Long and short of it
You can put a long shaft in place of a short shaft and visa versa but you have to change the pulleys on all of the other componets to match. be sure to check your alingment with a straight edge and if you can do this as a mock up before you install the motor it would be even better. Please read further about some of my other chevy water pump experiences.
Ok guys seem like just about every time I send to an existing post I stir up trouble I don’t mean to but it happens. Let me say that I am posting this not to brag or anything but I am worried about safety! I have seen at least four different size shafts two different lengths and two different diameters on older chevy small block water pumps. So rather then get in to an argument here about what years which ones were made let me tell you my experience. In about 1979 or 1980 I put a 350 crate motor in a chevy truck that I was building for my self. It originally had a six cylinder in it. I had a donor car that I took all of the pulleys and engine accessories off of and it was an older chevy station wagon with a chevy small block and it had been setting for a long time. Because I was installing a new crate motor in the pickup I wanted a new water pump. I can’t remember if the one out of the wagon was a long or short shaft. But even at that time I was aware that there was a long and short shaft. What I did not know about is that there are also at least two different diameters. And that is the statement that will probably stir up trouble. I installed everything including a brand new radiator, shrould, belts, hoses, fan clutch, water pump the whole nine yards and even bead blasted the fan and pulleys and brackets from the wagon and painted them nice and shinny black imron. Well everything looked good and after oh about twenty minutes of run in time setting the timing, idle jets and fiddling with everything I revved it up one good time and BAM all hell busted loose. The water pump shaft snapped and the fan, clutch and pulley went into the new radiator and shroud. And it did this with me and my arm up over the left front fender. I was lucky and everything went into the radiator and none of it came my way. But it sure as hell taught me a lesson. Don’t get in a hurry to hear that motor run! Check everything and check it good!
The story has a good ending in that “Big A” auto parts paid for all of it with everything new. It took the rep about a week to get out to the shop and we took everything apart and that is when we found that the center holes for the pulley, the fan and the clutch were bigger then the stub shaft that protruded out of the water pump shaft at the flange. I had turned in the water pump off the wagon for the core when I bought everything and told the parts guy I was not sure of the year, some where in the early seventies late sixties and I said lets just match one up. I still had the donor car in the field across from the shop and the rep looked at it also. Well the rep told me that there was a short and long shaft which I already knew and he also said there was a small diameter and large diameter shaft but I was not aware of that. The reason the water pump shaft snapped is because the part of the shaft that protrudes out of the flange is what the pulley, the fan and the clutch are centered on and the bolts just hold it all tight. If I remember correctly there is only about a 65 thousands difference between the two but this is enough to throw the balance off and that is what caused the failure. Later on as I used “Big A” water pumps I started seeing a warning tag attached to the pump that read “Warning check pump shaft length and pump shaft diameter to the pump that is being replaced! Catastrophic failure and serious injury can occur if the two pumps shafts are not the same!”
I don’t know if I am prone to bad luck or if during that time I was turning out a lot of work and I just saw more problems then the next guy. But I also encountered a problem with the reverse rotation pumps that were used on the early serpentine drives. To put it blunt don’t put a reverse rotation pump on a “V-belt Drive” and don’t put a standard rotation pump on a “Serpentine Drive” you will cook your engine! In the serpentine configuration the pump turns opposite from the “V-belt drive”.
In about 1990 I did an engine and transmission swap for a customer that had an early eighties late seventies 1-ton chevy truck with a GM/olds diesel in it. He had bought a donor car that had a 400 small block and turbo 400 in it and it did not have very many miles on it. It was an easy swap and everything went good. I insisted on a new water pump, thermostat and I wanted to rod the radiator as well. He went along with the thermostat and the water pump because it had signs of seepage from the weep hole but he passed on the radiator. When I was finished with the job I test drove it and was pleased with how good it ran. He picked it up and drove it home about twenty miles away and had no problems. The next day he put it to work in his lawn and clearing business and that is when it gave trouble. As soon as he loaded it with limbs and debris it ran hot and blew the bottom radiator hose off of it. He towed it to the shop and I checked everything and came to the conclusion that we needed to rod the radiator. I did that and put another thermostat in it, drove it all around and it seemed fine. Well the next day and under a load it did the same thing. He towed it back to the shop; I put it back together and checked everything and all was good. I have seen cases where the impeller has turned a loose from the shaft so something told me to take the water pump off and check it. When I took the back cover off the pump the impeller was intact but something didn’t look right. He had used the one off of the donor car for the core but I did have a few old ones lying around. I took the backs off of about three or so other ones and that is when I found the different impellers. Chevy makes up for the reverse rotation by using an impeller that is angled in the opposite direction but the housings are the same! The housing being the same is where the problems come from and chevy should have cast something different in them to keep this from happening. I put the correct pump on it and the guy put the truck to work and never had anymore trouble out of it. We were lucky that it did not crack the heads or blow the gaskets. We attributed this to the fact that he wasn’t completely sure of the truck and wanted to drive it himself for a few days before he turned it over to the crew. We were sure that if he had let one of his drivers in it then we would have been putting another engine it as well. It was one of the super chains that he had bought the pump from and they would not even warranty the pump because I had taken the back cover off of it. I ate my labor because I’m just that way but I learned a good lesson.
When it comes to Chevy’s and their water pumps turn the core in after you have done the job so that you can check everything! Check pulley alignment with a straight edge, check shaft length and diameter, check the pulley, the spacer (if used) and the fan and clutch for a snug fit on the shaft. Remember the bolts do not center it they just hold everything tight. And if you are not sure of the rotation check that by taking the back cover off as well. A gasket is a lot cheaper then a cooked motor. If you don’t have a donor car and you are piecing the pulleys together be real careful and get as many people to look at it as you can. Above all stay away from cheap flex fans (that’s another story) and be safe because you can be hurt or even killed!
Last edited by Chris Kemp; 01-03-2009 at 11:02 AM.