[wbnapier]

My clutch failed to disengage over the weekend and I had to tow the vehicle home. After tearing everything down, I discovered that my clutch fork was bent where it holds the throw out bearing. I have no idea how this could have happened. The pressure plate diaphragm looks fine.

Photos of clutch fork below.

Any ideas on what could cause this?

[1966socalgoat]

Driving a stick with sandals

[Tom Vaught]

Who did you buy the clutch fork from?

Tom V.

[wbnapier]

Update.

The clutch forks should be hardened steel. The repop clutch fork I used was not.

A stock or common aftermarket pressure plate requires 300 lbs. to move the pressure plate diaphragm. My Center-Force requires 350-375, so more stress on the unhardened clutch fork.

I should receive my OEM clutch fork on Monday, and I purchased a new pressure plate and clutch from the specialty clutch shop, which I installed today.

I am happy to have discovered this shop, they assemble / rebuild clutches, pressure plates, grind flywheels, and have all sorts of tools and machines for testing and servicing these things. The staff is very knowledgeable about all things clutch related.

[HWYSTR455]

Hm. So they are saying it was because the fork wasn't hardened? Not sure I buy that, or it would have bent on both sides.

Guess we will find out after some use.


.

[wbnapier]

Yeah, that is a working theory, and it is loosely supported by facts, but who knows for sure. Facts:

1) There was no damage on any other component other than the tranny front bearing retainer.
2) The clutch fork steel is not hardened. It should be.
3) My pressure plate diaphragm does require 15-25% more pressure to actuate, thus putting more stress on the clutch fork. We tested it on the machine.

Other tid bits of info from the clutch. The flat head pivot ball, that I didn't like as it doesn't cleanly fit the round recess in the clutch fork, they said it is that way for a reason. It traps / retains a nugget of grease. If they were a round, mated pair, it would push out the grease.

They don't like Center-Force. The PP weights are a gimmick that only work at really high RPMs (6k+). They had other comments as well.

They assemble most clutches from blanks there based on ones car and goals.

[HWYSTR455]

Originally Posted by wbnapier

...

They don't like Center-Force. The PP weights are a gimmick that only work at really high RPMs (6k+). They had other comments as well.
.

Been saying that since day one, the weights actually can fail or hang, and cause more issues than they supposedly help. I think Centerforce stuff is junk, but I will say 'that's my opinion'.


.

[Gary H]

Is it a repop?

[wbnapier]

Summit:

Goodmark GMK4330951641

https://www.summitracing.com/parts/GMK-4330-951-641

I will remove the pressure plate, clutch, and flywheel tonight to ensure it is all OK.

Thursday afternoon I'm visiting a clutch specialist to look over everything and get a new fork and throw out bearing. Hayes flywheel, Center-Force clutch, PP, and TO bearing. DF735552

https://www.centerforce.com/product/...269751-c545805

Question, Is there anything special about the Pontiac fork, aside from the groove for the 64-65 return spring? Specifically about the geometry?

[462gto]

I just went through the same thing with the Goodmark fork and then one from Inline Tube in my 1967 GTO with a Centerforce 2 clutch and a Autogear M22W. Where the throw out bearing goes the OEM fork is rounded and both aftermarket forks it was straight in that area. I ended up finding a OE fork part number 9787069 and put in a (Mcleod adjustable pivot ball 16908 and the part that goes in the bellhousing had to have the thread cleaned up to make it fit) and set per the Centerforce instructions and so far so good.

[wbnapier]

That's interesting. I was assuming that I put the throw out bearing on askew, and that caused the failure.

You are right, it is straight where the throw out bearing rides on the fork. I will run that by the clutch pro when I see him. He said on the phone that they stock clutch forks for old GM, but they are not Pontiac specific and he was unaware of the Goodmark repop clutch fork, and said it looked odd to him. He asked that I bring it in Thursday.

Do you have any idea where I can get an OE one for '65?

[Gary H]

I just did a 4 speed conversion for a 70' GTO and used pedals and linkage parts from our host. After finishing, I couldn't get the clutch play adjusted right for nothing. If I got a little play with the peddle up, it was out of adjustment at the bottom, and visa versa. I finally pulled the transmission back out and found the clutch fork was the incorrect length from the clutch pushrod to the pivot point where the clutch ball sits. That's comparing it to several original clutch forks I had laying around. Also, the clutch Z-bar had a lot of slop at it's pivot points and therefore was flexing. I put stock components back in, and reinstalled the transmission AGAIN, and it was good to go.

[wbnapier]

Thank you for that info. I have a line on a OEM clutch fork. I'm going to take all my components to a special clutch shop tomorrow and talk it through with them. I spoke to Russ at 4-speed Conversions at length this morning, and he doesn't know what could have caused the fork to bend as it did. I told him that I assumed I installed the TO bearing askew, but he says I would have known immediately.

[wbnapier]

Here's a pick of my front bearing retainer. Note that the damage / wear is not completely around the shaft. I ordered a new one tonight. I am unsure if I could have polished this and called it a day as opposed to buying a new one.

[wbnapier]

Yes, it could. But, better safe than sorry, I will replace. The TO bearing and snout were bone dry. Maybe I didn't lube the inside of the TO bearing and that caused binding and it seized?

[HWYSTR455]

Looks to me like the one sprung finger was placed on the wrong side of the throw out bearing during install, and it loaded the bearing cocked on the trans bearing retainer, and/or got hung on some pressure plate fingers. (see attached pic)

I bet it happened during install of trans, when trying to get the input shaft into the disc. Maybe when 'giggling' it, or using the bolts to pull the trans up to the bell. (which is a no-no)

I would make sure none of the pressure plate fingers are bent, and if not, you got lucky. Should be able to replace the fork and bearing, and proceed.

EDIT: NO lube should be used on the throw out bearing or on the bearing retainer.


.

[wbnapier]

That was my initial thought as well. During tranny install, my friend was helping and knocked the TO bearing loose and put it back on. I didn't double check it that he put it on correct and he isn't knowledgable about such things.

However, others have told me that I would have immediately known when I tried to drive the car, as I would have had major clutch issues.

I've put about 500 miles on it.

[HWYSTR455]

It would make some additional noise, but it could still operate somewhat normally. If you have a loud exhaust, you may not hear it.

The throw out wouldn't sit squarely on the plate fingers, and the one side could drop below the fingers even. That is what could have actually bent the one side of the fork, fingers holding the bearing towards the plate, while the other fingers pushed back into the released position.

But of course, it's only speculation.

Since it's apart, inspect the PP closely for damage. If it loaded the bearing enough to bend the fork, I would guess there is PP damage too.

Is there an inspection hole on the bottom of the bell, or is it a blow-proof? If a blow-proof, I would be looking for the piece that broke off the fork. Hopefully it's not in the PP somewhere, or worse, between the disc and flywheel/plate.

If there's any damage to the PP, don't screw around, replace it all. If the flywheel has a gouge, have it turned.

.

[HWYSTR455]

Rebuild the Z-bar, all the parts are available.

https://www.ebay.com/itm/11487203600...SABEgLomPD_BwE

If you want, you can upgrade the linkage too:

https://www.speeddirect.com/clutch-linkage

.

[wbnapier]

Everything is apart. Below is a picture of the pressure plate. No visible damage or wear. There was no debris anywhere. I am bringing all the parts to a clutch shop this afternoon and having them look at it and render an opinion.