[xk] 1950 XK120 brakes

List members:

  1. Is there anyone selling an upgrade kit to a modern dual master cylinder
    setup in the U.S.?

  2. If not, any suggestions as to where I can get brake lines and connector
    fittings?

Thanks

Jake
1950 XK120 OTS

Hi

I sent this message a few days ago but no response and I need help.

Any USA suggestions?

  1. Is there anyone selling an upgrade kit to a modern dual master cylinder
    setup in the U.S.?

  2. If not, any suggestions as to where I can get brake lines and connector
    fittings?

Thanks

Jake
1950 XK120 OTS

Jake,

I began a reply, then felt I didn’t know enough about the subject to express
an informed opinion. Since no one has responded, I’ll jump in with my
opinions (as opposed to facts).

My first question is why? I know there’s the chance of a catastrophic
failure in a line leaving you with no pedal, but an emergency (not parking)
brake on a drum brake system is just as effective as if you lost the front
brakes. The tandem M/C in the later 120s is a front/rear system, so there is
little difference other than the added time it takes to recognize the
problem and pull the brake lever.

Old cars, especially those with single M/Cs, are not to be driven in traffic
with abandon. There is enough compression braking in the XK engine that if
you anticipate a stop sign/light or perilous situation you can be going
quite slowly before you ever need the brakes. Of course a test pump of the
brakes is always advisable.

Keep in mind, too, that the usual mode of brake failure is a softening pedal
before loosing it altogether. It will show up when you step on the pedal and
it stops you initially, but the pedal slowly eases to the floor due to a
leak in the M/C or somewhere in the brake system. You’ll generally have
enough brake to get off the road and get a tow, which you should do any time
you suspect a brake problem. The only way I can think of that you would have
a catastrophic, sudden no brake, situation is if a brake line burst. While
not impossible, that is highly unlikely. As most of us have experienced,
these lines disintegrate on the inside and cause blockages long before they
show any signs of outward problems. If you drive as if you have brakes that
could fail at any moment, you’d probably anticipate more than 95% of your
stops far enough in advance that you’d have time to safely fall back on the
emergency brake, further reducing the slim odds of a catastrophic failure
that would lead to an accident.

Now we get to the engineering side of the problem.

The pedal arrangement of the XK120 is unlike any I have ever seen. Although
hydraulic brakes had been around for a while, power brakes hadn’t. Nowadays,
everything you see pivots at the top. XK120 brakes pivot at the bottom. The
brakes are very good for an unboosted system, but modern M/Cs are based on a
boosted system. So you’d have to install a vacuum booster and associated
hardware including a hydraulic line to the modern M/C. To do that you’d
either have to re-engineer the pedal system or set up a slave cylinder on
the booster. A modern M/C would probably be engineered to work with disk
brakes, so you’d have to change all the hubs and retrofit rotors. XK150s had
them, so it should be possible, but from the XK140 on, Jaguars had
rack-and-pinion steering. The easiest way to convert to disks that wouldn’t
involve a lot of parts fabrication would be to convert the steering system,
too.

That said, there are people who race these and I would guess that some of
the sanctioning bodies allow brake and steering conversions. I’m certain
that it would give a competitor an edge which means it’s been done. I just
don’t know at what cost. If you were racing, I’d say seriously consider it,
but if the car is just used for pleasure drives, you’ll spend a lot of money
and decrease the value of the car at the same time.

It’s a double whammy that I can see costing you as much as $20,000 in
conversion costs plus lost vehicle value. Given the adequacy of the stock
brakes and the overall cost of the conversion, it’s not something that’s in
high demand which explains the silence and lack of knowledge of any such
kits.

If you are looking for replacement brake lines for the stock system, any of
the usual suspects – XKs Unlimited, Terry’s Jaguar Parts, Moss Motors, SNG
Barratt, and Welsh Jaguar Enterprises should have what you need.

“Mark 1” Mark Stephenson
'52 XK120 S673129, '59 Mk1, '84,'85,'86 &'95 XJ6-----Original Message-----
From: owner-xk@jag-lovers.org [mailto:owner-xk@jag-lovers.org] On Behalf Of
Jake Aslanian
Sent: 05/01/2006 7:23 PM
To: xk@jag-lovers.org
Subject: [xk] 1950 XK120 brakes

Hi

I sent this message a few days ago but no response and I need help.

Any USA suggestions?

  1. Is there anyone selling an upgrade kit to a modern dual master cylinder
    setup in the U.S.?

  2. If not, any suggestions as to where I can get brake lines and connector
    fittings?

Thanks

Jake
1950 XK120 OTS

Mark S;
Let me add a “fact” or two to your opinions… which are more valid
“facts” than you may realize.
First, I’ll agree it’s a very rare occurrence, but a single stage
system “catastrophic” failure can happen… it happened to me a couple of
times… once with a busload of motorcycle parts (estimated at over 15,000
lbs, plus the weight of the converted bus!) as I was coming off a (then)
70mph freeway into an older area of downtown Dallas… I pressed on the brake
pedal and with absolutely no warning nor resistance it went to the floor…
talk about “pucker marks” in the seat!! (I “picked cotton” for a week!!
;-} ) Fortunately, and as you noted, I was able to “gear down” (the
park/emergency brake was useless), even cramming the non-syncro gearbox down
into “Granny Low” (that was really noisy and I was planning to try to cram
it into reverse!), thus slowing down enough to start rubbing the brand new
10.00-20’s against the old eighteen inch curbs to get stopped before hitting
something expensive.
Second, not ALL modern master cylinders are made for “boosted
systems”. I will agree that a lot of “engineering & fabrication” would be
required to fit a “modern” master cylinder into an XK120, the cost, in parts
and labor (even one’s own), would far exceed that of just buying a complete
“late 120” tandem (Lockheed) brake set-up and installing it… (tandem M/C,
all six wheel cylinders, a new Kunifer brake-line set, either standard
Lockheed flex hoses, or SS braded hoses along with “modern” fade-resistant
brake linings on the brake shoes-- well, as “fade resistant” as drum brakes
can be, but a "panic/emergency stop is generally a “one time deal”, so
“fade” is not an issue!) The “effective” braking power of this system is,
in my experience, enough to handle any “emergency stop” one might encounter
in normal day-to-day freeway commutes, as long as one isn’t “bump drafting”
the Hummer in front of the Jag! ;-}
Charles #677556� 2006.----- Original Message -----
From: “Mark Stephenson”

Jake,

I began a reply, then felt I didn’t know enough about the subject to
express
an informed opinion. Since no one has responded, I’ll jump in with my
opinions (as opposed to facts).

My first question is why? I know there’s the chance of a catastrophic
failure in a line leaving you with no pedal, but an emergency (not
parking)
brake on a drum brake system is just as effective as if you lost the front
brakes. The tandem M/C in the later 120s is a front/rear system, so there
is
little difference other than the added time it takes to recognize the
problem and pull the brake lever.

              <Snipped>

Jake,

I am not aware of anyone who offers a split system conversion with modern
parts. Among many, try XK’s Unlimited in California or Guy Broad in the UK.
Either would be capable of a one-off effort.

The easy way would be to convert to the factory split system master cylinder
used on late XK-120’s, as every thing will come close to bolting up. But,
the tilt valves in these can be problematic, and even Jaguar thought the
pain not worth the effort and switched back to the single cylinder system
for the 140. That said, Wilwood makes split system master cylinders for the
street rod and hotrod crowd. See:

http://www.wilwood.com/Products/006-MasterCylinders/008-CRTMC/index.asp

The 1" bore should be adequate, but you will have to fabricate your own
bracket to mount such a device. The 50/50 output will require a
proportioning valve to limit pressure to the rear brakes, so you will need
something like this:

http://www.wilwood.com/Products/006-MasterCylinders/001-PV/index.asp

regards,

Mike Spoelker

Thank you

I also have a Porasche 356 and it’s a very easy substitution to use a VW
Beetle master cylinder.

Anyway, no such readily available conversion appears to exist.

Also, I replaced all the lines (hard and soft) with XK’s Unlimited kits - it
leaked everywhere so I’m in the market for replacements.

Thanks

Jake----- Original Message -----
From: “Mark Stephenson” mark@jag-lovers.org
To: xk@jag-lovers.org
Sent: Tuesday, May 02, 2006 1:22 AM
Subject: RE: [xk] 1950 XK120 brakes

Jake,

I began a reply, then felt I didn’t know enough about the subject to
express
an informed opinion. Since no one has responded, I’ll jump in with my
opinions (as opposed to facts).

My first question is why? I know there’s the chance of a catastrophic
failure in a line leaving you with no pedal, but an emergency (not
parking)
brake on a drum brake system is just as effective as if you lost the front
brakes. The tandem M/C in the later 120s is a front/rear system, so there
is
little difference other than the added time it takes to recognize the
problem and pull the brake lever.

Old cars, especially those with single M/Cs, are not to be driven in
traffic
with abandon. There is enough compression braking in the XK engine that if
you anticipate a stop sign/light or perilous situation you can be going
quite slowly before you ever need the brakes. Of course a test pump of the
brakes is always advisable.

Keep in mind, too, that the usual mode of brake failure is a softening
pedal
before loosing it altogether. It will show up when you step on the pedal
and
it stops you initially, but the pedal slowly eases to the floor due to a
leak in the M/C or somewhere in the brake system. You’ll generally have
enough brake to get off the road and get a tow, which you should do any
time
you suspect a brake problem. The only way I can think of that you would
have
a catastrophic, sudden no brake, situation is if a brake line burst. While
not impossible, that is highly unlikely. As most of us have experienced,
these lines disintegrate on the inside and cause blockages long before
they
show any signs of outward problems. If you drive as if you have brakes
that
could fail at any moment, you’d probably anticipate more than 95% of your
stops far enough in advance that you’d have time to safely fall back on
the
emergency brake, further reducing the slim odds of a catastrophic failure
that would lead to an accident.

Now we get to the engineering side of the problem.

The pedal arrangement of the XK120 is unlike any I have ever seen.
Although
hydraulic brakes had been around for a while, power brakes hadn’t.
Nowadays,
everything you see pivots at the top. XK120 brakes pivot at the bottom.
The
brakes are very good for an unboosted system, but modern M/Cs are based on
a
boosted system. So you’d have to install a vacuum booster and associated
hardware including a hydraulic line to the modern M/C. To do that you’d
either have to re-engineer the pedal system or set up a slave cylinder on
the booster. A modern M/C would probably be engineered to work with disk
brakes, so you’d have to change all the hubs and retrofit rotors. XK150s
had
them, so it should be possible, but from the XK140 on, Jaguars had
rack-and-pinion steering. The easiest way to convert to disks that
wouldn’t
involve a lot of parts fabrication would be to convert the steering
system,
too.

That said, there are people who race these and I would guess that some of
the sanctioning bodies allow brake and steering conversions. I’m certain
that it would give a competitor an edge which means it’s been done. I just
don’t know at what cost. If you were racing, I’d say seriously consider
it,
but if the car is just used for pleasure drives, you’ll spend a lot of
money
and decrease the value of the car at the same time.

It’s a double whammy that I can see costing you as much as $20,000 in
conversion costs plus lost vehicle value. Given the adequacy of the stock
brakes and the overall cost of the conversion, it’s not something that’s
in
high demand which explains the silence and lack of knowledge of any such
kits.

If you are looking for replacement brake lines for the stock system, any
of
the usual suspects – XKs Unlimited, Terry’s Jaguar Parts, Moss Motors,
SNG
Barratt, and Welsh Jaguar Enterprises should have what you need.

“Mark 1” Mark Stephenson
'52 XK120 S673129, '59 Mk1, '84,'85,'86 &'95 XJ6

-----Original Message-----
From: owner-xk@jag-lovers.org [mailto:owner-xk@jag-lovers.org] On Behalf
Of
Jake Aslanian
Sent: 05/01/2006 7:23 PM
To: xk@jag-lovers.org
Subject: [xk] 1950 XK120 brakes

Hi

I sent this message a few days ago but no response and I need help.

Any USA suggestions?

  1. Is there anyone selling an upgrade kit to a modern dual master
    cylinder
    setup in the U.S.?

  2. If not, any suggestions as to where I can get brake lines and connector
    fittings?

Thanks

Jake
1950 XK120 OTS

Charles,

Yes, but everyone knows you once lived a life on the edge and somehow
managed to luck out. :wink: Did you figure out what caused the problem? I
mentally went through my 120’s braking system, and the most likely failure
point seems to be a burst flex-line. Road damage to a metal line or the M/C
might be possible if you hit something hard just right. However, on the 120,
you’d still have the hand brake which I use periodically to make sure it
works.

Jake,

Are you saying that the XKs parts had problems or that the other weak points
in the system became apparent after the new parts were installed. I bought
rebuild kits for three wheel cylinders up front and one for the rear plus a
rebuilt front wheel cylinder and all seem to be working flawlessly so far.
(Note: the recent XKs flyer has rebuilt front W/Cs on sale for $99.95 ea.
NAYYY)

Mark-----Original Message-----
From: owner-xk@jag-lovers.org [mailto:owner-xk@jag-lovers.org] On Behalf Of
BISHOP-13
Sent: 05/02/2006 12:47 AM
To: xk@jag-lovers.org
Subject: Re: [xk] 1950 XK120 brakes

Mark S;
Let me add a “fact” or two to your opinions… which are more valid

“facts” than you may realize.
First, I’ll agree it’s a very rare occurrence, but a single stage
system “catastrophic” failure can happen… it happened to me a couple of
times… once with a busload of motorcycle parts (estimated at over 15,000
lbs, plus the weight of the converted bus!) as I was coming off a (then)
70mph freeway into an older area of downtown Dallas… I pressed on the brake

pedal and with absolutely no warning nor resistance it went to the floor…
talk about “pucker marks” in the seat!! (I “picked cotton” for a week!!
;-} ) Fortunately, and as you noted, I was able to “gear down” (the
park/emergency brake was useless), even cramming the non-syncro gearbox down

into “Granny Low” (that was really noisy and I was planning to try to cram
it into reverse!), thus slowing down enough to start rubbing the brand new
10.00-20’s against the old eighteen inch curbs to get stopped before hitting

something expensive.

Charles,

Yes, but everyone knows you once lived a life on the edge and somehow
managed to luck out. :wink: Did you figure out what caused the problem?

      Mark S;
    On the bus deal, it was, indeed, the rear flex line.. it was rotted 

in two. It’s a wonder it lasted as long as it did as I was driving around
Dallas County and downtown Dallas six days a week…
The “other” single stage M/C" problem I had was a failed master
cylinder… it also went to the floor without warning… however, a couple of
quick jabs of the brake pedal was enough to get it stopped… once! I had a
can of brake fluid with me, topped-up the reservoir and made it home with
judicious use of the Volvo’s emergency brake and gearbox…
Racing “Flat-Track” (sans brakes by rule) for all those years paid
off big time ;-}
Charles #677556� 2006.----- Original Message -----
From: “Mark Stephenson”

Hi

I don’t know so will take apart and redo.

Jake----- Original Message -----
From: “Mark Stephenson” mark@jag-lovers.org
To: xk@jag-lovers.org
Sent: Wednesday, May 03, 2006 12:00 AM
Subject: RE: [xk] 1950 XK120 brakes

Charles,

Yes, but everyone knows you once lived a life on the edge and somehow
managed to luck out. :wink: Did you figure out what caused the problem? I
mentally went through my 120’s braking system, and the most likely failure
point seems to be a burst flex-line. Road damage to a metal line or the
M/C
might be possible if you hit something hard just right. However, on the
120,
you’d still have the hand brake which I use periodically to make sure it
works.

Jake,

Are you saying that the XKs parts had problems or that the other weak
points
in the system became apparent after the new parts were installed. I bought
rebuild kits for three wheel cylinders up front and one for the rear plus
a
rebuilt front wheel cylinder and all seem to be working flawlessly so far.
(Note: the recent XKs flyer has rebuilt front W/Cs on sale for $99.95 ea.
NAYYY)

Mark

-----Original Message-----
From: owner-xk@jag-lovers.org [mailto:owner-xk@jag-lovers.org] On Behalf
Of
BISHOP-13
Sent: 05/02/2006 12:47 AM
To: xk@jag-lovers.org
Subject: Re: [xk] 1950 XK120 brakes

Mark S;
Let me add a “fact” or two to your opinions… which are more
valid

“facts” than you may realize.
First, I’ll agree it’s a very rare occurrence, but a single stage
system “catastrophic” failure can happen… it happened to me a couple of
times… once with a busload of motorcycle parts (estimated at over 15,000
lbs, plus the weight of the converted bus!) as I was coming off a (then)
70mph freeway into an older area of downtown Dallas… I pressed on the
brake

pedal and with absolutely no warning nor resistance it went to the floor…
talk about “pucker marks” in the seat!! (I “picked cotton” for a week!!
;-} ) Fortunately, and as you noted, I was able to “gear down” (the
park/emergency brake was useless), even cramming the non-syncro gearbox
down

into “Granny Low” (that was really noisy and I was planning to try to cram
it into reverse!), thus slowing down enough to start rubbing the brand new
10.00-20’s against the old eighteen inch curbs to get stopped before
hitting

something expensive.

In reply to a message from BISHOP-13 sent Wed 3 May 2006:

Charles,

I’d pay big bucks to see you flat-track a school bus!!

Mike Spoelker–
The original message included these comments:

   Racing ''Flat-Track'' (sans brakes by rule) for all those years paid 

off big time ;-}
Charles #677556� 2006.


Mike Spoelker
Louisville,Kentucky, United States
–Posted using Jag-lovers JagFORUM [forums.jag-lovers.org]–
–Support Jag-lovers - Donate at http://www.jag-lovers.org/donate04.php

Mike S;
I have “Flat-Tracked” a '77 Mercury Marquis… came out of a shopping
cener parking lot trying to squeeze all twenty-two feet of that car in
between oncoming cars in both directions… needless to say, I leaned a
little heavy on the throttle on that four hundred cubic inch engine… I had
it sideways for about a block before I got it straightened out… Helluva
tyre smoke cloud behind me, as well…
Charles #677556� 2006.----- Original Message -----
From: “Mike S”

Charles,

I’d pay big bucks to see you flat-track a school bus!!

Mike Spoelker

Hello. I have an early car but I have to fit in the later type brake shoes and hardware. Can this be done without difficulty? I would appreciate any advice. Thanks.

john

What wheel cylinders and backing plates do you have?

Rob, I have the later type wheel cylinders and the original backing plates.

john

Jake,

If you still want to go ahead after reading the various comments, a firm in the UK does provide a conversion kit but for cars with front disc brakes: https://xkbrakes.com/

The later type wheel cylinders may have a different mounting hole pattern from the early type, something you could easily check anyway. Other than that, I am not aware of any other reason the later type would not work on early backing plates.
Here is my rear brakes. Thought I had a pic of my fronts but can’t find it.
PICT0022

John, those pictured brake shoes lack the slots for the micram adjusters. You’ll need to mill slots using a 7/16" end mill.

Edit: Later type wheel cylinders? Then maybe they’re not needed. I’m mostly familiar with the pre-'52 variants.

My front brakes
front brakes

Micram adjuster

Rob and all, really appreciate your help. I have just verified that I, thankfully, have all the right parts to put back the rear brakes as per original. The fronts, however, it appears that I may have to put together per the later type.

Incidentally, can someone tell me which of these is correct for the early type rear brakes? I have a pair of each. Thanks.

john

The one on the left with the turned up ridge is for the early type with the Micram adjuster. You can see it in my photo of the rear brakes above.

The one with the slot is for the later type brakes.