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

QB93Z · 12-20-2012

Here are some additional pictures of the broken clutch fork from a 1994 ZR-1 with greater than 130,000 miles.

The goal of our analysis was to determine if the failure could have been predicted by visual inspection prior to the failure.

The fork failure occurred during a routine shift from second to first gear while Yun was entering the parking space in the parking garage at his condo.

There were no prior indications of clutch operational degradation.

Here are some close up pictures of the fracture:

It looks like the fork suffered fatigue failure under tensile stress during clutch opeartion. There is no indication of deformation (twisting or bending) occurring prior to the failure.

There is no indication of mechanical damage (strikes, marks, or scrapes) to the fork prior to the failure.

The failure crack probably started in the edges of the rivit hole and spread outward to the edges of the fork.

I suggest visual inspection of any clutch fork that is to be reinstalled. Examine the area around the rivit, looking for cracks.

I would be intersted in any other comments.

Jim

Scrrem · 12-20-2012

Great write up Jim!!!

Makes me wish I had taken a better look at my fork before I put my new Bill B. transmission in. Oh well...not to fear...there always the Westminster Loaner Program

secondchance · 12-20-2012

Thanks for the write-up.
I agree with your assessment. Close inspection of rivet hole is about the best one can do.

Schrade · 12-20-2012

Quote:

Originally Posted by QB93Z

...

I suggest visual inspection of any clutch fork that is to be reinstalled. Examine the area around the rivit, looking for cracks.

I would be intersted in any other comments.

Jim

Magnaflux.

XfireZ51 · 12-20-2012

Jim,

What's your thought of just doing a weld along that bend to add some cross section as a preventative measure?

Blue Flame Restorations · 12-20-2012

You know what they say about big feet?......

Big broken clutch fork!!!!!!!!!

secondchance · 12-20-2012

Quote:

Originally Posted by Blue Flame Restorations

You know what they say about big feet?......

Big broken clutch fork!!!!!!!!!

Big feet?! I wear 8-1/2!

For it to be worthwhile reinforcing has to be on the open end on the break and around the begining of the crack - around the rivet. I don't know such small weld is doable. Maybe a plate with a hole for the rivet and weld over the hole/rivet and around the edge of the plate. A few holes on the plate filled with weld will be worthwhile. Again this is such a small area to work with... Not to mention clearance concern after adding the plate.

Blue Flame Restorations · 12-20-2012

Quote:

Originally Posted by secondchance

Big feet?! I wear 8-1/2!

For it to be worthwhile reinforcing has to be on the open end on the break and around the begining of the crack - around the rivet. I don't know such small weld is doable. Maybe a plate with a hole for the rivet and weld over the hole/rivet and around the edge of the plate. A few holes on the plate filled with weld will be worthwhile. Again this is such a small area to work with... Not to mention clearance concern after adding the plate.

Just remind me to NOT let you step on my foot at the Gathering in May. lol

On a serious note, I'm glad you got it fixed. The fracture is an anomoly, IMO. I don't think I'd ever bother reinforcing one prior to installation. Maybe if you drag race or do brutal shifting?

QB93Z · 12-20-2012

Quote:

Originally Posted by XfireZ51

Jim,

What's your thought of just doing a weld along that bend to add some cross section as a preventative measure?

The fork is forged steel. When you examine the fractured edge of the crack, the "skin" of the steel that was worked by the forging is visible. The working adds strength to a forged piece. I am afraid that welding without heat treatment would reduce the strength of the fork.

All of the suggestions are good, but the fork is not a very expensive piece. I was hoping to get a quick visual Go-No-Go inspection that could be used to decide if a replacement fork is prudent when the clutch is apart for some other reason.

Jim

nelson007 · 12-20-2012

Hello Jim,
Could heat have any effect on the part to cause it to break ?

Nelson007

12-20-2012	#1
QB93Z Join Date: May 2007 Location: Westminster, Maryland Posts: 3,689	Clutch Fork Failure Analysis Prediction? Here are some additional pictures of the broken clutch fork from a 1994 ZR-1 with greater than 130,000 miles. The goal of our analysis was to determine if the failure could have been predicted by visual inspection prior to the failure. The fork failure occurred during a routine shift from second to first gear while Yun was entering the parking space in the parking garage at his condo. There were no prior indications of clutch operational degradation. Here are some close up pictures of the fracture: It looks like the fork suffered fatigue failure under tensile stress during clutch opeartion. There is no indication of deformation (twisting or bending) occurring prior to the failure. There is no indication of mechanical damage (strikes, marks, or scrapes) to the fork prior to the failure. The failure crack probably started in the edges of the rivit hole and spread outward to the edges of the fork. I suggest visual inspection of any clutch fork that is to be reinstalled. Examine the area around the rivit, looking for cracks. I would be intersted in any other comments. Jim __________________ If it isn't fun, you aren't doing it right! 1990 Black ZR-1 - sold 1993 Quasar Blue ZR-1 1994 Competition Yellow ZR-1 1995 Dark Purple ZR-1 Maryland State Coordinator WAZOO Member

12-20-2012	#2
Scrrem Join Date: Feb 2009 Location: Alexandria, Virginia Posts: 1,467	Re: Clutch Fork Failure Analysis Prediction? Great write up Jim!!! Makes me wish I had taken a better look at my fork before I put my new Bill B. transmission in. Oh well...not to fear...there always the Westminster Loaner Program __________________ 1990 Bright Red Coupe #608 380 Stroker, Ported Heads/Intake/Housings/TB Haibeck Secondary Delete Chip / Pete's Cams George Braml Intake / FIC Injectors Coated SW Headers / Corsa Bill Boudreau B/B ZF6 / Viper 4.10 gears Ron Davis Radiator Pioneer AVIC-Z140BH NAV Fikse FM5's 285 / 335 / C6 Brakes WAZOO Member

12-20-2012	#3
secondchance Join Date: Aug 2006 Location: McLean, VA Posts: 3,721	Re: Clutch Fork Failure Analysis Prediction? Thanks for the write-up. I agree with your assessment. Close inspection of rivet hole is about the best one can do.

12-20-2012	#5
XfireZ51 Join Date: May 2007 Location: Chicagoland, IL Posts: 9,700	Re: Clutch Fork Failure Analysis Prediction? Jim, What's your thought of just doing a weld along that bend to add some cross section as a preventative measure? __________________ [SIGPIC][/SIGPIC]Former Membership Chairman Former ZR-1 Registry - BOD 1972 Corvette 4speed base Coupe SOLD long time ago 1984 Corvette Z-51/4+3 SOLD 1992 Corvette ZR-1 Aqua/Gray #474 SOLD 1992 Corvette ZR-1 Black Rose/Cognac #458 2014 Honda VFR Interceptor DX

12-20-2012	#6
Blue Flame Restorations Join Date: Feb 2010 Location: Pendleton, IN Posts: 3,904	Re: Clutch Fork Failure Analysis Prediction? You know what they say about big feet?...... Big broken clutch fork!!!!!!!!! __________________ 1988 KOH Prototype EX5023 sold 1990 ZR-1 #444 Convertible 1990 ZR-1 Black #966 1991 ZR-1 Quazar Blue #296 1957 Duntov SS Project

12-20-2012	#10
nelson007 Join Date: Sep 2012 Location: Westminster, Md. Posts: 436	Re: Clutch Fork Failure Analysis Prediction? Hello Jim, Could heat have any effect on the part to cause it to break ? Nelson007