Need some help

[76sierraclassic]

I don't know if I can describe this very well on virtual paper or not, but I'll try. Maybe someone out there will be able to tell what I'm talking about.

I have a stock 76 GMC Sierra Classic with a 350 4bbl and stock 3-speed automatic transmission. There is a little over 138,000 original miles on it and I just had the A/C completely redone (new compressor, evaporator core, drier, orafice tube, converted to 134a). Don't know if any of this matters or not, but thought I'd throw it out here anyway.

I've had the truck for about 6 months now and have done a lot of "little" things to it (valve cover gaskets, shocks, tires/wheels, belts, spark plugs, fuel pump, fuel filter, A/C as mentioned above, etc, etc, etc). It had set up for a while before I got it from my aunt and needed (and still needs) a little tender loving care to get it back to where it should be.

Anyway, the last few times I've driven it, it seems that the engine noise is louder than normal. It almost sounds like someone is turning on a huge fan under the hood when I accelerate, especially if I make it kick down into passing gear. It does accelerate, but it just doesn't sound right. I almost can't hear the pipes on it, just the loud engine whirrrr drowning out everything.

Tonight I drove it out to my folks' house about 15 miles away, and it was doing this almost all the way out there. Then just a couple of miles from their house while doing about 60 mph, I heard a difference in the sound and the truck sped up about 4 mph on its own. It was at that point that I could kick it down to passing gear and everything sounded "normal" again; I could hear my pipes and the normal small block "rumble" that we all know and love.

The truck sat in my folks' driveway for about an hour and a half. I got in it to leave, and it was making the abnormal sound again when I took off. There's not much difference in the sound at idle, only when accelerating. About a mile and a half up the road, things went back to normal, and stayed that way until I got home.

Does anyone have any thoughts as to what this might be or what I should look at?

Thanks in advance...

Mike W.

[Cole's 87]

Have you checked to see if the fan clutch is working. I had one freeze up on me. The fan was makeing a hell of a racket since it was always ingauged.

Hope you find out what it is...

[76sierraclassic]

Checked the fan while I was at my dad's house. It seemed to be doing fine.

Thanks for the suggestion...

[85Silverado]

sounds like the clutch on the fan to me...that's the only thing that i think could make that whirring noise.

[76sierraclassic]

OK. Thanks. I'll check it again.

[76sierraclassic]

Thanks for the advice. I changed out the fan clutch this morning, and everything seems ok now.

Thanks again,
Mike W.