Gear rotation

[M1llionb]

I just swapped 31's for 33's on my truck. I was reading that I need to conduct a gear rotation... How can I accomplish this task? 

 

[Bully Bob]

You probably mean "reduction"  From 350's to 411's  to bring the torque curve back in line.

Also, there's a small gear at the trannie/transfer (end of speedo cable) that brings the speedometer 

back to accuracy.

 

[M1llionb]

Bully, I'm new to my truck and need help accomplishing the task. Where can I find tips or maybe a video to complete reduction?

 

[miesk5]

Yo M,

Bob advised you of 2 possible changes needed due to increasing tire diameter.

One is the differential re-gearing that is costly, and will be needed for both front and rear differentials.

But 1st, we need to determine what differentials and gear ratios are in your Bronco now.. many previous owners may have swapped the gears and/or the type ...

Others here such as Bob, Ron, Fred, zNelbur and many others can help you out on the processes.

Here is some basic info...

Differential/GEAR, automtransmissions, etc. FAQs, Determine Ratio, Open or Closed Diff (Psi or Locker), etc. - http://broncozone.com/topic/24157-axle-type/

..Gear Ratio Guide for Larger Tires; Scroll Down or Click, Another RPM/Gear Ratio/Tire chart if site reverts to main page; MIESK5 NOTE, Rough Country removed this same chart from their site in FEB 2011 & company rep said it isn't there anymore.

http://web.archive.org/web/20140923193418/http://www.broncocity.com/old%20resources.htm#tire chart

"...Ford typically builds 4WD trucks with a slightly faster/numerically lower front gear ratio than the rear so that off-road steering is enhanced. So a truck built with 3.55 rear gears will have 3.54 front; 3.08 rear - 3.07 front; 4.11 rear - 4.10 front, etc..." 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. 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.

Gear Ratio Guide

http://web.archive.org/web/20140923193418/http://www.broncocity.com/old%20resources.htm#tire chart

****

Next change is for the speedometer:

Gear Color Codes, 80 and up

Source: by JBG via Seabronc (Rosie, Fred W) at http://www.supermotors.org/clubs/superford/vehicles/registry/showmedia.php?id=280161

.ca

Gear Change in a 90 (in Xfer Case Tail Housing)

Source: by Keith L (TTB Blows, Bling-Bling) at http://www.supermotors.net/clubs/superford/registry/139/13464

 

[Seabronc]

Bully, I'm new to my truck and need help accomplishing the task. Where can I find tips or maybe a video to complete reduction?

I'm not saying you should not do this by yourself, but it is not a job that can generally be accomplished properly by someone with no experience.  Getting the proper distance between teeth is critical.  If you don't do it properly you will be replacing the gears again not too far down the road.  It is well worth paying a shop that knows what they are doing.  It will cost you more up front, but it will save you a bunch in the long run.

>-

 

[Bully Bob]

Ditto Seabronc.., I wouldn't do a  differential myself, unless I had LOTS of time. 

There's lots of components to be removed just to get to the diff's.

At this point, it may serve you well to find a store with magazines & pick up a couple 4x4'n/off road'n copies.

There's lots of info/ideas as to what folks do & why.

Stop at your local driveline shop. They will be happy to give you the ins-n-outs.

You may be OK as is. Thay will know.

I would advise, don't make any more changes W/O doing extensive homework.

It's all fun..., enjoy the ride...!!

Bob

 

[Bully Bob]

If you enlarge this view, it's easier to read.

You're at 1982 RPM @  55 MPH.