Looking for your thoughts on why the XK120 tandem master cylinder has an
o-ring seal on the horizontal outlet and a copper washer seal on the
vertical outlet. Looking closely at the master cylinder body, the appear to have
exactly the same machining with a land for the rubber o-ring.
I have had a nagging leak on the vertical outlet at this copper seal for
years and I am considering using an o-ring like on the horizontal (no leaks)
outlet to stop it. Any thoughts on the matter? It seems to me to be an
equivalent application and I can’t figure out why they used two different
sealing methods.
If you have banjo fittings as the parts book shows, then you
should have two soft copper gaskets on each, one larger than
the other. Copper work hardens, meaning you can only use it
once, or maybe twice, before it is too hard and won’t seal.
Then if you want to use them again you can anneal them with
a propane torch, heat them up until they turn color, then
let them cool slowly, and they should be soft again. Then of
course they have to be flat and without surface scratches.–
XK120 FHC, Mark V saloon, XJ12L Series II, S-Type 3.0
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Steel needs to be cooled slowly but copper works just as well if you drop
the hot washer in cold water. That has the additional benefit of flaking
off the surface oxide.
Mike Eck
New Jersey, USA
'51 XK120 OTS, '62 3.8 MK2 MOD, '72 SIII E-Type 2+2> Then if you want to use them again you can anneal them with
a propane torch, heat them up until they turn color, then
let them cool slowly, and they should be soft again.
–
XK120 FHC, Mark V saloon, XJ12L Series II, S-Type 3.0
On the tandem master cylinder there are two outlet adaptors and two
tilting valves, which screw into the body of the master cylinder.
As John notes, the vertical outlet adaptor seals with a very large
copper washer. However, the identical horizontal outlet adaptor
and the two tilting valves seal with rubber o-rings.
On my master cylinder, the horizontal outlet adaptor and the two
tilting valves (each sealed by o-rings) have no seepage
whatsoever. Like John’s master cylinder, the vertical outlet
adaptor, sealed by a larger copper washer, seeps ever so slightly -
enough to ruin the paint on the master cylinder body.
The last time I had the master cylinder apart, I anealed and
dressed-smooth the vertical outlet adaptor’s larger copper washer.
Then I tightened the outlet adaptor using a large socket and
breaker bar. But it still seeps.
I see no way to stop the seepage using the specified copper washer.
I agree, it’s worth a try using an o-ring.–
The original message included these comments:
Looking for your thoughts on why the XK120 tandem master cylinder has an
o-ring seal on the horizontal outlet and a copper washer seal on the
vertical outlet. Looking closely at the master cylinder body, the appear to have
exactly the same machining with a land for the rubber o-ring.
I have had a nagging leak on the vertical outlet at this copper seal for
years and I am considering using an o-ring like on the horizontal (no leaks)
outlet to stop it. Any thoughts on the matter? It seems to me to be an
equivalent application and I can’t figure out why they used two different
sealing methods.
Where is your stop light switch? I had a “weepy” top and blamed the
copper washer, however I found the switch was weeping and it looked like
it was coming from the terminals. Switch was working normally too!
The copper washer adds a bit of volume to the upper chamber but I can’t
see where that matters after bleeding. You could “tin” ( coat with
solder) the softened copper washer once it is cleaned up. You true it up
on some wet and dry but leave some soft solder on it to effect a seal. I
don’t know if all the tops are chamfered like the ends are. An “O” ring
may not always work and could blow out unless nestled in the slight
space.
Regards,
Rick
On Wed, 6 May 2015 08:12:56 -0400 JBrady5282@aol.com writes:> Looking for your thoughts on why the XK120 tandem master cylinder
has an
o-ring seal on the horizontal outlet and a copper washer seal on
the
vertical outlet. Looking closely at the master cylinder body, the
appear to have
exactly the same machining with a land for the rubber o-ring.
I have had a nagging leak on the vertical outlet at this copper
seal for
years and I am considering using an o-ring like on the horizontal
(no leaks)
outlet to stop it. Any thoughts on the matter? It seems to me to
be an
equivalent application and I can’t figure out why they used two
different
sealing methods.
John Brady
678462
Bedford, MA
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On the banjo bolt you are saying copper washer SINGULAR but
there are TWO, one on each side of the banjo, Plate AR items
42 & 43, Lockheed parts KL44518 & KL44522.
In reply to a message from Rob Reilly sent Thu 7 May 2015:
Rob,
We’re not talking about banjo fittings. We’re talking about
the locations where the threaded outlet adaptors (and the
threaded tilting valves) screw directly into the cast iron
body of the master cylinder.
The upper outlet adaptor (between the two tilting valves)
seals to the body of the master cylinder by means of a large
and thick copper washer. That’s where the seepage is occurring.
My point (and I think John’s point) is that the threaded
horizontal outlet adaptor, as well as the threaded tilting
valves, seal perfectly using o-rings. So why does the
vertical outlet adaptor (between the tilting valves) call
for a large and thick copper washer, which does not seal all
that well?
The only possibility I can think of is that the large and
thick copper washer provides some necessary spacing to the
internal moving parts of the master cylinder. If that is
not the case, then an o-ring might be able to replace the
large and thick copper washer to resolve the seepage problem.–
The original message included these comments:
I’m not clear whether you guys are talking about the tilt
valve seal or the banjo bolt seals.
In reply to a message from Mike Balch sent Thu 7 May 2015:
Ok, in Parts Catalogue J8 you mean Gasket for Adapters
(33443) quantity 2, but not appearing on Plate AR.
The next item listed is Seal for Outlet Adapters (31593)
also quantity 2 item AR23.
If you look on Northwest Hydraulics, the Lockheed 1932-85
catalogue pdf file page 207, it is showing the 33443 copper
gasket on the top (quantity 1) and the 31593 rubber seal on
the front (quantity 1).
So it seems Lockheed intentionally did this. It also appears
to be yet another mistake in J8, the quantities should be 1
each.
Now why did Lockheed do this? The top surface is a flat
contact face, is it not? The front is machined for a cup or
step insert face? Normally an o-ring is never used in a high
pressure application where it is not laterally supported.
The two inlet supply o-rings work ok because they are not
under any pressure. The front port has the o-ring in a step
where it is radially constrained. But I think if you put an
o-ring in the middle port and there is no cup or groove to
constrain it, it may blow out under pressure.
If I am totally off in left field here I would need to see a
photo of the top of this body with the adapter removed to
understand the design.–
XK120 FHC, Mark V saloon, XJ12L Series II, S-Type 3.0
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Yes, we are talking about the outlet adapter seals to the master cylinder
body and not the banjo bolt seals. And I think we are now agreeing that
there are two different types of seals on the horizontal outlet and the
vertical. And that is the root of my question. I see no reason for them to be
different as the machined portions of the master cylinder bodies are the
same. Both have a counterbore that can accept and trap an o-ring. And for
the horizontal outlet, on every tandem master cylinder that I have seen,
they have an o-ring.
So, can we agree that if it works fine on the horizontal outlet, it should
work just as well on the vertical outlet and I can substitute an o-ring
for the copper washer seal (that leaks).
I looked in a couple KL71504 Lockheed NOS rebuild kits that I have in my
stash. One has two of these large o-rings and the other one has only one.
They are both dated 9/77 on the box. So not definitive, until I look in
some more kits that I have, but it appears that if two are supplied, the
realization was made that they work on both? I plan to put them on both.
Ok, that’s what I wanted to know. If the top port has a
stepped counterbore for an o-ring, then yes, it should use
an o-ring rather than a copper gasket. If it did not have a
stepped counterbore it needs the copper gasket.
John, can you post a photo of that top port with the adapter
removed?
Tadek’s photos show his cylinder as found unrestored
apparently had a copper gasket on top, but I don’t see one
on the front, so it may have been a rubber one there.
I begin to suspect that Lockheed made the tandem cylinder
both ways, that the copper version preceded the rubber
version, and there may have been a transition period where
there was one of each.
As you may have guessed, I am very familiar with both copper
and rubber o-ring seals in my design work in ultra-high vacuum.–
XK120 FHC, Mark V saloon, XJ12L Series II, S-Type 3.0
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I will shoot a picture later and try to post it on the XK Lovers site.
Haven’t done this in a while so will see how it goes.
My brother Tom turned up some more info on the subject.
Service Bulletin 106, April 52, mentions the tandem master cylinder
assembly process and specifically refers to the two rubber washers (o-rings?)
used on the two outlet adapters.
I know you must have the SBs, but here it is as well.
Interesting. So why the copper seal? We will probably never know, but at
least it appears safe to use the o-ring on both adapters.
I can appreciate your high vacuum design experience that includes o-ring
and copper seals as I was also involved with high vacuum process equipment
design (single digit mTorr vacuum range) for the coating of razor blade
edges with diamond like carbon (DLC) and chromium in mass production for a well
known razor blade manufacturer in Boston by a process called sputtering.
Has anyone successfully used an o ring in place of the copper washer on the top outlet fitting? Upon inspection of my master cylinder it looks like the copper washer acts as a spacer to provide enough clearance for the check valve. With the copper washer removed it looks like the check valve and spring assembly is fully compressed not allowing any movement of the check valve. I am thinking of replacing the thick rubber washer that the check valve seats against with a very thin one to compensate for the removal of the copper washer. The other option would be to cut off a coil or two from the check valve spring.
I had a similar issue with my E-Type master cylinder - the fitting with the large copper washer had very slight weep that was annoying more than anything. I tried annealing again but it still wept fluid. Since it was a flat surface I replaced the copper washer with a bonded seal rubber like this … problem solved.
Not sure if that will apply to your XK120 tandem master cylinder or not?
Yes, I replaced the copper washer on the top outlet of my tandem master cylinder about two years ago and it stopped the nagging leak. Has been dry ever since and have had no problems with the associated rear hydraulic circuit function. The spring is not compressed fully and there is adequate clearance for the valve system to work. I used a second NOS Lockheed O ring (same as on the front outlet) which is quite large and is captured by the MC body counter-bores on both the top and the front and seals nicely. The machining is identical for both locations.
If you study the thread closely, we researched the topic very well.
I recommend that everyone does this to their XK120 MC’s.
John, l was watching the thread back in 2015 as it developed. My master just started leaking at the center outlet and I revisited the thread. The last message was you saying that you were going to try the o ring. I was curious how that worked out. I’m glad to hear that there’s no problem with the check valve clearance as that was my only concern.
