Gear Ratio change

[Cummins12V98]

You guys looking at SRW trucks need to think outside the box. 3:42's and Aisin towing in the upper limits will do great and the lower limits the 3:42's and 68RFE will be good also. I towed very successfully 28-29K with 3:42's and 68RFE for 65K. One time I was on a steep grade and started to take off and it did not feel good so i put it in 4wd low and crawled top where I could take off in 2wd. I can tell you with the Aisin it would have taken off fine.

my Son has a 15 3500 SRW Limited with Aisin and 3:4s's. I have ridden with him towing his 14K dump trailer well overloaded at about 16-18K. He took off on hills with no strain at all.

Now saying all that if you are going Dually I would for sure recommend 4:10's and Aisin. I have towed my 30K combined load with my new truck and it takes off with ease and climbs like a Goat!

 

[Skypilot]

As was previously mentioned - if you have a 4X4 you will need to do the front differential as well. The other option stated was to replace the front hubs and lock them out but you will still have the different gearing conflict if you ever have to use 4-wheel drive (which you probably will given that you bought a 4X4). So basically double your cost so again, I'd recommend the 4:10s.

 

[Deleted member 995608]

Just my 0.02, but I would go 4.10's if you are spending the money. 4.10's will give you a 20% incresae in rear wheel torque over 3.42's.

You're really good with numbers. What RPM would an Aisin equipped truck run with 4:10 R&P at 70MPH?

 

[AH64ID]

You're really good with numbers. What RPM would an Aisin equipped truck run with 4:10 R&P at 70MPH?

1983 with 265/70R17.
1899 with 275/70R18.

 

[Deleted member 995608]

1983 with 265/70R17.
1899 with 275/70R18.

That's impressive. I can see why you suggest 4:10's. That RPM range is perfect at freeway speeds.

 

[Newsa]

https://www.turbodieselregister.com...-to-RPM-in-Aisin-Equipped-3500-w-4-10-1-Axles

 

[AH64ID]

https://www.turbodieselregister.com...-to-RPM-in-Aisin-Equipped-3500-w-4-10-1-Axles

Looks like his speedo is just a little bit off.

 

[Deleted member 995608]

Calibrated or not, 2100 RPM at 75 MPH is pretty good. My 04 would spin 2100 @ 68 MPH

 

[AH64ID]

Calibrated or not, 2100 RPM at 75 MPH is pretty good. My 04 would spin 2100 @ 68 MPH

Yes it's really good for 4.10's.

 

[SnoKing]

Looks like his speedo is just a little bit off.

Did you use the diameter of the rear Dually tires? SNOKING

 

[Newsa]

My G56 seems to spin at 2000 with 3.42's at 70 mph. I'm happy with the 3.42 since I have not needed to tow more than 6000#

 

[AH64ID]

Did you use the diameter of the rear Dually tires? SNOKING

Yes.

To be fair I really have never seen an OEM speedo that is accurate, they are all off just a little. Most of them tell you that you are going faster than you are and my guess is it is a mileage ploy.

 

[RVTRKN]

My G56 seems to spin at 2000 with 3.42's at 70 mph. I'm happy with the 3.42 since I have not needed to tow more than 6000#

That's odd, because my C&C with a G56 and 3:73 is 2050 RPM AT 70 mph with stock tire size.

 

[AH64ID]

235/80R17 G56 with 3.73's should spin about 2090 at 70.

265/70R17 G56 with 3.42's should spin about 1943 at 70.

That doesn't account for minor speedo error.

 

[Newsa]

Mine are 245 x 70's. Got the cheap tradesman

 

[AH64ID]

Mine are 245 x 70's. Got the cheap tradesman

That puts you around 2017 rpms at 70.

 

[Newsa]

Sounds about right. When these 245/70 17R transforces wear out. I'm going slightly larger. A 265/70 or 265/80 will easily fit on my stock 8 inch rims.

 

[dfb]

I just called my area's service center that does this…. 2500 for both front and back.. from a 3.42 to a 3.73…..

 

[Cummins12V98]

I had the opportunity to change from 3:42's to 4:10's on my 11 HO Dually. Dave Smith game me a GREAT deal at $1,500 front and rear axles. I decided not to swap since it worked fine towing 28-29K. Only negative was starting on a grade it would struggle. If the same combo had the Aisin it would have performed just fine in my book.

Those with 3:42's use 5th for towing same rpm's as 4:10's in 6th, 1,750 rpm's at 60.

 

[AH64ID]

I just called my area's service center that does this…. 2500 for both front and back.. from a 3.42 to a 3.73…..

I wouldn't bother with going from 3.42 to 3.73. If you are going to pay then go all the way to 4.10's. The double OD's of the Aisin makeup for the low gearing.