What a pain in the neck. I’m now on my second quart of
Castrol LMA brake fluid. Each time I bleed, I get a little
more air and then clear fluid. The pedal gets a little bit
better but still spongy. I’ve used a pressure bleeder and
the old pump-em-up-hold it - - - - pump 'em up again
routine. I pre-filled the wheel cylinders and follow the
procedure of the longest brake line first, but the danged
thing just keeps on slowly improving. At this rate, I’ll be
getting a thank you note from Castrol for all the brake
fluid I’m buying. Any suggestions?–
Roger, '54 120 (SE) DHC, BRG, S678300
Tamarac, South Fla., United States
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In reply to a message from Velocette sent Fri 3 Oct 2014:
Here is your master cylinder.
http://www.jag-lovers.org/snaps/snap_view.php3?id=956190721
Notice the item labeled ‘‘bleeding valve’’. That is an
operational description, not a Britisher’s opinion of it. 
One in the top center and one in the front end.
If these are in good condition you should be able to open
each bleeder screw, pump a few times, close the bleeder and
be done with that wheel. It will not suck air back in.
If it is sucking air back in, put a tygon hose on the
bleeder with the other end in a jar with some fluid in it,
so you will see bubbles when you pump, and no air will suck
back in.–
XK120 FHC, Mark V saloon, XJ12L Series II, S-Type 3.0
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In reply to a message from Rob Reilly sent Fri 3 Oct 2014:
What about speed bleeders on each of the wheel cylinders? I put
four on my 140, worked great. When I flushed my system, I put a
hose on the nipple, cracked it open 1/4 turn, pumped the brake
pedal from inside the engine compartment (that way I could keep an
eye on the fluid and fill as necessary), and once the fluid is
clear nI switch to another wheel cylinder. Once I was done I had
clean fluid ion the system and no air in the lines. Took less then
a quart of fluid to do the whole thing.
Joel–
ex jag, '66 E-type S1 4.2, '56 XK140dhc, '97 XJ-6
Denison, TX, United States
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Roger,
It sounds like your Mc is drawing air in past the rubber. This happens
because the fluid delivery can’t keep up with the “need” as you pull back
the pedal. The key is to push fluid out with a pressure stroke and ease
the pedal back (the hole in a single and the tilt valves in a double) to
let new fluid in. Pulling the pedal back or pumping rapidly doesn’t
allow this.
If you use a pressure bleeder you must apply it to the cannister and
leave the MC pedal home. If you use a vacuum at the wheel cylinder you
must not exceed the delivery rate from the cannister. Check that the
cannister tubes are not restricted and that they allow free flow. I
think you’ll find you have solved the usual bleed problem.
Regards,
Rick____________________________________________________________
The #1 Worst Carb Ever?
Click to Learn #1 Carb that Kills Your Blood Sugar (Don't Eat This!)
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It’s been many years since I have done any bleeding of the front brakes
but I remember being astounded that the bleed valve appeared to be at
the bottom of the chamber where you would expect any air to be at the
top. I finally decided to stop trying to figure out how that could be
possible to get the air out with that configuration and to just try
following the shop manual instructions closely (I have a lot of faith in
that manual) and it worked. I was not surprised and I still don’t fully
understand why it works. I think I have done it twice and it worked both
times. All the conventional methods I tried failed.
If I remember right, the tube on the bleed valve in the fluid in the
glass jar was critical to preventing air from getting back in.
Maybe it has something to do with flushing the air bubbles out the
bottom instead of bleeding them from a high point. It’s still a mystery
to me.
Bruce COn 10/4/2014 12:18 AM, holland-rick@juno.com wrote:
Roger,
It sounds like your Mc is drawing air in past the rubber. This happens
because the fluid delivery can’t keep up with the “need” as you pull back
the pedal. The key is to push fluid out with a pressure stroke and ease
the pedal back (the hole in a single and the tilt valves in a double) to
let new fluid in. Pulling the pedal back or pumping rapidly doesn’t
allow this.If you use a pressure bleeder you must apply it to the cannister and
leave the MC pedal home. If you use a vacuum at the wheel cylinder you
must not exceed the delivery rate from the cannister. Check that the
cannister tubes are not restricted and that they allow free flow. I
think you’ll find you have solved the usual bleed problem.Regards,
Rick
The #1 Worst Carb Ever?
Click to Learn #1 Carb that Kills Your Blood Sugar (Don't Eat This!)
Juno - Free Email
Roger,
As in my case this summer, the problem with the spongy pedal may not be
bleeding, but instead, the need to adjust the brakes to contact the drums.
Start with the back first. Make sure you have some drag when jacked up and
in neutral. Then, make sure that your adjuster teeth aren’t stripped out
on the front. And of course, be sure you don’t have a frozen wheel cylinder
or two.
If the cylinders are stroking (and they don’t stroke much) and the brake
don’t contact the drums, you don’t get any braking and still have a soft
pedal.
John Brady
678462
Bedford, MA
We bled the brakes on my 52 FHC a couple weeks ago and all went pretty well except for finding that the tilt valves allowed fluid to bypass and flow back into the brake fluid reservoir. I replaced the tilt valves (got a good UK made pair from Terry’s) and now I have a good pedal. All the cylinders are resleeved in brass, the dual master is sleeved in stainless, and I used all original Lockheed seals on cylinders and M/C. My brother John used his years of 120 brake experience to make this task pretty easy, I have heard of all the nightmares of bleeding XK-120 brakes, was not a problem for us.
I realize this is an age old topic but I want to share my recent experience for those 120 restorers that have not yet performed this task. We adjusted the rear brakes so they dragged, so the cylinders had something to push against. We did the same for the front wheels. This is the trick that so many are unaware of. In fact we bled the front brakes at first with the drums off, to visually see movement of both wheel cylinders before adjusting the shoes back to allow the drums to be reinstalled. On the rears, we lined up the adjusting holes in the drums to view the cylinder and see that they were moving. Once we reached the point where they were all moving, a vigorous pumping with opening and closing of the bleed screw on the downstroke took out all of the air. Another trick was to raise the tube and collection jar to a point above the bleeder screw so as to have a positive head and no air in the tube when bleeding. Picture attached.
Chasing leaks is another issue, the banjo bolts on the wheel cylinders all leaked, as well as the reservoir tank and hoses. Yes I used all new copper washers and the banjo bolts still leaked at the brake backing plates. A retightening stopped the leaks.
I am using silicone brake fluid so it was not a paint stripping issue. My brother has used silicone brake fluid on his 120 for over 20 years and has had no issue, I am hoping for the same experience, that is why I used NOS Lockheed seals, just as he did. And yes I unsuccessfully tried silicone fluid in a MK 9 and all of the seals swelled to a point of no return. I chalked this up to an incompatibility of the seal material with the silicone fluid, which is why the outfit that rebuilt the calipers warns against using silicone fluid. Original Lockheed seals are natural rubber, I believe. It’s been a couple weeks now and the brakes and master cylinder are showing no signs of trouble.
Tom Brady
679924
Brockton, MA
