Clutch Operating Forks C582 C9780 and Tapered Pins C568 C13055

I thought we might start a new thread for this, to make it easier to find with a Search in the future, as it’s sure to come up again.
(adding the decimal points for future searches) C.582 C.9780 C.568 C.13055

We’ve heard about failures of the pin, and failures of the fork.
The parts date back to the pushrod cars going back to 1936 when they were buying them from Standard Motor Co. and had a Standard part number.

From the 1936-37 Spare Parts Catalogue

The 1938-47 Spare Parts Catalogue shows both the Standard numbers and the Jaguar numbers.

The Mark V and XK120 SPCs drop the Standard numbers.

1954 XK120 SPC

Here is one from a LHD Mark V. Notice the hole in the arm above the screw pin.

Here is the lever on the end of the shaft, with the original wire wrapping.

They used the same pin in both places.
The idea was to have the tapered screw pin extend through the shaft and be in a loading condition called double shear, both ends gripping, so the pin would be less likely to shear through.
The fork arms measure 0.437" wide x 0.563" deep (11.1mm x 14.3mm).
The pin measures 1.562" overall with 0.937" long shank (39.7mm and 23.8mm). Taper is 0.326" to 0.309" (8.28mm to 7.85mm).
The 2 holes in the shaft that are used are also tapered. I discovered the unused hole for RHD was not tapered. Perhaps they reamed them as needed for LHD or RHD. The workman would also have had to make sure he didn’t ream them in the wrong direction.
The idea of the square head and tapered pin is that it should screw in until it is captured in the taper. But it might not fit tight in the hole on the other side of the fork bore, so would only be tight on one side.

The through hole in the fork is a manufacturing error, somebody just drilled them too deep and the drill bit broke through the side, and nobody caught it for years. This makes it a weak place, where bending force as it pushes against the pressure plate will eventually cause fracture there.

Maybe they never failed in the pushrod cars, but fail in the XK120 because it has stronger springs in the pressure plate than the saloons.
Something to be aware of in XK120 anyway.

The part number changed with XK140. No bogus hole in the opposite side of the bore, and it has arms a little stronger. The pin is shorter and does not extend through for double shear. Apparently they decided single shear was good enough.

Here is an XK140.

The fork arms measure 0.469" wide x 0.563" deep (11.9mm x 14.3mm)
The pin measures 1.219" overall with 0.531" long shank (30.1mm and 13.5mm). Taper is 0.319" to 0.316" (8.10mm to 8.03mm).

Here is C582 with C568 on the left, C9780 on the right. The pins are shorter, but the same part number C568 is listed.

It’s tough to get those rusty pins out. As you can see, even heating with the torch, 3 out of 4 sheared off. Since they are tapered, you get the broken piece back out the reverse of how it went in, with a hammer and punch.

If you broke a long pin in a C582 you might be stuck, can’t get the shaft out. Maybe that’s why the C582 has that hole, to drive out the broken piece of the pin. :laughing:

My Mark VII SPC only lists the C9780, but maybe it’s a later edition and it superseded the C582, but again with the C568 pin.

The shaft was superseded on 120, no reason apparent.

The C9780 fork appears to be a straight retrofit in the earlier cars with the C582 fork, but you need the shorter pin.

The XK150 SPC shows a tapered pin with a different part number, and a spring washer. I believe FG107/X would be a 7/16" single helical spring coil lock washer.
It is not clear why it needed a lock washer if the pin was tapered. If it was not tapered, it would screw in all the way, and a lock washer would make sense under a hex head. Did they go with a hex head on the pin?
XK150 and Mark IX were the last Jaguars to use this design for clutch operation.
Mark 1 & 2 did not use it.
All the above is reporting only on the original parts.

Now we need to hear about the reproductions. Are they taking these factors into consideration?

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Excellent write up Rob. I will check my fork later this week for the drilled hole. Possibly existing forks with the hole drilled all the way through could have a spot weld to close up the hole and possibly add some strength.


I believe the XK150 went with a non-tapered pin with a hex head, still lock-wired, though.

That is my understanding too. If you go to the Coventry Auto Components web site you can see that they recommend the XK150 set up with parallel pins with hex heads as a retrofit for XK120 and XK140:
Unfortunately, it seems that their clutch fork and operating lever (the one of the same shaft as the fork, outside the bellhousing) are out of stock, as they have been for the past six months as far as I can tell. I believe that the clutch forks (C.9780) listed on the web sites of “the usual” US suppliers (“cast in SG ductile iron”) are sourced from Coventry Auto Components, and are also on back order. The usuals used to list a much less costly part which appeared to be cast from some light alloy. The one I had failed, as did the two external operating levers made from the same material. I each case, the female threaded hole in the parts split - all of these were fitted with the “short” tapered pins. One note on the tapered pins - the originals had 7/16"-18 BSF threads while many/all of the repros are 7/16"-20 UNF. The repros don’t all have the same taper, or diameter at the start of the taper. As a result, fitting the pin to a shaft may require taper reaming the hole in the shaft to match the taper of the pin, and to allow the pin to thread far enough into the fork/operating arm to get the maximum thread engagement while still having the pin taper lock into the shaft. With many of the pins I bought, that simply wasn’t possible for one reason or another.

I’m struggling to understand why the parallel pins are viewed as an “upgrade”, as the diameter will never be a perfect match to the hole, so some slop is inevitable. The only thing I can think is that they are more robust because they can be tightened all the way down into the fork/operating lever, so side load is taken by the entire length of the thread, whereas with the tapered pin, there may not be nearly as much thread engagement.

Quite possibly, although looking at the bellhousing of my 150 it has a square head pin.
You will note that the previous owner took a shade-mechanic belt & bracers approach by having the pin, AND a few carefully laid beads of weld, applied in the master-craftsman’s manner that I have found on the rest of the car…
Didn’t even bother to run the bead around the shaft

Hi Rob, on the Mark V I have experienced the sheared tapered pin, but as you say, not seen a fractured fork on the pushrod application. Among the clutch assemblies I have taken off pushrod cars there is one C.9780. That C.9780 fork has a hole in the opposite from the threaded pin, however, that hole is completely in the flat of the square shape of the fork which gives it an offset to the threaded pin hole. The hole in the flat could not have been drilled in from the threaded pin hole side and only gives a partial overlap of where driving out a broken pin might be tried (but it might be enough overlap for that purpose).

I’m also waiting on some parts on back order at Coventry Auto. They said that some of their manufacturers are having trouble sourcing materials… The light alloy parts should definitely be avoided from what I have read.

Hi Roger,
Hopefully you were aware that I was making a joke about the hole in the fork having an intended purpose for which the designers would not have anticipated, 80 odd years in the future.
It is a mystery to me why a C9780 would have a hole at all.

Chris, I entirely agree that an alloy fork or even a cast iron fork does not make sense in this stressed application.

If I were reproducing them, a hot drop forging or hogging one out of cold rolled bar stock is my view, and I would use a large Woodruff key and put a set screw in the center.

Are you sure that the C.9780 has that hole? I thought that was only the original XK120 part C.582 that had it. Here’s a photo of the C.9780 in my XK140 before I replaced it (silly me!):

I replaced it with the “new improved” alloy part when the clutch wore out. Here is the alloy part:

The original C.9780 part is now back in the car - note that it is secured using the hex-headed short parallel pin:

One other comment. It’s always seemed strange to me that the pin in the fork is located at the far end of the “barrel” of the fork from the operating lever. Why not locate it in the center where it is stronger? Then I remembered that this was designed as a RHD car, so is it located where it is to be as close to the operating lever (RHD) as possible?

Thanks David for the confirmation on the hex head, and I can see where they would call for a lock washer on there to make sure it stays tight, since the pin was not tapered anymore. The wire would not guarantee that.

I only have information going back to 1936. It would be interesting to see what they were doing in the earlier side valve models and other cars made by Standard in the '20s.

My guess on why they offset the boss for the pin hole is they wanted to drill into more meat on the top, so they aimed at a fork arm rather than in the center. They should have drilled in only about 1/16" to 3/32". But the command didn’t follow through to the execution; the apprentice drilled them too deep.

Here are some photos of C.9780 fork to show the hole in the “tine” of the fork which is not coaxial with the securing pin threaded hole. From the photos it looks like the hole was deliberate in production of the part and not a later bodge. However, I have only the one piece and do not know if these holes were found always in C.9780. What is the purpose? It does surely look like the C.582 forks I have come with rather variable finishes on the partial holes in the sides of the tine area, different from this C.9780.

Also, I have the impression welding cast iron to steel is not recommended in joints with frequent mechanical jousting.

I bought my '60 XK 150 with a non-working clutch, A clean Left Hand Drive. Discovered one tine of the fork badly bent back and the Hex Head screw was sheared as well. Shaft is bent and fork removal is a fight. Waiting on the heavy Aluminum Alloy forks to emerge from supply chain. The clutch shaft is bent as well. So may I assume a bent shaft is damage and not some design attempt to keep the release bearing approach parallel as it rotates on a circular shaft.

Welcome David.
You are correct that a bent shaft is damage.
That is surprising damage, suggesting a monster pressure plate, way too much tension.
The release bearing always moves in an arc and is designed to move in a sliding manner against the rotating pressure plate.
Several on this forum have had bad experiences with the aftermarket aluminum forks.
If it were mine, I would cut the shaft and try to save the forged fork.
And measure the pressure plate operating force.
Here is the info for XK120. I don’t have any info on 150. It may be a little more than 140 pounds, but I would think not a great amount more.

Thank you Rob and good to see a timely subject. I hear the stronger aluminum bronze alloy forks are due in soon. Just waiting to confirm parts availability before shaft cutting, but a fork finger(tine) is bent back significantly and not sure it could be brought back enough to hold the release bearing. The 150 has the hydraulic clutch and I have a 3.8L(existing is 9-7/8 with white thrust springs, so I don’t think the pressure would be too high, not like the purple spring E-type covers out there. I will measure the pressure plate operating force and have to sort out the hydraulic clutch workings upon reassembly.

Was someone on here planning to use the Crosthwaite & Gardiner fork and tapered pins? I seem to remember seeing that - how did you get on? Do they sell the whole set - fork, arm, shaft and pins that will work in a 140? I ask because the website lists half the parts as for D-type, and I’m not sure if they are the same.

Well that was foresight, as a Google search of " Jaguar part C.582" brings me right here !

I have a box of Jaguar Gearbox parts from a deceased estate, and C.582 are identifiable as they have it stamped upon them.

Am I correct in assuming these would be considered worthless pieces of junk, as they have the hole drilled, which greatly weakens the structure ?

The pins are all good, and it’s a shame to junk them, but surely any sane person would go with the upgraded XK140 style (no hole)

I do know repro parts can also be junk, and these could probably have the (drilled) hole filled with weld.

Opinions welcome, I wont throw them away just yet :smiley:

will try and identify the other gearbox parts from the parts manual, or pics on this forum

I would weld up the hole, but stop where the straight drilling ceases, so the pin will still fit. You may have to redrill the pin hole, and guard against distortion of the main through hole, or ream it afterwards.