Well, with some great help from board members Keith Holowecky and Tom Hewitt, I think I figured out the difference between the 64-E66 and L66-81 clutch forks. As you may be aware, the L66-81 fork, GM #3887177, replaced the 64-E66 fork, GM #3844493, for SERVICE in February, 1967 , likely when the SERVICE inventory of the 3844493 was depleted. For many years I've wondered how these pieces actually differed. Now I think I know.
From my careful inspection of a known GM #3844493 loaned to me by Keith and from photos of another known 3844493 sent to me by Tom, I think I have it figured out. Here are the differences:
1) The GM #3844493 is stamped from material 0.020" thicker than the 3887177. The 3844493 material is 0.177" and the 3887177 is 0.157".
2) The two forks use slightly different , riveted-on retaining springs. I believe the GM #3844493 uses spring GM #3737456 whereas the GM #3887177 uses spring GM #3849698. There is little functional difference between these springs and configurational difference could not be discerned with the fork installed in the car.
3) There MAY be a difference in the configuration of the ball stud seat between the two forks. The fork sent to me by Keith appears to have extreme wear in the ball stud seat area. The one Tom sent pictures of also appears to suffer from extreme wear. So, there's no way to tell, for sure, what the original configuration of the seat was. It appears now that the original seat may have been somewhat larger, but, as I say, that could just be due to wear.
4) There are some other extremely minor differences in other dimensions between the 2 forks, but I believe these are either related to the difference in the material thickness between the two OR represent normal variances between stamped steel pieces like these. In any event, I would reard these differences to be totally inconsequential.
It so happens that the ball stud changed at exactly the same time as the fork during the 1966 model year. However, the only difference in the studs was the length. The ball was the exact same diameter---0.603" for both. Still, it's curious that the ball stud would change at the same time as the fork AND the ball stud seat configuration of the 2 forks now be the only difference that remains in question.
Save for the possible effect of the possible ball stud seat difference, from what I can measure or otherwise determine, there is no configurational difference between the 2 pieces that would affect the lever arms or mechanical advantage of either piece. So, I do not think that the change in these arms had anything to do with the other changes in the clutch release system that occurred during the 64-66 period. I've suspected that all along but now I feel confident that's the case.
From my careful inspection of a known GM #3844493 loaned to me by Keith and from photos of another known 3844493 sent to me by Tom, I think I have it figured out. Here are the differences:
1) The GM #3844493 is stamped from material 0.020" thicker than the 3887177. The 3844493 material is 0.177" and the 3887177 is 0.157".
2) The two forks use slightly different , riveted-on retaining springs. I believe the GM #3844493 uses spring GM #3737456 whereas the GM #3887177 uses spring GM #3849698. There is little functional difference between these springs and configurational difference could not be discerned with the fork installed in the car.
3) There MAY be a difference in the configuration of the ball stud seat between the two forks. The fork sent to me by Keith appears to have extreme wear in the ball stud seat area. The one Tom sent pictures of also appears to suffer from extreme wear. So, there's no way to tell, for sure, what the original configuration of the seat was. It appears now that the original seat may have been somewhat larger, but, as I say, that could just be due to wear.
4) There are some other extremely minor differences in other dimensions between the 2 forks, but I believe these are either related to the difference in the material thickness between the two OR represent normal variances between stamped steel pieces like these. In any event, I would reard these differences to be totally inconsequential.
It so happens that the ball stud changed at exactly the same time as the fork during the 1966 model year. However, the only difference in the studs was the length. The ball was the exact same diameter---0.603" for both. Still, it's curious that the ball stud would change at the same time as the fork AND the ball stud seat configuration of the 2 forks now be the only difference that remains in question.
Save for the possible effect of the possible ball stud seat difference, from what I can measure or otherwise determine, there is no configurational difference between the 2 pieces that would affect the lever arms or mechanical advantage of either piece. So, I do not think that the change in these arms had anything to do with the other changes in the clutch release system that occurred during the 64-66 period. I've suspected that all along but now I feel confident that's the case.
Comment