Gear swap question

[FlatbedHemi]

with the 6.4, am I to understand correctly that they have the 11.5” rear end, and that it is interchangeable with the 11.8”? So if true, if I search for new gears for my 6.4, those gears appearing for diesel applications will work? Just trying to track down some different options in preparation for the swap.

 

[RAM-pagingMN]

no, you'll need the 11.5 inch gear set. yukon makes em, so does aam depending on the ratio you want. the front will need a 9.5 GM conversion ring. i would go to Eastcoastgearsupply.com and they have everything.

 

[NewBlackDak]

The diesel uses the same axle. It’s only the dually that uses the 11.8”.


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[FlatbedHemi]

The diesel uses the same axle. It’s only the dually that uses the 11.8”.


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Ok. Gotcha. So I can do a search for a 2500 diesel option and get the correct gear? I only ask because there are a lot of vendors that specialize in diesels, and often what I find is that anything “gas” related is specific to the 5.7.

 

[Tumbleweed]

I assume that you are going to have a drive line/axle shop do the work? If so, then ask them where to get the parts. Sometimes a package deal is cheaper way to go. Then they would also be responsible for getting the correct parts. Crush sleeves, bearings, fluid etc.

 

[NewBlackDak]

I assume that you are going to have a drive line/axle shop do the work? If so, then ask them where to get the parts. Sometimes a package deal is cheaper way to go. Then they would also be responsible for getting the correct parts. Crush sleeves, bearings, fluid etc.

My problem with that is the shops I have spoken with only want to use noisy brand-X gears, and I don’t want those.


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[FlatbedHemi]

My problem with that is the shops I have spoken with only want to use noisy brand-X gears, and I don’t want those.


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I assume that you are going to have a drive line/axle shop do the work? If so, then ask them where to get the parts. Sometimes a package deal is cheaper way to go. Then they would also be responsible for getting the correct parts. Crush sleeves, bearings, fluid etc.

The shop I plan to use uses Yukon gears. I know the Nitro brand tends to whine. Do Yukons?

 

[Iron Outlaw]

I'm following this. I put 35s on my truck with 373s and 6th gear is useless under 75. I. Ant decide on what to go with as far as ratio.

 

[olyelr]

I'm following this. I put 35s on my truck with 373s and 6th gear is useless under 75. I. Ant decide on what to go with as far as ratio.

4.88’s. If 37’s are possible, then 5.13’s.

 

[FlatbedHemi]

What about 5.13s on 34” tires? Too much gear for highway driving?

 

[olyelr]

What about 5.13s on 34” tires? Too much gear for highway driving?

I honestly dont think it would be.

 

[NewBlackDak]

What about 5.13s on 34” tires? Too much gear for highway driving?

Probably is unloaded. Perfect if you’re towing near max.


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[FlatbedHemi]

Probably is unloaded. Perfect if you’re towing near max.


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Well that’s where Im torn. I don’t tow often, but my unloaded includes about an extra 1300 lbs of steel in the form of a flatbed. At first I was looking into 4.56, then I was talked into 4.88, and now I am torn between 4.88 and 5.13.

I know it’s stupid, but a big concern for me is fuel mileage, such as it is. I get around 12-14 now, and would like it to go up a bit. I know it will never be increased to the point of being the sole reason for the swap, but an increase is an increase. I just want to find the gear set that will net the best combination. Seems like they all increase mileage by decreasing engine load, but at what point is the point of diminishing returns, where engine RPM overcomes the fuel saving effect? That’s where Im trying to be.

 

[joshuaeb09]

Well that’s where Im torn. I don’t tow often, but my unloaded includes about an extra 1300 lbs of steel in the form of a flatbed. At first I was looking into 4.56, then I was talked into 4.88, and now I am torn between 4.88 and 5.13.

I know it’s stupid, but a big concern for me is fuel mileage, such as it is. I get around 12-14 now, and would like it to go up a bit. I know it will never be increased to the point of being the sole reason for the swap, but an increase is an increase. I just want to find the gear set that will net the best combination. Seems like they all increase mileage by decreasing engine load, but at what point is the point of diminishing returns, where engine RPM overcomes the fuel saving effect? That’s where Im trying to be.

The 1300lbs probably isn't enough by itself to warrant the 5.13's if don't have any additional load regularly. IMO if you plan to tow towards your max GCWR, regularly carry towards your max payload, or plan to go with larger tires in the future I would lean towards the 5.13's. Otherwise I think, based on your stated goals, the 4.88's would probably be what you're after.

 

[FlatbedHemi]

According to the calculator, RPM difference in 4.88 and 5.13 is 90 RPM at 70 (2078 vs. 2168), and 97 RPM at 75 (2226 vs. 2323). Most of the highways around here max at 75, and I dont speed much beyond that, but even at 80 there is only a 103 RPM difference (2375 vs. 2478). I guess the real question is, how many RPM is too much?

Speed__4.88__5.13___Difference
55........1632...1704.......72 RPM
65........1929...2013.......84 RPM
70........2078...2168.......90 RPM
75........2226...2323.......97 RPM
80........2375...2478.....103 RPM

 

[olyelr]

That difference is even less than switching from 6th gear to 5th gear.

Hate to say it, but neither of the gearsets are gonna gain you any kind of mpg’s per say... nothing to write home about anyway. And mpg difference between the two will be negligible. I know its hard to do, but I would simply put the mpg thing aside and move forward as to what overall ratio works better for your application. The mpg’s is really just a moot point IMO.