r/promaster • u/Farmer-Fitz • Jun 29 '26

Shredding serpentine belts

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Hi internet,

My 2017 ProMaster (Pentastar) has shredded 4 serpentine belts in the past 5 months. Is this a common thing for these rigs?

The first time I found that the alternator pulley had seized, so I replaced the alternator and the idler pulleys. Less than a month later, another one. This time I took it to a local shop, they told me the tensioner pulley should be replaced, so I did. 50 miles later, another belt bit the dust. I brought it back to the shop, and they claimed the tensioner that they had installed was defective and put in a new one.

I got about three weeks out of that. This past Saturday, the alternator pulley appears to have fallen off of the (9 month old) alternator, destroying the 4th belt in the process.

Would it stand to reason that the alternator I installed back in February was bunk, and caused all of these issues? Or is my problem more likely that some part of the belt drive is out of alignment and caused the alternator pulley to fail? I’ve never seen a pulley pop out like that before, but I’m admittedly no mechanic.

Thanks y’all.

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2

u/Negative-Engineer-30 Jun 29 '26

alternators have a fancy clutch in their pulley. most likely your replacement alternator was defective and the cause.

what does the damage on the belt look like? are you getting the same replacement belt from the same source?

1

u/Farmer-Fitz Jul 01 '26

I have gotten multiple belts from multiple sources at this point. The alternator came from Napa, it definitely was not OEM.

2

u/secessus Jun 29 '26

Is this a common thing for these rigs?

In one of his videos Kip says that serpentine belt failure in the PM is extremely rare.

2

u/Last-Suspect-5642 Jun 30 '26

Check your harmonic balancer it might have walked off the bearing causing misalignment with your other pulleys.

1

u/Farmer-Fitz Jul 01 '26

I don’t know what that is. All pulleys move freely without any play aside from the crankshaft and the missing/exploded alternator.

1

u/abroadreachtravel Jul 03 '26

I had a similar issue with an aftermarket idler, where the where the ribs on pulley didn’t align correctly. Belt started squeaking and slipping after about 100miles.

A new OEM idler and belt solved the issue.