What could have caused this alternator failure?

4BY4ADV

TJ Enthusiast
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Jan 2, 2020
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Oceanside, CA
Alternator went out the other day with no warning. From 14v to nothing. Thankfully the dual batteries kept me going and I was able to get home.

Had a chance to swap out the alternator this morning and found one of the negative posts was broken right off. Seems a bit odd as there is plenty of clearance with the body, even if a motor mount was completely torn, it doesn't look like there would be contact.
alternator.jpg
 
Wow, that'll do it!

I'd guess it's a combination of a poor casting run and vibration. I'll have to look at mine closer, but I wonder if they used different brand/models throughout the TJ's run?
 
I was surprised at how stiff the negative cable was at that point... but still, I'd expect the copper to give before the casting.

At least it was super easy to replace!!!
 
Might be worth replacing the battery cables at some point. If they're that stiff, they're probably corroded, and have higher resistance and may eventually break. Deal with it before it decides to give up the ghost in the Walmart parking lot with a trunk full of ice cream...
 
Might be worth replacing the battery cables at some point. If they're that stiff, they're probably corroded, and have higher resistance and may eventually break. Deal with it before it decides to give up the ghost in the Walmart parking lot with a trunk full of ice cream...
Ahhh, definitely not Walmart. And my freezer runs off the second battery and I have a solar panel. 😜
 
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Almost certainly a stiff/hard petrified older wire and engine vibration/movement that caused it. Possible casting issues during manufacturing. Possibly cracked when it was first installed. Most likely not though…

I’d definitely consider replacing the wire with a fresh more flexible piece though. May not make any difference, but the peace of mind is usually always worth the effort…
 
I’ll definitely look into replacing it, though it’s not that it wouldn’t flex, it was a very short section so it takes more force to bend it. Not to mention it’s the end of the link and has three other wires/bolted just prior that are all held together in a plastic block. So vibration from the wire actually doesn’t make sense at that point in the cable… the first link that bears all the stress, that would make more sense. Oh well, just another maintenance item on a 210k mile TJ. Hahaha
 
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I’ll definitely look into replacing it, though it’s not that it wouldn’t flex, it was a very short section so it takes more force to bend it. Not to mention it’s the end of the link and has three other wires/bolted just prior that are all held together in a plastic block. So vibration from the wire actually doesn’t make sense at that point in the cable… the first link that bears all the stress, that would make more sense. Oh well, just another maintenance item on a 210k mile TJ. Hahaha
I see what you mean. I thought the wire was coming around the back and getting bolted on. Instead it’s a super short section coming from that block. My bet is still on stresses from the wire/stud/nut arrangement and vibration…
 
I cannot see in the picture, but does the broken aluminum alternator tab have a flat spot to the left of the stud OR is there a mark on the metal behind the aluminum tubing and black plastic retaining clip (which has pulled free) ?
I am wondering if one or both of your motor mounts have gone bad causing a sharp hit to the aluminum tab when the engine rocked over breaking off the grounding tab.
 
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zooming in i see where something hit it . look beside the nut and see the scratches. or like charles said it flexed and hit the line which would make sense looking where the scratches are on the cover
 
The photo is not with the alternator mounted. It's completely unbolted, rotated 90 degrees, and moved a several inches away from where it mounts to get to the wires.

When mounted, it's *nowhere near the inner fender. In fact, mounted up, if it hit the inner fender I'd have a WHOLE lot more problems!!!! More than just motor mounts, trans mount, bent/broken exhaust, etc.

The AC line you see has a loose mount only because I was moving things around.

I'm just going to chalk this up to age and vibration.
 
The photo is not with the alternator mounted. It's completely unbolted, rotated 90 degrees, and moved a several inches away from where it mounts to get to the wires.

When mounted, it's *nowhere near the inner fender. In fact, mounted up, if it hit the inner fender I'd have a WHOLE lot more problems!!!! More than just motor mounts, trans mount, bent/broken exhaust, etc.

The AC line you see has a loose mount only because I was moving things around.

I'm just going to chalk this up to age and vibration.
Thanks for the clarification....
Haven't found a tab broken off like that without something impacting it or a lot of stress on it.
 
I changed mine at 212k miles. I felt pretty good about getting that much mileage out of it. It was the only thing on the SERP that had not been replaced in the last two years.
 
I changed mine at 212k miles. I felt pretty good about getting that much mileage out of it. It was the only thing on the SERP that had not been replaced in the last two years.
I feel like I'm in the same boat... both driveshafts, SYE, exhaust manifold, front wheel bearings, about to replace the AC evaporator, radiator, control arms, shocks, tires....

It's a constant project.