[xk] Clutch forks, again, again .... success!

[John]

Guys,
A good friend finished rebuilding my transmission. He’s a
professional mechanic who drives me nuts with his high
standards and unwillingness to do shoddy work. My clutch
fork needed replacing. One of the 2 arms was about 75%
cracked through (what good luck that I redid it this
winter). I ordered a new fork from one of the usuals.
Pretty, but the cast Aluminum part didn’t look very strong
and I’ve heard this part has failed on at least one other xk
owner. I tried another one of the usuals, nice part but very
expensive. Then I took a chance and ordered some parts from
a popular UK supplier. My finicky mechanic friend said,
‘‘very nice, let’s put it in.’’ The best part … it was half
the cost of the other ‘‘very nice’’ part. Based on this and
other parts I’ve gotten from them, I’d not hesitate to use
them again when one of our own domestic suppliers can’t satisfy.

PM me for details.

John–
John
MA, United States
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[Mike_Eck]

Hi John,

There’s nothing wrong with saying something nice about a supplier. How
about letting the list know where the proper part can be had.

Mike Eck
New Jersey, USA

jaguarclock.com

'51 XK120 OTS, '62 3.8 MK2 MOD, '72 SIII E-Type 2+2> expensive. Then I took a chance and ordered some parts from

a popular UK supplier. My finicky mechanic friend said,
‘‘very nice, let’s put it in.’’ The best part … it was half
the cost of the other ‘‘very nice’’ part. Based on this and
other parts I’ve gotten from them, I’d not hesitate to use
them again when one of our own domestic suppliers can’t satisfy.

PM me for details.

John

[karl]

In reply to a message from John7 sent Thu 12 Apr 2012:

John,

What was the manufacturing process used to make the fork you
installed ? Please indicate how you were able to determine this.

Karl–
karl
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[John]

In reply to a message from karl sent Thu 12 Apr 2012:

I wasn’t sure if it was okay to say something nice about a
supplier. It was Coventry Auto in the UK
(www.xkparts.co.uk). The part number was 3352 selling around
50GBP (roughly $80).

Their catalog says this fork is cast from a Bronze-Aluminum
alloy. All I know is that’s it’s of similar density to the
old fork, and much denser than the bright silver Aluminum
fork I got from the usuals.

The original fork, C582, is supposedly forged. All I know is
that the fork that was in my bell housing is a dense alloy
that looks like a forging. And, yet the fork arm where the
securing pin is inserted was cracked nearly all the way
through. I could open up the crack just by bending the fork
in my hands.

Perhaps more importantly, the old arm had the hole for the
pin drilled all the way through the ‘‘barrel’’ and up through
the bass of the fork arm. This hole surely must weaken that
arm (the one with the crack). The new one from COventry had
a hole for the pin that only penetrated the barrel. It did
not go into the part of the barrel where the fork arms
branch out from. This should make it stronger.–
John
MA, United States
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[Ed_Nantes]

In reply to a message from John7 sent Thu 12 Apr 2012:

Out here , that’s called ‘Aluminium Bronze’
Which is a very hard bronze alloy , I think also used on the gear
selectors

It has very good wear characteristics,. However that’s is not the
same quality needed for a clutch fork which is tensile strength.

Density means nothing in this context . Lead would be denser , but
useless.

I also don’t feel that the taper pin going all the way through the
fork is a bad thing.

What it does do is ease the load on the tapered pin The taper pin
is less likely to break if it is held at both ends.
In addition the hole for the pin, which from memory is a one
degree taperl needs to be reamed in situ and this would imply the
taper reamer must exit on the other side of the shaft during this
operation.

Hard to do with a dead end hole.

This is not to say the fork won’t work but the description
doesn’t necessarily back that up.

Personally I would have gone for an original factory item
They seem to have also been used on MK VIIs, and of course on MK
Vs [ although I don’t know whether that had the same offset]

But these cars aren’t of as great monetary value and parts
generally aren’t as expensive as the same items on an XK.–
The original message included these comments:

Their catalog says this fork is cast from a Bronze-Aluminum
alloy. All I know is that’s it’s of similar density to the
old fork, and much denser than the bright silver Aluminum
fork I got from the usuals.
Perhaps more importantly, the old arm had the hole for the
pin drilled all the way through the ‘‘barrel’’ and up through
the bass of the fork arm. This hole surely must weaken that
arm (the one with the crack). The new one from COventry had
a hole for the pin that only penetrated the barrel. It did
not go into the part of the barrel where the fork arms
branch out from. This should make it stronger.

–
Ed Nantes SS
Melbourne, Australia
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[karl]

In reply to a message from Ed Nantes sent Fri 13 Apr 2012:

John,

As Ed points out, the casting is a risk.

There was a very lengthy discussion of this same subject here
recently as you noted, and I think that the concensus [ knowing
full well that to say this may be problematic ] was that lacking
angineering information about the aluminum bronze fork, it was
safer to go with the tried and true forged steel part.

As to the input from your mechanic, I would say that spotting an
obviously bad part thah has rough appearance is far easier than
spotting a bad part that looks really nice but is made of the wrong
material. In this case, I think it is fair to say that an attribute
that may not be obvious - the process of manufacture - is critical
here because we are not simply concerned with tensile strength.

Given the large ‘‘cost’’ if you get it wrong; taking the car apart
would make me risk adverse.

Karl–
karl
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[Rob_Reilly]

In reply to a message from karl sent Fri 13 Apr 2012:

C582 Operating Fork and C568 Pin were used on all Mark V.
That is such a low part number that I suspect it was also
used on previous models.
Also listed for all XK120.
C9780 Operating Fork with C568 Pin is listed for all Mark
VII, but this is such a high part number that I suspect it
is the later replacement, and that early Mark VIIs also used
C582, and the catalogue writer simply left off the old part
in my book.
C9780 is listed for all XK140.
So it ought to be a direct replacement for C582 in all cases.
I agree with the others, I wouldn’t trust a cast part here
with such a bending moment load. Have you ever seen a cast
torque wrench?–
XK120 FHC, Mark V saloon, XJ12L Series II, S-Type 3.0
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[John]

In reply to a message from Ed Nantes sent Fri 13 Apr 2012:

(1) I couldn’t find anyone selling the OEM part. Everything
was a repro

(2) The hole for the taper pin that goes all the way thru
the barrel of the fork that I took out: There’s a problem
with this. That through hole takes a big chunk of the metal
away from the base of the fork arm. I don’t know if this is
why my fork is failing at that arm, but it sure seems like a
good hypothesis. (see http://tinyurl.com/8yfywwy ) On the
other hand, the failure mode of the pin is a shear failure,
which is pretty unlikely given the diameter and the good fit
between the fork and shaft.

(3)Yes, I know that tensile strength is what we’re after.
But, the density at least showed that it was not cast
aluminum like the one a very major ‘‘usuals’’ sells. One of
our local XK owners tried one of those only to have the
barrel section break apart within a couple years.

(4) The fork arms are substantially larger in cross section
than the C582 that came out of the car. So much so that the
retainers for the clutch throwout disc needed to be modifed
slightly to fit.

(5) Yes, I’d love to use a forged part, but for $164…
Were the originals forged or cast?

John–
John
MA, United States
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[karl]

In reply to a message from John7 sent Fri 13 Apr 2012:

John,

We are trying to help you, not frustrate you.

The reason a forged part is preferred for this application is that
forging process actually deforms the softened metal grains and
aligns them with the load paths in the finished part; it is much
more than just tensile strength of the metal per se. A casting
process just does not do this.

In the end you are going to decide what you decide, and live with
the choice, but I guess some pretty experienced people here seem to
be encouraging you to use the best part available, and it seems to
me to be fair to say that a few hundred dollars is a small price
for a pretty important part in the grand scheme of things.

Karl–
karl
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[Ed_Nantes]

In reply to a message from John7 sent Fri 13 Apr 2012:

John

To clarify

‘’ Bronze aluminium’’ or aluminium bronze is not aluminium.

It’s a particular bronze alloy that has presumably some %age
aluminium in it . In the same way that silicon Bronze is not
silicon but like many alloys has a percentage of silicon.

Personally I’ve seen far more pins break than yokes.

What is a worthwhile thing to do is after assembly put a dob of
MIG on the joint between the yoke and the shaft.

This will avoid the situation where there may be say .001’’ of
movement between them which through working gets to be more and
more and the operating of it eventually shears the pin.

This whole problem is why the pins were tapered and the hole in
the shaft needed to be reamed to fit that particular pin.

If you think that is tedious , remember in the 20s Roll Royce
used taper shank bolts[ same amount of taper] and every one was
individually reamed to fit that hole.

If it’s all done properly, by the time the shaft is worn inside
the bushes it will need to be replaced and one can cut it with an
angle grinder to remove it.

The earlier cars and maybe Xks also had a similar pin on the
operating lever outside the bell housing. This had the same
tendency to snap. One did a number of years ago on one of my cars
and I decided to MIG it in situ rather than pull the engine and
gear box out.

As to Rob’s comments about how long the same part had been used
… The 1936 SS parts book the same item … before they started
using C… partr numbers , but rather ‘’ detail numbers’ But one can
x ref the detail number with later SS parts book which provided
both and they were the same. It probably actually predates that to
the sidevalve SS1s.

As I said second hand ones should be available and not overly
expensive
Personally I’d always try MK VII parts people first as Mk VIi
owners are unlikely to pay as much as XK owners

Worcester Classic Spares would be a good start.–
The original message included these comments:

But, the density at least showed that it was not cast
aluminum like the one a very major ‘‘usuals’’ sells. One of

–
Ed Nantes SS
Melbourne, Australia
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[holland-rick (holland-rick@juno.com)]

John,

In the absence of a decent steel fork,

I’d go with your “new” bronze aluminum alloy.

I have used a fair amount of “bronze” wrenches gleaned from mechanics
working in explosive atmospheres. These are the non-sparking
replacements for steel. They are quite a bit tougher than one would
expect and they were “open end”.

If your alloy unit is anything near the composition of these wrenches, it
should be more than adequate.

As I said before, IMHO, fork damage is caused by mal adjusted linkages
that put too much travel (over travel) on the throw out that allows it to
bottom and eventually break, shear the pin, or crack the fork as it has
no other place to go.

You only need to release the clamping on the friction disk. Widening the
space to its limit has little purpose, but some folks not familiar with
the non synchro first gear (think the clutch is dragging) adjusted the
linkage well beyond the “stops” leaving the fork and pin vulnerable. The
applied foot pressure is tremendous! The normal effort needed to just
release the clamping pressure, IMHO, not so much!! Think on it!

Good luck,

Rick____________________________________________________________
Get Free Email with Video Mail & Video Chat!
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[JBrady5282 (JBrady5282@aol.com)]

John,

I saw your rebuilt tranny/bell housing assembly at Pete’s yesterday and it
looks great. I check out the new clutch fork too and it looks
substantial. As you said, the actual arms are larger than the originals. I doubt
that you will ever have a problem with it again.

I have two C582 clutch forks that have failed. One was on my car when I
got it in 1974. The other one I picked up on a parts buy several years ago
and I have kept it despite it being no good because it failed in the same
place as my original from my 120.

The failures occur exactly as yours was about to fail. The right side arm
has a major crack in it at the base where it meets the barrel, exactly
where the taper pin hole is located. It is an obvious design flaw as it
removes about half of the base of the arm. I suspect that the thinking was to
give the pin a double shear support situation but in doing so, it weakened
the arm itself to the point where the failure mode is transferred here
rather than the taper pin. I also note that this hole at the base of the arm
breaks through on the side of the arm, and the stops. It would not really
permit a reamer to pass through.

I also picked up a new C9780 clutch fork on ebay last fall. This is the
“improved” model. There is no hole extension into the clutch fork arm at
all. It puts the tapered pin back into single shear loading, but strengthens
the fork arm by not drilling the base of it out. So Jaguar figured it out
and corrected it on the XK140 and XK150 by going to the C9780. If you can
find one, it is a direct replacement (advice for other listers).

John Brady
678462
Bedford, MA

[John]

In reply to a message from karl sent Fri 13 Apr 2012:

Karl,
Yes, I know and I owe all of you guys all the beer that
would fit in the XK boot and more for the help and advice
I’ve received over the last year.

I agree with all that say I’m playing Russian Roulette with
a cast versus forged fork.

However, the original forged fork design is, IMHO, flawed
because the pin hole weakens the base of one of the fork
arms. And, as stated earlier, that’s exactly where my fork
was about to fail.

Here’s a picture (courtesy of another forum member) of a
cast Al fork that failed on him. Looks like it failed at the
pin hole. So, perhaps another design shortcoming is that the
force is applied to the fork at one point that’s all the way
at one side of the barrel. The load of the clutch diagphram
will be equal on both arms, so this introduces an asymmetric
stress.

So, the professional mechanic drilled a 2nd hole thru the
fork barrel and shaft at the end opposite of the usual pin
and installed a hardened steel bolt. So, the the load on the
fork barrel is halved for the bin, and there should less to
no twisting force on the fork arms.

Maybe it’ll fail on me after a few thousand miles. But, I
felt it was worth giving this part from Coventry a try and
I’m ready to pull the transmission if necessary should it
break. If that does happen, I may ask the boys at work to
mill me a new fork out of a solid block of high strength
steel alloy.

John

P.S. Brady, don’t ask how much it cost to do the
transmission. Let me just say it was more than it would have
cost to send it to Walt at Vintage Jag. But Pete’s a pal and
ultimately the price of the work was less important than
doing the job with someone I enjoy working with.–
John
MA, United States
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[Ed_Nantes]

In reply to a message from John7 sent Sat 14 Apr 2012:

To look at the issue from another direction

Would using a diaphram clutch put less load on the yoke??

I’ve used them in the last couple of my cars and they’ve been
great.–
Ed Nantes SS
Melbourne, Australia
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[John]

In reply to a message from Ed Nantes sent Sat 14 Apr 2012:

Ed,
Funny you should mention that, but yes I did switch to an
e-type diaphragm setup.

There is allegedly some reduction in pressure, not that
the spring type was excessive.–
John
MA, United States
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[Alban (Gorriz)]

Hi John,
I’m also thinking of making a second hole in the fork. What is your feedback after several years. Thank you very much. Alban France

[Robin_O_Connor]

Hi Gorriz, first welcome to the forums, second I’m not sure if John will be able to remember what he did as the post you are referring to was back in 2012

[John]

Alban,
Robin is right. I don’t frequent the forum much these days as my zk120 is pretty reliable.

My clutch fork (from Coventry Auto in the UK) with second hole continues to work well, and I have no reason to believe it won’t outlast me.

John

[gaetan (martella)]

Bonjour Alban , je vais bientôt refaire mon embrayage, et fourchette sur xk 140 ots , de qu’elle diamètre avez vous percé et de quelle profondeur ? merci gaetan dans le doubs

[Alban (Gorriz)]

Bonjour Gaetan
En fait j’ai retourné l’axe et utilisé le deuxième trou déjà percé pour la conduite à droite. Ensuite j’ai placé deux goupilles coniques, coupé les têtes des goupilles pour qu’elles ne frottent pas sur la cloche. Le résultat semble très solide.