Modifying A Clutch Fork

Late last year I discovered that I was overpowering my small block toploader’s 1 1/16” input shaft and needed to upgrade it to use the larger diameter 1 3/8” input shaft that is available from most manual transmission parts dealers. For details on swapping the input shaft, I created a separate tech article: http://www.fordmuscle.com/forums/tec...placement.html

This article describes how to modify the small block fork for use with the big block input shaft.

Although I could buy all the parts needed to update the transmission, the throwout bearing that was required to complete the conversion needed to be from a big block car. Much to my surprise, my existing small block clutch fork was too narrow to fit this new throwout bearing. Also, a factory big block Ford clutch fork was much too long to fit within my existing header configuration.



I made a quick call to David Kee and he told me what to do, as he has done many of these conversions. He suggested that I purchase a reproduction 428CJ fork and graft the forked end to my existing small block fork.

Below is a comparison of the 2 forks, with the typical small block fork on top and the 428CJ on the bottom:







I laid the 2 forks side by side and determined that they are practically the same except the part that sticks out of the bellhousing.



Before I did any cutting, I created a template out of cardboard that showed the shape of the original fork. Tracing it out was pretty simple and I marked a couple of key locations, such as the pivot area:





Once this was done it was time to get to work with the chop saw. I determined that the best grafting location was 1.22” from the primary pivot point and I cut the small block fork there.



I them moved on to the 428CJ fork and cut it so that it was 1/8” longer. The extra length allowed me to custom fit the ends for the best fit with the small block fork. A few quick swipes on the belt sander helped with the final fitting. I used my template to verify that the angles and length of the parts were correct. For strength purposes, it is important that all parts butt together squarely before welding:



Once I was satisfied that the butted fork pieces matched the template, I tig welded the parts together after practicing on the disguarded sections:



Interestingly, the material hardness of the original Ford fork and the reproduction was different so the practice run certainly paid off. I welded one side of the fork, letting it cool. Then I flipped it over to weld the opposite side and again let it cool. Note how tightly the parts fit together mechnically:



After all welding was complete, I cleaned the modified fork and gave it a generous coating of black paint. Here is the final product:











I installed the modified fork in my car and was able to successfully complete the remainder of the race season.

A companion to your input shaft upgrade: ?

What I'm waiting for is your story when you go to the local Auto Zone and ask for a replacement.fficeffice" />

OTOH - your tech article is a reminder, blueprint when/if this needs to done again in the future. Its great when "in the trenches" regular guys compile, publish these hints and how-to's.

I have to go back to the old Motors manuals, last published in the 70's (?) to get the illustrations, detail that comes from someone that has "been there - done that". Our local Library was going to toss all the old manuals many years, but decided to hold a used book sale first. Between what I bought and what I was able to "reclaim" from the leftovers - I started my own little technical library, 90% of what I learned about working on cars came from those old-style, hand illustrated manuals. As far as I am concerned, they were works of art as well as great manuals.

Most of the manuals that are currently published are woefully inadequate. They only give enough information to get the novice in trouble ... or provide technically correct information, but no hint of why it works nor the steps (gottcha's) that get you from step "A" to step "B"...

that pretty involved. how is it holding up...???? Im guessing you have a soft pressure plate...
What I did was simply cut the stock fork in two spots, spread the fork till it fit and welded it back up, no need to search for and buy a new fork...

Grafting the forks is a common way of making this conversion and the original idea (at least for me) came from David Key Toploaders. He said that he has done over a dozen of these and has had zero issues.

So far the fork has held up fine in week to week drag racing and some street driving and yes the racing clutch has a low pedal effort. I kept the template so I can do a comparison the next time I service the clutch.

If you have any pics of splitting the forks, please post them here as it gives readers yet another option. I considered doing that too, but really didn't want to mess with the riveted spring clip of the late 60's fork that I used.