Replacing clutch master cylinder

I have just removed the clutch master cylinder on my 3.2l manual x300. Sometimes the pedal didn’t come back and the fluid in the reservoir got dirty shortly after flushing the system.
Now I have got two questions:

Given the price and non availability of a replacement I will try and rebuild it. Should that not work, has anybody tried to install the XJ40 part? I found on another forum that it fits, but it looks like the plastic cover along the fender won’t fit anymore. Has anyone here tried that?

Has anyone successfully reinstalled the bolt that attaches the fork on the cylinder to the pedal without removing the pedal box? I found it tricky to even remove and lost the circlip behind the carpet…

I have a new clutch m cylinder and two complete manual pedal boxes. New slave also.

Looking at the picture you sent about a year ago (completely forgot about the whole thing, had it really been that long?) I would expect yours to be the XJ40 one.
Have a look at this thread, the two are compared here.

I went to the dealer and ordered one for my 1994 XJR6 manual, a press car but no XJ40. £180-ish IIRC in Jag packaging.
I actually have two new plus good used ones still fitted to each of my X300 pedal box assemblies.

I also still have the new clutch kit and flywheel…

I am confused. When I look at your picture of the master cylinder:

The port for the clutch line seems to be 180° rotated to where it should be.
Look at the orientation on the pedal boxes:

It looks like I am in need of a new master cylinder though. I bought a seal kit (the only one I could find) for the old one, but it doesn’t fit. One seal is the correct size, but the other one isn’t. Top row are old seals, bottom row the new ones. The right side fits, the left has too small an inner diameter:

I tried to install the piston with the new seal anyway, but now it is stuck :roll_eyes:
Both seals don’t seem to be correct. I pumped grease in to get the piston out (a lot of cleaning required afterwards) and replaced the seal that is obviously not correct with the old one. Piston still gets stuck…

The reservoir does not appear to be a hard/tight fit so I guess it can be flipped or the clutch hose re-outed but I will check. The pedal box casting is the same LHD/RHD but maybe there’s a slight variance.

I’ll look tomorrow before the Grand Prix.


My LHD pedal box does not look visually different from your RHD ones (other than the angle that pedals are at).
On my old master cylinder turning the reservoir around does not seem possible.
I have had another look at it and cleaned out the grease thoroughly and in doing so removed a lot of crud from what appears to be a check valve at the end of the piston.

The old seals don’t look worn, so I put everything back together and am tempted to install the old master cylinder. I wouldn’t be surprised if the crud is what caused the internal leak back to the reservoir.

I compared mine and the two used originals. Nothing needs turning on mine, you just screw the top fitting in from the other side by the look of it.

The original bodies are cast slightly T-shaped like a tap handle at the top, with one side blank and the opposite side drilled and threaded for the fitting where the hydraulic line screws in. These are visible pointing towards the camera on the pedal box photos (i.e. line would run backwards towards the driver when installed). My remaining new spare is steel bodied and instead of being T-shaped at the top, there are two flats and a cross-drilling between them.

One side has a plastic shipping plug fitted (seen in the pic) and the other side away from the camera has a hex fitting screwed in to receive the hydraulic line the same as the original drilled side of the T. So instead of flipping the reservoir, you would just flip the fittings if required. I can’t find the other m/c but I’ve provided a lot of Jag manual transmission stuff so must have sold it already. From memory they were the same except perhaps for the colour of plastic or plating? Either way, the mounting flange holes and hydraulic line are aligned the the same way.

Many thanks for taking the time to have a look Peter!
That sounds good. I guess the plastic plug needs to be replaced with something else, but that seems doable.
I have just come back from the garage. After a couple of hours of swearing I have managed to get the pivot pin through the spring, pedal and fork (with the spring in the correct position!) and secure it with the circlip. I am sure it is not intended to be done this way :sweat_smile:. I was in no mood to remove the pedal box though. Anyway, it appears I have managed to fix the old master cylinder. So I probably have bought some time.

David Manners also has a master cylinder available, so it probaly only makes sense to ship the master cylinder if I also take the clutch kit and flywheel. I’ll read through our old conversation again. I can’t remember what conclusion we got to and why we didn’t go ahead… I’ll get back to you


Well done if you were lying on your back using all three hands. Even with a head torch those jobs are never much fun.

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