Gear swap at 262,000

[94sub]

I am considering swapping my rear end gear ratio from 4.10 to 3.73 . Any ideas at such a high mileage. I currently get 17.5 mpg.

[christja]

ive got 232,000 miles on mine and 3.73 and im only getting 14 mpg at best

[94sub]

Help me out here. Do I change gears or not??

[wyo6.5]

I've been wanting to do the same thing on my truck. It only has 126,000 on it. I don't think the mileage would make that much difference. I have the New Venture 4500 5 speed in mine. I think I'm going to do a tranny rebiuld first and then change out my gears. I'm getting about 16.6 miles to the gallon so I'm thinking if I do the swap I could maybe get 20. That would really help. If any has done a gear swap out and knows what it would cost let me Know.:)

[njdevi11]

As always there's the right way and the down and dirty way:

Ring and Pinion: $150-$200 per axle
Master Install Kit: $80-$100 per axle (bearings and shims and mesh compound)

The ring and pinion is absolutely necessary, that goes without saying. The master install kit is one of those strongly recommended but optional things.

Its a good idea to replace the bearing and everything while you have everything apart at that millage. But everything can be reused even the shims...if your not looking to be 100% perfect. Reusing everything in the exact places should work.

One thing to remember: A dana 44/10 bolt has 2 different carriers one is 3.73+below and another is 3.92 and above. If you cross that threshold then you will need a new carrier. I know if you go from 3.73 to 4.10 you can get "Thick" Gears that makes up for the difference, I dont know if it goes the other way.

I think the dana 60/14 bolt has the same split in the carriers, I think its 4.10 and below for the higher gear carrier and everything over 4.10 for the lower gears. I'm not sure i could be wrong on that.


If you do the swap save those 4.10 gears! SELL THEM ON EBAY! If they are in good shape they are worth $70-$100 in the 4x4/offroad community.

[grancito]

Not worth it for fuel economy, I get 17mpg with the 3.73 diff from my suburban.
When the Chev was newer, I got 19mpg with a 4.27 diff, and 17mpg towing in 3rd gear, so ratios don´t change economy worth worrying about.

[94sub]

mine is 3/4 ton. Ithink the gear swap might help. Any ideas ??

[Husker 6.5]

mine is 3/4 ton. Ithink the gear swap might help. Any ideas ??
Figure a ball-park gain of 1-3 mpg for every jump taller in ratio, all other things being equal. Which axle are you running? For 3/4 ton you had a choice of 10-bolt truck, 12-bolt truck, 14-bolt 9 1/2" ring, and 14-bolt 10 1/2" ring (HD) for the rear axle! Is it Posi?

What are your goals? Maximum highway MPG? Heavy load towing capability? First one to the next stop light? Best combination?

For the 14-bolts (both diameters) I have yet to find any aftermarket manufacturer that offers anything taller than the factory 3:42, so taller tires is the only answer there if you're after max MPG.

Regardless, if you are installing a new ring and pinion, ALWAYS use new shims and crush ring (if equiped), as the proper pinion depth and tooth contact pattern is critical to the longevity of your new ring and pinion, and every gear set has it's own unique setting. Don't, and you can figure on replacing them in 10K or less miles:eek: ! You might as well instal all new bearings and seals for the pinion, diff, and axles while you are there, as they are now the weakest link in your rear-end. I had friends in high school (1976) that would drop in deeper ring and pinion sets into their chevelles, etc. and try to reuse the original shims thinking that all they had to do was just change the gears and drive. Ever see a pinion gear launch through a diff cover and across the high school parking lot in the middle of a hole-shot? I have, and it makes you feel damn glad it wasn't you, and thankful that you weren't behind it!!

You might be better off finding a low milage complete rear in the ratio you want, as they are very plentiful, at a parts yard and just swapping the entire axle.

Just some thoughts, hope this helps.

Husker 6.5

[grancito]

ask for more opinions on mpg I have had many diff ratios in the same vehicle and have not had any signifigant change in mpg. It takes X HP to push your vehicle, thats where the fuel goes, ratios save or wear the moving parts.

[Husker 6.5]

ask for more opinions on mpg I have had many diff ratios in the same vehicle and have not had any signifigant change in mpg. It takes X HP to push your vehicle, thats where the fuel goes, ratios save or wear the moving parts.

All thing being equal (vehicle weight, engine tune, body, tires, etc.) , taller gears WILL give you better fuel milage due to less rpm's = less times you fill the cylinder with fuel per given distance. Why do you think all the new vehicles have 5 and 6 speed trannys with one or two overdrive gears? To slow the engine down to get better fuel milage. The added bonus is reduced engine wear. Remember, HP is a measure of the energy consumed, Torque is a measure of the work produced. The closer you can get a 6.5 to 1800 RPM (max torque) at your highway cruising speed, the more efficiently you will be moving your vehicle for the amount of fuel consumed. Thus, deeper gears help you move heavy loads by getting you to the max torque rpm sooner, but you lose the rpm band at higher speeds. Conversely, with a taller rear ratio, you lose the ability of pure "grunt" force at low road speed to move heavy loads, but gain the ability to effortlessly and economically cruise at high road speeds.

This is how a 6.5TD 2WD Blazer with 3:42 gears can get 20+ MPG on the highway, when a 5.7L gasser barely gets 14MPG with the same rear: Amount of work produced for the same RPM, the 5.7 is trying to do it with 180 lb/ft, the 6.5 is doing it with 400 lb/ft.

Husker 6.5

Husker

[grancito]

For a start, one can not compare diesel engine MPG with that of a gasoline engine, they have a different calorific, or BTU, value per gallon of fuel . The other factor, is the part of the power/rev/fuel curve you are going to operate in. This curve is not provided to us as auto buyers, but it is, as boat engine or industrial engine buyers. It is possible to reduce the engine revs, and to get the same horse power, put the torque requirement into a situation where more fuel is used through inefficiency. The manufacturers of the vehicle had some idea of it´s performance requirements, and so chose the gear ratio. The older vehicles had a better rev range, like my 82, but if you consider the stick shift 6 speed Dodge diesel, they run out of power at 2,800 rpm, and the 4 speed I drove put me in overdrive at 55 mph overtaking, with no acceleration, thats why they need a 6 speed.

[94sub]

Great post Husker 6.5 !! I do very little towing, love my truck and plan on taking it well into the 500k mile range. I am just a bit leery of messing with the gears to gain more mpg. I usually run aroun 2700 rpm @ 70 mph and know that my engine is more efficient at a lower rpm. Already having oner 264k on the truck I know the mpg can be improved. I don't hot rod, could care less about black smoke and laugh at Ford's and Dodges who try to impress you with loud exhaust and squealing tires. I once dared a guy to hook a chain to his Ford and see aho pulled who around the parking lot. My 6.5 is plenty tough for what I use it for, hauling people and camping.

That being said, I am on the fence about the gears......

[sixnickel]

Hey 94sub what size tires are you running and what transmission ??? That RPM is to high for that MPH. Your tach is run off the alternator and a lot aftermarket alternators have smaller pulleys so they turn faster and put out more amps at low RPM but the tach reads a higher RPM than the engine is turning. Give me that info I'll tell you what itis turning.

[94sub]

Stock tires - 245/75R16 stock trans 4L80E

[sixnickel]

94sub Transmission final gear .750 differential gear 4.10 tire diameter 30.47 = 60 MPH 2,035 RPM 70MPH 2,375 RPM
That's still more RPM than you need if you are not hauling a trailer. My 99 Burb has 3.42s is about 1900 RPM at 70 MPH and gets about 19/20 MPG. And it still has a lot of get up and go with the up grades!!

[monolec]

Doug, be honest here and tell the other guys why you really get such great performance from your trucks, Monolec and Almasol!