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XK120 drum brakes

XK120 Drum Brakes

I believe that the XK-120 was shown at Earls Court merely as an exercise
and was not intended for production. That is why the first 80 or so were
made with hand-pounded aluminum bodies.  It wasn't until 1949-50 that
Pressed Steel Ltd. could provide steel body parts.  As for the brakes,
having owned and driven a MkV, I can tell you that they are awful. And
these were rebuilt to specs. They are mushy and definitely prone to fading.
The XK-120 and Mk VII brakes are no marvels, being drums, but they are
better than the Mk V. - William Kellner

With due respect ... I don't know much about MK V ,but I know that ,
despite their drums, 120 & MK 7 brakes properly rebuilt and adjusted are
perfectly adequate on
the road. I  have raced my 120 ( 660846) with steel drums / disc wheels.
and it is only on sprint type races / twisty circuits  that the brakes
would not last long. I have  been using my MK 7M for 27 years and the
brakes are OK for normal driving. Only when towing a trailer ( 3,5T total)
I have  to be cautious. I think that the problem is more with users /
mechanics who do not spend enough effort to make them work properly than
with the brakes themselves. The same is true about XK and MK 7 steering
boxes. - Michel Gosset

Dear Michel, thank you for your re-assurances.  Having not yet driven a
120, I am nevertheless in the middle of a total restoration of a car that
is intended to be "the one" that I keep "for ever" and have been quite
concerned due to the many claims of braking ineffectiveness.  Modern roads
are in superb condition compared to the surfaces I recall from my early
days of motoring in my Swallow Doretti, yet driving habits now make it
essential to be able to pull up rapidly as drivers are often very
inconsiderate in their habits, assuming that other drivers are in 4-wheel
disc-braked vehicles, as they
are.  As work progresses I may ask for details on the correct setup of the
braking system.  The Swallow was prone to brake fade, I recall, probably
due to my habit of testing its performance to the limit in the course of
trying to out-perform later model cars! - Regards, Phil Maurice

Dear Phil, The thing I forgot to mention is that the quality of brake
linings is crucial. It took me several attempts to find the right one ;  I
cannot remember what it was,  as this happened 25 years ago. There is
nothing magic about the set up. You have to have parts in good condition
and follow the manual's instructions. For road use , the important thing is
that the brakes are well adjusted and able to react perfectly in case of
emergency. Fading is not such a problem as you have to be quite
"uncivilised" to
reach this point on open roads. - Michel Gosset

My parents had a Mk1 from new (with drum brakes), and during the 1960s
there were import substitution programs and import restrictions in this
country.  One of the casualties was that you could only get New Zealand or
Australian manufactured brake linings (not to mention spark plugs). The
brake linings were apparently made to US specs which which had less
friction than UK specs.  This was OK for most of the old cars on the road.
But the Jaguar just would not stop (and fouled plugs).  Anyway, the point
is that a set of genuine Ferodo or Mintex brake shoes and a set of proper
spark plugs (bootlegged into the country) transformed the stopping and
going of the car. - regards, Mike Morrin

I had to think about the mushy comments for awhile, because my MkV brakes have
never struck me as being particulary mushy or otherwise bad in any way. They
can lock up the wheels if I hit them hard enough. And a road test by "The
Motor" reported braking distances that seem ok for a 4000 lb. 85 mph car with
non-vacuum-assisted drum brakes and bias ply tires, though perhaps marginal if
the car had been capable of 100 mph. I would have liked to try them again to
see if I agree or not, if I can detect what you guys are calling "mushy".
Unfortunately this discussion comes about a month too late, as I have already
drained my brake fluid (my MkV is into the disassembly phase of a body-off).

However, comparing the MkV system to the early XK120, I notice one difference
which may be related to the relative "mushiness". The length of the pedal arm.
The MkV pedal arm is a bit longer than the 120. So the difference between soft
braking and hard braking would translate into a bit more pedal movement for
MkV vs 120, thus possibly explaining the perceived impression of "mushiness".

I have often seen automotive history writers refer to the MkV as the stopgap
model, but I have never really understood what they meant by that. It sounds
to me like journalist's jargon. I don't imagine the factory people used the
phrase at the time. Factory people don't think that way, they look at each
model as a complete entity, intended to make a good profit for a time period.
The Mark V was designed in the 1946-48 period, and it was not designed to take
the XK engine because there was no serious hope of getting the XK engine fully
tested, wrinkles ironed out and into full scale production by late 1948. I
suspect some writer used the phrase in hindsight after the Mark VII came out,
and everybody else just copied him.

Dick mentioned the long bonnet. For any of you who haven't seen one with
the bonnet open, it is actually a bit deceptive. Some of that bonnet covers
firewall (scuttle); there is not nearly so much room available for the
engine. BTW Dick is correct in that the Mark IV was exactly the same as the
1939 models but with Jaguar badges replacing the previous SS hexagon
badges. Transitionary badges sounds like a great topic for pre-xk trivia
sleuths. Apologies to those who couldn't care less about Mark V's. This
maybe belongs on the saloons list. PS for Dick C. The XK100 was a 4
cylinder 2 liter version of the XK engine, which never got put into
production. According to "The Motor" it was to have 95 horsepower in
standard form, so maybe it wouldn't have been all that great in a MkV. I
wonder how many examples of this engine were made; I would guess less than
half a dozen. PS for Terry M. I have seen an original Mark V with light
blue leather and dark blue piping. - Rob Reilly



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