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-   -   Rear axle change to lower ratio in Journey (https://www.irv2.com/forums/f101/rear-axle-change-to-lower-ratio-in-journey-55010.html)

georgen 07-20-2009 12:34 PM

Rear axle change to lower ratio in Journey
 
Has any one tried a lower rear axle ration on a Journey GD with a cat 330.
I have checked out the capability but have not been able to find out if it will give much of an advantage. Thought of going from 4:13 to 3:68.;)

mfire1339 07-20-2009 01:14 PM

Georgen, Don't know what you're looking for, But an 11% drop would make it a real dog IMHO.

Mike

MrTransistor 07-20-2009 02:12 PM

Hi George,

In auto terms, a 4.13:1 seems like a race car rear end but remember the diameter of our rear tires is such that this ratio yields a pretty good cruse RPM for a diesel engine. If you were to change the ratio to a 3.68:1 it would drop the RPM by just over 12%. If the transmission goes into 6th gear at say 57 MPH, then after the change you would need to get your speed up to around 64 MPH to get into 6th. This may give you a slight increase in fuel economy at 65 MPH but below that, the economy would drop from being in a lower gear.

And as Mike said, the performance would suffer a great deal. Our old Journey had the same setup as yours and I thought the performance was great, a real hot rod. But the RPM at cruse was still quite reasonable. If I recall, at 65 MPH the RPM was around 1600, right where CAT says it should be. I believe they recommend 1440 RPM at 55 MPH.

Let us know what you decide to do and if changing the deferential is the way you go, please give us a detailed report if you would.

DAN L 07-21-2009 11:05 PM

Quote:

Originally Posted by georgen (Post 525089)
Has any one tried a lower rear axle ration on a Journey GD with a cat 330.
I have checked out the capability but have not been able to find out if it will give much of an advantage. Thought of going from 4:13 to 3:68.;)

in addition to what others have said...
the 10.9% change would be in all gears, not just od. that would be a pretty "tall" 1st gear. maybe too tall for your torque converter to handle without overheating.
it would change your speedometer and odometer readings by 10.9% also.:banghead:

BigSkyBob 07-21-2009 11:46 PM

Quote:

Originally Posted by georgen (Post 525089)
Has any one tried a lower rear axle ration on a Journey GD with a cat 330.
I have checked out the capability but have not been able to find out if it will give much of an advantage. Thought of going from 4:13 to 3:68.;)

I guess I don't understand the OP's question. He wants a lower rear axle ratio but going from 4:13 to 3:68 is higher. I can see all sorts of problems with the transmission with a 11% higher gear ratio.

MrTransistor 07-22-2009 01:16 AM

In the old days, we called it ‘taller’. Talking of the ‘Ratio’, it’s just the number is lower in the x.xx:1. You are correct that after doing the division, the number is higher, .242 as compared to .272 which is the true divisor of transmission final drive revolutions to rear axel revolutions.


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