So what's a broken pin really mean?

[Pete M]

Just popped open the '99 8.8 I got from the j-yard and discovered a broken cross pin. What could cause this? Is it an easy fix? Or should I return the axle? I got a pretty good deal on it so if the fix is cheap, I'll keep it. There aren't any chips in the teeth and everything seems tight (not that I'm an axle expert or anything). If it means anything, the engine was a v6 and the gears are 4.10s.
Thanks,
--Pete

 

[gijoecam]

If I was gonna guess at it.... I can think of two conditions that could cause that: One would be a side impact on an axle shaft like someone getting side-swiped on the rear 1/4 panel, and the other would be a rollover or tripping condition. Here's my rationale:

Ordinarily, there is no (or very minimal) load on the pin. All that pin does is hold the axle shafts apart from each other. If that pin was to break where it did while the axle was rotating, I suspect there would be evidence of such on the housing where it tried to spin it out. I suspect that, in reality, the pin might spin out far enough that it wedges itself in the housing, causing the carrier to grenade, and the inside wouldn't look anywhere near as nice as it does.

Now, I suppose it's remotely possible that it broke years ago and the piece has been sitting in the bottom of the canter section, but the odds of it not rolling over and getting caught someplace it shouldn't be are pretty remote. Also, it holds one of the spider gears in place, and without it, things might be OK, but only until the first time they made a turn, at which point it would likely have spit the spider gear out. Again, had it happened on the road, I doubt it would stay out of harm's way for long.

So, that leads me to a side impact of some sort.... got sideswiped, rolled over and tumbled, or something along those lines. Check the axle shafts for bends at the flange ends. I'd almost bet dollars to doughnuts that one of the axle shafts is bent. Also, check the squareness of the spring perches. Odds are they're fine as the spring bushings and u-bolts will flex long before the axle tubes even try to move.

My best guess. {Vincent LaGuardia Gambini voice on} Ms. Vito, does the defendant's case hold water? {/voice}

-Joe

 

[Pete M]

Thanks! I'll do some more investigating to see if anything more is bent/broken. Not that it's much of a clue, but there is enough pin remaining in the diff to hold in both spider gears.
--Pete

 

[Silver X]

Um Joe, how bout you drive over to Pete's house and check it out? You guys are probably 5 minutes apart, lol.

 

[CDW6212R]

Odd, that's a relatively strong piece, and little load on it, I'll bet that the locking bolt is what broke first. There is a too small tiny 8mm headed bolt that runs down inside the side of the shaft to hold it in. The bolt is too easy to break, be very careful when tightening or loosening them.

If that bolt broke just before the vehicle was no longer driven, then you most like;ly have a good unit, minus the shaft and bolt. Look hard at the spider gears, and the housing, etc. If you clean and inspect everything, you might decide that it was a recent issue, hopefully part of the wreck. How do the axles look at the outer bearings, if they aren't good you could spend as much just replacing those. Good luck,

 

[Pete M]

Um Joe, how bout you drive over to Pete's house and check it out? You guys are probably 5 minutes apart, lol.

Haha! Didn't even notice that.

After further inspection, the C-clip is warped, the locking bolt is intact (came out just fine), and the driveshaft is ever-so-slightly bent (as far as I can tell with my straight-edge). Looks like a side impact of some kind. :roll: I really really should have remembered my rule of having the 'yard pull the diff off before I buy an axle. Dang.

 

[gijoecam]

LOL! I didn't notice that I still haven't updated my location.... I'm a little farther south at the south edge of Newport now, and I've been in here for a little over two years. I spent seven years in Trenton, so yeah, I was right down the road.

I would be happy to go take a look at it, but I'm not about to invite myself over.

I wouldn't worry too much about it the damage though.... If the retainer had broken and it spun itself out while it was driving, the spider gear wouldn't have stayed in position for long. I suspect it either happened during the accident that put the vehicle in the junkyard in the first place, or it happened in the yard. In either case, a new retainer pin isn't expensive, and a bent axle shaft is a simple part to replace since it's opened-up anyways.

-Joe

edit: Just lookin' at the pics again.... is the broken piece of the pin from the middle, or from the end opposite the retaining bolt? If I could get my hands on the pieces, I could have one of the guys at work take a look at the fracture face and maybe give us an idea as to how it broke. I work for Ford in teh Dearborn Central Lab, and they do that stuff all the time. We could take a look at it under magnification and see what we can see.

Also, it just dawned on me that the pin is what drives the spiders.... you said that there was enough of the pin left to hold them in place??? If so, now I'm REALLY baffled...... There's no scarring on the inside of the cover?

-Joe

 

[Pete M]

Dang it! Why the heck is the forum not emailing me about responses like it's supposed to?

Anyway, I'm about to run out the door to make a trip to the other side of the state, I'll get back with you when I, er, get back.
--Pete

 

[Pete M]

It might just be me that's causing your confusion. About 45% of the big pin fell out. I don't know what would happen if you got it up to highway speed, but I could rotate the assembly again and again and nothing fell out. But then, it is a posi and the spiders don't really do anything unless you put more torque on one side than I can muster with my bare hands. My failure analysis experience tells me that a sharp impact at the lugnuts put stress right to the middle of the pin and it's apparently not a "soft" steel. But then, most of my experience is with plastics. (3 years with DuPont. I actually spent many-a-day at the Dearborn Engineering facilities since I was part of the team that tried to help bandaid the 4.6L manifold debacle.) Maybe we can have your guys at Ford check it out just for kicks. Will a drum braked shaft work in the disk axles? The pull-your-part 'yard on Telegraph doesn't usually get new enough Explorers to find disks.
Thanks,
--Pete

 

[gijoecam]

For more parts, check out LKQ in Belleville (off I-94 west of 275).

I think that the drum brake halfshafts may be longer, but I may be mistaken.... I honestly don't know.

I work up at the Dearborn Central Lab... We can certainly take a look at the fracture faces and figure out if it was an impact or a fatigue issue.

Also, take a look at the carrier and see if the hole is angled one way or the other.... That might give some insight as to whether it was a side impact or a rotational load.

I was telling one of the guys about it at work this afternoon... We were thinking it might actually be possible to drive it like that as long as the pin wasn't hitting the housing. As long as the other spider gear was in place with the other half of the pin, the gear missing the pin would stay put. It might wobble back and forth a bit, but it wouldn't spit it out.

-Joe

 

[Pete M]

My dad took the digi camera with him on his business trip, but I wanted to show you a pic of the C-clip. It is most certainly deformed in a way that indicates to me that the axle shaft was pushed in pretty hard. I get them up when I can.
--Pete

 

[Pete M]

Sorry 'bout the delay. The start of the semester has pushed my projects to the back burner.

So here's the C-clip from the bent axle side:

Between it, the bent shaft and the location and direction of the break in the center shaft, it looks like a heavy side ipact to me. Any chance this could happen if the junkyard dropped the axle somehow?
--Pete

 

['97 V8]

Why havent you returend that axle yet? I think the axle is trashed bieng that one of them are bent.

 

[Silver X]

Maybe if they dropped it off a 5 story building.

I dropped an 8.8 housing off the back of my pickup right on its end, and all it did was bend an axle shaft a little. No damage at all to the diff or anything else.

Did you get the whole assembled axle housing? If so, are the axle tubes straight on the housing? Seems like there would be some visible damage to the tubes if it was hit that hard.

Edit...I just re-read your first post and see you got the whole assembly. So is it straight or tweaked?

Also, I agree with the others...try to return it or swap it with a better unit.

 

[Pete M]

My untrained eyes haven't picked up on any problems in the housing itself. But I'm no expert.
Oh, and I would have returned it long ago, except the junkyard I got it from is 5 hours away and I picked it up as part of another journey. Serves me right for not having them pop the cover so I could check the innards.
--Pete

 

[Silver X]

Well that sucks.

 

[Pete M]

Well that sucks.

Yup. I'm hoping that I can simply replace the bad parts and sell it to a dedicated offroad rig to recoup my costs. I'd shy away from putting it under a daily driver, just in case.
--Pete