Clutch Fork Failure Analysis Prediction? - Page 5 - ZR-1 Net Registry Forums

A26B · 12-27-2012

It's a pull-release clutch, not a push-release, hence the "ball" surface on the underside of the pivot, where the load is.

LancePearson · 12-27-2012

Quote:

Originally Posted by 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.

Let me know next time you meet in Mt. Vernon...it's about 110 miles each way for me and I have to make arrangements for my two greyhound girls to have a dog sitter. These are such great cars. There are photos of my car in one of my albums.....

Lance...red/red 1991 0682

WARP TEN · 12-27-2012

I was looking at Marc Haibeck's website and saw he has a clutch fork failure mentioned, but it broke at a different point due to lack of lubrication. So I am not sure what will show when we are looking at a fork to anticipate possible failure. Here is what he showed and said :

This fork broke because it was subjected to high load during many clutch release cycles. It was used with an OE type Valeo pressure plate.
The root cause was lack of lubrication on the pivot ball. The pivot ball was dry with no lubricant. The pedal force required to release the clutch was about twice the normal amount.
With a new fork and a lubricated pivot ball the pedal force to release the clutch returned to normal. The correct pivot ball lubricant has a molybdenum disulfide high pressure anti-friction additive. The pivot ball should be freshly lubricated when a new clutch is installed. The tips that engage with the throw out bearing should also be lubricated.

LancePearson · 12-27-2012

Interesting that it broke along what may be a forming score line.....

secondchance · 12-27-2012

Quote:

Originally Posted by LancePearson

Let me know next time you meet in Mt. Vernon...it's about 110 miles each way for me and I have to make arrangements for my two greyhound girls to have a dog sitter. These are such great cars. There are photos of my car in one of my albums.....

Lance...red/red 1991 0682

Looks like you have black interior AND Borla exhaust just like I had.
May I sit in your car and reminise? I'll be back in 1991!

A26B · 12-27-2012

Virtually all fatigue breaks occur at stress risers, i.e. nicks, scratches, sharp corners, tooling marks, etc. That's why parts designed to shear at specific axial load pressures are polished.

This get me to thinking about "weak links." The cause of fork failure sure points to excessive pivot friction. if the clutch fork was strengthened and excessive pedal pressure ignored, eventually the pivot would break or wear to the point the fork would come off the pivot. I'm not sure what exactly might happen, but it could be much more catastrophic if the fork got tangled up in there.

The moral of the story is check the pivot, check fork, replace if worn and lubricate always.

12-27-2012	#41
A26B Join Date: Dec 2003 Location: Arcadia, OK Posts: 3,401	Re: Clutch Fork Failure Analysis Prediction? It's a pull-release clutch, not a push-release, hence the "ball" surface on the underside of the pivot, where the load is. __________________ Jerry Downey JERRYS LT5 GASKETS & PARTS http://www.jerrysgaskets.com 1994 *ZR-1*, Black/Black, Lingenfelter Aerobody, 416cu in, 3.91 gears, coil-over susp, Brembo brakes, etc. 2016 Black-Red, 3LT-Z51 Auto 8-speed.

12-27-2012	#43
WARP TEN Join Date: Apr 2007 Location: Lake Bluff, IL Posts: 2,143	Re: Clutch Fork Failure Analysis Prediction? I was looking at Marc Haibeck's website and saw he has a clutch fork failure mentioned, but it broke at a different point due to lack of lubrication. So I am not sure what will show when we are looking at a fork to anticipate possible failure. Here is what he showed and said : This fork broke because it was subjected to high load during many clutch release cycles. It was used with an OE type Valeo pressure plate. The root cause was lack of lubrication on the pivot ball. The pivot ball was dry with no lubricant. The pedal force required to release the clutch was about twice the normal amount. With a new fork and a lubricated pivot ball the pedal force to release the clutch returned to normal. The correct pivot ball lubricant has a molybdenum disulfide high pressure anti-friction additive. The pivot ball should be freshly lubricated when a new clutch is installed. The tips that engage with the throw out bearing should also be lubricated. __________________ 2016 Long Beach Red Z06 #10281 "POPS Z" 1995 Polo Green #409 "WARP TEN"--Haibeck 350/510 package, 4.10s, Hurst, Stock Exhaust with QTP Cutouts --Sold but still running strong 1993 Quasar Blue #161 "HIL KING" --Sold but still running strong, now with more than 120,000 miles 1967 Marlboro Maroon/Saddle Corvette Coupe 300 hp/4-spd --Sold a long time ago ZR-1 Net Registry Founding Member #95 NCM Lifetime Member Favorite Quote--Attributed to Mickey Thompson: "Too Much Horsepower is Almost Enough"

12-27-2012	#44
LancePearson Join Date: Dec 2012 Location: Chester, Virginia Posts: 457	Re: Clutch Fork Failure Analysis Prediction? Interesting that it broke along what may be a forming score line.....

12-27-2012	#46
A26B Join Date: Dec 2003 Location: Arcadia, OK Posts: 3,401	Re: Clutch Fork Failure Analysis Prediction? Virtually all fatigue breaks occur at stress risers, i.e. nicks, scratches, sharp corners, tooling marks, etc. That's why parts designed to shear at specific axial load pressures are polished. This get me to thinking about "weak links." The cause of fork failure sure points to excessive pivot friction. if the clutch fork was strengthened and excessive pedal pressure ignored, eventually the pivot would break or wear to the point the fork would come off the pivot. I'm not sure what exactly might happen, but it could be much more catastrophic if the fork got tangled up in there. The moral of the story is check the pivot, check fork, replace if worn and lubricate always. __________________ Jerry Downey JERRYS LT5 GASKETS & PARTS http://www.jerrysgaskets.com 1994 *ZR-1*, Black/Black, Lingenfelter Aerobody, 416cu in, 3.91 gears, coil-over susp, Brembo brakes, etc. 2016 Black-Red, 3LT-Z51 Auto 8-speed.