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2001 F-350 dually differential gear ratio questions

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2001 F-350 dually differential gear ratio questions

 
  #1  
Old 07-30-2016, 10:13 PM
mrm8174
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2001 F-350 dually differential gear ratio questions

Hello fellow FTE members. I have a few questions about the gear ratio in my 2003 F-350 dually.
It has the stock 4.10 ratio limited slip differential and 6 speed manual transmission. When I drive it on the interstate, it tacks about 3000 RPM at 70 mph in overdrive. What I want to know is if I could change the differential gears to say a 3.73 ratio. I drive on the interstate a lot and do not tow heavy loads very often. It is 4x4 so I know I would have to change both the front and the rear differentials. I have 265/75-16 tires on it. I am looking to lower the RPMs at higher speeds because it really sounds like the engine is winding tight.
Any input on this would be appreciated and if anyone knows of anywhere to get good differential gears, let me know. If more info is needed just tell me. Thanks.


Mike
 
  #2  
Old 07-30-2016, 10:28 PM
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Something is wrong 3k @ 70? At work we have one with the 7.3, 4.10 zf6 combo and it sits right 2400 at 70 mph, you sure you ain't got steeper gears? Maybe 4.30?
 
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Old 07-30-2016, 10:38 PM
mrm8174
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It has the 4.10 stamp on the axle ID tag and the original dealer window sticker is in the dash with the owners manual and it says 4.10 ratio. The gears may have been changed before I bought the truck. I have only had it for about a year and a half. All I know is that it sounds like it's running way too fast and pushing the engine way too hard at high speeds. When I'm going up a long grades, the engine oil temp will get up to 220-225 degrees. I have to pop it in neutral on down grades and let it drift so the engine oil temp will cool down.
I did change the rear differential oil a while back and the cover had been removed before. I could tell because it didn't have a gasket on the cover and waaay too much RTV sealant.
 
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Old 07-30-2016, 10:44 PM
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220-225 oil temp ain't bad and it should cool down going down hill. You should run a syn., blend or syn oil. As far as the gearing, it's not 4.10 in your in over drive. No way. Pop the rear cover and see what you have. They mitt of only changed the rear gears if your lucky.
They may of towed heavy and wanted lower gears or had big tires.
 
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Old 07-30-2016, 10:56 PM
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My dad has a F550 with the 4.88 gears and he doesnt turn that many rpms. I dont know for certain as i dont drive it , but i think he turns around 26-2700 at those speeds. You may want to look into a Gear Vendors aux. transmission. Gear Vendors under/overdrive transmissions the most awarded auxiliary transmissions.
 
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Old 07-30-2016, 10:57 PM
mrm8174
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Originally Posted by Bonanza35 View Post
220-225 oil temp ain't bad and it should cool down going down hill. You should run a syn., blend or syn oil. As far as the gearing, it's not 4.10 in your in over drive. No way. Pop the rear cover and see what you have. They mitt of only changed the rear gears if your lucky.
They may of towed heavy and wanted lower gears or had big tires.
I run Rotella T6 synthetic 5w-40 oil. It will cool down going down hills, but it cools down a lot faster in neutral. I don't really want to take the cover off again unless I'm going to change the gears. I already know I have at least 4.10 gears. I really want to know if changing to 3.73 gears would cause any problems and if it would help my current problem. Thanks.


Mike
 
  #7  
Old 07-31-2016, 01:13 AM
Dirtscooter250
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Originally Posted by mrm8174 View Post
I run Rotella T6 synthetic 5w-40 oil. It will cool down going down hills, but it cools down a lot faster in neutral. I don't really want to take the cover off again unless I'm going to change the gears. I already know I have at least 4.10 gears. I really want to know if changing to 3.73 gears would cause any problems and if it would help my current problem. Thanks.


Mike
There is no way you have 4.10 s if you are at 3000rpm at 70. my 4.88s are at 2250 at 60.

Changing to 3.73 will drop your rpms quite a bit but you will not tow really heavy loads nearly as easy. Where i am 3.73 loaded heavy either is wrapped out in 4th or not quite enough in 5th with the 6 speed stock. Having towed with a few 4.88, 4.10, and 3.73 7.3 super duties, I would go with 4.10 honestly if not extremely heavy or 4.88 for really heavy.

I don't know how changing to 3.73 would cause problems unless you have the setup installed wrong. Your rpms will definitely drop
 
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Old 07-31-2016, 03:39 PM
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If you change them, do both front and rear.
 
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Old 07-31-2016, 03:58 PM
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At 3000 RPM, with those tires and that transmission, I think you probably have 5.56 gearing. That would be fine if it was a school bus or dump truck, but it isn't. I think 4.10 would suit you just fine if you do any real towing, or you could go up to 3.73 or maybe even 3.55 if you don't tow much.

@70 MPH in OD:
4.10 ~2200 RPM
3.73 ~2000 RPM
3.55 ~1900 RPM
 
 
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