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Question: Anyone know what the correct length of the clutch fork ball stud should be for an LS5 C3

Bolisk

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Nov 2, 2007
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441
Location
Crystal Lake IL
Corvette
1972 LS5 Convertible PS, PB, A/C
When I bought this car, the previous owner said that the tans was rebuilt, and the clutch was replaced not long before the car was parked for 20 years. I pulled the trans because it was leaking. . .and found that it was rebuild by a monkey. Pulled the bell housing and the clutch looks new. Still very clean. It's a Borg and Beck.

Before pulling everything apart, the only problem I had with the clutch and trans was the fact that I had to push the clutch pedal through the floor to get the clutch to disengage. No matter how much I adjusted it. . .I could never get the clutch to disengage without pushing the pedal as far as I could get it to go.

When I got under the car, I found that I was pushing the fork into the firewall and it was leaving a mark in the fiberglass.

The first thing I can think of is that the fork ball stud is the wrong lenght. I pulled it out, and the stud is 1 & 3/8" long when you stand it up on a flat surface. The replacements from Paragon and Volunteer Vette appear to be 1& 1/2" long.

Does anyone know what the correct stud length is for a 72 LS5 car? Will the 1.5" really make that much of a difference?

Regards,
JonR
 

Tom Bryant

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1959 black 270hp (9/2/69) 1981 Beige L81(10/20/80)
The 1973 parts manual only lists one ball stud for 1966 through 1973 Corvette. Also only one clutch fork for 1964 through 1973 Corvette. No length listed. The 2 you list are probably the same parts, just measured differently, or maybe from different GM applications. There were different length fork push rods listed but 1967 through 1973 Corvette were the same, both small and big block. Length is 8 37/64".

It could also be that the previous owner used the wrong throw out bearing. Chevy V8s used 2 different lengths over the years depending on application. 4 speed cars commonly used the "short" bearing, measuring 1 7/32 overall length. Other manual cars mostly used the "long" bearing, measuring 1 7/8" overall length. Make sure that you have the short bearing.

Another possibility could be that the clutch fork is bent resulting in not allowing enough movement to release the clutch. Not uncommon. Also it could be as simple as the pressure plate not being correct for the car. If the release forks are too low it would take an unusually long throw to release the clutch. A pressure plate for a long bearing just won't travel far enough with a short bearing.

I hope this gives you someplace to start looking. It's either a bent fork or a mismatch of parts.
Tom
 

Bolisk

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Joined
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Messages
441
Location
Crystal Lake IL
Corvette
1972 LS5 Convertible PS, PB, A/C
I do know that there are two different clutch pivot ball lengths. . .maybe not for Corvettes. . .but there are two commonly used sizes. When I did this same job on my old car a few years back, the clutch pivot ball was worn, and when I went to the local Corvette restoration shop the owner told me that not only was it worn, but it was the wrong one for the car. He mentioned that some shops / people don't realize there are two lengths and people just order a part from non-corvette vendors without checking/verifying the length. . .and he saw that mistake all the time. He gave me a new one and it was clearly longer than the old one. After installing it. . .the car was much better.

Here's the rub. . .I never measured the original, nor did I ever measure the replacement. . .I just took him for his word (43 years of experience). . .and installed it. . .thinking I would never do this again or on another car. Well, the shop owner passed away earlier this year from colon cancer. So my friend and my corvette mentor, is no longer around to answer these types of questions for me. :ugh

So yeah, my minor fear is that the I do have the correct one. . .and I'm measuring it differently. . .and I don't want to buy a replacement if it's not needed. That said, logic would suggest that there is only one way to measure an over all length. . .so I cannot imagine someone would else would measure something longer that wasn't. :L

You raise a good point. . .I have to check the fork as well.

-Jon
 

Tom Bryant

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1959 black 270hp (9/2/69) 1981 Beige L81(10/20/80)

What I am thinking is that, with only 1/8 difference in the two measurements, one was measured overall and the other just to the base of the thread where it seats against the bellhousing. This picture is from the Zip catalog.

Back in my Chevy parts days we saw a lot of bent clutch forks. Also cracked ones through the ball seat area. Guys that ran heavy clutches had problems with clutch forks.

Tom
 

GTR1999

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New Haven CT
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1969,1972,1975
This was a problem that also arose about 15 years ago when everyone was on the "Centerforce clutch train". While the clutch may or may not have been what was expected the geometry was off using a stock ball stud. An adjustable ball stud was the answer. Guys had to install the trans, check the arm and linkage adjustment, set it where it worked, remove the trans, and weld the ball stud so it wouldn't move. Some were able to swap out the "Z" bars as the angle of the arms are different between some models, I don't recall which one but think it was the C2 BB cars and C3 SB cars. I installed a Hays and it bolted right in, of course I think Hays was bought out since so who knows.
 

Tom Bryant

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Good information Gary. That sounds familiar .

tom
 

Bolisk

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Crystal Lake IL
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1972 LS5 Convertible PS, PB, A/C
Thanks Gary,

Yeah, funny thing is, in my last Corvette I put a centerforce dual friction in the car. I actually had to go back to the stock pivot ball to meet the centerforce spec. I'm now trying to decide if I should replace the clutch in my current car. I was going to put another center-force dual friction clutch in because I really liked the way it felt and operated in my last car. This car already has a Borg and Beck clutch in it. . .and it's still looks clean and new. . .which seems to corrolate with the previous owners claim that the trans had been rebuilt, and the clutch replaced shortly before he put the car into a (as near as makes no differnce) 20 years storage. All I know is that the clutch in the car. . .does not operate the way I would like. So I'm trying to narrow down the possibilities.

-J

This was a problem that also arose about 15 years ago when everyone was on the "Centerforce clutch train". While the clutch may or may not have been what was expected the geometry was off using a stock ball stud. An adjustable ball stud was the answer. Guys had to install the trans, check the arm and linkage adjustment, set it where it worked, remove the trans, and weld the ball stud so it wouldn't move. Some were able to swap out the "Z" bars as the angle of the arms are different between some models, I don't recall which one but think it was the C2 BB cars and C3 SB cars. I installed a Hays and it bolted right in, of course I think Hays was bought out since so who knows.
 

Bolisk

Well-known member
Joined
Nov 2, 2007
Messages
441
Location
Crystal Lake IL
Corvette
1972 LS5 Convertible PS, PB, A/C
Tom,

Yeah I looked at paragon, vol vette, and zip. All of their photos show a pivot ball that just from the photo's I can tell that they are longer. I measured mine at "over all" length of 1 & 3/8". If these others are measured from the threads or anything other than over all length. . .and they claim it's 1 & 1/2" then in all cases theirs should be longer. I ordered one from Paragon, and I will see how different it is when it arrives. I will post my finding. :)

The 1973 parts manual only lists one ball stud for 1966 through 1973 Corvette. Also only one clutch fork for 1964 through 1973 Corvette. No length listed. The 2 you list are probably the same parts, just measured differently, or maybe from different GM applications. There were different length fork push rods listed but 1967 through 1973 Corvette were the same, both small and big block. Length is 8 37/64".

It could also be that the previous owner used the wrong throw out bearing. Chevy V8s used 2 different lengths over the years depending on application. 4 speed cars commonly used the "short" bearing, measuring 1 7/32 overall length. Other manual cars mostly used the "long" bearing, measuring 1 7/8" overall length. Make sure that you have the short bearing.

Another possibility could be that the clutch fork is bent resulting in not allowing enough movement to release the clutch. Not uncommon. Also it could be as simple as the pressure plate not being correct for the car. If the release forks are too low it would take an unusually long throw to release the clutch. A pressure plate for a long bearing just won't travel far enough with a short bearing.

I hope this gives you someplace to start looking. It's either a bent fork or a mismatch of parts.
Tom
 

Bolisk

Well-known member
Joined
Nov 2, 2007
Messages
441
Location
Crystal Lake IL
Corvette
1972 LS5 Convertible PS, PB, A/C
All,

I received the replacement pivot ball from Paragon today. Notice the difference, just like I hoped! :)
I'm hoping this really makes a difference in the way the clutch reacts to pedal travel!
image.jpg
 

Tom Bryant

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Joined
Nov 9, 2000
Messages
7,223
Location
Edgerton, Ohio, United States
Corvette
1959 black 270hp (9/2/69) 1981 Beige L81(10/20/80)
That should make a big difference. Good luck.

Tom
 

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