Rear End Gear Selection: 3.08 or 3.27, or 3.55? - Ranger-Forums - The Ultimate Ford Ranger Resource


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Old 07-11-2015
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Rear End Gear Selection: 3.08 or 3.27, or 3.55?

I need some advice here. I just bought a 1991 8.8" open rear end with 3.08 gears & 10" brakes to swap into my 1990 Super Cab 2WD 2.9L Ranger with auto transmission (A4LD). My Ranger came with 3.45 gears in the 7.5" rear end with 9" brakes.

The 8.8" rear end came out of a 1991 2WD Super Cab with the 4.0L V6.

Next week the rear end will be sandblasted & painted then it's off to the differential shop for a full rebuild.

Originally I was thinking that I would use 3.55 gears as it is close to the original 3.45 gears. 3.45 gears don't seem to be available in 8.8" size.

I will be driving 95% on streets & highways, 5% off-road on gravel/dirt/cow pastures to set up ham radio antennas. On occasion I will also be towing a light flatbed trailer with antennas.

I will also be upgrading to 15" rims and 235/75R15 tires (Goodyear Wranglers Silent Armor are the ones I'm looking at).

The 3.08 gears that I have should give me better gas mileage. I will also get less torque.

No matter what I do I will have to have the speedo re-calibrated.

Given what I plan to do, should I keep the 3.08 gears or swap in 3.27 or 3.55 gears?

The cost of the 3.55 gears (about $135) is irrelevant as the shop will install them during the rebuild at no extra cost.

Thanks!
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Old 07-11-2015
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3.08 are pretty much a highway gear. You need the torque for the occasional trailer pull, so I would probably go with the 3.55's. Did the truck tend to pull trailers alright with the 3.45's in the 7.5?
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Old 07-12-2015
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Quote:
Originally Posted by Fordzilla80 View Post
...... Did the truck tend to pull trailers alright with the 3.45's in the 7.5?
I don't know. I bought the truck a month ago and I have never pulled anything with it.
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Old 07-12-2015
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I say go with the 355's. Why not go with 373's?
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Old 07-12-2015
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Yes, I agree 3.55 would be the lowest I would go, so OD can stay engaged on slight grades

The 235/75R15(29") are probably only 1" taller than stock tires(28") but you would need to look at the door sticker to see stock tire size it came with.

That 1" taller tire would put 3.55 back close to 3.45(3.43) so speedo may be very close to acurate.

If tire difference is 2" taller then with 3.55 your actual would be 3.31
If that is the case the 3.73 might be a better choice, that would put actual at 3.47

1990 still used speedometer cable so you can regear the cable at the trans end to fine tune.

The 3.45 actual ratio puts engine RPMs at 2,100 @ 65mph in OD(.75 ratio), max torque on 2.9l is at 2,600 so 2,100 is a good place to be, you are within easy range of max torque for any grades in highway, and for 70-80mph as well, lol.
3.08 would put RPMs down at 1850, better for MPG but it would have to be very flat ground or trans would need to shift to 3rd all the time which negates any MPG gain.

Last edited by RonD; 07-12-2015 at 12:54 PM.
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Old 07-12-2015
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Thanks all! I am strongly looking at 3.73 given the tire size.
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Old 07-12-2015
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Yes, that would be a good choice even if you only tow once in a while.
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Old 07-13-2015
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Thanks for all the feedback. After considering all the info I got, I purchased a set of 3.73 gears today for my 8.8" rear end. Anyone need a 3.08 set cheap :) ?
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