I cannot accept that the use of rubber grease will cause the formation of a sticky gum inside the brake cylinders, in a Mark 2 Jaguar or any other car.
In several old cars I have bought (Mark 2 Jaguar, 1937 Buick, 1938 Buick) the brakes were frozen precisely because the previous mechanics had NEGLECTED to use rubber grease. The result was that the outer ends of the slave cylinders, where the only lubrication provided was that of a little brake fluid, had rusted and prevented the pistons from moving. Also, the sticky gum had formed inside the cylinders, despite the complete absence of rubber grease. Therefore this sticky gum can only have been formed by the drying out of the combination of brake fluid and water.
These problems are not unusual when a car has been standing idle for a considerable time. Brake fluid absorbs water, but does not prevent rust, whereas rubber grease smeared inside the ends of the slave cylinders inhibits the formation of rust.
Some owners of seldom-driven classic cars replace the normal brake fluid with silicone brake fluid, which does not absorb water.
In the case of my Mark 2 Jaguar, the brakes on at least one of the wheels would give trouble about once a year, and require disassembly and cleaning. Always the fluid would appear brown, apparently a sign of water ingestion, and it was not unusual for the pistons to stick. Unlike the large Mark 7, 8 and 9 sedans, which had brass liners in the shallow, but large diameter wheel cylinders, the Mark 2 cylinders were all ferrous metal.
Hi, I have just purchased a 1968 420 Jag. I am having the same problems with the brakes sticking, but only on the front. There is also a hissing sound that disappears once the brakes release themselves, usually after about 5 seconds. The brakes were completely overhauled 2 years ago and have just had a full flush and bleed. Can anyone help with other suggestions. Could it have something to do with the reaction valve or master cylinder???
I have run into this problem a couple of times on different cars. Although the brake hoses looked in good condition on the outside, they had delaminated on the inside and were acting like a one-way valve. After a period of time the fluid would seep back and the wheel would turn freely until the next application of the pedal. When I removed the brake hose, I couldn't blow though it. I am of the opinion that some brake fluids are not compatible with the rubber compounds used in some cars, but that is just my thought.