You definately need the same gear ratio in the front and back. If they are different one axle will spin faster than the other causing possible axle breakage, u-joint or driveline, and or transfer case failure. It all depends on which of these parts is the weakest in your rig as to which one will go first. In short it's a bad idea!

 

The '78 dana 30 should fit just fine. That's what I have in mine. It has the wider discs and stronger caliper brackets as an added bonus. You may need to change the pinion yoke since the Jeepster's is probably smaller. You'll probably need to change the tie-rods, too, since the CJ set-up is a bit different. I just used all the parts from the CJ when I did mine.

Don't forget to pop out the residual pressure valve for the front brake circuit on the master cylinder, too. A proportioning valve may also be required, but probably not. Yes, gear ratios must match.

 

If the Dana 30 from the CJ has 3:54 gears, I don't think that you can go up to 3:73's due to the pumpkin size. It is two different sizes for 3:54 and below and 3:73 and above.
I could be wrong but that's my story and I'm stickin to it!

 

Don't you mean carrier size? Just a bigger carrier in the same pumpkin to run 3.73s. Or are there really two different D30's? I don't know one way or another, but I'm curious.

 

3.73 is the cutoff for carrier size. D-30 housings are all the same.

 

You can keep the larger yoke on the D30 if you get a larger yoke for the transfer case. I was able to get mine from a driveline shop that made my driveshafts for me.

 

Toad,
I believe you but I have been told more than once that you can't put 3:73 and larger gears in a pumpkin that had 3:54's or smaller. Maybe I missed something.

 

Somebodies been fibbin' to you man!

The carrier is what determines what gear combo you can use in the pumpkin. Like Toad said, all the housings are the same.

 

I know that the carrier break for the Dana 44 is 3.90. Below 3.90 numerically will require one size carrier and 3.90 and above numerically will require another size carrier. If you don't have the right carrier for the gears you want to use, just buy one and you're set. You're only restricted by what gears are available on the market or after market for your particular model axle. I would assume that the Dana 30 has the same carrier breaks as the 44.

 

Dana 44 carrier break is 3.92 to 5.38 and 3.73 to 2. whatever. Dana 30 is 5.38 to 3.73 and 3.54 to 2 whatever.
Dana 60 is 4.56 to 7.17 and 4.10 to 3.whatever. The difference is in the offset of the flange that the ring gear bolts to. The lower the gear ratio (numerically higher, like 5.38's) the smaller the pinion gear diameter. This can be compensated to a degree with carrier bearing shims. When you reach a point that you can't compensate (like going from 3.54 to say, 5.38's) then you have to get a carrier with with LESS offset of the ring gear flange, meaning the flange is closer to the centerline of the carrier. This moves the ring gear closer to the pinion gear to compensate for pinion diameter differences. In some cases you can get a gear set with a thicker ring gear to compensate.
Hey Tim, how's things going? There is a swap meet in Eugene this weekend put on by the Junction City Jeeper's. I don't know exactly where it is but I know it is on Sunday. If you have time you cruise on down and see what they have. I'll be there, but I'm riding with someone else. You might give Paul a call at 503-557-8911. He know's where it's at. Nickmil.

 

There is a great article in off road magazine Sept. 2000 about differentials. The article is called "whats the diff". I refer to it every so often when I need info on differentials. It goes into pretty good detail about the different gearing and ways to identify different types of diffs. It also talks about different types of traction devices. If you can geat your hands on it, it's worth reading.

Jerry
1970 Halfcab