1971 fan clutch question

[Mike E.]

I have a Schwitzer fan clutch dated February 22, 1971, but where it mates with the water pump the center shaft opening is only 1/2" My understanding is that beginning in 1971, all water pumps had a 3/4" shaft. Is this sleeved to 1/2" and you just remove the sleeve, or??? Thanks!

[Bill B.]

Hi Mike,

It appears that a previous owner of that clutch installed a reducing bushing most likely to interface with an earlier vintage water pump. You should be able to pull out that bushing with a little persuading.

[Joe L.]

I have a Schwitzer fan clutch dated February 22, 1971, but where it mates with the water pump the center shaft opening is only 1/2" My understanding is that beginning in 1971, all water pumps had a 3/4" shaft. Is this sleeved to 1/2" and you just remove the sleeve, or??? Thanks!

Mike-----

It is POSSIBLE that some very early 1971's were built with 5/8" shaft waterpumps and associated fan clutches. I doubt it, but it's possible.

In any event, what is the casting number of the waterpump on the car and could you post some other pictures of the fan clutch?

[Ron G.]

Mike,

I would have to agree with Bill. However, like Joe mentioned it could be possible, especially if it is really early.

[Patrick H.]

I think that the proper question is what water pump is on the car, and what's the date on the pump?
Configuration?

[Mike E.]

It’s an after-market pump with a 1/2” shaft. Been on the car since before 1985. The clutch and fan are correct 1971 pieces, dated correctly for the car. (Late March car.)

[Joe L.]

It’s an after-market pump with a 1/2” shaft. Been on the car since before 1985. The clutch and fan are correct 1971 pieces, dated correctly for the car. (Late March car.)

Mike-----


Well, that makes determining what the original configuration was more difficult, if not impossible.

First of all, I presume that the car has a 1971 pulley set. The reason I say this is that you will note that the bushing installed in the fan clutch pilot orifice protrudes slightly from the flange. That must have been done to allow the engine to use the 1971 pulley set with a 1/2" shaft waterpump. The problem is that the 1/2" shaft waterpumps use a different flange spacing than the 3/4" shaft pumps. So, to use the 1971 fan clutch with a 1971 pulley system, the hub spacing on the 1/2" pump would have to have been adjusted. This is not that difficult. However, if the car had had its original waterpump and it was 1/2" shaft, then we would have known that the adapation was done at the factory.

As it is, with an aftermarket 1/2" waterpump, the adaptation could have been done in SERVICE. Why? Well, the Corvette 3/4" shaft, short leg waterpump are somewhat of a "rare bird" while the 1/2" shaft, short leg waterpumps are easily obtained. Need a quick waterpump replacement somewhere in the boondocks and an adaptation using a 1/2" shaft pump might be all that's quickly available.

Of course, it's theoretically possible that the adaptation was done at St. Louis. If the engine was delivered with a 1/2" shaft waterpump, then St. Louis would have had to adapt it for use with the 1971 fan clutch and pulley system. I actually HIGHLY doubt that something like that ever occurred, though, especially since this is not a very early build 1971.

By the way, I've assumed that this is a small block car although everything I've said above would essentially be true for a big block. The difference is that all big blocks use a 3/4" shaft waterpump. 1965-70 have a 1/2" pilot, though, while 1971-74 have a full 3/4" shaft pilot.

And, yes, you should be able to remove the bushing and install the original fan clutch on an original configuration waterpump, whether it's a big block or a small block.

[Joe L.]

A correction for the record-----

The posts above, including mine, refer to waterpumps with 9/16" shaft (my original post on this thread) or 1/2" (most of the posts including my later posts). However, in the back of my mind none of these shaft dimensions seemed correct to me. Well, none of them are. There was never a Chevrolet waterpump with a 1/2" shaft diameter. It's like this for Corvette waterpumps:

1955-70 small block----5/8" OD shaft, end-to-end

1971-82 small block-----3/4" OD shaft from outer end through the bearing; 5/8" OD shaft from the bearing end through the impeller

1965-70 big block-----5/8" OD pilot shaft to the bearing; 3/4" OD shaft through the bearing; 5/8"OD shaft from the bearing through the impeller

1971-74 big block-----3/4" OD shaft from outer end through the bearing; 5/8"OD shaft from rear of the bearing through the impeller