Took the truck out for a drive this morning and midway through the drive, I heard the fan ramping up with RPM, and varying speed each time I shifted. It used to do this in the early morning but once you hit 2k rpm or so, it would die back down. Now the fan is running all the time.

It could have been doing it for awhile, I usually drive with my music up loud, but it's hard to ignore the fan noise. At 3K RPM it sounds like the truck will lift off and take flight any second. Over 3K the belt starts howling, so there's no way I can drive it like this on the interstate for extended periods- which my daily commute is 90% interstate.

Is this just the fan clutch gone bad? When I move the fan back and forth with the truck off there's a lot of resistance, but it *does* turn. It has a feeling like rocks in a bearing where it'll be smooth for a second, then it will catch something that you'll have to force it through, then smooth again. Any suggestions would be appreciated.

 

OK, I answered my own question. I removed the fan & clutch and there's definitely something wrong. I can't turn the hub by hand without having the leverage of the fan. This was with the engine hot, so the hub should spin more or less freely.

I tossed it aside and am gonna drive the truck without the fan until I can get to a junkyard. I'm not paying $50 for a new clutch on a 30 year old truck. I never have to sit in traffic, plus it's winter and I can do the "turn the heat and fan on high" thing to keep it cool if I have to. If it seems like it's going to overheat, I'll eat the $50, but am going to try to avoid that if I can.

 

At least you took it off.
If locked up it will destroy your water pump in short order.

That's a great price.
Last time I bought one it was $90

 

Jim - Why will it destroy the water pump? Isn't it the same when locked up as the trucks w/o a clutch?

 

I don't know.

When it's being overdriven it is trying to pull the shaft right out of the pump.

Plus, I don't think the fan balance is good for 6,000 crankshaft rpm.

More than once I have had the fan seize up on the road, and the water pump didn't make it back home.

 

Maybe my failures were due to the clutch bushing failing and the fan being cocked killed the pump?

 

Hmmm. I wonder if when they seize it is because the bearings fail and the clutch is off-center?

 

Beat me to it. Same result, but different reason than the clutch seizing. Good to know though. Might be one small vote for electric fans.

 

When were fan clutches introduced?

If older engines had no fan clutches, they must have had a different sized pulley / drive ratio. Because at 3k RPM, the fan noise was deafening. I couldn't imagine it being configured like that for normal operation.

 

I've seen fan clutches on '60's cars, and I'm sure long before that.

My '79 302 truck had no clutch, just a spacer but the blades were a lot smaller and less pitch than my 460.

 

It depends on the configuration. My 1980 had the supercool option, and it had a multi-blade fan that was solid with no clutch, and it was a little noisy. Fuel mileage concerns, along with A/C becoming very common made the clutch fans more common. They also started overdriving the waterpump for better cooling when emissions came along and the engines ran hotter. This would also start calling for a clutch fan since like you said, it would make the fan turn at very high rpms all the time and use a lot of power.

 

Does this help? Looks like there might have been big differences in ones with and without clutches.

 

Is it a stock fan?

I replaced a 7-blade aftermarket fan & clutch on my truck with original parts, & it quietened it down a lot. Acceleration from standing improved too; no noticeable difference at road speeds when the air was already flowing through the radiator.

 

The stock 460 fan roars like an airplane when the fan clutch locks up, I guarantee it.

 

I believe so, here's a picture:



I'm betting the rather aggressive pitch on the blades are what makes it so loud. At 3K RPM, the two belts start slipping, so it won't spin any faster than that. Yes, airplane is a good word to describe the sound.