For starters, it's NOT sealed. It's only MOSTLY sealed. But you do as you like on your car.

On most of the S-Types you can't just push the rear piston back in...

Welcome to the forum jpvd,

Interesting first post, it might be an idea to post an intro in the new members section.

And you will avoid any acerbic reactions from other '????/// members.

cheers Norri...

I do love how people get so wound up on these car club forums.....everyone is entitled to their opinions....i'm just airing mine...it is a public forum after all...

Jagv8 - explain to me how exactly it is only 'partly' sealed?...the brake pipe has to be sealed, otherwise it will leak or introduce water and air into the system...simple...the same way in which one could describe the cooling system....its sealed until you remove the expansion tank or radiator cap....to state this is only 'partly' sealed is the wrong term

anyway, who cares....made my comment, apologies for upsetting any of you with a nervous disposition...

what pads does everyone use on here anyway?....i went for the pagid pads all round and so far so good....installed far better than the mintex are used to always use...seem to grab better, but then again new pads always do feel better once bedded in!...

Fact of basic physics. A true seal with things such as rubber piston "seals" is not possible. Doesn't matter if you change brake fluid as you're supposed to.

I really did mean it about not just pushing rear pistons in.

Right on!

Other than the STRs (I believe), the rear pistons screw into the caliper. I know first hand that you need the "special tool" whether it be a cube or the more professional type, to properly seat the piston into the caliper.

Don't want any newbies reading this thread thinking that the pistons "push in"

BTW George pretty much sums it up in post #7.

Well, that's quite an introduction to a forum!

In all fairness, with the exception of pushing the pads back into the caliper on non-R models vs. screwing them back in, the new poster is mostly correct.

Pushing the fluid back into the MC reservoir will not harm any component. While it's simple to open a bleeder to help with the piston retraction and it does partially expel old fluid, there's no technical reason not to simply allow the fluid to flow back to the MC reservoir. In that respect, there's also no reason to loosen or remove the M/C cap. As stated (debated/argued) many times before, MC caps are vented to atmosphere with newer cars featuring a flexible bellows separating the fluid from the air, so loosening the cap is redundant.

As to the point about the system being 'sealed' or not, the arguments being presented raise the bar on being pedantic to a new level. I see JagV8's point, but many people believe that the systems are still 'open' as they were back in the dark days when fluid changes every two years or so were justifiable. But that's a whole different subject.

You realize the jag piston is step threaded right. You don't just PUSH it back like an american car - aka he with the biggest c clamp wins. There's a specific tool you need which has two ears you attach to a socket and use to twist the piston back. Other than that yeah, no harm at all in compressing the piston by hand.

Take care,

George

So...back when I changed rear pads on the 2003 Jag S I just wanted to say that I tried to compress the calipers and they would not move...so I turned the bleeder screw to provide aplace for the brake fluid to go and the caliper pistons retracted... most likely I forgot to take the cap off the brake fluid resivour and that is why the calipers did not compress... no way to verify...I have never needed to turn a bleeder screw to compress caliper pistons...just assumed it was a jaguar and required special modifications !!! the best to you all wordman

Sure there is. I've never opened a bleeder or removed/loosened a cap on any vehicle in my life nor have I ever had a problem.

There is NOTHING preventing the fluid from flowing back to the MC reservoir. The rear calipers on a non-R MUST be screwed back into the caliper, not compressed with a c-clamp however. Maybe that was your problem.

what a debate I've res-erected!...

i am fully aware that the rear caliper has screw in pistons, so the handbrake can be applied to the disc without the use of a separate internal drum which a lot of the old rear disc motors used to have. stop being so **** about it...whether it screws in or pushes in, the fact still remains that you do not need to bleed the system....you are only giving yourself more work, unnecessarily in my humble opinion...

the argument about a sealed system is just daft....you can't honestly tell me that you truly believe that anything which involves rubber seals, cannot be classed as a sealed system?...its sealed until the rubber perishes, i'll give you that and it's not sealed as in welded shut, but its still sealed from the elements....the rubber is what helps create the seal (ie it expands to fill the gaps).

so anyway..... that's my rant over...lol

First you strongly imply that the system is sealed:

Then you go on to say that:

Other than compression of gas(the air at the top of the master cylinder reservoir), the laws of physics say that a sealed system will not allow a piston to move into the sealed bore. That's how brakes work to begin with. So, if the system is truly sealed as asserted, then the piston could not be pushed back.

Irregardless, most "hard copy" materials refer to opening the master cylinder and leaving the closure loosely in position to allow venting. They further go on to say that some brake fluid should be withdrawn if the reservoir is full to allow for the brake fluid being pushed back. That is in the event that the brake fluid has been topped up with worn brake components.

The situation posted by Wordman could very well happened exactly as described because his post does not specify front or rear. If front, then the "screw the piston" requirement does not apply.

That some open a bleeder before pushing the pistons back into the caliper probably dates clear back to problems with early ABS systems...such as the old style Teves systems used on older XJSs and many others cars.

Over the years there's been some pretty good anectdotal evidence that sediments in the calipers (or elsewhere) can be pushed back into the ABS valve block and/or "actuator assembly" and cause problems. Opening the bleeder before pusing the piston in allows prevents cruddy fluid from being pushed back into the system.

If someone cut their teeth using this method they may continue the practice even on cars that are not particularly sensitive to the (alleged) problem that the practice (allegedly) prevents from occuring.

At minimum it could be considered a "can't hurt, might help" type of thing.

Cheers
DD

Given your signature, I just had to.

Getting back to the subject matter- you seem to be confused regarding the construction and function of master cylinders. 'Open' master cylinders (not used in many decades) exposed the contents of the reservoir directly to air via the vent hole in the cap. Closed systems (as we see on all modern cars) have a diaphragm inside the reservoir or cap that isolate the fluid from the air. In that context, the system is sealed. All systems have a vent of some sort to allow air to replace the fluid as the level drops due to pad wear, so the air (gas) never rises above ambient in pressure.

No need to remove or loosen the cap accordingly.

I still wonder why we carry on with fluid changes at a 2 year interval with modern cars given that the fluid is not exposed to the dirt and moisture.

Doug makes a good point about not flushing junk from the caliper backwards and possibly contaminating the ABS stuff. Every time I've flushed fluid on a system in good condition, no junk comes out- just old fluid. Failed calipers or wheel cylinders is a different story.

Hi All

I have changed the rear discs on my 2005 S type 3 times in my ownership and never removed the fliud cap or had to reprogramme the EPB, why make the job harder, The fluid ammount is minimal and the system is not under any pressure at all. As for the EPB pump up the brakes after fitting the pads with ignition off, All done

When reseting the electronic parking brake you have to follow the correct jaguar proceedure or risk overstepping the motor and causing a failure.
1) depress brake pedal many times using your right foot only. Left foot causes pressure inclinations issues!
2) be sure the drivers door is open since youll be doing all this in gear with engine running. If the epb reseting proceedure fails and the car takes off on you , youll want to be able to jump out quickly rather than be driven down the road erraticlly without a working parking brake

Brutal,

That's when the ol' Fred Flintstone brakes will come in handy....

Why does the car need to be in gear to do this?

It makes it more exciting?

ABSOLUTLY! AND DID I MENTION YOU NEED TO HEEL AND TOE THE GAS AND BRAKE TO HOLD RPM AT 2000 OR BETTER. PREFERABLY IN REVERSE AS THIS MAKES IT FUN TO TRY AND MISS THE DOOR WHEN EXITING.