Nathan

I am replacing the fan hub bearing and an alternator on a '92 964 C4. When reinstalling the fan with a new bearing what type of fit should I expect? A light press fit? I had an alternator that had a slight amount of play between the bearing and shaft. The fan would rub on the alternator housing. Did I not get the fan installed all the way on?

Thanks for the help,

Nathan

jimq

my new one went on the shaft a whole lot easier than getting the old one off.

Vandit

Are you sure the alternator is fully seated in the fan housing? Are you sure the alternator shaft doesn't have play (possibly bad alternator bearing)?

Nathan

New alternator & new fan hub with bearing...
The old bearing did something similar, so I replaced with anew fan hub.

Vandit

Nathan, did you resolve this issue?

Nathan

the shaft on the "new" alternator from Autozone was too small. I acquired another alternator and the bearing had a slight press fit, as it should. I took my dead blow and seated it onto the spacer. So, yes I resolved the issue. Thanks for asking, I needed to post my findings.

Metal Guru

I wanted to revive this thread because my reman alternator appears to have an undersized shaft also. The fan hub was slip fit installation. Interesting thing is now the alternator is not charging the battery. I replaced the voltage regulator and the diodes check out so I assume that the alternator is capable of charging if it was spinning.
I have a feeling that the engine is spinning the fan only; the hub (containing bearings that no no can source separately) is actually a clutch of sorts, allowing the alternator to spin at a different speed than the fan. However, if the hub is not pressed on the shaft, it can't spin the alternator.
Thoughts?

robt964

Presuming you are referring to a standard fan hub with two pulleys? The alternator pulley (smaller outer pulley) is sandwiched between the 50NM nut securing it and the hub bearing. If this nut is tight I can't see how the pulley could be rotating and NOT turn the alternator shaft. An undersized shaft would not effect the ability to turn the alternator shaft. It would just mean the fan running out of true. I'd be more inclined to suspect a duff alternator or regulator.

Nathan

My previous post is true about fan bearing fitment. Make sure the bearing fits the shaft correctly. If still not charging make sure the light in the clock for the charging system is not blown & connected. Here's where my problem was. The charging circuit goes through the clock and the signal light. These clocks have the problem of loose solder connections. Make sure the solder connections are good. I had the clock resoldered; fixed my charging problem. What I thought might have been the alternator ended up being solder joints in the clock.

Metal Guru

Nathan, thanks.
Actually I had to replace the alternator due to damaged threads on the shaft rather than a charging issue. The clock check is on my list if locking down the hub doesn't solve the problem.

Metal Guru

About the hub bearings that no one can find in the aftermarket: I'm thinking that those bearings are "ball bearing freewheel clutches". The bearings freewheel until a discreet rpm is reached then lock up. These bearings need some press fit to function properly.
That would explain a few things.
http://www.gmn.de/en/freewheel-clutc...formation.html

Vandit

The fan and alternator spin completely independant of each other and at different speeds due to the different sized pulleys at the crank and on the alternator shaft and fan seat.

As robt964 explained, the alternator pulley is locked to the alternator shaft because those conical washers basically bottom out against the inner sleeve of the fan bearing and against the nut on the shaft.

The fan pulley is locked to the fan via those 3 studs.

Vandit

My new fan bearing (purchased individually from Sunset, not as an assembly w/ a new fan) did have a slip fit on the alternator shaft unlike the OEM bearing that was a tight pressed fit.

It really doesn't matter however since the spacer below the bearing, plus the inner bearing race, plus the conical washers, shims, and pulley halves, and the nut on the shaft basically come together to lock the whole assembly together.

Metal Guru

Vandit, on a Turbo, the fan pulley is the only pulley that directly drives the fan. There's a a/c pulley on the end of the alternator that isn't driving the alternator; it functions as an idler. So to drive the alternator that hub has to lock up as some speed.