C3 H20 pump problems and a tow home

[Dan Pepper]

I recently purchased a '69 L46 w/79k original miles. It's a very clean, well documented California car that came with an aftermarket H20 pump(one of the very few non-original parts on the car). The pump shaft was wobbly when I bought the car, so I replaced it with another aftermarket jobby while I began the search for a date/PN correct unit. The replacement pump that came on the car had only 2k miles on it before it went T/U. Figured it was just a cheap, bad part. I have put about 1k miles on the car since the new pump.

This evening my 2.5 y/o son and I were out in the car with the tops off enjoying one of the final glorious sunny days in Seattle. I was entering a highway from an on-ramp and wound the car up to 5500 and felt a heavy vibration. I immediately pulled off to the shoulder and shut her down only to find what looks like a very shot wobbly H2O pump shaft. A call to tripple-A and a flatbed ride home later, I'm writing to ask what's going on?

Maybe I over-tightened the belts (PS, Alt, K19)? Maybe two crappy pumps in a row? Bad pullys? Bad balancer? With two pumps going in an identical fashion, something doesn't seem right. I'm afraid replacement H20pump #3 will end up the same way... Aside from using the best quality pump, what else could be the problem?

[Mike Cobine]

Re: C3 H20 pump problems and a tow home

I've always had good luck with aftermarket rebuilt pumps. However, they were GM castings that were rebuilt, not a no-name casting from overseas or wherever.

Two things make them go: too tight and no lubrication. Make sure the blets are not too tight as they only have to be tight enough not to slip. Make sure you have coolant in there, not just water. Water gives no lubrication.

However, lately, I have found the new style (late 809s/early 90s) alternator goes away quickly, too, in about a year or so. I think they are using cheap bearings. The same may be for the water pumps.

[Joe L.]

Re: C3 H20 pump problems and a tow home

Dan-----

There is a fundamental weakness in all 1955-70 Corvette small block waterpumps. That weakness is a 5/8" OD pump shaft and associated bearing. GM didn't switch to the 3/4" shaft pumps in 1971 because the 5/8" shaft size worked just as well.

In any event, a 5/8" shaft pump should last a lot longer than 1 or 2 thousand miles. About 50,000 is the norm. For the shaft to go bad, I expect that there's some sort of imbalance in the rotating assembly. This could be the fan blade assembly, itself, or, more likely, the fan clutch. Check the fan clutch for any looseness or wobble.

Also, make sure that the fan clutch is the correct unit with a 5/8" pilot hole. If the fan clutch is a "one-size-fits-all" aftermarket-type piece with a 3/4" pilot hole, then you MUST have a precision reducing bushing installed. The pilot is what precisely centers the whole assembly and it must be PERFECT. Check the waterpump pullies, too, to make sure that the pilot holes have not become enlarged for any reason. The pullies should fit rather tightly on the waterpump pilot shaft.

Most rebuilt waterpumps use an FAG or NGK bearing/shaft assembly. These are quality pieces that are as good as those used in new waterpumps. Often, these days, they are the same as those used in new waterpumps.

[Duke W.]

Re: C3 H20 pump problems and a tow home

The OE water pump and aftermarket replacements are built with a two row ball bearing. There is an interchangable SAE 5/8" bearing that has rollers in place of the front set of balls. This "ball/roller" bearing was used as OE on some engines that had lots of front end accessories, and it's an excellent upgrade to a pump with the ball/ball bearing

If you have the original casting (or any other serviceable casting), find a local rebuilder and have him rebuild it with a ball/roller bearing. As long as the casting is not cracked or improperly machined, the ball roller bearing should increase life by about 50 percent.

It's proved to be the solution to Cosworth Vega owners, whose 7000 rev engines eat the ball/ball bearing in no more than 40K miles.

Duke