New rear diff
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Junior User
Joined: Sep 2005
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New rear diff
I am changing out the stock rear diff on my 98 Ranger with a new limited slip diff. I currently have 3:73 gears. I wanted some of your opinions on rather or not I should keep the same gear ratio or change? And if I do change it what do you all think I should change it to?
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Junior User
Joined: Sep 2005
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Colony I have the 2.5L engine and the 4 speed automatic with overdrive. I have 17" low profile tires on my truck, the 17's our actually not as tall as the stock 15's that were on it but a lot wider.
Thanks for your input too CowboyBill.
Thanks for your input too CowboyBill.
Senior User
Joined: Apr 2005
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Here's a calculator that should help you greatly. It deals with changes in tire size. http://www.csgnetwork.com/lttrucktireinfocalc.html
Another calculator, and one that's even more helpful is this one: http://www.4lo.com/4LoCalc.htm
It lets you plug in every variable in the driveline and calculate what changes will do.
So let's say that you had my Ranger. It has 225/70R15's, a 4.10, and the Mazda 5 speed with a fifth gear ratio of .79. With that combination my truck is turning 2383RPM at 60 MPH, and 3177 at 80 MPH. Those numbers are good for the 2.3 because it makes its peak torque at 3750 RPM.
If I switched to a 3.73, my RPM at 60 MPH would drop to 2168. That's not a very big difference in the way the engine sounds (the main issue of most people at cruising speeds), but it would be sufficiently different to cause a performance difference because it gets me further away from the peak HP and torque bands.
With all that in mind, you need to find out what the gear ratio is for the OD in your truck and go from there. I know the 5 speed auto's OD gear is .75. If yours is the same, I'd almost certainly go with the 4.10 to prevent extra shifts out of OD and prolong transmission life.
Another calculator, and one that's even more helpful is this one: http://www.4lo.com/4LoCalc.htm
It lets you plug in every variable in the driveline and calculate what changes will do.
So let's say that you had my Ranger. It has 225/70R15's, a 4.10, and the Mazda 5 speed with a fifth gear ratio of .79. With that combination my truck is turning 2383RPM at 60 MPH, and 3177 at 80 MPH. Those numbers are good for the 2.3 because it makes its peak torque at 3750 RPM.
If I switched to a 3.73, my RPM at 60 MPH would drop to 2168. That's not a very big difference in the way the engine sounds (the main issue of most people at cruising speeds), but it would be sufficiently different to cause a performance difference because it gets me further away from the peak HP and torque bands.
With all that in mind, you need to find out what the gear ratio is for the OD in your truck and go from there. I know the 5 speed auto's OD gear is .75. If yours is the same, I'd almost certainly go with the 4.10 to prevent extra shifts out of OD and prolong transmission life.
