Just How Strong Is A 58 Jeep CJ6 Dana 44 Rear Axle Housing?

Depends where the fulcrum is.
If the fulcrum is out close to the applied force, only a fraction of the force is transferred to the far end of the bar. If the fulcrum is centered, 100% is transferred.

 

Ever wonder why a postal jeep's springs are outboard? I'll bet it was to enable a higher payload.

 

Where did you come up with the spring perches being closer to the ends compared to a jeep? I measured my rear axle, there is 6-1/2" between the spring and backplate.

 

No it was to make the springs flatter, that way the ride was more comfortable, remember the DJ was designed to drive on the road all the time, the CJ not so much.

 

From experience. I'll be the first to admit these are just my theories, but the physics behind it makes sense.

I'll admit I pulled the 12" number out of my butt without checking (hence the question mark), but the higher the gvwr on the truck, I've noticed a direct correlation to how close the spring is to the wheel bearing. The three I have on hand:
CJ5 - 7 1/2" to spring centerline
Dakota - 6 1/2" to spring centerline
F350 - 4 1/2" to spring centerline

Utility trailers and older minivans get away with having a piece of stamped sheet metal for a rear axle, and their springs are so far outboard they're almost rubbing the tires.

Again, just my theories and observed patterns. I'm no engineer.

 

So your thinking you can bend a 3" diameter tube with a 1/4" wall thickness easy because it has a 7-1/2" length to it and a little weight. Let me enlighten you about my jeep.
When I bought it back in 1992 it had a bent front axle on it, the original dana 27, I replaced the axle right after buying it with another dana 27, kept that one until
2005. I was at a local 4x4 shop about 25 miles away one day in 1997 when a guy that was one of the owners came in and wanted to know who's red jeep was in the parking lot. This guy was one of the owners, I said me. He then asked me where I bought it and if the front axle was still in it. I told him where I bought it and no I replaced the bent front axle. He then showed me a picture of my jeep and the original owner and how the front axle got bent. The guy jumped it at around 45 miles an hour over a creek on a bet, the picture showed my jeep 5' in the air and it landed on the right front tire, bending the axle and frame. Thats a 2900lb jeep 5' off the ground landing on one tire at 45mph on a rocky creek bank. My front axle tube was bent about 3/4" and the frame the same, I drove the jeep for 12 years with a bent frame and the guy before me had driven it for 10 years or more with a bent frame and axle tube. I don't think having an extra 1300lbs added between 2 axles and towing a trailer with a tongue weight of maybe 350lbs is really gonna effect this axle unless he is racing over really rough terrain. Think about that, thats an extra 900lbs or so on that rear axle (max). Guys load there pickups on a regular basis to far more than this, like another 25%-30% more. I have had my Dakota loaded with 2200lbs in the bed, thats a truck rated for 1400-1500lbs total and towed a trailer with hay in it at the same time.

The springs take most of the stress anyway unless they are bottomed out. What about those puny 3/8" bolts that hold the springs on.
I really think you guys are over thinking this way to much.

 

My point is, the spring is the fulcrum and the axle is the lever. If the distance between the spring and the wheel bearing is 7 1/2", then 7 1/2" from the perch on the inside will have the same force pushing down as the outside has pushing up. The wider the space between the spring perches, the longer the distance that force is spread across and minimized. The shorter the distance between the perch and wheel bearing, the less the leveraging effect is on the center of the axle.

I'm just saying these axles are unique because of (a) the wide distance between the perch and bearing, (b) narrow distance between the perches which increases the leverage on the center of the axle, and (c) the fact that the dimensional center of the axle falls almost directly on the tubing/carrier connection, where on a D30 I know from multiple experiences is the first place to fail from abuse.

I'd be less concerned with bending from momentary impact than I would be with metal fatigue over time.

 

I don't believe the early axle tubes are .250 but I will go measure. These tubes usually bend just from having the u-bolts overtightened.

 

I have a 1\4 inch thick, 5 inch tall frame under the CJ6. There are disc brakes all around, I tow some small trailers camping (about 2000#). I have posted pics here towing my two axle 2400# equipment trailer and a 5500# skidsteer. Yes I have trailer brakes. Not a lot of tongue weight, 750# or so. This is towed infrequently. I do tow a 1 axle trailer fairly regularly with a Ford 8n. Trailer is 1000# and load is 3500#. About 500# tongue weight. I treat it like a half ton truck. I just like to plan for the worst scenario....ie, loaded 2 axle trailer, on brakes, trailer brakes engaged which adds to tongue weight, hitting one of Pennsylvania's notoriously uneven bridge approaches. The tubes on the old 44 are small (2 1\2") and the center section looks thinner than the front Scout 2 Dana 44 I narrowed. I was thinking about the leverage on that long side tube as well as the fatigue from the rear being from 1958. The plug welds seep a bit which concerns me as well. I have a scout 44 and a 60 at hand I could use to make what I need, or get a 3 inch tube 44. Decisions decisions...

 

NICE..........................

 

At the very least I hope you have brakes on the trailer. That load would be like ringing the dinner bell for a local LEO to pull you over. Here brakes are required for any load over 40% of the towing vehicles weight or 2000 pounds. Remember that just because you can pull it doesn't mean you can stop it. In stock form that CJ6 just barely had brakes that could stop it without a load. Another thought to ponder is that when you are that overloaded,(I believe the original towing rating was 1200 pounds for the Jeep) it gives your insurance company an easy out to not cover you if you do have an accident.

 

There are trailer brakes on everything now. I've been through DOT multiple times and maybe because all the new Jeeps are so big and towing larger campers and such, I usually get waved through or told how nice the Jeep is. Where I am in the process of moving, there is no local law enforcement. Just state police. I am putting together a C600 Ford for my larger loads now. 26,000 gvwr. The Jeep won't be pulling the tandem trailer much anymore.

 

A friend of mine has a clean, not pitted centered 44. The tubes are 1/4 inch larger diameter and the casting appears thicker at the center section plus not leaking at the plug welds. I have a Dana 20 case my Son found in the shed that's like new. I am going to truss the 44 and give my son the rebuilt Dana 18 for his Jeep, since his is shot. I have waffled back and forth on this but I hate to lose the clearance and he needs a good xcase so I guess this is a marginal improvement, but an improvement nonetheless. I appreciate all the wise input on here. That's why I like this forum.

 

That plan sounds just like the centered 44 I have in my 3b. From a '75 CJ5, trussed over top just like the pic in post #10, disc brakes... The only flaw the 20 has is the gearing. Besides that, I absolutely love D20s. Take the pill out and you can control the axles independently. Left shifter is rear axle, right shifter is front axle.

At risk of being called a liar, I won't say how many times, and how high I've had this thing off the ground, landing awkwardly. It is a seriously strong setup.

Be extra cautious when welding. A truss like this can bend the axle like a taco if you aren't careful.