71 BB Fan Clutch Restoration/Cleaning

[Joe L.]

Re: 71 BB Fan Clutch Restoration/Cleaning

On the issue of the color code marks, some research needs to be done before assuming these are correct for your '71 car...

If I remember correctly, this was a running change item and you need to lay the '71 AIM next to a copy of the '72 AIM book. Here's a copy of the '71 AIM where the fan clutch for the BB is called out (3991426). Note it changed PN at the beginning of the model year from the 3937771 clutch used in 1970 (different hub geometries for the different model years in addition to mating hub changes on the water pump).

View C shows the pump came with a cardboard seal that was removed and discarded prior to the fan and fan clutch being installed on the water pump. You can see there are NO notes on the drawing regarding any color codes!

Now, still going from memory, if you compare this to the equivalent page from the 1972 AIM book, all of a sudden there ARE call outs for aligning the fan clutch to the water pump during assy based on each having distinct color codes (one yellow, the other green?) to achieve the best overall alignment/balance.

I also remember the '72 AIM drawing documenting the AIM date associated with these parts having color coded alignment marks on them. This makes me believe this was minor a running change associated with drawing release for the upcoming 1972 MY release of Corvette.

So, despite what you've read/heard about the fan clutch having a daub of color (it would have been rather sloppily applied to the outer edge of the drive hub), methinks this is an early vs. late car running change issue...

Jack-----


Note the date of the change for the fan clutch. I don't think the 3937771 ever got into PRODUCTION for the 1971 model year.

I don't think that the 3916139 was ever used for 1971 small blocks, either, although the AIM shows that number and no supercessive number, at all. The small block also shows the GM #3888366 fan blade assembly being used but I don't think the 3888366 fan blade was even still being manufactured at the outset of the 1971 model year.