All midyears originally had the 3729000 1-1/2" ball stud installed.
-
-
Re: Clutch ball stud - which length to use?
The August 1966 printing of the parts book shows that the 3729000 ball was used from 55 to 65. The 66 (all engines) is listed as a 3887159.
For the start of production 1966, several changes were made to the clutch linkage that have been confusing people for the last 40 years and creating a nearly unadjustable clutch. The ball/stud was just one of the changes.
Along with the new stud, a new rod from the release fork to the cross shaft (lever assy) was included. The cross shaft was also changed and so was the throwout bearing.
Everything went somewhat smoothly for a few years until the 3887159 ball/stud was discontinued for the 66 and later cars and replaced with the 3729000.
All of these new (for 66) items were designed to be used together as a package but when the ball stud changed length, it would have required the 64-65 rod from TO arm to cross shaft.
Unfortunately, the parts book doesn't give dimensions on the original 64-65 rod so it's difficult to know if you have the original or the different length replacement.
Also, the original throwout brng is no longer available from GM or most aftermarket sources. However, I have the original number from the 66 book and I've tracked down the original source. They still make the correct length brng. Can't remember who it was but I'll dig it out and post it later.
I'll also dig out all the correct original part numbers for the rod and lever assy and post. Pretty confusing stuff and no one seems to have a clue about the changes that occured, especially GM. -
Re: Clutch ball stud - which length to use?
Michael------
It's true that there were a lot of changes made regarding the clutch actuation system componets. It's also true that having an incorrect mix of parts can cause clutch adjustment problems. However, I don't think that the use of the 1-1/2" 3729000 stud as a SERVICE replacement for the 1-3/8" 3887159 will cause any problem. Here's several reasons why:
1) the 3729000 is a fully approved GM replacement part for the 3887159. If GM engineering did not feel that it would work in a satisfactory (or, possibly, an improved) manner, then I doubt they would have specified it as a SERVICE replacement for the 3887159. In case they had wanted to otherwise discontinue the 3887159, they would have simply done so without supercession. They do that sort of thing all the time;
2) the 3887159 was not just used for 1966. It was used beginning with 1966 and ending in early 1975. After that time, the 3729000 was used in PRODUCTION for all Corvettes with 4 speed. No other part of the clutch actuation system changed at that time. Plus, the 3887159 stud was not discontinued at that time either. It was available in SERVICE for many years thereafter until it was finally replaced by the 3729000. I've got to believe that GM changed the PRODUCTION stud back to the 3729000 in early 1975 for a very good reason. If so, certainly that "very good reason" would apply to 68-74 Corvettes since they use an IDENTICAL clutch acuation system to the 75-81. 1967 uses a clutch actuation system which is virtually the same as 68-75, except for the pedal and pedal push rod. All this implies that the 3729000 should work just fine for 1966, too, but that would be the only year that there would exist some question about it;
3) I've used the 3729000 in my 1969 to replace the original 3887159. I believe that it SLIGHTLY improved the clutch adjustment problems I had with the car since it was new.
4) If one wishes to use a 1-3/8" ball stud, it's quite simple: just purchase an aftermarket adjustable ball stud, set the length to 1-3/8", and install it. Presto, original ball stud length! I don't think that it will help anyone, but if one wants to try it......
On the clutch relaese bearing issue, the original bearings used for 1964-1980 Corvettes were the 1-7/32". Late 1955 through 1963 used the 1-1/4" bearing as did 1981. The fact that the 1-1/4" bearing was used for 1981 PRODUCTION strongly implies that it should work equally well for 1967-80 Corvettes in SERVICE. As I say, the 1981 clutch actuation system was absolutely identical to 1968-80 and virtually the same as 1967.
There were several successive part numbers for this bearing, the last of which was discontinued more than 20 years ago. As far as I know, all of these bearings were manufactured by New Departure Hyatt Division of General Motors. All the NOS bearings that I have are stamped "NDH". Certainly, New Departure Hyatt (now part of DELPHI) no longer manufactures the 1-7/32" bearing. As far as I know, they don't even manufacture the current version of the 1-1/4" bearing which GM catalogues as the SERVICE replacement for all late 1955 through 1981 Corvettes with manual transmissions.
There were several successive part numbers for this bearing. As far as I know, all of these bearings were manufactured by the New Departure Hyatt Divsion of General Motors.
I have used the 1-1/4" bearing in my 1969 and I had no more or less problems with clutch adjustment after its installation. I have not used the current GM replacement bearing yet, but I intend to soon use it. I think that it's a better design and will represent a functional improvement over the old design.
The clutch fork pushrods are as follows:
64-very early 66 (except Mark IV)-----GM #3844209----10-9/16" OL
65-66 Mark IV + later 1966-81 ALL-----GM #3872960----8-37/64" OL
However, in addition to the above change, there were also several slightly different clutch cross shafts used during the period:
1963-very early 1966 except Mark IV------GM #3832857
1965-66 Mark IV--------------------------GM #3872962
later 1966 small block + all 1967-81-----GM #3888279
It's possible that after very early 1966, Mark IV installations also used the 3888279. I've not been able to confirm that, though.
The only difference between all of the above cross shafts is the angular relationship between the levers. The differences are very slight and virtually indiscernable unless one compares the parts side-by-side. No part numbers are usually stamnped on these pieces to aid identification.In Appreciation of John HinckleyComment
-
Re: Clutch ball stud - which length to use?
Actually, I was going to address the problem of installing/mixing 66 and later components in a 64-65, and I will as soon as I have time to look up all of the ingredients and numbers. (hurricane prep, again) If all of the currently/past recommended GM replacements were interchangeabe, people wouldn't be having all the problems that they do with clutch adjustment, and it's not just the 1/8" that you mention. How many have you seen with the adjustment all the way out to the end of the threaded rod?
All of the new parts released for 66 were designed to be used together and if mixed with 64-66 components, this adjustment problems previously described is usually the result.Comment
-
Re: Clutch ball stud - which length to use?
Michael-----
Yes, as I mentioned, installing an incorrect mix of clutch actuation components in any year Corvette will cause adjustment problems. However, this means installing components that were never either originally used or a later-approved SERVICE replacement part. The 1-1/4" release bearing was never originally used on 64-80 Corvettes and the 1-1/2" fork stud was never originally used on L66-E75 Corvettes. I believe that those particular SERVICE components can be used on any 63-81 without causing problems. As I say, I've used them with no problems created, at least, no problems exceeding those I had from the beginning and prior to installing them.
Using the SERVICE ball stud (for L66-E75) and release bearing (for 64-80) is entirely different than "mixing in" other clutch actuation components that were never used or approved for use on a particular year model Corvette. For 63-66 models, in particular, the problem is much greater because there was a much greater range of components that were originally used. Getting an improper mix of these components on a particular year model car WILL CAUSE clutch actuation problems. It's quite common, actually.
In addition to the parts that I described in my previous post, here's a run-down of the rest:
clutch pedal pushrod:
63-65 (except Mark IV)-----GM #3819154----18.0" OL. This part was discontinued and replaced in November, 1966 by the L-66 to 67 pushrod GM #3888213. That pushrod is 19-3/16" OL. GM says that it's an approved SERVICE replacement for the 3819154;
1965 Mark IV------GM #3872961---19-5/16" OL. This part was discontinued WITHOUT SUPERCESSION in October, 1971. So, since then, there has been no GM-approved replacement for the 1965 Corvette L-78 pedal pushrod application;
L66 to 1967-------GM #3888213. This rod is 19-5/16" OL. It remains available from GM;
1968-81-------GM #3921654. This rod is 16-1/2" OL. It remains available from GM, too.
clutch pedals:
63-66-----GM #3832855 (discontinued without supercession May, 1986)
1967 only----GM #3904880 (discontinued without supercession March, 1976)
1968-L69----GM #3921645 (discontinued July, 1969 and replaced by GM #3960621)
L69-81--GM #3960621 (discontinued January, 1984 and replaced by GM #14020844)
GM #14020844 was discontinued in January, 1996.
The short of it is that for any given year one must use ALL of the original components, exact reproductions of the originals, or approved GM SERVICE replacement parts. Otherwise, one is virtually assured of having clutch actuation problems.
Other things that can cause clutch actuation problems (since the Corvette system is so "delicately balanced" from the get-go):
1) a flywheel which has been surfaced which may cause a very slight change in overall clutch actuation system geometry;
2) a non-GM clutch which may differ in some minute dimensional way from the original GM clutch (only ONE of which remains PARTIALLY available from GM in SERVICE).In Appreciation of John HinckleyComment
-
Re: Clutch ball stud - which length to use?
The clutch fork pivot ratio is about 2.5:1; changing from the 1-3/8" stud to the (3729000) 1-1/2" stud (1/8" forward movement of the pivot) moves the pushrod end of the clutch fork forward about 5/16", which moves the pedal pushrod clevis on the upper arm of the cross shaft rearward on the rod about 3/8" (cross shaft lever ratio is 1.2:1), gaining some adjustment (assuming the height of the clutch fingers and the throwout bearing length remain constant).Comment
-
Re: Clutch ball stud - which length to use?
There is another part that affects the mix, especially when 64-65, and 66 and later are involved. Along with all of the other changes, the release lever (fork) was changed. The original 64 to early 66 was something like 3844xxx and the late 66 was a 388xxxx. The early style that was designed to be used with all of the other early components was discontinued and replaced by the 66 part some time in 1967. If you use any 66 components, the only way to get a near correct clutch adjustment is to use ALL of the 2nd design 66 components. Bet I've seen 50 64-66 cars with the adjustment all the way at the very bottom end of the threaded rod and most are clueless as to the cause. I think most of the problem can be corrected by using the correct rod from the cross shaft to the TO arm. Long story and I'll round up all the info that i've gathered over the years later. (preparing for our latest by-weekly hurricane)
By the way, the original throwout bearing for 64-66, the 907538, was a CT241K. Not sure who the source was. May be Delco Hyatt?? I thought I remembered that this part was supplied by some outside source until the late 60's, for some reason.Comment
-
Re: Clutch ball stud - which length to use?
A good example of this problem is Tim Bonds original post on this matter. He has all of the correct components, by part number, but still wound up with no adjustment left at the end of the rod. I don't know what caused this but it's avery common problem. There has to be more to the story and I'l bet that some of the diaphragm heights of replacement clutch pressure plates could have something to do with it too. There's an incredible assortment of things that can go wrong and cause these adj problems and as soon as we get through our next by-weekly hurricane, I'll dig into it again.
If you ask 10 people that have replaced clutches or linkage components in a 64-67 if they were successful the first time, I'll bet at least half had problems with the adjustment and had no idea what changed. Would be a great research project and probably deserves a page in the Restorer.Comment
-
Re: Clutch ball stud - which length to use?
I agree Mike, would be a good research topic for the Restorer. For me, it seems that I probably should change my pressure plate assy due to the unevenness of the fingers, and the replacement will probably be a LUK or Sachs replacement. I plan to switch to the longer stud also, since it seems to make sense to do so. No telling how things will turn out. I plan however to assemble the clutch and bell-housing and can check the fit and function prior to installing the trans. If I need to, I can make a change....Comment
-
Re: Clutch ball stud - which length to use?
Excellent idea Tim. Testing for proper linkage operation and adjustment BEFORE complete assembly is one of the things I wanted to suggest to all who are in the process of replacing any clutch components. More discussion and a possible research survey/topic will probably be on my list, as soon as I know I still have a house and computer to work with after Hurricane Wilma passes. Thanks...
MichaelComment
Comment