'52 XK120 FHC - convert to tandem master cylinder?

Our 120 has a single circuit master cylinder, and I’d like the safety of a dual circuit.
I see that some later XK120s used a dual circuit setup, but then reverted back to single(?).

Is a conversion to a dual setup as easy as swapping in a later tandem MC and routing new lines (lines sold as sets by the usual vendors), or are there other issues or reasons why this should not be done?


Not easy, the mounting bracket on the chassis is different.
The dual MC has tilt valves which give trouble.
Maybe that is why they reverted back to single on the 140.
If kept in good condition, there is no reason to worry about the single system.
I’ve been driving mine 25 years and it has always been fine.
You always have the hand brake as a backup.

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<Reminds me I must tighten my handbrake!>

@baloo what is your chassis number? I believe #679622 was when they started installing the Tandem MC.

I ask because 1953 FHC #680000 currently has a single MC setup (and manual adjustable brakes). It all looks very stock (to my untrained eye), but everything I have researched points to the car originally being a Dual MC. I guess perhaps at some point it was swapped from dual to single due to the issues @Rob_Reilly mentioned (and probably lack of dual MC parts, if even 140’s used the single MC…). I am a bit of a purist, so may at some point try to return the car to it’s dual-MC originality.

And as to whether you need to worry about a single MC failure - not if you have the great Scott Henderson around (RIP):

CTann – my chassis number is 679526

Concerns about a single MC prob related to personal experiences, and one can never guarantee perfection.
Last one was with a 1960 Lincoln with a single unit. Line failed and all fluid shot out of the system thru that point.
Just would rather not get into that hopeless feeling again.

HOWEVER, if extreme modifications are necessary to mount a tandem unit, it just might not be worth the time – too many other projects needing simpler repairs, huh.

BTW, Rob, what are “tilt valves”?

Tilt valves aka compensating valves are in the supply line ports from the reservoir.

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