corvette specific/water pump question

[jon79flavette]

does a 79 350 sbc have to use a short water pump?? Why does it when most short water pumps are pre 1969. In other words, can I change it out with a long water pump without any prblems, clearences etc.

 

[JohnZ]

Nope - the "short" water pump was used on SB Corvettes through 1970, and changed to the "long" water pump for 1971 (two years after the passenger cars changed). The correct "long" water pump for a '79 is casting #330813. If your '79 has a "short" water pump now, someone has put the wrong pump on it, and must also have changed some of the pulleys and accessory mountings in order to make the belt grooves line up.

 

[mvftw]

I believe the '79 350 uses a 'Short' pump.

 

[Crimson Thunder]

There are two different short water pumps.The 70 and earlier pumps have a 5/8 shaft while the 71 later have a 3/4 shaft.The 3/4 pump is just a bit longer.The Edelbrock catalouge has the exact dimensions.

 

[JohnZ]

I believe the '79 350 uses a 'Short' pump.

Nope, Corvettes went to the "long" water pump in 1971; "long" and "short" refer to the length of the standoff legs from the block, not the shaft (although the shaft diameters did change). Any '79 with a "short" pump has the wrong pump on it, and "doctored" pulleys to align the belt grooves.

 

[Tom73]

This is from the Edelbrock web page:

Short-Style Pump for most 1955-72 cars and trucks (5/8" pilot shaft)
Fits all 1955-68 small-block Chevy passenger cars, 1969-70 350 c.i.d. Corvettes and 1955-72 light duty trucks. Has 3/4" ball/ball bearing. Dimension from block surface to hub: 5-5/8".

Long-Style Pump for 1969-87 V8, 90° V6 and 1973-86 truck (5/8" pilot shaft)
Fits all 1969-87 small-block Chevy or 90° V6 passenger cars and 1973-86 light duty trucks. Does not fit Corvettes or late-model vehicles with serpentine accessory drive belts. Has heavy-duty 3/4" ball/roller bearing. Dimension from block surface to hub: 6-15/16".

Short-Style Pump for 1971-82 Corvettes (3/4" pilot shaft)
Fits all 1971-82 small-block Corvettes. Comes with heavy-duty 3/4" ball/roller bearing. Dimension from block surface to hub: 5-13/16".

And this is from the Stewart Water Pump web site:

1955-68 Passenger Cars, 1955-72 Light Trucks, 1955-1970 Corvette. 5.625" Length. 3/4" bearing, 5/8" shaft.

1955-68 Passenger Cars, 1955-72 Light Trucks, 1955-70 Corvette. 5.625" Length. 3/4" bearing, 3/4" shaft.

1971-82 Corvette. 5.795" Length. 3/4" bearing, 3/4" shaft.


tom...

 

[JohnZ]

From the Chevrolet P&A30B Corvette Parts Manual:

55-70 (exc. 396,427,454)....3998206 or 8207 ("short" pump)

'71-'72 350......3998205 ("long" pump)
'73-up 350.......6258551 ("long" pump)

 

[mvftw]

JohnZ, this is confusing??? I have been looking for a new water pump for my '78, and All the research says the C3's came with a 'Short' pump...nowhere have I seen long for a C3. Look here at Jim Pace Parts... http://www.paceparts.com/product.asp?0=243&1=254&3=960

 

[jon79flavette]

Yup, now I am confused. John, you always seem to really know your stuff, but everything I look at also tells me a 79 and other late c-3's would use the short pump. what would be the drawback to using a long pump, assuming an entire new pully package was used based on a long pump configeration??

 

[Jack]

semantics?

No doubt in my mind John & others here have more experience than I ... experience I value. But I think the short vs long issue might possibly be confounded by semantics. In my limited experience, all small block C3's have what is commonly referred to as a "short" pump. AFAIK, All of those short pumps share one common attribute ... they all have short legs of same length. On the other hand, those short pumps' other attributes do vary ... pilot shaft diameter and position of the hub on the shaft. The hub's position is an important determinant of how long or short a pump is ... but pales in comparison to the leg length's critical effect. Perhaps some references show "long" and are referring to long legs ... while other references may show "long" and are referring to "long" hub-to-block surface ... perhaps semantics?

BTW, my 71 sb came with what is commonly referred to as a short pump. It has short legs ... but the hub is positioned a bit further (longer) away from the block than earlier pumps ... and it has a 3/4" pilot shaft.
JACK:gap

 

[Paul Borowski]

I myself believed '68-'82 Corvettes had the "short leg" pump. I know at least all four of my cars in my strorage(1980 included)has the short leg pump. I don't believe I've ever judged a C3 with a long leg pump for that matter & I've been judging '73-'82 Corvettes since '98.

 

[JohnZ]

After further researching this issue, I think there's a semantics problem referring to "short" and "long" water pumps when applied to Corvettes vs. passenger cars. I don't have the assembly drawings (that show the shaft and hub), just the casting drawings; going back through these again, the traditional "short" water pump had about 1.2" from the back of the pump (the surface where the rear cover attaches) to the surfaces where the "legs" mate to the block. When the passenger cars switched to the "long" pump, the length of the legs on those pumps increased substantially, and they had about 2.6" clearance in that same dimension.

When the Corvette pump changed in 1971, the actual length of the "legs" didn't change, but the casting configuration did, including the nose (and probably the shaft/hub).

The new casting number was 3991399 for 1971, which then changed during March or April, 1972, to 330813, which remained as the Corvette pump casting through 1982.

The name "long" pump is probably a misnomer for the '71-up Corvette water pump; although the shaft and hub dimension from the face of the block increased, placing the hub further forward, the "legs" of the casting didn't get any longer, and the dimension from the back of the pump to the block remained the same.

Whew!

 

[Tom73]

It still confuses me when I look at the Eldobrock numbers I posted above.

They show three pumps:

A short pump that fits 1969-70 350 c.i.d. Corvettes Dimension from block surface to hub: 5-5/8".
Then another short pump for 1971-82 Corvettes (3/4" pilot shaft)
Fits all 1971-82 small-block Corvettes. Dimension from block surface to hub: 5-13/16".

Only 3/16" difference there.

Then a long pump that fits all 1969-87 small-block Chevy or 90° V6 passenger cars and 1973-86 light duty trucks. [/b]Dimension from block surface to hub: 6-15/16".

Now to me the 6 15/16" pump would be the long pump and it does NOT fig corvettes. But the other two with only 3/16" difference is confusing.

I would think that the mesurement from the block surface to the hub would be the key to get the pulleys aligned correctly.

tom...

 

[Jack]

does a 79 350 sbc have to use a short water pump?? Why does it when most short water pumps are pre 1969. In other words, can I change it out with a long water pump without any prblems, clearences etc.

You should use what is commonly referred to as a "short" pump ... it has short legs. A "long" pump with long legs will not work without changing bracketry/pulleys.

I would think that the mesurement from the block surface to the hub would be the key to get the pulleys aligned correctly.
tom...

Bingo! ... we have a winner! And those minor differences (3/16" or less) can often be corrected with a hub-to-pulley shim kit ... fits between the wp pulley & hub ... weiand, moroso & MrG make em ... $5-$10/kit. Conversely, on most pumps the hub can be pressed inward an 1/8" or so (you must remove coverplate and press directly on rear of shaft to do so).
JACK:gap