72 series one xj6 master cylinder leak

(cdscds) #1

Hello all,

Bought an NOS brake master cylinder about 6 months ago, Worked great after reusing the old tipping valve.

Now I’m losing brake fluid at an uncomfortable pace.
Visible leak at the connection between booster and master.

Do I just get a rebuild kit and install, or would the bore sizes be suspect?

I do have spare masters that need re-sleeve, but I’m hoping that perhaps the rubber on the seals had become brittle in storage.

At this time I’m not interested in the series 3 master mod.

Any advice is welcome.

cds (the other Carl)

(Frank Andersen) #2

liquids may follow odd paths, Carl…

Master cylinders cannot leak externally without internal seal leaks affecting braking. Ie, pedal goes halfway down, indication one brake circuit has failed - if pedal bottoms; both circuits are affected…so…?

Basically; the external seal is just a dust-cover - there should be no fluid inside it.

xj6 85 Sov Europe (UKNZ)

(tony) #3

master cylinder seal kits are inexpensive, and should be renewed, as they go soft after many years

It should be possible to inspect & hone the bore once apart

(the bore is ever so slightly stepped inside)

if it is not acceptable, sleeving can be done, I had mine sleeved in SS anyway

carefully check the new seals, it is possible to get one too “long”…if you do, the MC will not bleed out the rear ports at all…I believe this is a supplier error

(cdscds) #4

I’ve ordered the reseal kit from xk’s and will separate the master from the booster to see if the master is the culprit.

I’ll update you all once I found out

(cdscds) #5

Hello All,

The brake master cylinder was the culprit. the seals were rather mushy

Fortunately for me the bores were i great shape, no honing required. I did notice lots of junk in the brake master, the culprit, a perished brake cap seal. Any suggestions on where I can get one?

The new seals from xk’s unlimited were a bit different, but the orientations (cupped sides facing forward) were noted.

The only issue I had was the front piston seal, couldn’t really sort out how to take it apart, so I just placed the seal over the stem.

bled the brakes and Im not leaking anymore.

cds (carl)