clutch pushrod wore through fork pocket???

[my kids took the truck]

my clutch pushrod has worn through the clutch fork pocket --> '74 K5 SM465

I can't find anything describing this problem - I doubt I am the first

I replaced the clutch fork 30k miles ago. The pushrod was modified a bit by my grandpa when it was his K5, short story, the pushrod functions the same and just looks different.

There is a vibration in the clutch linkage I suspect is caused by align boring the crankshaft journals, and I did not use offset bellhousing pins to correct - it causes an annoying tap sound sometimes.

It looks like a hole has been neatly drilled through the clutch fork pocket and the pushrod has pushed right through. Probably related to the annoying vibration; tap, tap, tap, and 30k later a little hole in the pocket.

have you seen this?

what is the cause?

what is the solution?

 

[tRustyK5]

The stock pushrod has a ball on the end matching the cup on the fork. Great for any misalignment, and the greater surface area spreads the load so wear is slow. If your Grandpa's creation didn't have the same ball matching the cup on the fork I could see it wearing through.

There should be little to no contact between ball and cup unless the clutch is being depressed.

 

[my kids took the truck]

really... that explains a lot

I ordered a replacement pushrod as part of a larger order and have it in the box of spare parts. It did not come with a ball to fit the tip. Where do I get the ball?

There is a spring that holds the pushrod tight with the fork. So wouldn't the ball be held tight just by the spring?

A few months back I noticed the hole in the fork, it had not popped through so I thought it was some sort of positioning hole. That little tip on the pushrod seemed like way too much pressure. I went to the hardware store and made a couple trial solutions using acorn nuts and round headed bolts, but after looking online it looked like the pushrod to fork is just that.

Over on Pontiac Street Performance this guy felt the small tip was going to be a problem and redesigned it.

over on trifive another redesign, this one uses hemi joints; I can't get the image to embed so here is the link http://s137.photobucket.com/user/jlow1979/media/clutchfork.jpg.html

 

[tRustyK5]

I would see how the rounded part of the new rod you have fits a new fork (that you need anyways) and decide what to do from there. I'm with the guy on the Pontiac forum...more area, less wear.

There is no separate ball part, but I probably mis-remembered how small the rounded part at the tip was.

Could be the spring you had on there was too strong. My last mechanical linkage set-up had a pretty light spring keeping things together.

 

[my kids took the truck]

the springs are OEM, for some unknown reason (either slightly wrong spring or poor mfg tolerance) the longer spring does not reach the frame hole where I think it is supposed to attach, I have it attached to the upper shock bolt - it doesn't seem excessively strong

you can see here that the spring coils are just barely tensioned at rest - I plan to make a bracket or find a longer spring to remove even that small tension - the spring tension at rest is nothing compared to the clutch pressure plate resistance when disengaged.

I think the pontiac solution will be my route tomorrow afternoon

 

[my kids took the truck]

I pulled the pushrod and took some pictures of the hole. I don't understand why the pushrod decided to bore a hole through the clutch fork cup. Maybe I had it adjusted without enough freeplay on the clutch to throwout bearing. The clutch felt nice, I think it had enough freeplay. This time I put more emphasis on the freeplay and less on where the clutch 'grab point' is when letting the clutch out.

I pulled it all apart a couple months ago and saw that it looked like it could. I took a grinder to the pushrod an blunted the tip. I don't think I sharpened it... I tried to match the tip on the new puchrod. Maybe I should have just used the new one rather than rework the old one. Trying to save a buck.

 

[my kids took the truck]

So far after a few hundred miles everything is holding together.

The solution: a piece of allthread and a brass acorn nut.

In the picture I show the modified push rod that my grandpa built for reasons not fully understood but probably good; he'd swapped in a v6 that I then swapped back to a v8 and kept the same pushrod.

Next to that is the OEM replacement pushrod.

Next to that is my new pushrod built from allthread, a sleeve, and a brass acorn nut. I like the brass since it is self lubricating and has a broad surface area. The brass should act like a cushion and absorb some noise. I added a sleeve to give the all thread more support so it would not bend. It is not high strength steel like to OEM part. The sleeve extends beyond the midpoint of the alltread, this where the maximum bending force is located. If it will fail, it will bend right were the allthread stops. My hope is that the force is low enough at that point that it will not bend. The sleeve also acts as a locknut for the acorn nut. The brass acorn nut is replaceable so later as it wears down I can put a new one on. If I find some high strength all thread, I will swap that.

On the left is an alternative design based on the 'pontiac guys' brazed ball bearing and sleeve. If the brass acorn nut does not work, I will go with plan B.

The clutch still rattles sometime. Sometimes it is quiet. I think the engine align hone has thrown the bellhousing alignment off so there is clutch fork movement that otherwise should not be there. Overall, according to my wife, the noise is much better than it was and is now livable. So, I can stop working on this.