Highway gears or the Eco Hubs or both

[daniauction]

Hello to everyone.
I just purchase a Stewart and Stevenson M1085 A1 with Cat 3126 from 1999 , to make the truck faster do I need to change the Highway gears or the Eco Hubs or both ?
Thank you

 

[GeneralDisorder]

Depends what you are doing and what your GVW will be fully loaded and equipped.

NEVER recommend highway gears and ECO hubs at the same time. That is never something you want. People have done it by circumstance not by choice.

 

[hike]

Here is a link tp a post with the spin ratios at certain rpm's with and without EcoHubs on 3.07 and 3.90 differentials.

My thought is both are unnecessary. Though, I think @ckouba has both 3.07's and EcoHubs on his—

 

[Ronmar]

I think you will probably be very happy with the eco's... the only people who have done both that i am aware of are the ones who already had the 3.07(6.14 final ratio) before the eco's were created and did not want to, or go thru the hassle to revert(diff swap is a LOT of work). Both together is a step too far as IMO the ideal final ratio would be ~4.1-4.2(but you are not going to find that ratio in a pumpkin our size)... ECO's with the OEM 3.9 final ratio is very close (about as close as you are ever going to get) and the trans really doesn't care if it never sees the 2nd overdrive gear(7th) and will be perfectly happy motoring along in 6th at highway speed just a little over peak torque RPM, although some can even hold 7th in a high cruise under certain circumstances... Anything further down the chain (3.07 final ratio) will sacrifice initial starting thrust and exhaust braking. For the most part even at the lower ratio, I think most are still running out of traction before they are running out of torque.

I know there is a whole lot of info in the original eco thread, but I did thrust calculations for various engine and final ratio configurations like General's and Ckouba's that illustrate the differences. basically having both moves a 3126's overall performance a little closer to that of a 3116 powered A0...

 

[GeneralDisorder]

My thought is both are unnecessary. Though, I think @ckouba has both 3.07's and EcoHubs on his—

Which he is in the process of swapping out like two other guys I know - because ECO hubs are already falling down the backside of the benefit curve with 3.90's. 3.07's with ECO hubs is just a transitional state that is not preferred over one of the two options on its own.

 

[ckouba]

Here is a link tp a post with the spin ratios at certain rpm's with and without EcoHubs on 3.07 and 3.90 differentials.

My thought is both are unnecessary. Though, I think @ckouba has both 3.07's and EcoHubs on his—

Can confirm, 3.07's and ECO hubs, but done as Rick says "by circumstance" and not choice. I have 3.07's because they were in the truck when I got it, and I have ECO hubs because "half the drivetrain speed." I will go back to the 3.90's when the opportunity arises.

The truck is certainly functional with 3.07's and ECO's (I've done several thousand miles in this configuration), but as has been stated, it's a bit of a bridge too far from a ratio perspective, in my opinion.