gear question

[90bronco86]

I looked at the axle tags on my axles and it says i have 3.54 gears in the front and 3.55 gears in the rear, is this normal for a bronco? And are they considered low or high?

 

[Bully Bob]

Hi gearing..... (or actually normal for stock)

The larger the number, the lower the gear. 411's then 456's would be lower in that order.

 

[90bronco86]

Ok, so thats good for a stock truck with 31s and dosent see much offroad?

 

[miesk5]

yo,

Ford built our Broncos & other 4x4 trucks & vans with a numerically lower front gear ratio in the front Dana 44 than the rear so that off-road steering is enhanced.

A Bronco built with a 3.55 rear ratio would have a 3.54 ratio in the front Dana 44.

Following was in my MS WORD Notes and the source, Randy's Ring & Pinion has removed it from their current web site; The gear ratio in the front of a four wheel drive has to be different from the front so the front wheels will pull more. There have been many different ratio combinations used in four-wheel drive vehicles, but not so that the front will pull more. Gear manufactures use different ratios for many different reasons. Some of those reasons are: strength, gear life, noise (or lack of it), geometric constraints, or simply because of the tooling they have available.

I have seen Ford use a 3.50 ratio in the rear with a 3.54 in the front, or a 4.11 in the rear with a 4.09 in the front. As long as the front and rear ratios are within 1%, the vehicle works just fine on the road, and can even be as different as 2% for off-road use with no side effects.

A point difference in ratio is equal to 1%.

To find the percentage difference in ratios it is necessary to divide, not subtract. In order to find the difference, divide one ratio by the other and look at the numbers to the right of the decimal point to see how far they vary from 1.00. For example: 3.54 ÷ 3.50 = 1.01, or 1%, not 4% different.

And likewise 4.11 ÷ 4.09 = 1.005, or only a 1/2% difference.

These differences are about the same as a 1/3" variation in front to rear tire height, which probably happens more often than we realize. A difference in the ratio will damage the transfer case.

Any extreme difference in front and rear ratios or front and rear tire height will put undue force on the drive train. However, any difference will put strain on all parts of the drivetrain. The forces generated from the difference have to travel through the axle assemblies and the driveshafts to get to the transfer case. These excessive forces can just as easily break a front u-joint or rear spider gear as well as parts in the transfer case.

Source: by miesk5 at Ford Bronco Zone Forums

Tire Diameter/Circumference & Air Pressure Differences; "...You will recall that at the beginning of this section, we mentioned that we had made sure that all four tires on our truck were the same size, were worn the same amount, were inflated to the specified pressure and were subjected to reasonable loading. Avoiding driveline windup was the reason for this. Figure 18A shows that tires of even slightly different size roll different distances every revolution. Figure 18B shows that the same effect is true for tires that are the same size but inflated or loaded differently. Operating a 4 x 4 in 4WD with tires of different size or inflation will produce driveline windup, even when driving straight ahead! If the vehicle is being driven in 4WD on dry, hard pavement, the driver will notice drag and may experience the hop, skip, bounce effect as the front or rear wheels release the windup..." in Four Wheel Drive (4X4) General Information, Operation & Troubleshooting TSB 92-1-8 for Bronco, F Series & Ranger (COMPLETE); Includes Electric Shift On The Fly (ESOF) Troubleshooting & Hub Operation; see page 4-6 & Figures. miesk5 Note, The tires must match in size to ¼” (.250).

Source: by Ford http://content.chiltonsonline.com/TSB/displayTSBHandler.ashx?assetID=36059&key=6kAUBD5BruOJf%2f3tgozUqjXM3RdbjcQqW4sVWiE%2fp2IojfpfKqM07dr61%2bQAWHtTZr4ceHaQGlj8NylACcNZ4qedMqy4JdYyAXN5akgfkpHUz4aCpJyaaA%3d%3d

 

[90bronco86]

Thanks that really helped alot! I appreciate it