Why 3.73 Rear on the Duramax for towing?

c5hd · May 2, 2003

I was just at my dealer and we were searching for a new Duramax 2500HD. All we could find were 3.73 rear ends. Nothing came up for the 4.10. On top of that, I was reading the brochure and it stated that for the Duramx with the Allison or 6-speed required the 3.73 to reach its maximum towing capacity. It goes on to say in a footnote that the 4.10 is better for towing, but hurts gas mileage.

Is it that the Duramax operates better in the lower RPM and the 4.10 would raise the RPMs at speed? The 8.1 says that either gear is acceptabe.

I am not as concerned about gas mileage as I am about towing preformance. Although, I don't plan on being anywhere near the max (probably only 8000lbs). Who has Duramx + Allison + 4.10?

Thanks

BadBowtie · May 2, 2003

I cannot offer anything but speculation, but I would think that the 4.10 would cause the truck to run through the gears much faster in town, I read somewhere that in a truck w/ dmax and 4.10 you were always shifting or downsifting, the owner said it was hardly worth it to him. ???

Shaners · May 2, 2003

Generally speaking, most diesels make their big torque numbers alot lower in the RPM band than gassers.

c5hd · May 2, 2003

I just went back to Gmbuypower to configure a truck and the 4.10 is not available with the Duramax/Allison combo. I was looking at the 8.1 before and the 4.10 is available.

1BADHD · May 2, 2003

Trust me. With the torque a Dmax puts down, a 3.73 rear is PLENTY!!

sutak · May 2, 2003

I am not as concerned about gas mileage as I am about towing preformance. Although, I don't plan on being anywhere near the max (probably only 8000lbs). Who has Duramx + Allison + 4.10?

Thanks

Hi There,

If you're not concerned with the fuel mileage I would recommend the 8.1L with Allison tranny anytime. For example when you drive at 60 or 65 mph and encounter a hill or want to pass, the odds are both engines Duramax or the gasser will shift down. Both trucks will handle the load no problem, but you will be able to carry a conversation in the gasser. If the hill is steeper the diesel will slow down because of its max rpm limiter. The gasser will easily purr away at 4000 rpm. However I would rather slow down and take it easy with either power plant.

Larry.

2001 Chev k3500 Dually, CC, LT, 8.1L Ally 1000

BadBowtie · May 3, 2003

I'll dispute that. My uncle's new Duramax is just as quiet as my 91-350 I think on the highway it might even be quieter. We had a 12K# dump trailer and about 4tons of FA-6 in it last weekend, had to drive about an hour with it. I hardly noticed it back there (I was riding, not driving) and when it down shifted, it was still quiet enough to carry on a conversation. Yes, you might have to turn the radio up, or talk a little louder, but what vehicle stays the same db level thoughout its entire RPM range? It is much quieter than his 97 F350 PSD, thats for sure!

-John

Firetiger(MN) · May 4, 2003

I just went back to Gmbuypower to configure a truck and the 4.10 is not available with the Duramax/Allison combo. I was looking at the 8.1 before and the 4.10 is available.

That's correct. The 4.10 is not an available option with the Duramax/Allison. Believe me, you don't need it.

Mortgage Paul · May 6, 2003

I wouldnt say a 3.73 is enough. I know a grade thats between 8500 and 9600 feet and 26% grade with 5 MPH swithcbacks that you need both lanes when going around the turns and when towing 8-10,000 lbs in low 1, you get all the speed you can around the turns to make the next uphill before another switchback

If the HDs in any brand offered a 4.56 stock with the Big block motor for that matter Id be all over it. Especially once you lift, that combines with almost a 30% loss of HO near 10 grand, theres been times Ive almost had to stop and go to low 4

TruckFreak69 · May 7, 2003

Well, I'd say yours is an extremem case, and you probably need something above a 1-ton pickup, because you have too much a load if you need to shift into 4 low. I would say that they should bring back the granny gear though. It'd be really helpful maneuvering a trailer around a yard, and why is reverse such a high gear, who needs to go fast in reverse, make it just as low as granny.

Ag Teacher · May 7, 2003

" I would say that they should bring back the granny gear though. It'd be really helpful maneuvering a trailer around a yard, and why is reverse such a high gear, who needs to go fast in reverse, make it just as low as granny."

Amen to that statment. I've got a 98 K-2500 with 3.73 and a NV-4500 and I don't see how you'd back a trailer up without the 4Low. I be afriad to buy a two wheel drive with a manual for fear of burning out the clutch while backing.

BlackSilver · May 8, 2003

Is it that the Duramax operates better in the lower RPM and the 4.10 would raise the RPMs at speed? The 8.1 says that either gear is acceptabe.

I am not as concerned about gas mileage as I am about towing preformance. Although, I don't plan on being anywhere near the max (probably only 8000lbs). Who has Duramx + Allison + 4.10?

Thanks

I tow a 5th wheel, and sometimes a boat behind that, approaching 9-10,000# with a Duramax/Allison/3.73. The performance of the DuraMax/Allison at all speeds is absolutely phenomenal. Remember, this is an electronic 5-speed transmission and it seems to ALWAYS be in the right gear for conditions.

At road speed (65-70MPH) then engine is humming right on the sweet spot of the torque curve. With a 4.10, it would be running at several hundred more RPM's for no good reason.

Mortgage Paul · May 17, 2003

I dont need 4 low, (you would if you ever had to stop on that grade 26% to get going) but remember at 10,000 feet youve lost 30% of your sea level HP. thats alot.

The corners are 5 MPH swithcbacks climbing too so you cant even get a run at each straight section.

Stepside Z · May 18, 2003

For example when you drive at 60 or 65 mph and encounter a hill or want to pass, the odds are both engines Duramax or the gasser will shift down. Both trucks will handle the load no problem, but you will be able to carry a conversation in the gasser.

I have to dissagree with this comment. I own an old Ford 7.3 and on the highway it is very quiet. Many of my friends have commented on how quiet the truck is. I have towed as much as 6500 lbs and though that is not much it was still quiet and I got 15 mpg to boot. I have towed loads with gassers and they were much noiser becasuse I always had my foot in the gas.