If I change the rear differential gear ratio, do I also need to change the front transfer case or differential for them to match?

Asked by Aug 21, 2007 at 01:11 PM about the 1999 Jeep Wrangler Sport

Question type: Car Customization

My son's Jeep has a low rear-end gearing. I haven't investigated it thoroughly, but it seems to be set more for rock crawling than anything. I'd like to give him some street performance and still have a little "off roading" capabilities, for sand and mud.

If I change the ratio of rear end, do I have to change something in the front end to match the drive ratios between the 2 axles?

Corey

9 Answers

4,875

I don't see why you shouldn't have to. The fronts and rears kind of like to go the same speed...

2 out of 2 people think this is helpful.

That was my thought, but being a 4wd newbie, thought I'd ask for some experienced advice.

25

YES you have to change them, or else you will screw up your t-case bad. my friend got a whole new axle off some one instead of re gearing it, it was cheaper. he has to get gears to match his ford 8.8 in rear

1 out of 1 people think this is helpful.
7,805

Terrence would be correct on that one. On most 4wd vehicles they advise replace 4 tires at a time for the same reason...(Different tread wear will result in a minute change in final drive ratio)

35

Both diffs have to match, I know of a chart, i think its in the Jeep owners Bible, tells best gear ratio according to tire size. you are best off leaving it stock for "STREET Performance" ( =P )

1 out of 1 people think this is helpful.
35

OMGawd! this is old! aug 2007 =P

160

if you do not change them both and make them the same ratio the jeep prob wont even move or the axle or t-cace will destroy itself

1 out of 1 people think this is helpful.
10

By reading these posts it seems that it might be eaiser to swap the transmission out (4spd to 5spd) to gain the highway milage and still keep a bit of the "off road" - Am I right in my thinking there??

1 out of 1 people think this is helpful.
10

Can I put a complete rear end housing from a 1990 jeep cherokee under a 1994 jeep wrangler yj

1 out of 1 people think this is helpful.

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