Why did the Atlas blow?

[Jared]

My bro-in-law and I just got back from a weekend trip to Moab. We both flat towed our rigs to and fro. He has a 1990 Jeep MJ Comanche with an Atlas transfer case.

As we were loading up to head home, he noticed a worn u-joint on his rear drive shaft so he decided to pull the shaft and toss it in the bed. He planned to replace the joint once we got home. However, about 5 miles out of town a fire erupted under the Comanche! As he was braking hard and pulling over, the front drive shaft was tossed out the side. We quickly doused the flames with some water and found that the front output shaft had rapidly heated and broken off flush with the front of the case. The front half of the output shaft was still bolted into the thrown drive shaft.

The oil level was checked prior to the trip down and there are no leaks evident. Do these things have an oil pump run by the rear shaft or something?? We're both at a loss here.

Secondly... what do you think it will take to fix the case?

Thanks,
Jared

 

[Chevycrew]

Was the atlas in the towed rig? If so, why was the front shaft spinning?



Sounds like a bearing went out, super heated the shaft and it twisted off.

 

[Jared]

Was the atlas in the towed rig? If so, why was the front shaft spinning?

Yes it was. It was spinning because the later model Jeeps don't have front locking hubs.

The Atlas is a fairly low mile unit, and the lube level should have been good. It doesn't seem like the bearing should have had any reason to just randomly go out.

 

[cruiseroutfit]

I would get it over to someone that is familiar with the Atlas II and have them diagnose at least the damaged parts. Ben Hanks Racing would be my first suggestion as they have done plenty of internal work on Atlas's.

 

[notajeep]

There is no oil pump on an atlas.
Some good news.... kinda... is that the front output is fairly easy to replace.

 

[Milner]

There is no oil pump on an atlas.
Some good news.... kinda... is that the front output is fairly easy to replace.

The gears spin the oil around to lube it. With the rear shaft out and the case in neutral or rear wheel drive, there was nothing spinning the gears, thus no lube. In rear wheel drive (and neutral)the front output is disconnected from the main drive gears and it sits above the oil level.
So his shaft was spinning the front input and there was no lube due to the lack of gears spinning. So the front input bearing got hot and broke....

 

[DaveB]

Too bad on the Atlas. Did you by chance run into my kids that were down doing the trails in Moab over the weekend ? My son had his red Comanche, son in law in a white XJ, SIL brother in a red TJ, and his friend in another XJ ? They said they met someone with a black comanche and an XJ and I thought it might be you guys.

 

[reddman]

Sucky!

What type of oil was in it? Probably doesn't really matter since Milner's post explains it.

 

[Kiel]

Just another reason why I don't flat tow anything over a block

 

[bryson]

Just another reason why I don't flat tow anything over a block

x2. Another reason out of several...

 

[Jared]

Too bad on the Atlas. Did you by chance run into my kids that were down doing the trails in Moab over the weekend ? My son had his red Comanche, son in law in a white XJ, SIL brother in a red TJ, and his friend in another XJ ? They said they met someone with a black comanche and an XJ and I thought it might be you guys.

We did meet a guy and girl in a red MJ at the parking area for Poison Spider, but they were alone. They had 6 lug axles and a RigidCo front winch bumper. As far as I saw we were the only black MJ / white XJ combo running around.

Just another reason why I don't flat tow anything over a block

I totally agree and simultaneously disagree with you... and I'm sure others will feel compelled to share their feelings on the matter. Flat towing flat out sucks compared to hopping in a $40K diesel and hauling a $20K built rig around on a $3K trailer.

I'm not really a fan of flat towing. However, I have to face up to a few facts. Flat towing in my quiet, comfy Dakota totally rocks when compared to driving my bouncy, noisy XJ for 300 miles with two kids in the back. I also still get 14MPG while towing in my current setup... which is about what the XJ gets by itself. Having the Dakota in town gives me a place to lock up extra tools and spare parts... as well as having something nicer to drive if we head out to dinner or over to Arches NP, etc.

A decent trailered setup would cost me over 5 times what I have into the XJ (which still isn't much). I've looked... a lot. A trailer would put me over the towing limit on my "Big Block" 3.7L Dakota. Essentially, I'm now towing a 3,600 lb trailer with no brakes.

The gears spin the oil around to lube it. With the rear shaft out and the case in neutral or rear wheel drive, there was nothing spinning the gears, thus no lube. In rear wheel drive (and neutral)the front output is disconnected from the main drive gears and it sits above the oil level.
So his shaft was spinning the front input and there was no lube due to the lack of gears spinning. So the front input bearing got hot and broke....

I figured it was something similar. Thanks for the explanation.

Thanks guys,
Jared

 

[bryson]

If you're dead set on flat-towing, I'd recommend removing both driveshafts before you leave... that way there is no chance of issues like this.

 

[mbryson]

....... and I'm sure others will feel compelled to share their feelings on the matter. Flat towing flat out sucks compared to hopping in a $40K diesel and hauling a $20K built rig around on a $3K trailer.

I'm not really a fan of flat towing. However, I have to face up to a few facts. Flat towing in my quiet, comfy Dakota totally rocks when compared to driving my bouncy, noisy XJ for 300 miles with two kids in the back. I also still get 14MPG while towing in my current setup... which is about what the XJ gets by itself. Having the Dakota in town gives me a place to lock up extra tools and spare parts... as well as having something nicer to drive if we head out to dinner or over to Arches NP, etc.

A decent trailered setup would cost me over 5 times what I have into the XJ (which still isn't much). I've looked... a lot. A trailer would put me over the towing limit on my "Big Block" 3.7L Dakota. Essentially, I'm now towing a 3,600 lb trailer with no brakes.



I figured it was something similar. Thanks for the explanation.

Thanks guys,
Jared

Not to bag on the Dakota, as I flat towed with an '89 Suburban for quite a while. Not my favorite at all. However, I don't have quite the investment into my towing setup/Jeep as you have illustrated. I've got $17K in Dodge deezel pickup, $4K in trailer (can haul two rigs), and who knows in my "Jeep" (somewhere around $8-10K?, but probably more in the $10-12K range?).

There's really nothing that's the "silver bullet" to fix your problem or mine. I'd rather daily drive a Dakota or something other than a diesel pickup. However, the Dodge is fairly civilized compared to the Super Duty I drove before and gets respectable fuel mileage. Maint. is kind of more expensive and I've got a turbo, fuel system, trans and motor catastrophe hanging over my head at all times. I really like gassers (and almost bought another one over the Dodge) as you just have to worry about the motor and trans.

IMHO, you'll look for greener grass from whatever side of the fence you're on. Just enjoy your journey. If it works for you, it's cool.

If you're dead set on flat-towing, I'd recommend removing both driveshafts before you leave... that way there is no chance of issues like this.

If/when I ever flat tow again, I'd follow that advice. I'd really prefer a trailer. You can get a used trailer for $1K or thereabouts. About what a built transfer case costs?

 

[Tacoma]

I'm selling my Burb for $600. Add a trailer for say, $2k, you're well under the towing limit... of course, the mileage isn't awesome buuuutttt

Point is there are cheap tow setups available. Some of them are cheaper than transfer cases.

I personally hate flat towing after stupidly towing a 7,000lb military ambulance home from Phoenix.. didn't have a whole lot of choice due to time constraints, but I haven't been that nervous before or since. Harrowing, I'd call it. The whole "no brakes on the towed load" makes me a little jittery.

 

[Jared]

Agreed... there are cheaper tow setups out there. You can get an old F-250, a beat up van, or an older Burb for pretty cheap. But, then you have to inspect, license, insure, and store it. All of which rewards you with single digit fuel economy. Toss in the price of a trailer as well as licensing and storing it and you have a very substantial investment in both cash and space that you use a half-dozen times annually.

Unless money is really not an issue, I agree with Marc - there really is no ideal setup to haul a "less than street friendly" rig on a tight budget. For those with a lighter-duty tow rig and a lighter-duty off road rig, flat towing makes great economic sense and to me is worth the drawbacks. When I said over 5x what I have into the XJ... understand that I'm into the XJ for less than a grand. I bought it for $1,500, sold it for $3K, bought it back wrecked for $700, and then built it mostly from stuff I had laying around. So to me, spending even 5-6 thousand on a good towing setup seems ridiculous. It's like buying $500 Italian leather shoes for a hooker.

As far as pulling both drive shafts is concerned it really is a good idea. Locking hubs would eliminate the need to pull the front, of course. And if you just tie it up you would only have to pull the rear shaft at one end which is like a 10 minute job. It's good advice, but I've never done it and I've also never had an issue in a dozen or more trips to Moab, totaling over 5,000 towed miles. If I were going farther than Moab or didn't have time to double check all of my drive train I would likely pull the shafts.

To me it just boils down to knowing and religiously maintaining the towed rig. This never would have happened had the u-joint been inspected and replaced prior to the trip. It also would not have happened if either of us had known more about the internal workings of the Atlas. There is no more wear and tear (probably less, really) on your drive train when a vehicle is flat towed vs being driven down. The only real drawback is that you aren't inside the vehicle hearing and feeling problems before they become catastrophic as was the case here.

 

[Tacoma]

I think it comes down more to safety. How's that Durango deal with a panic stop?

.. not bashing you, just jawboning.

 

[Jared]

I think it comes down more to safety. How's that Durango deal with a panic stop?

.. not bashing you, just jawboning.

Not as well as I'd like, but much better than I'd feared. Not much worse than towing 4 ATV's or a large boat. Because there is no tongue weight it tows about like having a good equalizer hitch, rather than making the front end of the truck feel too light. Especially when you load the bed up with tools and coolers.

It's definitely a trade off. You get what you pay for and it's a CHEAP setup. I keep having thoughts of building a car dolly type setup with brakes if I keep the Jeep much longer.

 

[DaveB]

We did meet a guy and girl in a red MJ at the parking area for Poison Spider, but they were alone. They had 6 lug axles and a RigidCo front winch bumper. As far as I saw we were the only black MJ / white XJ combo running around.

Yeah that was my son and my wife. The other jeeps joined them later in the day.