Broken alternator shaft

Todd · Post by **Todd** » Wed Feb 26, 2014 6:05 pm

Hey guys. I'm sorry if this has been discussed before, but I searched and couldn't find it. Today I replaced my fan belt. Had no problem getting the nut off. Replaced the belt put it all back together with no problems. Drove about 25 miles and my charging light came on. Got everything apart and my alternator shaft had sheared. I don't have a parts manual or repair manual. So I guess my question is can I just replace the armature or am I gonna need a whole new alternator. Thanks in advance for the help.

Jimm391730 · Post by **Jimm391730** » Wed Feb 26, 2014 7:09 pm

Wow, I'd think that if the shaft sheared that the fan, pulley, and belt would just fall loose. Can you explain better how it "sheared"?

I would think that you should just be able to replace the rotor, if that is all that was damaged (and assuming you can find just the rotor without the rest of the alternator). Else you'll have to replace the whole assembly.

pcolette · Post by **pcolette** » Wed Feb 26, 2014 7:11 pm

The armature is available as a separate item on SAV's website. I would guess EI has it too.

Todd · Post by **Todd** » Wed Feb 26, 2014 7:27 pm

Jimm391730 wrote:Wow, I'd think that if the shaft sheared that the fan, pulley, and belt would just fall loose. Can you explain better how it "sheared"?

I would think that you should just be able to replace the rotor, if that is all that was damaged (and assuming you can find just the rotor without the rest of the alternator). Else you'll have to replace the whole assembly.

Yes sir. The shaft broke right where the shims were pressing against the outside of the pulley half. When i took off the doghouse, the fan nut, belt, and pully half were laying in the splash guard, with part of the shaft still in the nut. The shims are gone. I guess those are the least of my worries right now though.

Jimm391730 · Post by **Jimm391730** » Wed Feb 26, 2014 7:33 pm

The "fan nut" is really a bolt that threads through into the end of the shaft. Just on the off chance, could it have been that the bolt sheared and let everything loose? I would think if the shaft sheared, then the fan (which is keyed to the smooth shaft) would have fallen off, too... the bolt is easier to replace than the shaft/rotor (assuming you can eazyout the rest of the bolt threads). Pics of the end of the shaft would help.

Todd · Post by **Todd** » Wed Feb 26, 2014 7:41 pm

pcolette wrote:The armature is available as a separate item on SAV's website. I would guess EI has it too.

I did see those at SAV. I wasn't sure if that would solve the problem or not. I have no idea what even caused this. Maybe it will be fairly easy to fix though. Thanks.

Todd · Post by **Todd** » Wed Feb 26, 2014 8:03 pm

Jimm391730 wrote:The "fan nut" is really a bolt that threads through into the end of the shaft. Just on the off chance, could it have been that the bolt sheared and let everything loose? I would think if the shaft sheared, then the fan (which is keyed to the smooth shaft) would have fallen off, too... the bolt is easier to replace than the shaft/rotor (assuming you can eazyout the rest of the bolt threads). Pics of the end of the shaft would help.

Maybe mine was already messed up and been rigged somehow. When I removed it only the nut came off it actually threaded onto a bolt which I was calling the shaft. Sorry bout that. That bolt is what is broken. Here are some pictures of it as it sits now. They aren't real good but maybe you can make it out.

Todd · Post by **Todd** » Wed Feb 26, 2014 8:08 pm

Looks like my pictures didn't come through. Ill try again

Todd · Post by **Todd** » Wed Feb 26, 2014 8:10 pm

Jimm391730 · Post by **Jimm391730** » Wed Feb 26, 2014 8:16 pm

Nope, I see that the threaded portion of the end of the shaft has truly sheared off. This is the part that engages the bolt threads.

It might be possible to use a very large, thin nut to clamp the belt pulley half in place by using the large diameter external threads. Not optimum, but could save $$$. You'd need to carefully measure the diameter and thread pitch and see if you can find a thin nut to fit, perhaps McMaster Carr. They might have similar shims, too.

Todd · Post by **Todd** » Wed Feb 26, 2014 8:43 pm

Thanks for the help Jim. If I can't find a nut to fit that , would replacing the armature be the best course of action? I also have no idea how to measure thread pitch so I guess that is first on my list of things to do.

Jimm391730 · Post by **Jimm391730** » Wed Feb 26, 2014 10:07 pm

If you don't have one, get a $15 digital caliper from Harbor Freight. It's the most accurate way of measuring the diameter (in millimeters) of those external threads. Then carefully measure from the tip of one thread (highest portion) to the tip of the next, or second next, or third, etc. Then divide the reading by the number of valleys between the tips that you measured. You will probably come very close to the proper diameter and thread pitch. FYI, metric threads are defined by the max OD of the threads (easy to measure on the shaft) and the millimeters from thread to thread (tip to tip, with one valley between). I don't know exactly what size that thread is, but I was checking McMaster Carr and they had a 30mm nut with 3mm threads (that is pretty coarse) but also 2mm and 1.5mm thread pitch. You will be looking for similar numbers.

edzz · Post by **edzz** » Wed Feb 26, 2014 11:30 pm

FWIW The nut is in Group 1 20 Fig 1/ 712.1.06.113.3 / Fixing nut / M14x1.5 (so that would be a metric 14 mm 1.5 pitch nut)
Alternator is in Group 9 20

Todd · Post by **Todd** » Thu Feb 27, 2014 2:02 am

Thanks a ton for the help. I will get on that torrow

Todd · Post by **Todd** » Thu Feb 27, 2014 5:29 pm

Got them measured. 34.5x1.5. Ill be looking at McMaster later tonight. It still seems like I should be able to drill out that bolt and put a stud in, but for now the thin nut seems like the best option.

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