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Old 10-21-2013, 01:14 PM
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Rear Diff. Ratios and Trannys

Alright, so I owned a 1994.5 With a 5spd and 4.10s in the back. I could hit 65 at 2200rmps in OD.

I just got another truck. 1997 E4OD with supposedly 4.10s too. I can drive comfortably at 75 at 2500rpm.

This leads me to believe that the rear diff has been changed from the 4.10 to 3.73s or 3.55s.

Am I true in thinking that or are the final drives of the 5spd and E4OD really that different?
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Old 10-21-2013, 01:24 PM
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Final drives between the two are very close. The Manual is a tad taller meaning that two trucks side by side with the same everything but trannies the Auto will be rolling at a slightly lower RPM. A truck going 75 mph and have 31" tires should be spinning the motor at approx. 2533 RPM. To be correct you must make sure that your tire's circumference is matched to the programming in the PSOM.
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Old 10-21-2013, 01:28 PM
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1994.5 was 2WD.
1997 is 4x4 so it's a little but taller.

Both trucks are where wearing the same tires.
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Old 10-21-2013, 01:41 PM
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The transfer case is 1:1 when set to 2wd. This just leaves the final drive in the manual being .76:1 and the final drive in the Auto being .71:1. With this and doing some math I feel that the rear ends in both vehicles is the same 4.10.

2200 (rpm) / 65 (mph) = 33.846

2500 (rpm) / 75 (mph) = 33.3

With less than a 2% difference between the two I think that I'm safe in my assumption.
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Old 10-21-2013, 01:44 PM
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Thanks for the reply!

That makes pretty good sense to me.

This truck just feels like it drives so much easier up there in the 70+ range.


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Old 10-21-2013, 02:12 PM
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The end all is:

-lift the rear tires off the ground
-release the parking brake and put the trans in neutral
-with chalk or sharpie draw a line on the inside of the tire straight down and onto the ground
-where the d-shaft connects to the pinion (neck) draw a straight line left to right through the u-joint
-rotate the tire one full turn and count the number of times the d-shaft line crosses the pinion neck on the Pumpkin
-you now have you tires ratio to the ring gear. (goes around just over 4x-> 4.10s, goes a little under 4x->3.73s, goes 3.5x->3.55s)
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