Clutch Fork Failure Analysis Prediction?

[scottfab]

Originally Posted by secondchance

... snip...
. Fact that it ripped makes me suspect defect around the rivet hole.

Sounds like we should all take a look at the rivet hole next time we're in there. (can't believer I just said that)

Maybe a dental mirror and a few double jointed fingers?

[HAWAIIZR-1]

Originally Posted by scottfab

Sounds like we should all take a look at the rivet hole next time we're in there. (can't believer I just said that)

Maybe a dental mirror and a few double jointed fingers?

G spot?

[BlackWidow#2]

I had a similar problem back in 98 or 99. The problem was traced back to a CenterForce pressure plate. The weights and fingers had worn somewhat, causing a bind when engaging and disengaging.
George

[Marc Haibeck]

Maybe high pedal force can break the fork? We encountered a car that had a problem with excessive force needed to depress the clutch pedal. It felt like the car had a racing clutch. The owner ignored the high pedal force. After about 10k miles the fork broke. When we disassembled the clutch we found an OE pressure plate. The fork pivot ball was totally dry, and had a lot of red fretting corrosion. I wonder if someone replaced the clutch and cleaned the bell housing and then did not re-lubricate the pivot ball. We installed a new fork with moly disulfide lubricant on the pivot ball. We put the clutch back into service because it was in good condition. Then the pedal force was normal.

Here is a picture of the broken fork.
http://www.zr1specialist.com/HAT%20W...tch%20fork.htm

[secondchance]

Originally Posted by Marc Haibeck

Maybe high pedal force can break the fork? We encountered a car that had a problem with excessive force needed to depress the clutch pedal. It felt like the car had a racing clutch. The owner ignored the high pedal force. After about 10k miles the fork broke. When we disassembled the clutch we found an OE pressure plate. The fork pivot ball was totally dry, and had a lot of red fretting corrosion. I wonder if someone replaced the clutch and cleaned the bell housing and then did not re-lubricate the pivot ball. We installed a new fork with moly disulfide lubricant on the pivot ball. We put the clutch back into service because it was in good condition. Then the pedal force was normal.

Here is a picture of the broken fork.
http://www.zr1specialist.com/HAT%20W...tch%20fork.htm

Hi Marc,

I think my clutch may have gone thru a similar situation as you are describing.
About three months ago I felt a driveline slop, suspected overly loose flywheel (original unit w/ 134,000 miles) and disassembled to replace the flywheel. Prior to this clutch felt a little odd - sort of like pivot point was changing as the pedal was pushed down - not progressive.
Upon disassembly we found the pivot stud was worn badly where the fork was riding. However, the fork look ok visually and was not replaced. Jim V and I came to a similar conclusion that the fork may have been over-stressed while being operated w/ wornout pivot stud.
It's interesting the failed fork you came across failed closer to the slave cylinder side. Whereas mine failed right at the rivet hole. It may be the fork in my car had a defect at the rivet hole and relatively small stress caused by the pivot stud was all it took to fail.
And I did lubricated the pivot stud and fork ends that slip over the throwout bearing w/ high temp bearing grease. Whether it has molybdenum disulfide additive or not - I have no idea.

[secondchance]

Here is a pic of the pivot stud - don't let this happen to you!

[LancePearson]

I'm no metalurgist but that fracture is not a crack propagating from stress. It looks very much to me like a failure of the steel to be heat treated correctly and was too brittle and not elastic enough to handle the load as a result. If parts were trackable all the way back I'd bet it was not heat treated before forming correctly.

Lance

[secondchance]

Lance,

You may be right.

We, the WAZOO gang, need to meet you. You are not that far away.
We meet occasionally at Westminster, MD or at Mt. Vernon, VA.
Gotta see your new ride.
My first Z was a red w/ black interior-may have been a twin to yours if you have black interior.

[scottfab]

Originally Posted by secondchance

Here is a pic of the pivot stud - don't let this happen to you!

You have to wonder about the geometry of the design. I'd expect to see wear on the top rounded surface. Looks to be a lot of sideways wear. Simple lack of lubrication should still wear on the designed pivot surface. Not good.

[secondchance]

Originally Posted by scottfab

You have to wonder about the geometry of the design. I'd expect to see wear on the top rounded surface. Looks to be a lot of sideways wear. Simple lack of lubrication should still wear on the designed pivot surface. Not good.

Scott,

Where it wore is the pivot surface.