Random brake pedal travel issue

[Laird Scooby]

Originally Posted by CNGBiFuel

It's a complex subject. SWMBO is a chemist.

That's what the green stuff bunged in Citroen is... used in the military too. You want your military kit laid-up for years, hence green fluid. We use DOT4 etc stuff because the boil-point is high for its price. The classic brigade have alternatives, but pricey and awkward. Water-less coolants too.

As far as i've always known, Citroens green fluid (lime juice to go inside a lemon ) is called LHM - Liquide Hydraulique Minerale or in English, Mineral Hydraulic Fluid.

To my mind, that suggests the presence of trace minerals in all of that fluid, always been concerned they could adversely react with the atmosphere given the right circumstances.

Rolls-Royce also used the Citroen self-leveling system for some time and i believe the power brakes too, Jaguar used power brakes in the XJ40 but not sure exactly which fluid was used. Also BMC/BLMC/BL/ARG used a green fluid in the Hydrdagas suspension system, i think that was again the same fluid.

As for waterless coolants, i've seen so many bad reports on those that i wouldn't entertain using them.

[Martin Cox]

Luxobarge, I've good reason to believe they were doing it properly. Certailny there were signs that the bleed nipples had been disturbed.

One one occasion they declined to do the job on my 2002 V40 because one of the bleed nipples had siezed and asked me how I wanted to proceed. It's not economic for them to spend time freeing it off whereas I could and did free it with the usual combination of heat, cold, shock, penetrating oil and an undersized socket over the course of a week and fitted a replacement nipple.

As an aside, if I'm changing the fluid myself, I remove the reservoir from the master cylinder, clean the outside of it and give it a thorough rinse out with methylated spirit followed by a couple of changes of new brake fluid and then put it back. There's not much sense in putting clean fluid in a dirty reservoir.

Martin

[CNGBiFuel]

I kill a chicken over my socket-set? Can't hurt. Might help.

As an aside, if I'm changing the fluid myself, I remove the reservoir from the master cylinder

Why?

,

clean the outside

If you're the sort that has things sparkle, fair enough, why can't this be done in situ?...

and give it a thorough rinse out with methylated spirit followed by a couple of changes of new brake fluid and then put it back.

But why?

There's not much sense in putting clean fluid in a dirty reservoir.

Now we're baffled. Is this a new make-work exercise? Back in the day, we had coloured fluids to see the colour-change as fresh would flush thru' Why can't we do as usual, simply flush thru' the old fluid with fresh?

If we're putting meths in the reservoir, why do we stop there? Should we do the calipers ABS unit, hoses, pipes as well? If not, why not? Why do the reservoir at all?

Luxobarge seems to have thought this lot thru' - LB, spill the beans.

Unless the rest of the time - when not cleaning with meths - is spent shovelling porridge in there, what gives? I really would like to hear this one...

[Martin Cox]

Fair enough; it is perhaps a bit over zealous although I have worked on some people's cars where it certainly would not have been.

Will any breed of chicken do or are some more effective than others?

Martin

[CNGBiFuel]

Fair enough; it is perhaps a bit over zealous although I have worked on some people's cars where it certainly would not have been.

Only that doesn't give clear explanation for what you were blathering about? eg: when; limited to the reservoir, is methylated spirit not over zealous?

Clearly you know you were talking out of your rectal passage. Thing is... Luxobarge seems to have been taken in? This is brakes for chrissakes..

If you're going to use your rectum to suggest people apply your elixir of choice, to car parts - fine, I suppose. If you wish to talk rot, it's a free country, carry on - only keep away from the safety-critical.

[Laird Scooby]

Originally Posted by CNGBiFuel

Only that doesn't give clear explanation for what you were blathering about? eg: when; limited to the reservoir, is methylated spirit not over zealous?

Clearly you know you were talking out of your rectal passage. Thing is... Luxobarge seems to have been taken in? This is brakes for chrissakes..

If you're going to use your rectum to suggest people apply your elixir of choice, to car parts - fine, I suppose. If you wish to talk rot, it's a free country, carry on - only keep away from the safety-critical.

I'm a bit confused and have obviously missed something somewhere in this thread - what's the problem with flushing the brake system through with meths?

It's an excellent cleaner, degreaser and dewatering agent and i've used it many times over the decades to remove condensation from fuel tanks. I've also used it a few times to bleed/flush brake systems to ensure i removed all traces of water/condensation in the lines.

Also being purple, it gives a good colour change when it comes through the bleed nipples and also when the fresh fluid comes through.

Reading between the lines (and perhaps getting it wrong) am i to understand someone was suggesting only bleeding the MC with meths but not the rest of the system?

To me that would be a waste of time, money, effort and deprive a tramp of a well-needed slurp of meths. If said vagrant is going to be so deprived, at least do the job properly and flush the whole system from reservoir to nipples complete.
Granted said hobo would probably cry at seeing so much of his favourite tipple flushed through the braking system and into oblivion thereafter but at least the system would be clean and moisture-free.

[PNuT]

I reckon I would just replace old fluid with new fluid & be done with it....

[CNGBiFuel]

To me that would be a waste of time, money, effort and deprive a tramp of a well-needed slurp of meths. If said vagrant is going to be so deprived, at least do the job properly and flush the whole system from reservoir to nipples complete.

Exactly. Or rather not use meths in the first place? There's not much wrong with meths, only in a brake-system? Why? Meths contains water, and because of its hygroscopic properties (hydroscopic is for idiots), the very best thing to remove water from a brake system is guess what?

Orange juice. Mr Cox's rectal passage would be proud of you. Well, you may as well. Then to clean the orange-juice out, meths would work. To eliminate the water in the meths, try er....

Brake-fluid.

Put a gallon thru' there if you have to, and it'll be cheaper than meths. Its hygroscopic properties is one reason we use it. And why as brake-fluid ages it requires flushing.

I can't believe I've had to even say this?

[Martin Cox]

Dear me!

I do seem to have stirred up a hornets nest which was never my intention. I'm sure the original poster has long since lost interest since we are now well off-topic.

PNuT's suggestion is eminently sensible and indeed it is what I do.

Halfords will sell you 5 litres of Dot 4 fluid for £25 which which can easily be discounted by 10% which makes it cheaper than meths. (e.g. Screwfix £2.99 for 500 ml)

Meths and water form an azeotropic mixture and indeed ethanol/water is one of the classic examples, so unless you are using anhydrous alcohol there will be water in it. Does this matter in the context of cleaning hydraulic braking components?

Not really, because it will be flushed away by new brake fluid. It's an effective solvent and is usually considered safe to use on the seals and flexible hoses.

I cannot see any benefit in flushing through with meths. If the system is that dirty, it needs dismantling and mechanically cleaning: meths may be appropriate but it's highly likely that components will have deteriorated so badly that replacement is the only safe answer.

Brake fluid is indeed hygroscopic. This is a very good reason to change it regularly which is something I think we agree on.

As for cleaning the cylinder reservoir, should anybody be interested, a little background may be in order. My V70 Tdi was off the road for about 8 months whilst repairing the damage caused by a broken cambelt which has been well documented elsewhere on this forum.

For many years the outside of the master cylinder reservoir always seemed to get particularly dirty for no obvious reason. During the course of repairs I discovered the exhaust downpipe just downstream of the turbo had cracked and had been allowing exhaust to escape in the region of the brake master cylinder. It was not easy to spot and the leak was small.

The result was that the outside of the master cylinder reservior was effectively covered in soot. I had other brake work to do at the time including replacing disks and pads and a seized caliper. Brake disks to not take kindly to standing doing nothing for months on end particularly if it's wet. Changing the fluid was the obvious thing to do so I thought I'd take the opportunity to clean up the outside of the master cylinder and its reservoir too. This was most easily done by detatching the reservoir which turned out to be an easy thing to do.

The exhaust has been welded up and the master cylinder has stayed soot free.

Thank you for your interest but may I respectfully suggest it may be time this discussion was put to bed. However I am keen to hear how the original poster got on.

Martin