Another Front Diff Blown!

Guyute1210 · **Posted:** Tue Feb 21, 2006 1:55 pm

I'm glad to see that it's being covered by warrenty.

Is this something that should be reported like the Ball Joint issues?

Bakerkj · **Posted:** Tue Feb 21, 2006 4:51 pm

I'm going to report it after I have it fixed and get pictures.

Guest · **Posted:** Sun Feb 26, 2006 10:49 pm

Bakerkj wrote:

I'm going to report it after I have it fixed and get pictures.

Any pictures yet?

jpzkj · **Posted:** Mon Feb 27, 2006 1:24 am

KJ-BOL wrote:

It happened the same way as most of them....
Tires spinning freely in the air - KJ comes down onto front tires, take grab of the ground and first thing it goes crack is the Front Diff
Is there anything going with DC trying to fix this problem?

As temporary fix, therewas a thread a while ago about re-inforcing the front diff:

http://www.lostjeeps.com/forum/phpBB3/vie ... al&start=0

just want to share

EDIT: BakerKJ was the victim - not mine - sorry - should have been more specific.

So...exactly what was the situation that led up to your broken diff :?:

Eddo · **Joined:** Thu Jul 07, 2005 7:01 pm **Posts:** 1214

jpzkj wrote:

KJ-BOL wrote:

It happened the same way as most of them....
Tires spinning freely in the air - KJ comes down onto front tires, take grab of the ground and first thing it goes crack is the Front Diff
Is there anything going with DC trying to fix this problem?

As temporary fix, therewas a thread a while ago about re-inforcing the front diff:

http://www.lostjeeps.com/forum/phpBB3/vie ... al&start=0

just want to share

EDIT: BakerKJ was the victim - not mine - sorry - should have been more specific.

So...exactly what was the situation that led up to your broken diff :?:

Very steep ledge, nearly vertical. Probably 7-8 feet high if I remember correctly. It was covered in loose sand and slightly moist so there was very little traction. Didn't exactly see what happened, I was off looking at something else. But I know he made several attempts. I saw him high center at the crest of the ledge once and get stuck. I heard tons of wheel spin and the engine revving way up for a little while as he made a couple attempts. Then I heard the grinding noise from the gears inside the broken diff. Went over to see what happened and he broke his front diff. I'm sure all the wheel spin and sudden traction is what broke it. He might have gotten the front end air born as he crested the edge of the ledge, because the crest/lip of the ledge was too protruding to just go over and not be stuck resting on you tranny skid. So he probably need some momentum to slide up and over it. But once again I really didn't see what happened at the moment he broke the diff. Just heard tons of wheel spin , the engine revving way up and then the infamous grinding noise. However, there was no real way up the obstacle but to just punch the gas and hope for the best.

Ed · **Posted:** Mon Feb 27, 2006 9:24 am

Strewth! And is anyone surprised that it broke? Doesn't exactly sound like normal off-road use to me!

Quote:

However, there was no real way up the obstacle but to just punch the gas and hope for the best.

Electric winch?
Snatch strap?
Hand winch?
Chicken Track?

Or a $4000 repair bill. Your choice.

Eddo · **Joined:** Thu Jul 07, 2005 7:01 pm **Posts:** 1214

Ed wrote:

Strewth! And is anyone surprised that it broke? Doesn't exactly sound like normal off-road use to me!

Quote:

However, there was no real way up the obstacle but to just punch the gas and hope for the best.

Electric winch?
Snatch strap?
Hand winch?
Chicken Track?

Or a $4000 repair bill. Your choice.

Well there was a whole discussion about it on the Midwest board. The obstacle was completely optional. I'm sure he knew the risk of breaking something and decided to just take the chance. Diff probably shouldn't have broken, but since it is already a little weak to start out with it didn't really suprize me with all the wheel spin. I've broken hubs on my CJ doing less and seen u-joints on other Jeeps break from similar type attempts. I think we all know that it was pushed pretty hard and that is why it broke. However, you would think something else would give before the entire case split. Like a CV joint blowing or something.

Bakerkj · **Posted:** Mon Feb 27, 2006 11:35 am

O.K I have to step in now.

I just read Eddos discription of the crackage. So everybody knows the facts behind the crackage. . The ledge is a 40 degree angle (not vertical). It was one attempt, (not several). I never got stuck. The only gravel or sand there was at the top of the ledge were I got the wheel spin. I do high center briefly on the boulder bars (not the tranny skid) so I did get the front wheels off the ground for a second or two. The most important fact is that it is a poor design and we need to find a fix for it.

And I also want to mention:

We all take a chance of breaking something ever time you wheel. I went there to have fun and for me that means pushing the limits of my driving skills and my jeep. If I break something then so be it. At least I tried, I learned something new and I had a good time.

KJ04 · **Posted:** Mon Feb 27, 2006 12:36 pm

Ed wrote:

Strewth! And is anyone surprised that it broke? Doesn't exactly sound like normal off-road use to me!

Quote:

However, there was no real way up the obstacle but to just punch the gas and hope for the best.

Electric winch?
Snatch strap?
Hand winch?
Chicken Track?

Or a $4000 repair bill. Your choice.

That sounds like normal Off-Roading to me!

One doesn't spend $3,000.00 for a lift, lockers, full armor, mud tires, bumper, winch, and other modifications to go on Bunny Trails, splashing through a few mud puddles, and call it Off-Roading!
Real Off-Roading is not for the faint of heart, it's full of challenge, it tests a driver and his vehicle, it includes white knuckled, heart pounding exhilaration, and obstacles are considered part of the norm.
My hat's off to the man, he put his Jeep to the challenge and confronted the obstacle. Sometimes the obstacle wins, but then, that's all part of Off-Roading.

Ed · **Posted:** Mon Feb 27, 2006 7:46 pm

Sorry, I didn't mean to criticise anyone's driving abilities, it's just that from Eddo's description it sounded like the diff broke trying to tackle an impossible obstacle with the engine bouncing off the rev-limiter. Bakerkj's description sounds much more like everyday offroad use. Which is rather worrying!

I wonder what DC's position on this is, presumably they're admitting it's a fault otherwise they wouldn't be replacing it under warranty.

Bakerkj · **Posted:** Mon Feb 27, 2006 8:56 pm

No offense taken here. I assumed you were speaking from Eddos description. However I do like his description, it sounded like I was really doing some hardcore wheeling.

The sad part is back in November, several of us watched a guy in a Geo tracker go up the same Ledge and then he turned around and went down it with no problem

Tokyojoe · **Posted:** Mon Feb 27, 2006 9:13 pm

Geo Tracker = Very short wheelbase

jpzkj · **Posted:** Mon Feb 27, 2006 10:25 pm

3rd post down....http://www.lostjeeps.com/forum/phpBB3/viewtopic.php?t=3595&start=30

LOOK FAMILIAR ? :cry:

Bakerkj · **Posted:** Mon Feb 27, 2006 11:49 pm

Jpzkj,

I thought mine was bad. You blew that thing up. Nice Job! Were you able to drive it home like that?

Did you tell the dealer you were wheeling or at the store getting groceries?

jpzkj · **Posted:** Tue Feb 28, 2006 12:56 am

Not mine thank god...it belongs to San Diego Dave.

They were on a run just south of...you guessed it...San Diego, when he cracked it wide open. Dave is a pretty mellow / responsable offroader so Im surprised that he had this damage. They were on a fossile hunting run and he said that terrain wasn't that rough. I guess it was just the perfect combo of wheel spin and sudden traction that did it.

He says the dealer is going to warrenty it (extended warrenty)so theres that at least.

Guest · **Posted:** Tue Feb 28, 2006 8:51 am

I've been looking at all the pictures of failed front diffs for quite a while now. From an engineering point of view - I don't think a reinforcement collar is going to help here. We would need to determine an exact pre-tension that is suitable for the collar, but with different impact loads being expected, this may be impossible to find the right one. Plus, the aluminum will still compress and fracture under the collar due to its material makeup. Too tight, and you will pre-compress the aluminum and cause binding inside the diff.

It's a Materials failure. Aluminum is too soft in this use and it will just blow out like the San Diego guy - which could have failed just as easily in the thick part, not the thin collar area - it just doesn't look good.

I can see why aluminum is used, it's a perfect material for such a complicated shape with multiple openings. I think the only solution will be a steel replacement, but that will add who knows how much weight up front.

Eddo · **Joined:** Thu Jul 07, 2005 7:01 pm **Posts:** 1214

Bakerkj wrote:

No offense taken here. I assumed you were speaking from Eddos description. However I do like his description, it sounded like I was really doing some hardcore wheeling.

The sad part is back in November, several of us watched a guy in a Geo tracker go up the same Ledge and then he turned around and went down it with no problem

All I was trying to get at was that from my point of view the KJ was pushed quite hard to make it up the obstacle. Not just this obstacle, but others also. From my limited experience of wheeling out in Moab with LOST and out in New Mexico/Colorado, what was done was exactly what we where told not to do. Use lots wheel spin to get up an obstacle. Now that doesnt make anyone a bad person or someone a real offroader or not. What happened it was happened. The more you push your Jeep the further you get , but risk breaking something. I still don't think the diff should have broken, but it didn't really surprise me as I've seen another one break under less stress. However, I've broke my CJ attempting a very similar obstacle in similar manner. But I didn't break an axle, just the hub. I think something else should have gone first like the CV joint or something before you split the entire case.

I guess moral of the story is that the front diff is from from indestructible and that if you beat on it it WILL break. So if you are concerned about breaking it you need to take it slow and be careful if you start getting lots of wheel spin. It doesnt mean you can't wheel your KJ hard just be conscious of its weak parts.

KJ04 · **Posted:** Tue Feb 28, 2006 9:21 am

Bakerkj,
mine broke just past the 2nd. rib very simalar to the one in the pic. The chunk was 3" X 4" and the crack ran the same way. You guys lucked out with warranty, I had to pay for mine.

Eddo · **Joined:** Thu Jul 07, 2005 7:01 pm **Posts:** 1214

alljeep wrote:

I've been looking at all the pictures of failed front diffs for quite a while now. From an engineering point of view - I don't think a reinforcement collar is going to help here. We would need to determine an exact pre-tension that is suitable for the collar, but with different impact loads being expected, this may be impossible to find the right one. Plus, the aluminum will still compress and fracture under the collar due to its material makeup. Too tight, and you will pre-compress the aluminum and cause binding inside the diff.

It's a Materials failure. Aluminum is too soft in this use and it will just blow out like the San Diego guy - which could have failed just as easily in the thick part, not the thin collar area - it just doesn't look good.

I can see why aluminum is used, it's a perfect material for such a complicated shape with multiple openings. I think the only solution will be a steel replacement, but that will add who knows how much weight up front.

I have to disagree with you a little on some of that. My last job involved looking at trying to fail pressurized aluminum cylinders. We all know aluminum is not as strong as steel and steel probably won't have this problem. And aluminum is the perfect metal for forming into areas like this.

Aluminum doesn't just blow out though, no metal does that. That is what appears to happen if under enough pressure, from the casual observation. However what happens first in any metal failure is a crack start to form. The crack almost always starts in the weakest area if under equal stress. Also it usually takes quite a bit of deformation of the metal for the crack to start (even in aluminum). So there would be some bludging and it would be probably be noticeable to the human eye before the crack started to form. And once the crack forms it grows very easily. Eventually leading to a part just falling off which can appear to be blown out. It's easy to see if you do a high speed video analysis. Thickness of aluminum makes a huge difference. If the cylinders where just made a fraction thicker it takes considerable more pressure to make them pop. Also a large factor was the alloy that was used. They all have vastly different properties when it comes to stuff like how easily the crack propagates and the plastic region.

Overall, I'm not really convinced about my collar fix. We still need to know exactly where it fail from and how it fails. I could be completely off. But I think it is worth a try. Yes getting the right pretension would be important and very hard to achieve, but we are only need a little extra strength to keep her failing. Just keep the metal from expanding or bluding outsides its plastic region. For 20 dollars it is worth a try, but we really don't have the money to honestly conduct tests to figure out it it worked.

Guest · **Posted:** Tue Feb 28, 2006 10:26 am

Eddo wrote:

I have to disagree with you a little on some of that. My last job involved looking at trying to fail pressurized aluminum cylinders. We all know aluminum is not as strong as steel and steel probably won't have this problem. And aluminum is the perfect metal for forming into areas like this.

Aluminum doesn't just blow out though, no metal does that. That is what appears to happen if under enough pressure, from the casual observation. However what happens first in any metal failure is a crack start to form. The crack almost always starts in the weakest area if under equal stress. Also it usually takes quite a bit of deformation of the metal for the crack to start (even in aluminum). So there would be some bludging and it would be probably be noticeable to the human eye before the crack started to form. And once the crack forms it grows very easily. Eventually leading to a part just falling off which can appear to be blown out. It's easy to see if you do a high speed video analysis. Thickness of aluminum makes a huge difference. If the cylinders where just made a fraction thicker it takes considerable more pressure to make them pop. Also a large factor was the alloy that was used. They all have vastly different properties when it comes to stuff like how easily the crack propagates and the plastic region.

Overall, I'm not really convinced about my collar fix. We still need to know exactly where it fail from and how it fails. I could be completely off. But I think it is worth a try. Yes getting the right pretension would be important and very hard to achieve, but we are only need a little extra strength to keep her failing. Just keep the metal from expanding or bluding outsides its plastic region. For 20 dollars it is worth a try, but we really don't have the money to honestly conduct tests to figure out it it worked.

I hope the collar idea does work. Any thoughts of what kind of pretension would be useful for this situation or how much we can achieve with the collar?

Another Front Diff Blown!

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