Lower Clutch Rod

[Alexander M.]

Hi,
After reading about the correct type of Lower Clutch Rod in the 1966 Judging Guide I looked at the one on my car and it does not look anything like it should. The one on my car is threaded and has a system that looks a lot like the upper clutch rod. So I ordered a correct replacement and when I went to install it, it was too long by 1/2 inch. There is not enough play between the clutch cross shaft and the clutch fork arm to get it to fit. Any ideas on what would cause this and are there any adjustments that can fix it?
Thanks,
Al

[Joe L.]

Re: Lower Clutch Rod

Hi,
After reading about the correct type of Lower Clutch Rod in the 1966 Judging Guide I looked at the one on my car and it does not look anything like it should. The one on my car is threaded and has a system that looks a lot like the upper clutch rod. So I ordered a correct replacement and when I went to install it, it was too long by 1/2 inch. There is not enough play between the clutch cross shaft and the clutch fork arm to get it to fit. Any ideas on what would cause this and are there any adjustments that can fix it?
Thanks,
Al

Al-----


Assuming that all the rest of the clutch actuating system parts are correct (not always a correct assumption), the clutch fork pushrod for your application should be as follows:

early small block----------------------GM #3844209 (10-9/16" OL)

later small block and all big block-------GM #3872960 (8-37/64" OL)

There were NO other fork pushrods used for 1966 Corvettes, so one of the above has to be the right one. If neither one will work for you, then something else is wrong with the system. Both rods are still available from GM.

[Alexander M.]

Re: Lower Clutch Rod

Hi Joe,
Thanks for the info. The car is a late June 66 small block. I ordered the rod from Paragon which did not specify the change in design. I see the two part numbers you mentioned in the AIM. The overall length of the one I purchased is 10 7/8". I don't know if everything else is correct, but based on the AIM and the Judging Guide they appear correct. I don't know about installing one that is 2" shorter. Would that pull on the clutch fork too much, or is there some adjustment I have not figured out yet?
Al

[Joe L.]

Re: Lower Clutch Rod

Hi Joe,
Thanks for the info. The car is a late June 66 small block. I ordered the rod from Paragon which did not specify the change in design. I see the two part numbers you mentioned in the AIM. The overall length of the one I purchased is 10 7/8". I don't know if everything else is correct, but based on the AIM and the Judging Guide they appear correct. I don't know about installing one that is 2" shorter. Would that pull on the clutch fork too much, or is there some adjustment I have not figured out yet?
Al

Al-----


As I mentioned, there were only 2 possible clutch fork pushrods used for 1966. You've tried the longer one and, apparently, you've found it too long. That means the correct rod MUST be the shorter one. The shorter one is the one that I would expect would be correct for your application considering I now know the build date of your car.

As I mentioned previously, all this depends upon the rest of your clutch and clutch actuating system being as-original. If other things have been changed it may well be that NO GM-available fork pushrod is going to work. That may very well be why you found the non-standard pushrod there in the first place.

[Alexander M.]

Re: Lower Clutch Rod

Hi Joe,
Do you know the distance from the centerline of the hole to the centerline of the 90 degree bend on the later pushrod? If I get the later pushrod, I will need to adjust the distance between the clutch fork and the bell crank attachment points. Can I adjust the upper threaded rod to effect the total distance of the lower rod? There appears to be about 3/4" of thread between the stop nut and the end of the upper rod.
Thanks,
Al

[Wayne M.]

Re: Lower Clutch Rod

...Do you know the distance from the centerline of the hole to the centerline of the 90 degree bend on the later pushrod? If I get the later pushrod, I will need to adjust the distance between the clutch fork and the bell crank attachment points. Can I adjust the upper threaded rod to effect the total distance of the lower rod? There appears to be about 3/4" of thread between the stop nut and the end of the upper rod. ...Al

Al -- Joe has given the dimension you ask in his first post (also available in Noland's Vol 2, pg 394; GM engineering dwg [dimension = 8.60"].

So installing the proper shorter rod is going to require the swivel on your clutch (pedal) rod to move 1.60 inch forward -- seems you don't have enough threads, per your description.

So either you have the wrong bellcrank (arm angles) or the wrong pedal push rod [or the wrong throw-out bearing]. The correct# 3888213 pedal rod measures 19_3/16" (threaded tip to center of pin on pedal arm), but difficult to measure with rod installed.

[Wayne M.]

Re: Lower Clutch Rod

Al -- here's a quick reference sketch I use to make sense of all the C2 clutch component variables.

[Alexander M.]

Re: Lower Clutch Rod

Hi Wayne,
Thanks for the info and drawing. I looked at the Noland Adams book as well. I measured the upper puch rod and it appears to be about 19.25+- since it goes throught he firewall. I measured the amount of thread left on the upper push rod and there is only about 15/16" left, so installing the shorter rod probably won't work. I have a better chance installing the longer rod by moving the bell crank attachment back about 3/4 inch. However, after reading the AIM about the adjustment procedure, I am not certain I can get it correctly adjusted. What are the ramifications if I don't get the 5lbs force on the fork and don't leave .400" gap (x) between the nut and swivel? I would rather not mess it up!
Al

[John H.]

Re: Lower Clutch Rod

I measured the upper puch rod and it appears to be about 19.25+- since it goes throught he firewall. I measured the amount of thread left on the upper push rod and there is only about 15/16" left, so installing the shorter rod probably won't work.

Al -

With the "long" (19-1/4") pedal pushrod, the correct lower (fork) pushrod for your application is the 3872960, which you have. Remember that as the clutch wears, the adjusting swivel (to compensate) will move toward the firewall, NOT toward the front of the car.

[Joe L.]

Re: Lower Clutch Rod

Al -

With the "long" (19-1/4") pedal pushrod, the correct lower (fork) pushrod for your application is the 3872960, which you have. Remember that as the clutch wears, the adjusting swivel (to compensate) will move toward the firewall, NOT toward the front of the car.

John and Alex-----


Yes, and also, if you cannot get this pushrod to work no matter what you do with the clutch activation linkage, then I suspect that someone has installed an improper clutch or, perhaps, an improper clutch release bearing. It seems like some folks, some parts stores, and even some Chevrolet dealerships parts countermen just have a "penchant" for supplying the "long" clutch release bearing for Corvette applications. However, the last Corvette that used the "long" bearing was early 1955.

I don't know if a Corvette clutch can be made to work regardless what a person did to "compensate" if a long clutch release bearing were installed; I've never had the mis-fortune of installing one (although once-upon-a-time I was sold one by a GM counterman for a Corvette application). However, I could see the possibility of someone installing one, finding out it didn't work, not wanting to "go back in" (especially after struggling to get the transmission seated on the bellhousing), and, thus, "jury rigging" an improvised fork pushrod to compensate and get the car "back on the road". Especially if the person doing it was a mechanic working in a shop on flat rate.

[Alexander M.]

Re: Lower Clutch Rod

Hi Guys,
Thanks for your help. Someone else suggested that there were two possible clutch forks and I probably have the shorter fork. The idea being that the longer fork will provide more freetravel and allow the installation of the shorter rod (which I don't have). The amount of free travel of the fork now is 1in. If I measure the amount of fork that sticks out of the housing when the rod is disconnected and the fork is pushed toward the back of the car, can we determine which fork is in place now?
Thanks,
Al

[Joe L.]

Re: Lower Clutch Rod

Hi Guys,
Thanks for your help. Someone else suggested that there were two possible clutch forks and I probably have the shorter fork. The idea being that the longer fork will provide more freetravel and allow the installation of the shorter rod (which I don't have). The amount of free travel of the fork now is 1in. If I measure the amount of fork that sticks out of the housing when the rod is disconnected and the fork is pushed toward the back of the car, can we determine which fork is in place now?
Thanks,
Al

Al----


As far as 64-82 Corvettes go, there were 2 different forks (64-65 and 66-82). However, these forks are very similar and, in any event, 100% functionally interchangeable. There was NO "shorter" fork used for any 64-81 Corvette.

Forks with the clevis pin attachment of the fork pushrod are Corvette forks. I don't know of any other Chevrolet application that used a clevis pin attachment fork. However, the 57-62 Corvette forks and the 64-81 Corvette forks both use the pin-style attachment. However, they are definitely NOT interchangeable. I suppose it's possible that someone installed a 57-62 style fork; they are somewhat similar to the 64-81 fork. I don't know if there's a length difference or some sort of off-set difference.

[Alexander M.]

Re: Lower Clutch Rod

Hi Joe,
I did some additional research today and I think you are quite correct. I was doing some measuring and I appear to have the 19+ in upper rod and the crank with 158 degree angle difference between the tabs. I can't get a good measurement on the exact length of the tabs to the centerline of the holes so I can't confirm the bell crank model definitely.

Again, I have purchased the longer lower clutch rod (10+incles). If I hook the front of the lower clutch rod in place on the tab, and I push the clutch fork as far as it will go toward the back of the car, I need another inch to put the clevis pin in. I have 1.5 inches of thread on the upper rod available for adjustment until I reach the end of the threaded part (beginning of the unthreaded rod section). Do you think I will have enough real room for the adjustment so I can get a comfortable clutch operation and no throwout bearing problems?
Thanks,
AL

[Joe L.]

Re: Lower Clutch Rod

Hi Joe,
I did some additional research today and I think you are quite correct. I was doing some measuring and I appear to have the 19+ in upper rod and the crank with 158 degree angle difference between the tabs. I can't get a good measurement on the exact length of the tabs to the centerline of the holes so I can't confirm the bell crank model definitely.

Again, I have purchased the longer lower clutch rod (10+incles). If I hook the front of the lower clutch rod in place on the tab, and I push the clutch fork as far as it will go toward the back of the car, I need another inch to put the clevis pin in. I have 1.5 inches of thread on the upper rod available for adjustment until I reach the end of the threaded part (beginning of the unthreaded rod section). Do you think I will have enough real room for the adjustment so I can get a comfortable clutch operation and no throwout bearing problems?
Thanks,
AL

Al-----


You MIGHT be able to get enough adjustment as you describe. However, I think it's a "band-aid" kind of solution. I think something's wrong internally. I think you need to get in there and sort it all out.

As far as the cross shaft goes, your very late 1966 small block application should use a cross shaft with 158 degrees angularity between the levers. That sounds like what you've got and that should work with the 8-37/64" fork pushrod.

[Rich P.]

Re: Lower Clutch Rod

I just thought I'd add that sometimes the wrong clutch fork ball/pivot studcan give fitts to the proper adjustment procedure. I don't have the dimentions off hand. If this was already said and I missed it sorry.

Rich