Interesting Discovery.....

The weather here in Western New York is unusually mild (50 degrees) so I figured I'd take advantage of it and pull the axles out from under my Jeep. I got them out and tore them down. Much to my surprise my Dana 27 front axle has 8 ring gear bolts! It was always my understanding that the 25 had 8 and the 27 had 10. :? How big is a 25 ring gear? Mine measures just about 7 inches.
Anyway, just wanted to share that bit of info. Everythings all taken apart....now I just need 4.88's to put back in

 

the 25s I have measure 7 1/2" diam
one is 4.27
one is 4.88
I have a new set of Spicer 4:88s for D25 8 bolt FYI

 

7 1/4" I think.

 

This makes sense to me. Last year I pulled the open carrier from my dana 25 out of my '60 cj5 (yes, i'm 100% sure it is a dana 25-cast into housing). It has the 8 ring bolts as is the norm. I found a dana 27 powerlock that came out of an early scout. (all early scouts came through with 27 front ends, none had the 25, plus the powerlock had the smaller diameter 27 ring gear still bolted to it and the smaller carrier bearings). This 27 carrier had 8 ring bolts also, despite the norm for a 27, which is 10 bolts. Thus I was able to bolt my 25 ring gear to the 27 powerlock and use it in my 25 housing. There were other modifications that had to be made to make this work, such as replacing the small 27 carrier bearings with the larger 25 bearings. so do not think this was a perfect swap. but your discovery and mine proves that there were both 8 and 10 bolt dana 27 carriers built. Perhaps the early 27's used the 25 carrier but with an 8 bolt 27 ring gear and smaller bearings to fit in the 27 housing. Then later in production, dana increased the bolt count to 10 on the 27 ring gear, thus needed to change the bolt count on the carrier - just a guess here that may explain the 8 and 10 bolt 27 carriers that are out there.

FYI - a 27 has a 7 1/5" diameter ring gear, but the gear is thicker.
a 25 has a 7 3/4" diameter ring gear, but the gear is thinner.

And the ratio has nothing to do with the outside diameter of the ring gear. 27's and 25's were both offered in 4.27, 4.88, and 5.38 ratios, among others....

 

Mine has 27A cast right into the case. I thought my gears looked just slightly larger than 7", so I guess they are 7 1/5". I also have a set of 4.27's here that measure 7 1/5" that have 8 ring gear bolts.

Now the question is, will a Dana 25 CARRIER OR LOCKER work in an 8 bolt 27? I can't see why not if the smaller carrier bearings are put on it. :?

This info should probably be put on the FAQ somewhere

 

In my experience i put an 8 bolt 27 carrier in a 25. I had to use the larger 25 bearings and races. The outside edge of the races had to be machined down just slightly to get it to fit in the 25 housing.

I can't say what would happen in your proposal, but I would guess that if you go the opposite direction (an 8 bolt 25 carrier in a 27 housing) and use the smaller 27 bearings and races, you may have to put a shim on each side of the races as there MAY be side to side slop in the 27 housing with a 25 carrier. The size of the shims would be critical not only to elimate the slop, but to ensure that the ring gear properly engages the pinion gear.

 

That's what I thought, but it definately is doable... I actually stumbled across a Power lock for a 25 yesterday, we'll have to see how this all works