XK 120.brake master cylinder

Has anyone used a firewall mounted MC on a left hand drive xk120? Objective is to move it to a cooler place than in such close proximity to the exhaust manifold.
Mechaniker 54xk120fhc

no need to do that…do use the heat shield part, use a quality hi temp brake fluid, Dot 3 or better Dot 4 which has a boil point that is 25-45 deg F higher thant Dot 3. . Good fresh fluid …as old fluid can have (no…WILL HAVE) moisture absorbed (water)…and as we know water boils at 212F sea level…lower at altitude…so if water in the fluid…then it is a problem.
Sure you could engneer a move…have to fiddle with linkages, pedal travel, push rods to get the correct master cyl travel. Why bother. Thousands of XKs raced and driven…with MC where it is…Install the heat shield. Use Dot 4.

Agree, I had to bend the repro Falcon down pipes away from the MC, I got a 3-layer heat shield from British Auto, always use DOT 4, and I’ve never had a problem with fluid boiling in mine.

That’s one problem that those of us with RHD cars don’t have to contend with! But then, we have other problems - like restricted access to carb jets, starter, solenoid etc, with that big steering column in the way…

Thanks Nick !

Thanks Rob! Is that a single MC in your photo? I’ve relined my double MC in brass but still haven’t solved the tilt-valve problems.

Yes, my MC is a single.
The bolt hole spacing is different for the tandem, so there is a different heat shield.

I’m wondering why Tom and Martin are having problems with the tandem MC.
Are there different versions, and thus possibly wrong parts in some of them?
What about wrong spring strengths?
Is there a service bulletin about it?
Can someone post a picture of one disassembled with all the parts shown in order of assembly?



You have shown about all the drawings one can find on the subject. Unfortunately, I didn’t take pictures when a dis(assembled) my original Lockheed version.

There is one additional source available: on the website of our Bristol colleagues. See this link.

Page 13 to 15 describe the Lockheed tandem master cylinder, that was also used by Bristol during a short period: similar problems as Jaguar had? The disassembly description (made by Bristol engineers) is short but complete and may be of use for Forum members.

Bob K.