gear change
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Cross-Country
Joined: Mar 2012
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gear change
Hello Got 1 E99 350 dually 4x4 with 4:10 gears. the only weight it pulls is 2 sleds up on the sled deck. the speeds where we go are 60 to 75 mph (100 to 120 KM). I'm toying with a gear change. At 62 (100k) the engine is 2,000, i was going to go to 3:73 but wondering if anyone has done 3:54 gears. Has 4" turbo back S&B cold air hydra with Dans tunes (sdk) BD charge air cooler Sinister charge pipes.
TIA
TIA
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Cross-Country
Joined: Mar 2012
Posts: 63
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truck performs great 70 up a 6% grade with 2 sleds on the deck that's about 1500 lbs with deck and gear. If i gear it faster it probably on that grade end up around 60. We do a lot of trip's that are close to 500 miles with less then 500 lbs in the back. she gets 11 to 12 mpg and just toying with the idea if i get it down to 1600 to 1700 millage will improve some. No I don't pull heavy with this dually like my service truck, but it was low millage great price and the original owner was a heavy duty mechanic he took great care of it. So at 7.10 a gallon just a thought to re gear 3.73 and she will still pull what I need. Have to do carrier swap in rear to go 3.73 carrier swap in the front to go 3.54. But what a great reason to go E locker or true track though. parts I can get good pricing on and its just my time to swap out. It defiantly wouldn't be worth it if had to pay a shop that's for sure. Just curious if anyone went 3.54. I read a post guy was talkin 3,33 or something that fast but that's all I found.
Laughing Gas
Joined: Apr 2016
Posts: 850
Likes: 114
From: Virginia
You could try a slightly taller tire. Doing that will also lower the RPMs like a gear change will. If all you tow/haul is the 2 sleds, then 3.73s will still be plenty of gear.
For reference: I'm running 305/70/16 tires (33x12.50r16), and they are about 1.5-2 inches taller than the stock tires which were 265/75/16. My truck has 3.73 gears...at 70mph, the motor is right around 2100rpms. From my experience, as long as you keep a 7.3 at or above 2000 rpms, it'll pull good.
What size are the tires are you running at the moment?
I don't have any experience with 3.55s, but I believe that all of the obs trucks either had 3.55s or 4.10s from the factory. The 3.73 option replaced the 3.55 option when ford started making the super duty.
For reference: I'm running 305/70/16 tires (33x12.50r16), and they are about 1.5-2 inches taller than the stock tires which were 265/75/16. My truck has 3.73 gears...at 70mph, the motor is right around 2100rpms. From my experience, as long as you keep a 7.3 at or above 2000 rpms, it'll pull good.
What size are the tires are you running at the moment?
I don't have any experience with 3.55s, but I believe that all of the obs trucks either had 3.55s or 4.10s from the factory. The 3.73 option replaced the 3.55 option when ford started making the super duty.
More Turbo
Joined: Jun 2009
Posts: 661
Likes: 186
From: Lakeland, MN
3.73 would work good for you, drop the rpms but also not lug it down much on the low end getting moving. 354 might get you even better highway mileage but your gonna labor some around town and that will burn more diesel. I'd 373 and play with another inch of tire diameter.
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Cross-Country
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Joe7.3 got 255/85/16 32.8 tall had 235/85/16 31.78 tall. My CTS2 seemed off so I i put my hand tack on vibration damper & @ 2000 truck tack hand held was 1975, fairly close. CTS2 was 2400 so now I question all the numbers it gives there is a couple others that don't line up with proper gauges. At 100 KM (62 mph) tack says a needle width over 2000.
nydiver I do agree 3.54 would probably be to fast and would have to drive with overdrive off in town. In class 8 trucks they see better mileage with faster gears and in direct drive not in overdrive so a bit of a twist there called super downsped.
Hopper123 you are correct its a lot of money but I'm a heavy duty mechanic so labor is my time. parts I get wholesale. That been said it would take a while to pay off. But the bonus would be e lockers with a gear change thrown in lol, I should have also added this to my original post.
nydiver I do agree 3.54 would probably be to fast and would have to drive with overdrive off in town. In class 8 trucks they see better mileage with faster gears and in direct drive not in overdrive so a bit of a twist there called super downsped.
Hopper123 you are correct its a lot of money but I'm a heavy duty mechanic so labor is my time. parts I get wholesale. That been said it would take a while to pay off. But the bonus would be e lockers with a gear change thrown in lol, I should have also added this to my original post.
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Laughing Gas
Joined: Apr 2016
Posts: 850
Likes: 114
From: Virginia
Ah so you've already gone to a taller tire. I'd still say go for the gear swap. In your second post, you state that you do a lot of long trips with relatively little weight on the truck. Since that's all you do with the truck, I'd say 3.73s or 3.55s would be a good choice. Should still have plenty of power with just the sleds on the back.
With the 3.73s and your current tire size (which is pretty much exactly the same height as my tires, just skinnier) you should be in the 2100-2200rpm range at 75mph. This should get you a little better mileage and the truck will probably be a little quieter which will help on those long road trips. Next time I'm driving, I'll either take a pic or just try and remember exactly what rpms I'm turning at 70-75mph.
With the 3.73s and your current tire size (which is pretty much exactly the same height as my tires, just skinnier) you should be in the 2100-2200rpm range at 75mph. This should get you a little better mileage and the truck will probably be a little quieter which will help on those long road trips. Next time I'm driving, I'll either take a pic or just try and remember exactly what rpms I'm turning at 70-75mph.
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