I could have said that up until my present car, which had a total brake failure almost certainly due to boiling brake fluid, followed by a seized piston.

Sounds to me more likely that the boiling brake fluid was due to the seized piston!

Well, you are sort-of-correct, though I don't see how that would support (or be consistent with) your view that hygroscopic brake fluid is immortal and wont cause corrosion if left unchanged for ever. Never mind what it "sounds like", it looks, in the pictures, already, like rusty sludge in the braking system, because that's what it was.

Of course I have the advantage over you in that its my car, my near accident, and my investigation, so I have a bit more to go on than what it "sounds like" to you.

What I believe actually happened was a wheel cylinder (pictured stripped in the second link) leaked, due to corrosion. This in turn caused a brake shoe lining to detach, locking up the rear brakes, which in turn caused the ancient wet brake fluid to boil, and a total pedal-to-the-floor brake failure.

Initially I just flushed the system thoroughly and replaced the wheel cylinder and brake shoe. Function was restored, but (as can be seen) flushing does not remove corrosion debris which subsequently caused a caliper to seize, so I stripped and cleaned them both.

I posted a description of the original incident on here and IIRC was told my master cylinder had definitely, unquestionably failed (though there was no explanation for its subsequent spontaneous recovery). Ideally I would have stripped the master cylinder too but would only risk that if I could get a seal kit, so its unchanged.

I suppose the skepticism about boiling brake fluid is because, without an unusual heat source, you can get away with driving on wet brake fluid indefinitely, until corrosion requires a component replacement which will incidentally include a brake flush.

Edited by edlithgow on 04/12/2022 at 11:53

...i'm not aware of the handbrake operating on the front wheels on Wartburgs, can't remember now, but from the braking effort from the handbrake this could have been the case...far as i know it was only older Citroens (that ended with the first C5 if i recall) that applied the front brakes as park brake but no doubt there were others.

Think some SAAB did this. I think the rationale was that Swedes wanted to use the handbrake as a "poor man's LSD" in slippery conditions, and since the SAAB was FWD, that meant the handbrake had to operate on the front wheels. This would also make it more effective as an emergency stopper.

I had a (mechanically clueless) neighbour with a SAAB I coveted, who scrapped the car when he had trouble with its (relatively complex) handbrake linkage. If I'd heard about it in time I would certainly have bought it off him and attempted a fix.

This also had a freewheel, since the transmission was originally designed to work with a 2-stroke engine. I'd guess a Wartburg would probably have one for the same reason. Wouldn't explain your brake failure but it might explain a lack of engine braking...

<< I've never been one to belt up to junctions requiring hard braking and the commendable handbrake did the business stopping the car in good time, better handbrake than many modern cars .. >>

I haven't been surprised like that, but about 1990 I borrowed a work pool car for a 100-mile journey - an F-reg Pug 309. It was soon very clear from the noise that the brake pads were shot. After that I used gears as much as possible, then mostly handbrake and footbrake if really necessary. Busy pool cars are easily neglected, especially if no-one reports problems. That car had only done about 16K IIRC .....

It's not a sealed system.

As pads wear, the brake travel increases. The fluid level in the reservoir falls. AIr is dawn into the space vacated by the fluid.Air contains water molecules in the UK.. Often lots.

This is basic physics..

I agree Bolt........, we sell ( I work for a motor factors) dozens of calipers due to the old ones seizing.

So no conflict of interest here, then ;-). I'll wager you'll probably also recommend changing brake pads when there are still at least 3mm (at least 10,000 miles in normal use) wear left on them.

<< ... regarding pads most cars have wear indicator leads, when the pads get low the light on the dash lights up and it's time to change them >>

I suspect John-F's suggestion is that the warning comes unnecessarily early. That is if it comes at all. No doubt things have improved, but in the days of the Pug 205, by the time the warning was due, the warning wire attached to the pad had broken during normal wear and tear.

"Interesting thread from 'bob....' - usual nonsense about brake fluid 'absorbing water'. "

So how does the moisture get in then because there are testers to check the water content?

<< Many people want their motoring to be as cheap as possible - preferring to spend their income on other things. >>

Exactly. There is a whole range of points on the Safety Spectrum between doing the absolute minimum while getting away with it, and going unnecessarily far in the other direction. Manufacturers may err on the latter side, in order to help sales; or not (as in the case of oil change intervals for diesel engines, to help fleet sales).

Haynes manuals try to recommend midpoints on the spectrum, but probably err slightly on the side of safety, for good reasons. John-F goes in the other direction because he (believes he) knows what he is doing, and so far has been proved right. Others here go the other way, changing their tyres with 3mm of tread left because of a marginal peace-of-mind benefit in a possible but unlikely situation. I once worked with a guy who MoT-tested his Renault-5 every 6 months.

Silicone brake fluid is not hygroscopic, and was introduced to avoid the moisture-attracting tendency of normal ester-type fluids. Whatever John says, it is not feasible to totally seal a hydraulic system, which has a pumping action whenever it is used. So after (say) 5 years that system will have absorbed some moisture. In normal driving that will never cause boiling, so it can be ignored. But after 20 years on original fluid, who knows ? By then a long-term owner may have forgotten all about the idea of 'scheduled maintenance'.

Edited by Andrew-T on 04/12/2022 at 10:07

Does anyone know if this thread will finish before Christmas?

Hang in there. No one has mentioned ABS yet. I believe that is sort-of-electrical, so might spark your interest.

Does anyone know if this thread will finish before Christmas?

I can start one about globalist illuminati baby eating elites if you like?

.

Gordonbennet seems to have had good results with "traditional" red rubber grease. This is supposed to be castor oil based (for rubber compatability) and I've seen somewhere the suggestion that its oil component is a blend of castor and silicone oils. This would make sense since the silicone would stop it going solid, with the castor component becoming a suspended semi-solid as it ages. I dunno if it has other solid content like bentonite in it.

I

With reservations, yes.

Whilst it provides a good anti high frequency rubbing (squealing) base between piston and pad, i find it gets a bit too sticky for my liking after a year on slide pins hence i'm going to clean the Subaru slide pins out completely and try some Ceratec, but agree red is the stuff to use on pistons and i have used a cotton bud to feed some onto the pistons themselves after gently peeling back the dust cover.

Does anyone know if this thread will finish before Christmas?

Probably only our respected Mod. But I thought the original question had been answered, so a little topic drift might not matter ? :-)

Whatever John says, it is not feasible to totally seal a hydraulic system, which has a pumping action whenever it is used.

It's not like a bicycle pump! The caliper piston O ring flexes to allow the tiny movement of the piston without allowing fluid to escape or air to enter. No air should enter the master cylinder. The reservoir is nowadays equipped with a diaphragm to prevent any contact with the air beyond the tiny amount between the max level and the cap, and allows the pressure to remain the same when tiny movements of the fluid level occur.

I have heard of this "nowadays" of which you speak, but have so far managed to avoid it in an automotive context, by running "yesterdays" vehicles.

I thought you did too?

My cars brake fluid reservoir has a breather hole. It has no diaphragm, and certainly managed to get its brake fluid in a very sorry state indeed. (see above)

The same applied to a Honda Accord that I had brief custodianship of, though I don't think I took any scary pictures of that.

In addition, its alleged that water vapour can permeate through rubber brake hoses, pulled in by the hygroscopic nature of DOT3 or DOT4 brake fluid.

I can neither confirm nor deny the existence of this mechanism, nor can I confirm or deny that it would operate via your diaphragm, if such a diaphragm did in fact exist.

But it does seem like a theoretical possibility.

Edited by edlithgow on 05/12/2022 at 10:58

My cars brake fluid reservoir has a breather hole. It has no diaphragm, and certainly managed to get its brake fluid in a very sorry state indeed.

The diaphragm is in effect the seal with a hole/split in that when the pressure is higher than it should be allows air in. so yes it does allow air in but more controlled than the hole in the cap. simples

I was assuming this "nowadays diaphragm" would be a flexible membrane in contact with the surface of the brake fluid, since something like that, IF impermeable to water vapour, would indeed greatly reduce its uptake.

But maybe it doesn't exist.

If its just the old rubber cap with the breather hole that was meant, well, that's where we (and probably some water vapour) came in.

(Think you probably mean "pressure is lower than it should be" above)

Edited by edlithgow on 05/12/2022 at 21:30

Whatever John says, it is not feasible to totally seal a hydraulic system, which has a pumping action whenever it is used.

It's not like a bicycle pump! The caliper piston O ring flexes to allow the tiny movement of the piston without allowing fluid to escape or air to enter. No air should enter the master cylinder. The reservoir is nowadays equipped with a diaphragm to prevent any contact with the air beyond the tiny amount between the max level and the cap, and allows the pressure to remain the same when tiny movements of the fluid level occur.

No diaphragm in any system I have serviced: BMW,Ford, LRover, VW, Audi, Toyota, Honda, Chevrolet..

For once John I actually agree with you ( please don't faint mate! ) , the diaphragm is built into the cap, just checked my car and van just to make sure I wasn't going nuts :)