Fan Clutch Reinstall ?

[Paul Gordon]

All,

I seem to be a little confused about the studs that attach the fan clutch and pulley to the water pump. The bolt has a corse thread on one side and a fine thread on the other. The fine threaded side is shorter then the corse thread side and as a side note, the attaching nuts are of course thread . Now, my problem is. It seems that both the corse thread and the fine this go into the water pump fine, but the nuts only seem to run down on the fine side. Now if I try to install the corse side into the water pump and the fine on the outside, the bolts are too long and wedge to the water pump. If I swap ends and run the fine thread down and put the nut on the corse side. The nut will not start down, but keep turning the stud. Even after the stopping point on the stud reaches the water pump, it will keep going and start to thread the blank area. I though maybe because they are older studs, I when and bought new ones and it's the same story. I guess I should of looked closer at the studs before I removed them... Can someone that has been down this road before shed some light for me ?

Thanks Paul Gordon NCRS Member # 31173 '71 350/270 Warbonnet Coupe

[Paul Gordon]

Re: Fan Clutch Reinstall ?

The answer was fine end into the water pump. Local hardware store had the nuts needed to fit the corse side.

Thanks Anyway Paul

[Joe L.]

Re: Fan Clutch Reinstall ?

Paul-----

I don't know how, but I missed your question earlier. It looks like you now have it worked out, though. Just a few comments for future reference: with most GM waterpumps, the water pump stud/bolt holes are 5/16-24 NF thread. So, the fine thread side of the studs always threads to the water pump hub. Studs supplied by GM for this application, GM #3964274, had 5/16-24 on one end and 5/16-18 on the other. On these studs, though, the fine thread end is longer than the coarse thread end. That's really the OPPOSITE of the way that it needs to be, since you don't want an overly long stud hub end protruding excessively through the hub and contacting the the water pump snout. Usually, however, the GM studs will not contact the water pump snout.

In any event, more appropriately configured studs can often be found in auto parts stores. Studs with 1/4" length of the fine thread end are perfect. The other end of the stud can be either fine or coarse thread-----just use the nuts with appropriate thread pitch.

By the way, the water pump hub studs were used from 1969 through 1982 on Corvettes. Earlier cars usually used bolts rather than studs.