1985 xj6 brake master cylinder

(francois panzieri) #1

Hello everyone, I’m having master cylinder failure in my XJ6 ( I think… pedal goes all the way in at times)
What are the latest and greatest recommendations on this topic? I did a search and got some info but i thought i’d still ask :wink:
Looks like i have the choice between getting just a rebuild kit, master cylinder with reservoir, master cylinder with reservoir and booster. I’m reasonably handy with tools and think i could handle just rebuilding the master cylinder but i also gotten lazy with age so, i’m also interested in the easy way to fix my issue even of it would cost a bit more.
What say you? Thanks

(W. Schuster) #2

Those things all depend on how many miles on the car, if you flushed the fluid
once in a while etc.

You can rebuild the master or buy a new one.

(Doug Dwyer) #3

Master cylinders are usually easy to rebuild…if the bore is still smooth and rot-free, which isn’t always the case. If you can leave the car down for a few days remove and disassemble the m/c to see whatcha got before ordering parts.

Personally, on the basis of “just be done with”, I just buy new master cylinders and move on


(francois panzieri) #4

Thanks y’all. I have discovered this morning that one of my pads in the rear was down to nothing so, I’m going to address that first, hopefully the Master issue was due to that. Or is it wishful thinking? :wink:

(Paul M. Novak) #5

You should check the condition and thickness of your rear rotors while you are at it. According to the Jaguar Series III Service Manual the minimum thickness for the rear rotors are 0.45 inches. BTW the minimum thickness of the front rotors is 0.90 inches.


(francois panzieri) #6

Yes, they look very slim and the piston that appears to be causing the problem has corrosion on it. For sure I have rotors and calipers to be done in the future and i’ve been reading about how to do that with the cage in place, i dont feel like dropping it, I m still recovering from dropping the one on my 89 xjs years ago :wink: For now, i’m going to just replace that one pad so I can keep on driving the car and find the energy and courage to attack more serious in depth solutions. Thanks!

(Robin O'Connor) #7

Sorry to say that if the piston is showing signs of pitting then a rebuild is the only way to go, once the piston is back inside the bore it’s going to leak when the pitting gets to the seals. I believe you can dismount the callipers and ‘roll’ them over to the back of the cage to get them out.
And no the worn out brake pad is not the reason the pedal goes to the floor ‘sometimes’ also one worn out pad out of four, how do the others look? If they have plenty of life left in them then you have seized pistons on them.

(ronbros) #8

i use a GM truck master cylinder, aluminum (not cast iron).

seemed less cost , new like $45. bucks!

(Frank Andersen) #9

It is a fault, Francois and should certainly be addressed ASAP…

It is unlikely to effect a master cylinder failure - the piston travel inside is unaffected. But excessive caliper piston travel may introduce leaking in/around the caliper. The difference between a failing master cylinder and an external leak is loss of brake fluid in the latter case…

The usual m/s problem is failed seals, it doesn’t take much - even a grit of sand will ‘unseal’ it, disabling it. A clean-up and seal changes is usually adequate - using a rebuild kit. But if there is visible corrosion in the m/s bore; the appropriate remedy is re-sleeving in stainless steel - or m/s replacement…

xj6 85 Sov Europe (UK/NZ)

(francois panzieri) #10

it was wishful thinking but hey, one can dream, right? I replaced the pad and with great effort was able to push the seized piston back to put a new pad in. No leaks for now and hopefully it’ll buy me enough time to source the new master cylinder and a rebuilt caliper. Thanks Franck!

(Frank Andersen) #11

If the caliper piston was actually seized, Francois; you should really attend to the calipers - just freeing the piston may be inadequate. If the brakes are now working as they should; the master cylinder was innocent - though caliper anomalies may still cause anomalies…

xj6 85 Sov Europe (UK/NZ)