Help me identifying the gears in my diffs

Guys and gals,

I was under my truck today, and decided to clean up the diffs in order to find any info I could, trying to verify what gears are in there. Well, here is what I found:

1. Front Axle

On the rear of the housing, towards the center of the truck, there are the followings:

30-7AF
137

On the front of the diff, on a metal label attached by two of the diff cover bolts:

8953000395
3 73 41-11

2. Rear Axle

No label except the number "4132" at one of the ears of the diff (those parts in which the tubes are inserted) and on the right tube, near the shock absorber mount, but facing the rear of the truck, the following "5-21" written upside down. Right under the U-bolts, there are some more letters, but I think these are a date only, can't read them all.

For your information, it is a 1984 Cherokee Chief, 2.5 lt, 5-speed manual.

If you can define what gears it has, I would appreciate the input.

Rgds

Looks like from the metal label on the front you have 3.73 gears.
The 3 73 stands for 3.73 and the 41 11 is the division number, you can divide 41 by 11 and thats the gear ratio.

"41 11" refers to the amount of teeth on the ring gear and the amount of teeth on the pinion gear. 41 teeth on the ring gear divided by 11 teeth on the pinion gear equals 3.73. 3.73 revolutions of the pinion will result in one complete revolution of the ring.

Thank you gentlemen, time to do some maths, to calculate the proper gearing for my 32" tires.

Thank you and rgds

IMHO, just go with 4.56, if you want a better crawl ratio go 4.88.

Right now you are 15% undergeared for your 31's, to get equal or lower to stock gearing you need to be at 4.28 with 31's, and 4.42 with 32's. I rounded actual tire size but it's definitely close enough.


31" tire size / 27" tire size = 1.148, 1.148 * 3.73 = 4.28

31x10.50R15 tires run through 3.73 gears turn exactly the same RPM at 60 MPH as stock tires and stock 3.54 gears. This means John is, indeed, undergeared for a 4-cyl even with 31" tires, and very under-geared for 32" tires.

The conventional rule of thumb is 4.10 gears with 31" tires, 4.56 gears with 32" tires -- but that's for a 4.0L 6-cylinder engine. With a 4-cyl and 32" tires, I think 4.88 gears would be required to get back close to the original overall final drive ratio. However, since I don't like to see that little 4-cylinder spinning around at such high RPMs, I would probably go with 4.56s.

That's exactly what I had in mind, 4.56:1. Unfortunatelly, I'll still have to live for some time, with the 3.73 I have at the moment. I do not think it is worth it to open the diffs to change gears and then to re-open them again for lockers. And since I cannot afford lockers at this moment, I am staying stock.

UNLESS: and there is a big issue here. I know that the 2.0 lt Mussos (I have another truck, a Daewoo Musso, see signature) have 4.56 gears in their Dana 30 front and Dana 44 rear. Now, if I could adapt the rear D44 to fit the Cherokee, and if I could remove the carrier from the front D30 (it is an independently sprung D30 so I cannot use it as a replacement), I would have both a stronger rear axle and the right gears together.

I need to go and check that burned Musso that someone left in a friend's property!

Many thanks to all who replied, I appreciate it.

Rgds

The D44 may work (get dimensions), but your D30 is High Pinion, which means a reverse cut R&P. may not be the same.

I have to look Chuck, if memory serves me right, it might be a High Pinion one as well.

I think I have to spend a weekend at that Musso, taking things apart.

Again, thanks for all the contributions, appreciated.

Rgds