Transfer Case

Mmm, well... the M20 has a terrible reputation, but it's probably not as bad as all that. They have 2-piece axles (thus the cover on the hub for the nutted end) and they tend to loosen and spin the axle in the hub. They also have problems with thin axle tubes, either breaking the pumpkin at where the tube inserts or bending the tube.

No personal experience with them, but I recall one of the experts here (Jim, jpflat2a) saying that they will last if you keep the axle nuts tight.

What kind of engine do you have? Have you driven this Jeep in 4WD yet? I ask because either the front or rear axle ratio has to have been changed in order to make the two ratios the same. There's no overlap in ratios between the M20 and D27. One or the other may have been changed, but you should check it out if you don't know.

 

Definitely an AMC 20 as Timgr stated. They are light duty at best. They have a large ring and pinion, plenty strong in that respect but have thin wall tubes and carrier casting (center section or pumpkin). They also suffer from 2 piece axles that are actually weaker than the normal CJ dana 44 tapered axle as they have self cutting splines and a very small key. If you keep the axle nuts tight and keep tire size to around 32" or below you probably will be ok. If you have a heavy throttle foot and go above that tire size it probably won't last. You can get 1 piece axle conversions for these which takes care of the axle issue but you still have the thin tube and casting issue to deal with. Many people truss them and go through all kinds of gyrations to make them hold up, but then they still suffer from small axle bearings.

Again, if light trail running and normal street driving is your plan it will probably be fine if you keep the axle nuts torqued. If difficult trails or hard driving is your plan and you want to keep the centered model 20 transfer case I'd look for a '72-'75 CJ rear Dana 44 to put in. Much stronger.

Definitely check the gear ratios to make sure they match.

 

"self cutting splines"?

 

Yup. The axle shaft has very small external splines and one very small key. As you tighten the axle nut the flange or hub is pulled on to the shaft and the splines cut deeper into the inside of the hub to help keep the hub from spinning on the shaft and to help hold the hub in place. Very poor design. As you can imagine they tend to get loose when the hub has been removed several times. It's a leftover axle from '60's AMC cars. My buddy's '68 Ambassador had the same designed axle.

 

Kind of worried now. PO installed a small block chevy 283. This Jeep sat in a field since 1995. With the snow gone I finally got it inside last weekend and started the engine. Took a 3 mile drive in 2 wheel but nothing in 4 wheel yet. I have no working brakes so that's the next project. At this time no plans for frame off resto. Just want to enjoy messing around and driving it. First two items will be brakes, and electric. Need to find the ground in the electrical that is draining the battery.

I'll determine if the front and rear gear ratios are matching and then keep a look out for a DANA 44 rear axle with a matching ratio.

I think I have fairly tall gearing based on my short drive. The engine didn't wind up like my 69 cuda did with 4:88 gears in my high school days.

 

Sitting 15 years, and still runs

Gotta love small block Chevys

 

I would go with a centered 72-75 Dana 44 rear axle over that AMC 20 for sure.

 

Another advantage to the 72-75 Dana 44... there's a good possibility that your front axle ratio is 3.73:1 - this was common for the CJ in that era. The '72-75 CJs also used this ratio, so (depending) it may be possible to find an axle with that ratio that you can bolt in.

Another possibility is to get both the front and rear axle from a '72-75 CJ - that too will bolt in with minimal effort.

 

Just an amazing amount of help on this forum. Thanks. I add stories or updates from time to time.

 

BTW: Those caps for the t-case shift rods can be bought online at quadratec.com and 4wd.com. They are cheap. The shipping costs more then the caps. I had one spit on my Dana 20 and it was easy to get a replacement.

The AMC 20 rear axle is not that bad unless you intend on hard wheeling. If so you will bend the tubes even if the axle is trussed. I have seen several Jeeps this has happened too. Better to find a NT Dana 44 from a 72-75 CJ-5. It has 30 spline flanged axles and it should pretty much be a bolt in.

 

Just an update. Finished the installing 11" drums, every brake component replaced with new except for the little shafts (what are called) the wheel cylinders push out to force the brakes against the drum.

After the brakes I thought I would install a new gasket on the front diff cover due to a leak. Pulled the front cover and oil dropped out (which is good) and then some chucks dropped out (which is not good). My D27 had 4 teeth missing from the ring gear and the spider gears were toast. Gear ratio on the D27 is 3.73 (remember this number.

Decided to check the AMC 20 rear axle for damage. All looked good but the ratio was 3.54. I few PM's to some of the forum members and they all concluded I was hosed.

I simple brake job has now turned into a project. I have found a centered D44 and its in the garage waiting for pinion seal replacement, and found another D27 and its in transit. Both will have 3.73 ratio.

I'll remove the brakes from the old axle and put them on the new ones and see what happens next.