Master cylinder grease

[xjray]

Hi,

I need to replace the brake master cylinder on my S3 XJ6 after finding it leaking and quite badly corroded. They are currently on back order from the usual suppliers so I’ve used the time to clean up the mess the leak has left behind!

When I removed it from the servo there was quite a lot of grease in and around the back end and around the servo push rod. There’s no mention of using grease when replacing the cylinder in the service manual.

My question is whether I need to grease the area and, if so, is there a particular type needed?

Any advice appreciated.

Thanks
Ray

[PaulGover]

It's a while since I overhauled one, but AFAIR overhaul kits come with a small tube of reddish rubber grease to lubricate the large seal over the back of the master cylinder where the push rod from the pedal enters. There's probably a hinged joint in the pedal linkage that should be greased too, but that would be normal grease. I guess when your new master cylinder arrives it will already be appropriately greased, hence the lack of any mention in the manual. It's all about keeping dirt out of the cylinder while not wearing out the seal.

You definitely want to keep all forms of grease away from anything that actually touches brake fluid - the sealing surfaces on the piston and cylinder themselves - brake fluid is (was; modern ones are probably synthetic) vegetable-based, and doesn't mix with petrochemical-based grease. The red rubber grease may well be formulated to reduce problems if it meets brake fluid; indeed the large amount you see may be diluted with brake fluid that leaked past worn piston seals.

[xjray]

Hi Paul, thanks for your reply.

I did initially plan to overhaul the original and bought a seal kit from one of the main suppliers. Although the Jaguar parts manual shows the small pack of grease with the original kit, none of the ones I found online came with any, just the seals.

I’ve now managed to find a cylinder from a parts supplier. As you suggest, hopefully the new one will be appropriately greased. Or, maybe, with more modern materials it’s not considered necessary these days?

I’m beginning to think the master cylinder been off before, perhaps to try to cure the leak. As well as the amount of grease at the back, a rubber seal of some sort has been put over the outside of the stubby shaft that fits into the servo. I assumed it was a standard fitment and asked the supplier I found (who is also a classic Jaguar workshop) whether the new cylinder came with this seal. He says there is no such seal and has never seen one in the dozens of cylinders he’s fitted over the years. Looks like it may have been a bodge, along with one or two others I’ve found in my year of ownership!

I will grease the pedal linkage before it gets refitted, thanks for the reminder.

Ray