Clutch Fork Ball Stud Length?

[James B.]

What is the correct length of the clutch fork ball stud that mounts in the FWH on a 1967 Corvette L79 (327CID, 350 HP)? I've got clutch engagement problems on a new clutch and may have ended up with a ball stud that is too short; won't know for sure until we pull the clutch. I believe the correct length is 1.5" but at the shop measured a shorter one that is 1.36". Please let me know which is correct.

Also, just ordered a LuK clutch (04-021) which from past posts here seems to be a popular choice (despite the plastic composite throw-out brng). The engine is rebuilt to stock specs so I don't need anything heavy duty & I want reasonable pedal pressure (like original). If there is anything negative in LuK's recent past please let me know.

As always, thanks for the help and advice, Jim

[Stephen L.]

Re: Clutch Fork Ball Stud Length?

Check the "similar threads" at the bottom of this thread... The length is discussed at length.

[James B.]

Re: Clutch Fork Ball Stud Length?

Yes Stephen, had just found John Hinckley's post from 2005. Looks like a real bad (confusing) deal. Sorry, I have a habit of posting a question and then thinking to look in the archives.

[Joe L.]

Re: Clutch Fork Ball Stud Length?

What is the correct length of the clutch fork ball stud that mounts in the FWH on a 1967 Corvette L79 (327CID, 350 HP)? I've got clutch engagement problems on a new clutch and may have ended up with a ball stud that is too short; won't know for sure until we pull the clutch. I believe the correct length is 1.5" but at the shop measured a shorter one that is 1.36". Please let me know which is correct.

Also, just ordered a LuK clutch (04-021) which from past posts here seems to be a popular choice (despite the plastic composite throw-out brng). The engine is rebuilt to stock specs so I don't need anything heavy duty & I want reasonable pedal pressure (like original). If there is anything negative in LuK's recent past please let me know.

As always, thanks for the help and advice, Jim

James------


The original ball stud for your application was 1-3/8" in overall length and of GM #3887159. So, the one the shop measured from your car is likely the original. GM discontinued this stud many years ago and replaced it with a stud that is 1-1/2" overall length of GM #3729000. I think you will find it extremely difficult, if not impossible, to find a 1-3/8" replacement stud in the aftermarket. The 1-1/2" stud works fine.

Addendum:

Well, I found that I am wrong. Corvette Central offers a reproduction of the 1-3/8" ball stud

[James B.]

Re: Clutch Fork Ball Stud Length?

Joe,

Thank you so much for looking into it and finding 1-3/8" stud (i've got one on order now)! I had just ordered a 1-1/2" from Paragon and I have both clutch push rod lengths (fork to cross shaft) so when I put the new clutch up I can see how the adjustment will be with both and choose best fit/travel/actuation.

Also, thank-you for your (and Michael Hanson's) post from 2005 explaining the history & changes in all the clutch actuation components in C2s & 3s.

Jim

[James W.]

Re: Clutch Fork Ball Stud Length?

I know this thread is over a year old, but I am in the process of installing a different clutch into a 1965 Corvette equipped with a 396 engine. I've read the the 2005 post that John Hinckley, Mike Hanson and Joe Lucia gave their best information and to what the problem could be for having clutch adjustment problems in 63-67 Corvettes. So for the install information about this clutch. The flywheel is a GM over the counter service replacement spec'd for a '65 Corvette with a 396 engine. The clutch kit to be installed is the LUK brand 04-021 that has been described a suitable replacement clutch kit. The ball stud installed in the bell housing measures 1-1/2 inches overall length with an installed height of approximately 7/8 of an inch measured from inside the bell housing. The clutch fork is a reproduction purchased from Paragon. The through-out bearing to be used with the LUK clutch is a GM replacement that measures 1-1/2" in height, I am not going to use the plastic composite through-out bearing. The pilot shaft bushing is a brass (oil-ite) that measures the correct 1.094 inches outside diameter per John Hinckley. The bell crank is the original that was installed in the car. The clutch rod from the clutch pedal is a GM NOS service replacement spec'd for the 396 equipped engine. The previous clutch that was installed during the restoration in 2013 exhibited the same problems of no adjustability on the clutch rod. The clutch rod to bell crank was adjusted all the way to the end of the clutch rod. The clutch never did "feel" right.

My question is this. Since the correct specification for the ball stud in the bell housing was 1-3/8" free length, would an adjustable ball stud set at 1-3/8" total free length give me more adjustability at the clutch rod or should I stay with the 1-1/2" ball stud? Speedway Motors in Lincoln, Nebraska has adjustable ball studs, p/n 5503855 "Adjustable GM Bellhousing Clutch Fork Pivot" for $19.99. I have one on order that will arrive on 8/9/18.


Thanks in advance.


James

[Joe L.]

Re: Clutch Fork Ball Stud Length?

I know this thread is over a year old, but I am in the process of installing a different clutch into a 1965 Corvette equipped with a 396 engine. I've read the the 2005 post that John Hinckley, Mike Hanson and Joe Lucia gave their best information and to what the problem could be for having clutch adjustment problems in 63-67 Corvettes. So for the install information about this clutch. The flywheel is a GM over the counter service replacement spec'd for a '65 Corvette with a 396 engine. The clutch kit to be installed is the LUK brand 04-021 that has been described a suitable replacement clutch kit. The ball stud installed in the bell housing measures 1-1/2 inches overall length with an installed height of approximately 7/8 of an inch measured from inside the bell housing. The clutch fork is a reproduction purchased from Paragon. The through-out bearing to be used with the LUK clutch is a GM replacement that measures 1-1/2" in height, I am not going to use the plastic composite through-out bearing. The pilot shaft bushing is a brass (oil-ite) that measures the correct 1.094 inches outside diameter per John Hinckley. The bell crank is the original that was installed in the car. The clutch rod from the clutch pedal is a GM NOS service replacement spec'd for the 396 equipped engine. The previous clutch that was installed during the restoration in 2013 exhibited the same problems of no adjustability on the clutch rod. The clutch rod to bell crank was adjusted all the way to the end of the clutch rod. The clutch never did "feel" right.

My question is this. Since the correct specification for the ball stud in the bell housing was 1-3/8" free length, would an adjustable ball stud set at 1-3/8" total free length give me more adjustability at the clutch rod or should I stay with the 1-1/2" ball stud? Speedway Motors in Lincoln, Nebraska has adjustable ball studs, p/n 5503855 "Adjustable GM Bellhousing Clutch Fork Pivot" for $19.99. I have one on order that will arrive on 8/9/18.


Thanks in advance.


James

James------

I would use the 1-1/2" stud. This stud is SERVICE for all Corvette applications. I believe that the 1-3/8" stud was an experiment that didn't pan out. The 1-1/2" stud was used for C1 through about 1964. Then, the 1-3/8" was used from 1965 through early 1975. Then, it was back to the 1-1/2" stud for PRODUCTION even though the rest of the clutch system had not changed.

I think if you use a 1-3/8" stud you're going to have more adjustment issues than you have now.

[Ray K.]

Re: Clutch Fork Ball Stud Length?

James,

I am in agreement with Joe that 1- 1/2" ball stud should work just fine for your application.

Ray

[James W.]

Re: Clutch Fork Ball Stud Length?

Joe and Ray,

Thanks for your input, I will use the existing 1-1/2" clutch fork ball stud.


Thanks,

James

James------

I would use the 1-1/2" stud. This stud is SERVICE for all Corvette applications. I believe that the 1-3/8" stud was an experiment that didn't pan out. The 1-1/2" stud was used for C1 through about 1964. Then, the 1-3/8" was used from 1965 through early 1975. Then, it was back to the 1-1/2" stud for PRODUCTION even though the rest of the clutch system had not changed.

I think if you use a 1-3/8" stud you're going to have more adjustment issues than you have now.