Question on 66 BB clutch linkage

[Glen C.]

I read alot of the threads on clutch problems, but didn't seem to get an answer for this. Is this a problem? I'm not sure.
I was trying to get rid of some of the free play (slop) in my clutch linkage. Most of the slop was in the rod (3872960 per AIM) between the clutch fork and the clutch lever assembly (Z bar). The rear of the rod that is pinned to the clutch fork has what seems to be an unnecessarly large hole compared to the diameter of the pin that attaches the two items. The pin is 5/16" & the hole in the rod is 7/16". The hole is not elongated, as in being worn. It is perfectly round, as if it was drilled. Question, is there some design reason for this hole to be larger than the pin? I can't think of any. I want to find out if this rod is "GM normal" before I order a new rod. Maybe it has been drilled out before I got the car. In addition, when the clutch pedal is pressed, before the clutch fork starts to move the outer end of the fork will jump slightly downwards before it starts to move toward the rear. Problem or normal? Thanks in advance. Glen.

[Joe L.]

Re: Question on 66 BB clutch linkage

I read alot of the threads on clutch problems, but didn't seem to get an answer for this. Is this a problem? I'm not sure.
I was trying to get rid of some of the free play (slop) in my clutch linkage. Most of the slop was in the rod (3872960 per AIM) between the clutch fork and the clutch lever assembly (Z bar). The rear of the rod that is pinned to the clutch fork has what seems to be an unnecessarly large hole compared to the diameter of the pin that attaches the two items. The pin is 5/16" & the hole in the rod is 7/16". The hole is not elongated, as in being worn. It is perfectly round, as if it was drilled. Question, is there some design reason for this hole to be larger than the pin? I can't think of any. I want to find out if this rod is "GM normal" before I order a new rod. Maybe it has been drilled out before I got the car. In addition, when the clutch pedal is pressed, before the clutch fork starts to move the outer end of the fork will jump slightly downwards before it starts to move toward the rear. Problem or normal? Thanks in advance. Glen.

Glen-----


I don't recall the exact size, but the hole in the clutch fork push rod is significantly larger than the size of the pin. So, it sounds like the situation you have is normal.

[Glen C.]

Re: Question on 66 BB clutch linkage

Glen-----


I don't recall the exact size, but the hole in the clutch fork push rod is significantly larger than the size of the pin. So, it sounds like the situation you have is normal.

Joe, Thanks for the feedback. Since I started this thread, I went back and inserted a brass sleeve in the large hole in the rod, taking the slop around the pin to almost zero. I also noticed that the slot in the yoke that the flat part of the rod rides in had widened to 1 1/2 times the width of the rod. I was able to squeeze the end of the yoke and reduce the slot down to a width that just accomodates the flat portion of the rod. A pair of vice grips worked well to reduce the gap. It now seems that the jumping downward of the yoke that I mentioned earlier has stopped. If I notice any side effects from the addition of the brass sleeve, I can always take it out!

[Joe L.]

Re: Question on 66 BB clutch linkage

Joe, Thanks for the feedback. Since I started this thread, I went back and inserted a brass sleeve in the large hole in the rod, taking the slop around the pin to almost zero. I also noticed that the slot in the yoke that the flat part of the rod rides in had widened to 1 1/2 times the width of the rod. I was able to squeeze the end of the yoke and reduce the slot down to a width that just accomodates the flat portion of the rod. A pair of vice grips worked well to reduce the gap. It now seems that the jumping downward of the yoke that I mentioned earlier has stopped. If I notice any side effects from the addition of the brass sleeve, I can always take it out!

Glen-----


My suspicion is that the designers of this system had a reason for the size of the oversize hole in the rod compared to the size of the pin. They could easily have specified that the hole in the rod be very close in size to the pin, but they did not.

Also, the Corvette clutch fork push rod and clutch fork were Corvette-only pieces. They were not used for other applications.

[Wayne M.]

Re: Question on 66 BB clutch linkage

Glen - the diameter of the clutch pushrod hole on the rod at the fork end is 0.42"-0.44", per GM drawings in Noland's Vol 2. Page 207 for the long rod ('63-65 small block) and on page 394 for the 396 and '66-up . There are a lot of wear points in the clutch linkage -- another spot to check is the forward end of the same rod, where it goes into the lever, intermediate, clutch rod pedal (aka Z-bar). The two lower push rod springs should help to keep the slop at these two locations to a minimum.

[Glen C.]

Re: Question on 66 BB clutch linkage

Joe & Wayne, Thanks for more input. As you mentioned the front of the rod was worn but I repaired it to minimize the slop. what had the most impact was squeezing the gap on the yoke. Probably overthinking this, but, I'm wondering if the larger hole in the rod would cause a very slight delay in the de-actuation of the clutch. Maybe an asset at high RPM. Would this have any affect on overcentering?