car bodging

[Dave Plowman (News)]

If you do regular changes, there's no doubt in my mind the seals etc will last longer. But may not be worth the effort if you change your car every couple of years.

[tim...]

why didn't they change it them

who was it who "voted" against that idea when it *was* up for discussion?

tim

[Adrian]

It really doesn't make any difference whether there's an advisory from the previous year or not. He should be checking the brake pipes...

And, as I said, he doesn't KNOW if there was an advisory or not the previous year.

[Adrian]

It can, and it does - and it should be changed at two-year intervals.

Neglecting changing DOT fluid is the single biggest reason for replacing brake and clutch cylinders and calipers, not to mention the risk of the fluid boiling.

[Roger Mills]

You need to satisfy yourself that it's just surface rust, and that the corrosion hasn't weakened the pipe. Then wire brush it and wipe it with an oily rag.

[Mr Pounder Esquire]

At a main dealer of course. More bollocks.

I used a wire brush and grease for 5 years on my Mk 3 Cortina. It passed on the brake pipes every time.

[polygonum]

Why does not changing the fluid make it more likely to boil? I'd understand if you said that any water in the fluid could turn to steam... Or if I were convinced that any water content would cause depression of boiling point...

Not in the least arguing against changing the fluid.

[Mr Pounder Esquire]

Mk 2 Cortina?

[Roger Mills]

Not so. My wife's 2000MY Puma only does about 2k miles per annum. The MOT (always done by the same garage) throws up a variety of advisories such as slightly corroded brake pipes or slightly worn suspension bushes. We do nothing about it between times and, as often a not, an advisory which appears one year isn't repeated the next despite no remedial work having been done. Seems to depend more on the whim of the tester than anything else.

[RJH]

I think 'pitted' used to mean a fail or at least a pipe on the way out, and slight corrosion not much more than normal, and one to watch.

I'd suggest posting on uk.rec.car.maintenance for some more insights.

[Clive George]

DOT fluid is hygroscopic, ie absorbs water. The longer you leave it, the more water there is in it. Changing it means you get back to fluid with no water in it.

And yes, water in it will cause problems other than corrosion - get it hot and you do inded lose your brakes as things boil.

[Adrian]

Fail is having lost 1/3 of the original thickness or more.

[Adrian]

...and the boiling point of the water in the fluid is much lower than the boiling point of the fluid. Heat the fluid to 100degC or more, and the water in the fluid boils, turning to steam. And steam is compressible.

The old DOT3 boils at 205degC. DOT4, the most common stuff today, boils at 230degC. DOT5.1 boils at 260degC, as does the silicone DOT5, which isn't miscible with the other three.

[polygonum]

I am delighted to read about absorbing water, creation of steam, changing the fluid so it is dry, and the actual boiling points. All relevant and some mentioned in my question/response. But none of them seem to support the claim I was questioning: that not changing the brake fluid makes the brake fluid itself more likely to boil.

[dennis]

Just go for the MOT, it wont fail unless its dangerous. You don't want to drive a dangerous car or are you planning on passing it off on some mug?

[T i m]

Or the advisory that the front brake pads are quite worn ... when the car may only do 100 miles between MOT's. But I'm guessing they can't know or should assume that so they would mention it because they looked lower than most brake pads should get for a driver doing 'typical' miles / year.

And all the advisories that mysteriously vanish between tests without anything being done about them. ;-)

Or the pass that's issued for something to fail on the way back from the MOT station (I had a brake pipe fail on my Morris Minor because it sat inside the chassis and couldn't be inspected).

Cheers, T i m

[Andy Burns]

Previous advisories now come up on the computer, don't they?

[Harry Bloomfield]

jim a écrit :

I agree, the thickest most waterproof grease you can lay your hands on.

Check it is ONLY surface rust, clean it off, paint it with oil, then grease. This is as advised by my MOT inspector and it said it is no reason for an inspector to be suspcious - they can feel the condition easily through the grease.

Underseal will only seal in the moisure and rust - the rusting will continue under the underseal, besides it is a reason for the MOT guy to be suspcious.

[Tim Lamb]

OK, OK but. The water can only come from the air in contact with the fluid. In most modern vehicles this is the space above the fluid in the reservoir. If the vehicle is unused, that bit of air will have lost all the moisture it contained. There is no mechanism other than atmospheric pressure changes to cycle fresh moisture containing air to that space.

In my view the 2 year fluid change must be based on an assumption about the number of pedal operations and hence air changes in the reservoir.

[Clive George]

If you were able to ensure that the brake fluid was unable to absorb any water then yes, you would not have to change it so often.

However since that's apparently rather hard, you do need to change it, because it does absorb the water and boils at a lower temperature.