I need help with regearing ratios??

Run4Jesus

New Member
Joined
Dec 6, 2013
Location
Robbinsville, NC
I am new to lifted vehicles and just bought a 1997 Jeep Wrangler with a 10 inch lift kit and 39.5 inch pit bull rocker tires. Pictured here...
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When I bought the Jeep it didn't have the drive shaft in it and I had to take it to a shop to get it regeared. It was a family member that was a mechanic and his response was that I needed to give him the regearing ratios. I don't have a clue how to calculate them and after multiple phone calls to Jeep dealerships I was told to create a forum here. I am trying to get the Four Wheel Drive completely operational. Is there any information or help I can get to find out what the ratios are? I have the drive shaft and just need the ratios. Thanks.
 
What axles do you have under there? If they're the stock ones I wouldn't put money into trying to get them to work with 39s, they won't last. To determine gear ratio jack up the jeep and rotate a tire while counting driveshaft revolutions.

Edit: oops looks like I misread your post. The instructions above are how to determine what gear ratio is installed in the jeep currently. The link posted below will show you suggested gear ratios for tire size. Although you still need to know what axles you have because that will limit your available gear ratios. If you don't know, post up closer pics of the axles and we can tell you
 
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For the four wheel drive aspect of the Jeep to work properly, both the front and rear differentials must be geared the same. If the front drive shaft was not installed, it is possible that the previous owner had a different gear ratio in the front than in the rear. He may have regeared the rear or put a totally different axle in the rear with different differential gearing to compensate for the big tires.

cj777 posted on how to go about finding your current differential ratios.

Assuming you are asking about regearing the differentials to compensate for having larger than stock tires, conventional gear by tire size charts will recommend 5.29 differential gears for 40" tires. Depending on what you intend to do with the vehicle will influence your final decision.

http://www.jeep4x4center.com/jeep-tires/tire-gear-ratio-chart.htm
 
I'm pretty sure that the axles aren't stock, here is a picture of the suspension
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I am unsure of the back ratio, it is already done... Do I need to find out the ratio that the back is in by using the method that cj777 mentioned and match the front to the back when I put the drive shaft in and gear the front? or should I just use the chart and gear the front to whatever I want to use four wheel drive most for as stated in the chart that JC provided in the link http://www.jeep4x4center.com/jeep-tires/tire-gear-ratio-chart.htm? Thanks for all the info as well...
 
Your front and rear axles need to match. If the rear axle was already geared, then yes, do the method I posted on the rear axle and gear the front to match. Can tell what axles you have from the suspension pics, but if you can get pics looking straight at the axles I can
 
I may be able to post pictures within the next thirty minutes... So if the front needs to match the back then all I need to do when I install the drive shaft is make sure that the front rotates the same amount? Correct? Thanks again!!!!
 
I would recommend pulling the covers off and reading what is stamped on the ring gear itself. The tire rotating deal can be sketchy if the differentials are open

Look for a pair of numbers stamped on the side of the ring gear such as 41-11 divide the 41 by 11. That would be a 3.73 gear ratio.
Or as the pic below shows...(40 div by 7) is a 5.71 ratio (sometimes the ratio is even stamped on the ring gear...like this one!

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I am having a difficult time getting a good picture that shows the front axle facing rearward. I live in a the mountains of western NC and the jeep primarily operates in first through third gear. Could you recomend the gear ratio you would use for this type of driving.(4.88 to 5.71) I will crack open the diffs to confirm ratio before we install front drive shaft as suggested by ol' jeeps Here is the front...
mail


here is the back
mail
 
cj777 said:
What axles do you have under there? If they're the stock ones I wouldn't put money into trying to get them to work with 39s, they won't last. To determine gear ratio jack up the jeep and rotate a tire while counting driveshaft revolutions.

Edit: oops looks like I misread your post. The instructions above are how to determine what gear ratio is installed in the jeep currently. The link posted below will show you suggested gear ratios for tire size. Although you still need to know what axles you have because that will limit your available gear ratios. If you don't know, post up closer pics of the axles and we can tell you
Click to expand...


I am having a difficult time getting a good picture that shows the front axle facing rearward. I live in a the mountains of western NC and the jeep primarily operates in first through third gear. Could you recomend the gear ratio you would use for this type of driving.(4.88 to 5.71) I will crack open the diffs to confirm ratio before we install front drive shaft as suggested by ol' jeeps Here is the front...
mail


here is the back
mail
 
Looks like you're trying to link a picture directly to your gmail, which won't work. Easiest thing to do is to upload them to a photo sharing site like Photobucket and use the IMG tag to link to them. If you can't get that working, you're welcome to email them to me and I'll post them for you Welcome to the forum!
 
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Like Scott said, pop off your covers and let us know what numbers you see stamped on the ring gears.
From a purely performance aspect, 5.13s may be your best bet assuming that is a 44 front (can't clearly tell from the pic). If it is a Dana 30, 4.88 is the lowest you can go. Lemme know if we can help you out anymore!
 
Yep, hard to tell without seeing the other side. You can just compare your diff cover to this chart

awww.getahelmet.com_jeeps_tech_axleid_axle_id_corrected.jpg
 
It's a ratio.
stock tire diameter/old gear ratio=new tire diameter/new gear ratio
or stock tire diameter/new tire diameter=old gear ratio/new gear ratio
30/3.73=39.5/4.91->4.88
or 30/39.5= 3.73/4.91->4.88
or use the chart posted above.
Those axles look stock. I think it would be a waste of money to regear them. Plenty of experiences out there on the net of people breaking factory axles with smaller tires.
 
Those definitely look like stock axles. To answer your question I would go 4.88. Before I would do that though, I would look at a smaller tire/ wheel combo. Those axles will not hold up off road if that is the intent. If not, the smaller combo would make it more road worthy and in my opinion make it look a lot better. Either way I would start by pulling the covers to see what gearing you actually have. A wrong guess would be ugly immediately.
 
Looks like the rear has drum brakes and stock mounts with a round bottom on the diff so id say its a d35.
I would not put a dime into regearing those axles you will regret it if you do
at a minimum with those tires on a mild street/sunday trail ride jeep I would recommend a dana 60 rear and a 8 lug dana 44 in the front with 5.13-5.38 gearing if you live in the mountains.
If you ever intend on any serious offroad use then a 14 bolt rear and dana 60 in front.
Also their are some safety issues that could be addressed with the axle upgrades.

Buckeye Performance Inc.
828-779-2242
 
I wouldn't spend 1 cent on regearing those axles.
 
Novacayne75 is spot on with his recommendation, if you want to keep running those tires. If you want to run it on the road I would sell the tires, step down to a 35" tire. Replace the rear with a 8.8, go with a Dana 44, in the front. Gear both axles 4.88:1, address the suspension safety issues, and end up with a nice road Jeep.
 
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