 70mph. I have 35s and a set of 4.30s ready to go in, this will put my end ratio halfway between what it would be with 3.73s and 4.10s with stock tires.
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From all the reading I've done, the general conclusion is that for stock tires on a 6.0L you'll get better mileage with 4.10s than 3.73s if you keep it under 70mph. I have 35s and a set of 4.30s ready to go in, this will put my end ratio halfway between what it would be with 3.73s and 4.10s with stock tires.
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Lead Driver
Joined: Jun 2007
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From: Corvallis, OR
It all depends on what the engine's most efficient rpm range is. The 6.0L has a lot higher rpm torque and horsepower curve than the 7.3L, so it does better with higher gears than the 7.3L.
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As for the question of torque........I know the 3.55 rear end is not available with the 20 inch wheels. That may be an indicator the gearing is on the edge. I drove a Job #3 King Ranch with 18's and 3.55's, the truck "drove" what I would assume is normal. It was a test drive at a dealership though, so no towing was involved, nor any fast starts.
Vincent
Vincent
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From: Alexandria, Ohio
With the amount of torque the PSD/V10 or even the 5.4 put out why are the gears required to be 4.10 and up? My '79 F250 came with a 351M that had 150 hp if it was lucky and maybe 200 lb/ft of torque. It was an auto with full time 4wd and 3.54 gearing. 7700 GVWR. I built a 325-350 hp 406 with a 4 speed and part time 4wd, 4" lift and 35x12.50's and kept the 3.54 gears. It would easily tow everything I hooked to it. Car trailers with trucks on them, skid loaders, 2 300 bale hay wagons. Why the need for the low gearing when even the 5.4 has "almost" the power as my built 400. Todays trucks have 4/5 speed autos or 6 speed manuals also.
