Different diff ratios front & rear

[cj]

I see people talking about running different diff ratios front and rear and that if it is only a slight difference that you can get away with it. What is the acceptable difference? 1%, 2% etc ?

[christover1]

I see people talking about running different diff ratios front and rear and that if it is only a slight difference that you can get away with it. What is the acceptable difference? 1%, 2% etc ?

I don't know numbers, sorry, but some early 4wd's (part times) had slightly higher ratios on the front, to allow better control of steering and less chance of rear overtaking front down steep hills. So if you do go for different ratios, then I suggest the higher to the front. Sorry can't back this with any facts or figures. It was long ago
christover

[sierrajim]

Hilux diffs are available with 4.88's CJ. Come on, you know you want to

[cj]

Hilux diffs are available with 4.88's CJ. Come on, you know you want to

Not yet James. I'm still trying to see what I can get out of the IFS.

I've got the 5.83 for the front and I need a way to fix my rear. So far my options are a Scout D44, a CJ Widetrack D44 if I could find one and a Bronco Ford 9" all of which I can get matching gears and they all have the right stud pattern or another option I thought of is a Hilux rear wth a 5.7(1 or 9? seen both figures mentioned). I figured if it was 5.79 it was close enough but if it was 5.71 it's a 2% difference and wasn't sure if it would be OK.

[cj]

To answer my own post I found the following info on Randy's Ring & Pinion 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.

1 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.

So a 5.83 in the front and a 5.71 in the rear will give a 2.1% difference and as it's for offroad use only it could be acceptable.

[rockluxme]

You all have no idea

[AussieCJ7]

Hilux diffs are available with 4.88's CJ. Come on, you know you want to

Not yet James. I'm still trying to see what I can get out of the IFS.

I've got the 5.83 for the front and I need a way to fix my rear. So far my options are a Scout D44, a CJ Widetrack D44 if I could find one and a Bronco Ford 9" all of which I can get matching gears and they all have the right stud pattern or another option I thought of is a Hilux rear wth a 5.7(1 or 9? seen both figures mentioned). I figured if it was 5.79 it was close enough but if it was 5.71 it's a 2% difference and wasn't sure if it would be OK.

Given the CJ wide track D44 rear only came out in part of one year and was about the time AMC Australia had ceased operations your chances of finding one of these in Australia is pretty rare If you find an 86 CJ7 with d44 rear before you grab parts out of it please let us know cause if worth saving this is a collectable CJ7.

[Beastmavster]

I've heard up to 3% is ok but no personal experience in it.

Remember even with identical diff ratios, the different wear rates on tyres can lead to an effective difference of that much.

Perhaps even greater, with a new set of tyres on just one end.