Hi everybody. I've got something I wanted to pass by you and get your opinion on before I do the actual work. First, a little background info.

I got this latest Cherokee, a 91 with a 4.0 and a AX-15, a couple months back and I've been slowly repairing all the little problems to get it where I feel comfortable to drive it. One of my quests is to get it to be a little better in the fuel economy area but still maintain it's usefulness off road. It will be a daily driver and go off road on weekends. I have read a lot of forum posts and I understand it is an uphill battle to achieve any significant mileage with a body style of a brick pushing it's way thru the air, but I'll be happy to get it close to 22 mpg or better. One of the roadblocks I've found is getting the engine into it's sweet spot to where it is the most efficient is the diff gearing, which mine is original at 3.07's. I've come across someone who is selling complete diffs, a D30 and D35 from a 88 XJ which have 3.73 gearing in both and in good shape. From all my searching this is the gear ratio I need, not only for playing off road, but getting my vehicle into that sweet spot.

I have one question to ask:
1. How difficult is it to swap the internals instead of swapping complete diffs?

And my reason for asking that is I've noticed that not all the parts interchange between both years like wheel bearings, brake calipers, track bars, etc.

My version of playing off road is driving down gravel roads and dirt trails, so it won't see mud or rocks unless I get adventurous but I know my weak link will be the rear diff. Later on, when funds permit, I'll look into getting a 8.25 to replace that D35 so for now I need to baby it.

Any thoughts would be appreciated. Thanks.

 

What about getting a 29 spline D30/8.25 with 3.55s they're a dime a dozen and the 8.25 is better than a d35. I know they're not 3.73s but they're better than 3.07s

 

Google/read up on "differential/gear set-up".

Clearances/tolerances/tooth patterns/back lash, etc. are all involved in properly "setting up" a diff after a carrier/gear change. Not saying it's hard to do, but what's easy for one may not be easy for the next. Bottom line is, any job is easier to do when u fully understand what it takes to do the job and have the tools to do it.

 

A couple reasons why I'm going this way is:

All the calculators I've used on other websites suggest that the 3.73 will work good for my needs and,

I'm getting both diffs for a hell of a deal, like $200! As long as I take care of them for now I can look for a 8.25 soon down the road, hopefully before winter.

 

The gears are not a job for the first timer, so plan to pay a shop $500-1000 for the gear swap.

Complete axle swap is a 4-8 hour DWD job that only requires basic tools + a tape measure to complete. tape measure is to set alignment.

 

The rear D35 from -88 is a non C-clip with 10x1 3/4" brakes and if it is complete axle with brake drums and all , I would use it as it is and for the front D30 you can replace the outer knuckles with the one on your old one if you want to have the old brakes and bearings.
Just swap the complete axles in and be happy with it.

 

Thanks Cherokee89, that was my biggest concern about whether I could use my original 91 knuckles. The brakes as they stand are good, so going to a larger rear brake will work for future plans.

As it looks right now, both front and rear diff will get swapped as complete units.

Thanks for the advice everybody!