Swaping gears out for fuel mileage?
05-14-2009, 06:57 PM
#17
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I'm looking at going the other way. 3:55's to 4:10. The easiest way is to swap the entire rear assembly. I've priced gears and the carrier needed. Parts at the best are about $750.00 (new) Figure about $500.00 to install.
I want 4:10's for towing my fiver. 3:55 work good for a light truck getting me about 18.5-19 on the hwy at 68mph. Towing is consistant 10-11 mpg, sometimes less. I'm sure the mpg will increase towing to 12-13 consistant with the load off the engine with the lower gears.
So if anyone does swap out, that has a 4:10 please let me know. It seems every time this comes up, everyone is more than a 1000 miles away. Must be a Dana 80 rear.
You can contact me at MarServs@Bellsouth.Net
Dave
I want 4:10's for towing my fiver. 3:55 work good for a light truck getting me about 18.5-19 on the hwy at 68mph. Towing is consistant 10-11 mpg, sometimes less. I'm sure the mpg will increase towing to 12-13 consistant with the load off the engine with the lower gears.
So if anyone does swap out, that has a 4:10 please let me know. It seems every time this comes up, everyone is more than a 1000 miles away. Must be a Dana 80 rear.
You can contact me at MarServs@Bellsouth.Net
Dave
I'm pullin 80 MPH at 2000 RPM in OD locked up and wanna see 2K RPM about 65-70........that seems to be the sweet spot for towing for me.
Already have gears for my front but not rear.
On a side note..... all you guys here serving.....THANKS for your service to our country.
BTW carrier change not req'd..... cutoff for a 60 and 70 are between 4.56 and 4.88, not possitive about the 80??
05-14-2009, 07:27 PM
#18
Administrator / Scooter Bum
05-14-2009, 10:50 PM
#20
Same boat here...... see sig line but have a 70 rear with the auto. Plus I'll demand a disc brake rear.
I'm pullin 80 MPH at 2000 RPM in OD locked up and wanna see 2K RPM about 65-70........that seems to be the sweet spot for towing for me.
Already have gears for my front but not rear.
On a side note..... all you guys here serving.....THANKS for your service to our country.
BTW carrier change not req'd..... cutoff for a 60 and 70 are between 4.56 and 4.88, not possitive about the 80??
I'm pullin 80 MPH at 2000 RPM in OD locked up and wanna see 2K RPM about 65-70........that seems to be the sweet spot for towing for me.
Already have gears for my front but not rear.
On a side note..... all you guys here serving.....THANKS for your service to our country.
BTW carrier change not req'd..... cutoff for a 60 and 70 are between 4.56 and 4.88, not possitive about the 80??
05-15-2009, 10:23 AM
#22
Registered User
gear change doesn't change the speedo reading. the speed sensor is on the ring gear (not sure what year they changed that) so the reading is not changing. rpm will change, but as long as your speedo is correct now it will be correct after a gear change! now tire size change will affect the speedo and a Smarty can adjust the speedo/odo or a dealer can change the revs/mile with their scan tool (i corrected for 37s with the factory scan tool, but no more buddy at the dealership 
)
)
05-15-2009, 10:55 AM
#23
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Hey guys - I also wanted to say for all of you in the military, thanks for your service.
I am a CPA so I just had to give a math scenario for changing gears for better mileage - if that is the only reason. FYI - It may take a bit just to recover the cost.
I am just throwing out numbers here, but lets say you go from an average of 13MPG to 16MPG, an increase of 3MPG. If you fill up with 30 gallons each time, you will get 90 more miles per fill up (3MPG * 30 gallons). At 16MPG you save 5.6 gallons per fill up (90 miles /16MPG). Lets estimate diesel at $2.30/gallon - you save $12.90 per fill up (5.6 * $2.30). If you fill up every 10 days, you are filling up approx. 36 times per year for a savings of $464 a year (36 * 12.9). Take the cost to change the gears and divide it by $464 and that is how many years it will take for you to break even. After that, it will be beneficial to you. You can change any of these numbers to figure out the cost/benefit.
I am a CPA so I just had to give a math scenario for changing gears for better mileage - if that is the only reason. FYI - It may take a bit just to recover the cost.
I am just throwing out numbers here, but lets say you go from an average of 13MPG to 16MPG, an increase of 3MPG. If you fill up with 30 gallons each time, you will get 90 more miles per fill up (3MPG * 30 gallons). At 16MPG you save 5.6 gallons per fill up (90 miles /16MPG). Lets estimate diesel at $2.30/gallon - you save $12.90 per fill up (5.6 * $2.30). If you fill up every 10 days, you are filling up approx. 36 times per year for a savings of $464 a year (36 * 12.9). Take the cost to change the gears and divide it by $464 and that is how many years it will take for you to break even. After that, it will be beneficial to you. You can change any of these numbers to figure out the cost/benefit.
05-15-2009, 11:49 AM
#24
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hmmmmmm,mine with 4.10's in 3rd no o.d. im at 60-65 mph and 2k rpm and 15psi on the gauge, sweet for towing , but in o.d. i don't even know the top speed with the GSK on now, I'm thinking of 456's , to me it would be better towing capabilities utilizing less throttle.
05-15-2009, 12:02 PM
#25
gear change doesn't change the speedo reading. the speed sensor is on the ring gear (not sure what year they changed that) so the reading is not changing. rpm will change, but as long as your speedo is correct now it will be correct after a gear change! now tire size change will affect the speedo and a Smarty can adjust the speedo/odo or a dealer can change the revs/mile with their scan tool (i corrected for 37s with the factory scan tool, but no more buddy at the dealership )
)
05-15-2009, 06:34 PM
#26
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Thanks for all the help guys!!! I did something similar well pretty much the same as what Offroadcpa did and I dont really know that is see it benificial so unless i come across a swap or a killer deal I'll stick with the 4.10s. Ickk
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