Reaction Valve

[PoB]

My question lies with the brake master cylinder which I've stripped ready to fit a new seal kit. The workshop manual and parts drawings show that there is a small piston fitted inside the forward end of the master cylinder. The seal kit that I got has some tiny seals and o-rings to refurbish this piston. The piston operates a white plastic pushrod connected to the diaphragm of the reaction valve. My problem is that this piston is not present in my car. I thought that I may have dropped it during dismantling as it’s so small. But no. On further inspection, the port in the master cylinder where it should fit is blanked by a steel plug. This plug looks to have been fitted by the manufacturer as it’s very neat and has a little recess to accommodate the pushrod from the reaction valve.



So as far as I can see, the reaction valve on my car is redundant as there seems to be no connection between it and the master cylinder. I’ve owned the car for about three years and found that the brakes were adequate. I’ve never driven another E Type so I’ve nothing to compare the braking performance to. However, if I’m correct in saying that the reaction valve is basically disabled, does that mean that the servo is unable to work?



I would appreciate your thoughts on this. Also, to rectify the problem, do I need to buy a new master cylinder? Why do you think that my M/C has this plug fitted? Is it from a different vehicle?



Any input would be greatly appreciated.

[PoB]

OK. Apologies for time wasting. And yes, I do feel like a plonker.

After a chat with Scott at J&L Spares, it turns out that the "plug" which I described is actually the rear of the missing piston. It was seized so tightly in the bore that it may as well have been a plug. But anyway I've got it out now with a new one on it's way to me. Onward and upward! Hopefully this topic may be of help to some other short-sighted Jag lover in the future.

[NATONEIL]

PoB

We all learn from mistakes, and that is the benefit of this Board, without doubt someone will read this is a month or two and suddenly it will all seem clear. Thanks for posting your original question and your follow up.