Gentlemen
To my surprise my 1973 XJ6 S1 4.2 brake master cylinder had no rust inside the
first piston bore . Even the rubber piston looked "new". I am quite adamant it is
the original master cylinder as it was " welded" onto the brake booster.

Now i note there is offcourse a 2nd piston bore, yet i cant determine the release
mechanism for it. What type of witchcraft is this?
I recall i did this on my s3 brake master cylinder, but this is slightly different in design,
can someone advise on how to release the 2nd piston?

best regards
Peter

 

I have the answer to my own question:
In the S1 brake master cylinder, the 2nd piston is not pinned in the bore, it will just drop out of the bore once the 1st Piston is removed, give it a good thump on the ground , it is just jammed in there after 50 yrs.

This is a bit different to the S3 brake master cylinder, the 2nd piston has a secret little pin under one of the rubber grommets located under the resouvioir attachment area.
That hidden pin , locks the 2nd piston and needs to be removed to dissemble it fully .

hope some obe finds it all useful

regards
Peter