Modifying A Clutch Fork - Ford Muscle Forums : Ford Muscle Cars Tech Forum
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post #1 of 9 (permalink) Old 01-22-2009, 12:10 PM Thread Starter
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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.
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Dennis

65' Stang Street/Strip. Dart 434W NA, Victor heads, G101A 4 Spd, 4:56 rear gear, on 93 octane pushing 3550lbs. [email protected]

Last edited by FATNFAST; 12-23-2015 at 09:13 PM.
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post #2 of 9 (permalink) Old 01-25-2009, 08:23 AM
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Thumbs up Re: Modifying A Clutch Fork

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"...

" ... It is dangerous to be right in matters on which the established authorities are wrong. ..." - Voltaire
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post #3 of 9 (permalink) Old 07-26-2009, 08:39 PM
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Re: Modifying A Clutch Fork

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...

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post #4 of 9 (permalink) Old 07-27-2009, 03:53 AM Thread Starter
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Re: Modifying A Clutch 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.

Dennis

65' Stang Street/Strip. Dart 434W NA, Victor heads, G101A 4 Spd, 4:56 rear gear, on 93 octane pushing 3550lbs. [email protected]
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post #5 of 9 (permalink) Old 12-13-2012, 03:14 AM
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Re: Modifying A Clutch Fork

Very nice work! Im about to do this with a Galaxie setup, as i cant find anyone with the right one. Next time, leave a tiny gap before welding, it will assure complete penetration.
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post #6 of 9 (permalink) Old 12-13-2012, 07:26 AM
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Re: Modifying A Clutch Fork

Quote:
Originally Posted by EXracer4speed View Post
Next time, leave a tiny gap before welding, it will assure complete penetration.

Assuming that you have limited skills yes, but not necessariy a 'gap'. A slight bevel would work. Also depending on welder used will dictate the proper lay-out. TIG welding you would want no type of gap, as it uses very little filler metal. On the other end, the ole 'cracker box' lincoln welder you might want a 1/16th or hair more gap. EX if yo do one for the Gal, need to add to article, for others to follow...

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'61 Fairlane 500 292 2v Cruise-o-Matic also needing tlc
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post #7 of 9 (permalink) Old 12-13-2012, 07:36 AM
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Re: Modifying A Clutch Fork

Quote:
Originally Posted by dennis111 View Post
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.
dennis, i have actually had to use small nuts/bolts to repair a riveted fork in the past, back in the young dumb, no money days, and just wanting it fixed... lol Never had an issue doing them that way. I need a correct complete fork now for my '70 C-powered car now, for fitment/clearance checking issues, just havent ordered/bought one. (the one on car now has had about 3-4 inches cut off the end for header fitment from 'back in the day', when my leg was much stronger..... (probably why I was always chasing down the next gremlins for the time i drove the car..lol ) (twisting/bending the z-bar, bending the rods etc)... but did manage to make it work for over 10 years.... Once I got everything all "beefed" up.

Cheap, Fast, Reliable... Pick 2...
'70 Mach1 351C 4v 4sp 4:56's Been abused sense '79, needing tlc
'61 Fairlane 500 292 2v Cruise-o-Matic also needing tlc
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post #8 of 9 (permalink) Old 12-16-2015, 06:38 AM Thread Starter
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Re: Modifying A Clutch Fork

Feedback.

Its been over 5 years since I did the fork mod and I am happy to say that its still in action after over 1000 hard strip runs and 1000's of street miles.

Dennis

65' Stang Street/Strip. Dart 434W NA, Victor heads, G101A 4 Spd, 4:56 rear gear, on 93 octane pushing 3550lbs. [email protected]
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post #9 of 9 (permalink) Old 12-23-2015, 09:14 PM
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Re: Modifying A Clutch Fork

Images Restored
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Rick DeVito in Indy "Blue Thunder 408W" [email protected] mph 1.27 60ft Rod & Custom MII Sales
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