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Old 05-09-2008, 06:56 AM   #1
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3.73 vs 4.10 gears?

Just realized my van has a 3.73 limited slip rear axle. I thought most of the 4x4 vans used the 4.10 gears

What are the main differences? FYI - van is a V10 w/ Quigley 4x4 w/ 285/75/16 Toyo MT's

When I get around to eventually getting lockers installed is it worth the few extra $$ to also swap out the gears while the diff is all opened up?

thanks

-d
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Old 05-09-2008, 08:31 AM   #2
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The SMB uses 4.10s. I don't know about the Quigley.

3.73 gears are "taller" than 4.10, and 4.10s would referred to as "lower"... just to get the terminology out of the way. They are changed by changing the ring and pinion (R&P) which are the gears inside your axle pumpkin.

If you look at a chart such as this one you'll see that as you go up in tire size, to maintain the same ratio you need to have lower gears.

So for the same size tires, 3.73 give you better gas mileage, and 4.10 give you more power. With the automatic transmission the "power" end is less noticeable as the torque converter helps out.

Reasons for going with 4.10s are:
Towing, having more low end helps get the trailer going
Larger tires, having more low end helps get the tires going
Offroading, having more low end means your engine brake is more effective and over all gearing is lower
Performance, having more low end means you can take off quicker

The reason to get 4.10s when you get lockers is that the labor for doing them is combined- since you have to take the ring and pinion out anyway to do the locker. If you do the lockers and later decide to do the gears or vice versa, you're paying twice. If you don't need more power or lower gears, and don't expect to- (e.g. larger tires in the next two years) there is no reason to change the gears.

Oh yeah, and you have to do gears in both axles so they match.... where as you can do lockers separately.
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Old 05-09-2008, 08:26 PM   #3
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There is only a 10% difference between 4.10 and 3.73 gears. Unless you need to tow heavy loads, I would keep the 3.73 gears. Or maybe if you are going to big, big tires. Otherwise you probably won't notice the difference. And, If you get some big tires (35-37") you probably would want to go to a 4.56 or so ratio.

When I ordered my van, I probably would have ordered 3.73 if it were available, but the choices were 4.10 and 3.55, so I went with the 4.10

I have 4.10 and 33" tires on my SMB and I have 3.73s and 31.5" tires on my pickup. The tire difference makes them very similar.

If you don't notice a problem now then you don't need to make a change. And if you do notice a problem now, a 10% change probably isn't enough to justify the expense of tow gear changes (front and rear) - $1200-1800.

Mike
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Old 05-10-2008, 08:34 PM   #4
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Actually, I think, to get the terminology correct, 4.10 gears are ''shorter" than 3.73's, which are "taller". 4.10s are also lower, terminology-wise.
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Old 05-10-2008, 09:49 PM   #5
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OK, believe I got the terminology fixed, thanks Sky.
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Old 05-11-2008, 09:36 AM   #6
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'Taller' and 'Shorter' gears come from old bicycle terminology.

The first bicycles were the ones with big wheels up front and direct pedal drive. A taller tire was harder to pedal, but could go faster at the same pedal speed. A shorter tire was easier to pedal, but didn't go as far on each revolution.

The big change in bicycles came with the chain drive and gears. A 'Taller' gear simulated a taller tire. A shorter gear simulated a shorter tire.

Thus a 4.10 is shorter than a 3.55 gear.

A shorter gear can go by many other names, some of the names have been used for both taller and shorter gears. In the long run it is probably easier to just call out the numbers, certainly it is less confusing.

Mike
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