Alternator Decoupler Pulley Came Apart

[The Critic]

Application: 2008 Toyota Camry V6

This was a 4.5 year old, reman Denso Alternator with 45,000 miles.

What do you think happened?

 

[DougR]

A genuine Toyota 4Runner remanufactured alternator doesn't include the decoupler. It has to be bought separately. Did you buy a reman alternator from Toyota for your Camry? Did you test the decoupler for smooth operation when the reman was installed?

There appears to be a lot of dirt inside decoupler. Is the grease contaminated with any dirt? Was the plastic cover compromised? Is the belt tensioner in good condition? Why is your alternator housing so dirty in 45,000 miles? Is it oily and holding dirt?

 

[JimPghPA]

Someone please clue me in. Why in the world would anyone ever want a de-coupler on an alternator? Simply remove power to the rotor and the force required to turn it goes away. Something does not make sense here.

 

[Jetronic]

Someone please clue me in. Why in the world would anyone ever want a de-coupler on an alternator? Simply remove power to the rotor and the force required to turn it goes away. Something does not make sense here.

the decoupler reduces vibrations and stress on the belt

 

[GSCJR]

There's a lot of rubber residue on the front of that alternator. Incorrect belt tension and/or a defective bearing would be my guesses.

 

[DougR]

OP, post images of the belt, contact side. How many miles on the belt?

 

[JRay’07]

Some lubricant appears to have been thrown off which indicates that a seal may have been compromised. I think that the overrunning clutch had an insufficient supply of clean grease and began to overheat and gall the shaft. Was the nut on the end tight or did the alternator fall apart while in service?

 

[spackard]

All those rough marks on the inner race show the thing was not free-spinning for a while.
At some point it was shocked enough by a shift to come apart.

The most common reason for overrunning sprag clutch failure is wear between the sprags and the mating surfaces. The sprags require a lubrication film to maintain separation between the sprag and the mating surfaces so that wear is minimized. However, if the lubrication is not sufficient to maintain a thick enough oil film to overcome the microscopic surface roughness of the sprag and the mating surface, then there can be some metal-to-metal contact.

This can happen with lubrication that doesn’t have a sufficient viscosity to work at the application operating temperatures. Additionally, if contamination is present in the application, the contaminants will bridge the oil film gap and can act as sandpaper against the sprag, speeding up the wear.

(This is only my armchair guess.)

 

[dfarr67]

Simply more parts- more chances of failure. I'm sure when new there were a few failures too.

 

[Astro14]

Like others, I suspect that the remanufacturing process simply reused a functioning run-on clutch pulley.

So, that run on pulley could potentially have hundreds of thousands of miles on it.

I’ve had to replace a couple of them at the 150,000 to 200,000 mile mark

So, when I had the alternator rebuilt on the 240,000 mile XC 90 last year, I just installed a new run-on clutch pulley to replace the original.

 

[clinebarger]

Technically a Roller Clutch.

 

[The Critic]

A genuine Toyota 4Runner remanufactured alternator doesn't include the decoupler. It has to be bought separately. Did you buy a reman alternator from Toyota for your Camry? Did you test the decoupler for smooth operation when the reman was installed?

There appears to be a lot of dirt inside decoupler. Is the grease contaminated with any dirt? Was the plastic cover compromised? Is the belt tensioner in good condition? Why is your alternator housing so dirty in 45,000 miles? Is it oily and holding dirt?

This Denso alternator was purchased from Rockauto. The belt was installed at the same time. Tensioner was replaced about 15K afterwards for unrelated reasons.

All of the dirt was from the grease that flung out when the pulley came apart.

Also, Genuine Toyota reman alternators do come with the decoupler. I purchased one for a Highlander recently and it was ready for service.

 

[fantastic]

In 2011 Volvo went from needle bearings to ball bearings to fix their de-coupler. If there is some uneven pressure etc they wear faster than ball bearings.

 

[fantastic]

Someone please clue me in. Why in the world would anyone ever want a de-coupler on an alternator? Simply remove power to the rotor and the force required to turn it goes away. Something does not make sense here.

Space constraints