Rear End Question

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Dec 12, 2005 | 02:35 PM

rhowell

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Rear End Question

ok i dont know what gear ratio i have, i have a number off the front of the rear end, its RF-F07W-AA, is that of any use to finding out the ratio, theres supposed to be a tag but there isnt one on this rear end so how do i figure it out?

Dec 12, 2005 | 02:41 PM

CowboyBilly9Mile

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From: Eastern WA

The axle code, found on the sticker on the drivers door or door jamb itself, can be used to look up the ratio from a table. From the sticky titled technical information: http://members.aol.com/chris2ac2/200...ationCodes.doc

Dec 12, 2005 | 02:45 PM

rhowell

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identifying the ratio

this rear end came from a wrecking yard and thats the only number i have off of it

Dec 12, 2005 | 03:01 PM

CowboyBilly9Mile

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From: Eastern WA

Hold one axle from rotating, rotate the other axle one full turn and count the # of revs the yoke makes. Divide that by two and you have your axle ratio (non LS).

If it's LS both axles rotate together; make one full turn of the axle and count how many revs the yoke makes. You now have the ratio.

Dec 12, 2005 | 05:40 PM

rhowell

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i never knew that trick, thanks for the advice i appreciate it, one thing i cant remember which is which on the gear ratio, but like a 3.73 or 4.10 would be better for gas mileage and higher speed right?

Dec 12, 2005 | 05:52 PM

john112deere

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From: Maine

The lower the gear ratio (numerically higher) the better acceleration/low speed power, and the worse gas mileage. So, 3.08:1 (highway gears) have poor acceleration at low speeds but a higher top speed and get better mileage on the highway because the engine is turning at a lower RPM for a given wheel speed. Shorter gears (i.e. 4.10:1) have better acceleration and pulling power at low speeds, but worse highway mileage because the engine has to turn faster to get the same wheel speed.

So- low gear ratio (numerically higher, e.g. 4:10) is worse for gas mileage and top speed. Taller gear ratios (lower numerically) get better gas milage and have a higher top speed.

Wheel diameter also affects overall gearing, this all assumes that everything else on the truck is the same.

Confused yet? I could say more, but it would make less sense...

Dec 12, 2005 | 06:31 PM

rhowell

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i originally thought that but typing on here i get confused but it does make sense. its just hard to explain. thanks and by the way i dont think the gear ratio trick worked,do you divide that or multiply the revolution of the output shaft to get the ratio?

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Dec 12, 2005 | 07:15 PM

RangerPilot

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From: Durant, OK (SOSU)

You spin one tire one full revolution and count how many times the input shaft spins. That's the gear ratio. I'd mark it though, it's bloody hard to follow since most of the ratios are in the 3s and if you aren't really paying attention, it'll spin right by.

When I changed my fluid in my rear diff a few weeks ago, 3.08 was stamped on the big gear in the diff. So your ratio will be in there if you wanna dig in and look.

3.08 (mine) gets great highway mileage, but not all that great acceleration (it'll still move if you floor it).
4.10 will fly off the line, but shifts will be closer and top speed will suffer a good bit, especially in terms of cruising RPM.
3.73 is a good performance compromise, 3.55 is a good cruising compromise.

So, if I am doing the math right, a 3.08 would top out almost 25% faster than a 4.10?