3.07 vs. 3.08 ratio - Off-Road Forums & Discussion Groups
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post #1 of (permalink) Old 12-02-2002, 06:30 PM
dakota617
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3.07 vs. 3.08 ratio

Just before school started this year, the rear end on my sons jeep bound up. He took it apart and discovered that the short shaft that the pinion gear is on had snapped and when it went it took three teeth on both the ring and pinion with it. It had been rebuilt about one year before by a local shop. We only had four days to get it fixed before school started, so I looked online and found a used set of axles. We were told they were stock and a match for his jeep(1989 Wrangler) All went well and less than 24 hours later we had the old rear axle out and the new one in. It helped that we had done a 3" lift a few months before as all the hardware and bushings were new and came apart OK. Last week we had some snow and he used high 4wd for the first time and he didnt think things sounded quite right. We took the rear cover off and counted teeth and discovered that we have 40/13 vs. the stock 43/14. (3.0769 vs. 3.0714) I get the feeling that we need to change the ring and pinion in the rear ro match the front.(43/13). It seems like a minor difference but he does not want to cause any other problems. Any thoughts or advice will be greatly appreciated.
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post #2 of (permalink) Old 12-02-2002, 06:55 PM
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Re: 3.07 vs. 3.08 ratio

As long as you're on a slippery surface, I don't see a problem. According to my brain box, that difference is equivalant to about 0.028" difference in tire radius.
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post #3 of (permalink) Old 12-02-2002, 07:00 PM
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Re: 3.07 vs. 3.08 ratio

You're all set, no need to change anything, they're the same ratio. It's common for axles to be similar, but not exact. Anything within a few percent is good enough, as you may have that just in the difference in tire wear from front to back. It's common to see 4.09 in one axle and 4.11 in the other, not a problem at all.
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post #4 of (permalink) Old 12-02-2002, 07:46 PM
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Re: 3.07 vs. 3.08 ratio

Like everyone else said, that little bit of difference will not make a difference. What will make a difference is tires. Make sure they are all aired up to the same pressure or run the back ones about 5 pds less. The taller tire in the front, because of more air, will pull the back tires. What didnt sound right? Was there bearing noises or just that he hasnt heard it in 4wd before. I would find a dirt road and try it out and see what the noise is.
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post #5 of (permalink) Old 12-02-2002, 07:48 PM
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Re: 3.07 vs. 3.08 ratio

Thanks for the reply. Could the different sound in 4wd be caused by the 3" lift changing the angle to the front diff.? The new rear springs had a built in wedge to change the angle of the rear driveshaft but the front did not. Can we use shims on the front axle or is that not the way to go?
post #6 of (permalink) Old 12-02-2002, 09:53 PM
 
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Re: 3.07 vs. 3.08 ratio

I used to play with a 1977 chevy 3/4 Ton Camper Special. It had 4.10 front and 4.11 rear. I was told the reason was that in 4wd having the front trying to outrun the back by just a little would help in turning. Every 1/2 ton (and my Jeep) that I've owned has had the same ratio front and rear, and so did my Hi-Boy. I'd probably just run as is if it were mine.

Also, on the noise, you might have a look at both drivelines to make sure they are in phase. Had an AWFUL vibration this summer after going completely through both rearends (had an even worse one before I replaced some U-joints and bearings). Got to looking at it, and the rear driveline was 90 degrees out of phase. I'd bought it that way, and never thought to look. If it is only happening in 4wd, you might see that the front driveline went back in in phase. Just a thought. Let us know what you find!
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post #7 of (permalink) Old 12-02-2002, 10:01 PM
 
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Re: 3.07 vs. 3.08 ratio

</font><blockquote><font class="small">In reply to:</font><hr />
The new rear springs had a built in wedge to change the angle of the rear driveshaft but the front did not. Can we use shims on the front axle or is that not the way to go?

[/ QUOTE ]

No, if you use shims in the front you will change the castor....not a good thing!
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post #8 of (permalink) Old 12-02-2002, 10:14 PM
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Re: 3.07 vs. 3.08 ratio

The reason the front and rear are different on many 4x4's isn't because one end is designed to "outrun" the other. The reason is very simple: they are usually different model axles. With different models, such as a dana 30 front and 35 rear, the ring gears are different diameters. That means that the teeth count probably won't be the same which is where the slightly different ratio NUMBER comes from. From a design view, 4.09, 4.10, and 4.11 for example, are the SAME. They are that close. Again, the difference is just due to the different diameter ring gears and pinion gears. That's all, nothing else.
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post #9 of (permalink) Old 12-03-2002, 06:38 AM
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Re: 3.07 vs. 3.08 ratio

What axle has the 43/13 in it? Because that's a 3.31 ratio. The other gear counts you mention are 3.07, and those two ratios do not get along with each other.
post #10 of (permalink) Old 12-03-2002, 07:41 AM
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Re: 3.07 vs. 3.08 ratio

You have the numbers mixed up. He has a 43/14. I did the same thing when i first read the post.
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