Supercharger rattle

Bought a 98 GTP last summer. Supercharger had a rattle in it that I suspected was a bad coupler. I've never had a bad coupler (or any s/c failure) before, but it seems to be a common failure that can cause a rattle.

Well, the rattle has gotten worse. The ZZP web site has a link to a video of a rattling supercharger where the rattle is due to a "bad rotor pack" - whatever that it. I have attached a short video exhibiting the rattle that my supercharger is making. Note also the noise when the engine is stopped. Can one tell from that sound if the problem is a coupler, a rotor, or something else?

I'm breaking new ground here. and trying to get my ducks in a row so when I get into it, I have some idea about how to identify the cause and fix it. I'll also break out the shop manual this week. But any advice from those with supercharger repair experience is greatly appreciated.

Check the noise with the SC'er belt removed, just to verify it's the supercharger? With belt removed, and engine off, rotate the SC'er pulley by hand....hear noise? feel any play in the bearing? If no play in the pulley, bearing is probably alright....if you grab pulley and quickly rotate CW and CCW, and you hear/feel noise, then it usually is the coupler.....made of plastic, and it becomes sloppy(holes elongate), creating the noise....

Be careful seperating the nose cone, don't want to damage the aluminum....also suck out all the sc'er oil before removal, and replace with the GM SC'er oil or equivalent(expensive)......DO NOT USE MOTOR OIL!!!!!!!!!!!

Thanks for the quick response.

Took belt off and the noise vanished. So it's gotta be the supercharger. There's some slop when I quickly rotate CW/CCW by hand; I feel the thud when the pins hit the other side of the coupler (I presume). I don't hear anything unusual when a turn the pulley in one direction continuously and I don't feel anything grinding or binding (like bad bearings). It feels pretty smooth with some drag; i.e., when I spin it, it won't keep going.

So sounds like a coupler to me.

If I put the belt back on and have someone run the engine at 1500-2000 rpm while in park, should the noise abate if it's the coupler?

Not sure if the noise will abate at that rpm, but it does sound like the coupler.....you will know for sure when you feel the slop in the old coupler compared to the new...

If I put the belt back on and have someone run the engine at 1500-2000 rpm while in park, should the noise abate if it's the coupler?

I had a bad coupler and that is what happened with mine. It was only at drive through windows where it was embarrassing. I actually changed my water pump first, thinking it was that.

The coupler is a common issue. It is not hard nor expensive to change. You can do it in a couple of hours. Just remember to wear gloves because the supercharger oil is super smelly. Make sure to have a bottle of oil to replace the old oil. ZZP sells both the coupler and the supercharger oil at a reasonable price.

Ordered the coupler from ZZP yesterday. Changed the s/c oil about less than 1,000 miles ago, so I hope to recover that.

Now I have a no-start on the other Grand Prix. It's stuck in the parking lot at work. Suspecting fuel sender...wish me luck.

Fuel sender will not cause a no start....

That one was the fuel pump - replaced and on the road again. Shop manual calls it a sender. So my terminology may have been off. What's the difference between pump and sender?

Pulled off the supercharger snout today. Although there is a some play in the coupler, it's hard for me to believe it caused the loud rattle I was hearing. The s/c actually came loose at two seams: the first b/w the snout and the next section with the rotors, and the second b/w the rotors and the s/c housing. When I turned the gears, the rotors made a noise similar to the rattle I had been hearing...just at a much longer interval as I was turning it by hand.

Inspection of the rotors shows spots that suggest the rotors are banging into each other. See the attached photos.

What would cause this, and how I can I fix it?

As always, any guidance is greatly appreciated.

For some reason your pics aren't showing. I've never done an sc on a GTP. But I've done alot of Detroits. If the rotors are touching "she's gotta go before she'll blow"!

For some reason your pics aren't showing.

Replaced .bmp with .jpg images. I see the thumbnails now...hope everyone else can, too.