XK120 XK140 XK150 1948 - 1962

Still plagued by my brakes

 
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Old 06-28-2018, 05:47 PM
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Default Still plagued by my brakes

Recently installed a new Tandem Master Cylinder in my XK120. Everything has been gone through in the brake system. Today we pressure bled the brakes for the 7 or 8th time in the last month. I'm getting absolutely no bubbles when I bleed. We've used over 3 quarts of New Dot 4 brake fluid. The pedal is firm and doesn't fade or go to the floor board. I've adjust the rear brakes and have the shoes back off 1 to 2 clicks, there's some drag but not severe. The front brakes have the automatic adjustment and they still feel too loose or free, I've no way to get the shoes to drag a little, I"ve pumped the brake pedal many times to actuate the front brake adjustment. To no avail. The brakes seem to work but not to extent they should. A panic stop is definitely out. I've received so much advice on brakes I feel embarrashed to still be seeking advice. Just as a follow up, I've turned the drums, relined the shoes, replaced all the wheel cylinders, the flexible brake hoses, multiple banjo bolts, washers, etc. The emergency brake does work when I use it. Just for the records, it's an XK120 1953 Roadster, very low miles. It sat in my garage for 24 years not running. It's taking me over a year to get it running again. I've owned the vehicle since 1979. I've accomplished most of the work myself and gotten professionals that are close friends to turn a wrench on it from time to time. A close friend taught Auto Shop for over 20 years, but he hasn't had Jaguar experience. We both feel that the British are getting back to the Colonist through the Engineering on the XK's. At any rate if anyone out there has an idea please share it with me. george
 
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Old 06-28-2018, 08:57 PM
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Are you saying that it seems that the brakes are not grabbing?
Your line, about automatic adjustment gives me a clue. I'm not familiar with the XK120, but there has to be a way to over ride the self adjuster as when the shoes are replaced.
Then,I'd make sure that the curvature of the shoes fit the drum. Look at the shoes and see where the wear is.
 
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Old 06-29-2018, 04:02 PM
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Drum brakes from a 1953 car will not give the kind of braking performance we today take for granted, and these were notorious for fade, hence the later discs on the XK150, but before fade set in did work quite well according to the road tests of the time. It has to be noted, however, that UK roads were mostly empty at that time compared to today.

Are your brakes the ones with a frictionpad-based adjuster ? (SNG Barrat have the layout drawings of the early and late front brakes. I looked at the parts layout and the bar connecting adjuster to the shoe has a slot the adjuster bolt goes through. Clearly there is only a limited amount of travel on this device, and one thing that could happen is the drum is machined too large internally thus on assembly, the adjuster runs out of travel and hits the bolt when the wheel pistons move the shoes out to the drum. You mentioned that you had machined the drums, so maybe this has been done too many times or you've taken off too much metal.

Just my two cents worth.

PS: a lot of people have converted to the XK150 disc set-up.
 
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Old 08-27-2018, 03:28 PM
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We had a similar issue with our automatic adjustment which wasn't holding it's position and dropping the pedal to the floor. The handbook wanted us to tighten the automatic crimping mechanism to catch and hold the shoe against the drum. This might be where your issue is... Replacing the catch clips could help.

 
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Old 08-27-2018, 05:42 PM
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thanks very much, I'm traveling for the next month, but upon return will see if I can't get to the bottom of the problem I have several very good suggestions that I intend to investigate. thank you to all. sincerely, george
 
 
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