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Sticking Brakes

Sticking Brakes

When I brake fairly hard It seems all four wheels brake and then lock up. They do not release until about 10 minutes have gone by. I filled the system with fresh silicone fluid. - Andy Ottolia

Hello Andy. Your message was passed on to the XK-lovers list. Been there, done that. Extremely embarrassing to be blocking traffic because the 120's brakes were stuck. Took me two weeks of head scratching and disassembling and reassembling the brake system to diagnose the problem. I am assuming you have the Lockheed single master cyl. the same as early 120, not the tandem one like late 120. If you have something different, what I have to say may not apply. I am also assuming your brake pedal and thus the master cyl. piston are retracting fully. Your problem is the tiny bleed hole between the piston bore and the upper chamber is blocked. This hole is identified in the 120/Mk7 manual on page L29 as hole "X". There are two possible causes: 1. Rust or other crud has blocked it. You can clear it out with a #70 (.028" dia.) drill bit attached to a stick. 2. Silicone has swelled up the rubber cup, making it a bit thicker (i.e. longer in the front-to-back direction as installed on the car), and it is covering up the hole even when it is fully retracted. Probably easiest to see this with the master removed from the car and cleaned and sitting on your workbench. You may need a strong light to see down into the "X" hole. Stick your #70 bit down the hole and if you feel the rubber cup, that's your problem. Get a new rubber cup for the master, remove and clean all the brake cylinder cups, flush out all the silicone with alcohol, and go back to Castrol LMA. Check for both causes. Either could occur separately or they could both occur together. This problem seems to be specific to the Lockheed single master; I have not heard of it occuring on any other car. Let us hear what you find. We would also like to know the stamped numbers from your ID plate. - Rob Reilly

I am happy to report that I have finally solved the sticking brake problem. Car is breaking like a gem. Upon dissassembly of the master cylinder, Its reservoir was full of sludge and the tiny pinhole was completely clogged(what ingenious design). After battling with this for months I am so happy. I want to thank the many of you who gave me various solutions possibilities in your responses. Thanks Andy the rookie Ottolia

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