All at once, my 75 (350) threw her fan belt * and * spewed copious coolant from a croaked water pump-to-block gasket. The question is: which failure was the cause and which was the effect? Replaced the gasket (actually, the pair) and the belt ... but --- as they say in electrics --- "replacing the fuse doesn't repair the short." I'd feel a lot better knowing I eliminated the cause, and not just the symptoms.

Any ideas, y'all???

Well, I have had belts thrown, and never wasted the gaskets, and have had bad waterpump gaskets that never caused the belt to jump. Have you driven it since replacing to gaskets and belt?
Any problems now?
Were the waterpump bolts all still tight when removing the pump?
Did you check the pumpshaft for wobble(bad bearing)?

Let's say the upper bolts coulda been tighter ... certainly were not at 30 ft lbs. No wobble that I could see, or noises I could hear; without belt, spun straight and free ... pump is an Edelbrock with about 1000 miles on it. Road test after repair was absolutely ordinary.

is that water pump aluminum???

Yep ... Edelbrock.

Noticed today that the (original) clutch fan bearing was toasted. Could the locked fan set up the mother of all wobbles at higher rpms? (TH400 into 3.70 on 27.4" rubber says about 3500 rpm to make about 75 mph ... which was my approximate speed when things came unglued.)

Couldn't say definately, but I would guess that is where your trouble began. If it wobbled enough to to damage the gaskets at the block, I would keep an eye on the waterpump in the near future to make sure there isn't any unseen damage.

Bill, my sense is that it did a high velocity shimmy (i.e. tried to play helicopter) that would have taken the pump "if" the upper bolts weren't undertorqued. Since they were, they took the shake ... and the gaskets spewed. Same shake likely sheared the belt, as ... at speed ... the pulley ridges would have stretched the belt as it momentarily crossed them, rather than riding between them. There's not an ounce of wobble in the pump shaft ... we'll see how it likes the lightweight approach of a flexfan. The parts are due here tomorrow.

Thanks, Doc!

have to be extra careful with gaskets with aluminum against steel as they have different heating levels and can cause gaskets to fail easier as the alunimum heats quicker then the steel. make sure you use the best gaskets you can get. Be sure the surfaces are flat and clean and torqued properly

"Roger"

Already done ... scraped, acetone'd,FelPro'd, Permatexed and torqued to 30 ft lbs. Road tested, no leaks.

I didn't do the original pump install; farmed it out two years ago when arm injury only let me write checks, and not spin wrenches. My bad; I shoulda verified the guy's work wih a torque wrench later. (He also managed to install 8 out of 16 roller rockers with the trunions upside down! And he's a for-pay "Vette Guy!" Live and learn.)