Can anyone tell me at what interval should brake fluid be changed ??.
I have recently purchased a 2.7D 2008 which is coming up to the 60K service.
The vehicle has always been serviced by a main agent. I have the itemised invoices for the first 2 services & it was not replaced,... the 3rd invoice is missing & don't know if it was done then.
Any information would be appreciated.

 

Every two years. All manufacturers agree on this interval. In dry climates you can extend this but nobody knows by how much.

Water contamination is dangerous. Pedal fade due to fluid boiling is as dangerous as pad fade. Water contamination lowers the boiling point of the fluid.

Long term water contamination corrodes nd degrades the internals of the entire braking system.

If you aren't sure when it was last done do it today.

 

This is more or less true, but I have to wonder why. The standard two year interval appeared back in the 40's and 50's when master cylinders were vented directly to the atmosphere and had no diaphragm to separate the fluid from air. This meant that water from the atmosphere would be absorbed at a far greater rate as compared to today's cars where air never come in contact with the fluid primarily due to a flexible bellows inside the M/C that segregate the fluid from the air.

The design and technology of the brake system has advanced greatly, but the servicing interval has not altered to match.

Having said that, later XFs have a three change interval but not XJ or XK (?)

 

As brake pads wear, air is drawn into the master cylinder reservoir through a vent in the cap. Nothing has changed except you can now check the fluid level without taking off the cap. I don't know what you are referring to about flexible bellows, I've not seen that in any MC I've looked at. Atmospheric air pressure has to exist at the surface of the brake fluid for the master cylinder pump to work, that's just physics.

Modern disc brakes operate at much higher line pressures than old drum systems. Water contamination is a much more serious safety problem now than back then. Boil your brake fluid on a mountain road and then get back to me with your revised opinion, after you do your laundry.

 

I think it was established in a lengthy post a year or so ago that yes, master cylinders do have a bellows or diaphragm that separates the air from the fluid. One non-believer went out to his his own S-type only to discover that it's built into the cap as stated. I can't remember the last car or bike I've owned that didn't have one, either laying on top of the fluid when the cap is removed or more commonly built into the cap itself.

Here's a cross section of a typical '60-'80s M/C. You never wondered about the funny looking 'reservoir seal?'

 

It's meant to reduce the volume of air, and hence moisture, that the brake fluid comes in contact with. On some vehicles the "bellows" is convuluted and actually comes in contact with the fluid. The bellows separates the air from the fluid but still allows the effect of atmospheric pressure to operate.

 

The Jaguar maintenance schedule for the 2009 model year says change the brake fluid every two years, except XF which is every three years.

The XF master cylinder reservoir is the conventional single cap style. I do not see how a membrane could be included inside that design.

 

Many thanks guys for all your assistance, very much appreciated.

 

One thing to take into account folks.........

Unfortunately, "Factory Maintenance Schedules" are at times misleading. What you don't always realize is they're purpose is two-fold. First is to provide recommended maintenance, yes, but also to provide a SALES TOOL for marketing. It's called "Cost of Ownership" in the lingo of the marketing people. Sometimes those are manipulated to meet a Cost of Ownership target for sales departments. It's a "Look how inexpensive this car is to maintain over the life of the warranty period" compared to Xxxxxx V8.
For instance, brake fluid specs changed between the 2005 and 2006 model years. For 2006 Jag adopted the Shell ESL Dot 4 brake fluid, across the board. That change allowed extending the replacement interval from two years to three, as the ESL [Extended Service Life] fluid was a bit less hygroscopic.
Any deviation from the three year change interval on any model after 2006 was a MARKETING change, having nothing to do with service life. You will find other instances of inexplicable interval differences in Maintenance Schedules between models or model years, even when you know there were no technical differences in those instances.

Bean counters at work! I hate it. Believe me, it irks me when I have to try and explain such differences to people that are multiple Jag owners. They are not stupid, and I find it hard not to be honest. So I give them the same story, and service their car accordingly.

Cheers,

 

The XF brake fluid cap does have the "bellow" or "membrane" in the cap.

 

Yes, agreed. I don't think I've ever seen a brake fluid reservoir cover that doesn't have the rubber membrane built into the cap.

 

The cap seal doesn't float on the fluid surface, it is merely a gasket sealing the cap. There is no feasible way to have a floating membrane that drops with the fluid level and seal it from outside air. Outside air has to get into the reservoir or the MC piston will be unable to draw fluid from the reservoir.

 

I agree on 2 points, the rubber seals the cap plus the bellow does not float on the fluid but it must move in response to something or there would be no need for the bellow to be there. It is not there just to seal the cap.

 

You're correct. The bellows separates the outside air from the fluid.