K3500 Gearing

[BNielsen]

I like the 3.73s, it cruises so nice down the interstate; but I don't know if it's my fuel pump not running full pressure or something tune wise or if it's really just the gearing itself but my truck is just gutless starting out with 9K on back.
Gas mileage on 245s with 3.73s was around 10-11,
Gas mileage on 285s with 3.73s is around 9-12; my speedo isn't calibrated so it's throwing it off a little.

My father had 4.56 gearing in his old C3500 and that thing got 10 no matter what, empty or pulling our 6500# camper at 70.

Plus regearing to 4.10 is gonna let me add in a front locker that's in the differential I've hopefully secured.

 

[stutaeng]

I like the 3.73s, it cruises so nice down the interstate; but I don't know if it's my fuel pump not running full pressure or something tune wise or if it's really just the gearing itself but my truck is just gutless starting out with 9K on back.
Gas mileage on 245s with 3.73s was around 10-11,
Gas mileage on 285s with 3.73s is around 9-12; my speedo isn't calibrated so it's throwing it off a little.

My father had 4.56 gearing in his old C3500 and that thing got 10 no matter what, empty or pulling our 6500# camper at 70.

Plus regearing to 4.10 is gonna let me add in a front locker that's in the differential I've hopefully secured.

I just looked at my '00 manual and it has towing capacity of K3500 crew cab with 7.4/4.56 as 12,000 lbs. 10,000 lbs with 4.10. Again, no 3.73 listed.

There is no 2500 crew cab option. I had not noticed this. Maybe they didn't make 2500s crew cab in 2000?

Anyway K2500 with 3.73 (regular & extended cab?) is 9,500 lbs. Still pretty good! Crew cab may be a tad lower.

Does anyone have a 96-98 K2500 crew cab to check 7.4/3.73 combo?

 

[oldbrown]

Thanks guys for the feedback. I see the pros-cons for both the 3.73 and 4.10. So towing with 4.56 is just under 8mpg. Same with 25 foot RV or 16 foot open trailer. Speed is at 63 mph/2500 rpm. I never expected good mpg but at under 8 it limits how far you can drive without stopping. It stays in OD with what I am pulling but I think dropping the RPMs would help quite a bit. I don’t need to drive fast but also would like to keep up with traffic. The thought of taller tires crossed my mind but more rotating mass is a little anti productive. And my wife is short. Ha ha

 

[andy396]

Thanks guys for the feedback. I see the pros-cons for both the 3.73 and 4.10. So towing with 4.56 is just under 8mpg. Same with 25 foot RV or 16 foot open trailer. Speed is at 63 mph/2500 rpm. I never expected good mpg but at under 8 it limits how far you can drive without stopping. It stays in OD with what I am pulling but I think dropping the RPMs would help quite a bit. I don’t need to drive fast but also would like to keep up with traffic. The thought of taller tires crossed my mind but more rotating mass is a little anti productive. And my wife is short. Ha ha

The additional rotating mass is negligible. Really only comes into play for rapid acceleration like in racing. As for the short wife....I already see you have a step, so not sure what else you can do.

 

[Supercharged111]

You're not gonna see much if any better than 8 towing regardless of the gear.

 

[oldbrown]

So has anyone run 235-85-16 on their K3500 dually in place of 225-75-16 without any modifications with no issues? Gets me real close to 4.10 ratio. Thanks

 

[BNielsen]

So has anyone run 235-85-16 on their K3500 dually in place of 225-75-16 without any modifications with no issues? Gets me real close to 4.10 ratio. Thanks

I think Dave @88GMCtruck had them on his K3500; @DanteGTZ owns it now so either of them can chime in; and I also think Devin @83GMCK2500 runs the same brand/size Dave did.

 

[Supercharged111]

So has anyone run 235-85-16 on their K3500 dually in place of 225-75-16 without any modifications with no issues? Gets me real close to 4.10 ratio. Thanks

My flipper has them on stock rims and you might be able to get a piece of paper between them. Definitely gonna need spacers for that.

 

[92_Bahama]

So we bought our 98 K3500 crew cab 454 dually to haul a camper. We ended getting a relatively small camper (25 ft, 4500 lbs empty). Just my luck someone swapped the 4.10 gears for 4.56 gears. Obviously overkill and poor mpg/high cruising rpm has limited its use to just hauling. I have finally decided to change gears. I am contemplating 3.73 gears instead of 4.10s. If it had 4.10s, I would leave it alone but since I need to change anyway, that’s why I am considering 3.73. Factory tow rating is 12k, 10k and 8k respectively based on gears. Truck has stock size tires, runs well and is in good mechanical shape. Anyone have my truck with 3.73s? Most I am sure have 4.10s. Even if I had to tow in drive with 3.73s in the hills, I think it may make the truck overall more user friendly. Thanks.

What RPM do you see in OD at your tow cruising speed?

 

[Supercharged111]

What RPM do you see in OD at your tow cruising speed?

He said 2500 RPM at 63mph. I wanna say mine hits 2000 around 57. I have 4.10 and 225/75/16.