Changing brake fluid without bleeding

Of course it did. It mixed with the stuff in the master cylinder.

Full hex so it don't round off. Just crack it open and nip up, then you can use an open enden spanner for bleeding.

The message from Peter Hill contains these words:

And a smear of copper grease (only on the threads) to stop it siezing in the future.

Surely the point is that brake fluid absorbs the water? That's why you change it? Dunno if it ever reaches saturation point - I've never seen it.

I've never seen it either, but I've seen corrosion inside cylinders that could only have been caused by water. My guess is that saturated or not, water can still damage the metallic parts of the brake system, ally or steel, if left for long enough. Mike.

Yep - I.m never without my tub of copper grease ...... well in the garage anyway.

Indeed - although I've only ever seen it on old vehicles. It's possible uncontaminated fluid will cause the same damage over the years - after all it's not exactly a benign material given the way it lifts paint.

FWIW, I overhauled the calipers on my '84 SD1 recently. The cast iron bores cleaned up perfectly - it was the chrome plated pistons that had failed. But they are exposed to the elements. But I'd earlier replaced the rear wheel cylinders and master cylinder due to wear/ corrosion. It's had fluid changes at approx 3 year intervals.

I'm not quite convinced by anyone's arguments yet. The consensus seems to be that fresh brake fluid applied only to the master cylinder won't migrate down to the callipers to 'refresh' the old fluid. However, the other consensus seems to be that water vapour gets into the brake fluid in the master cylinder and then migrates down to the callipers. Both of these assumptions can't be right at the same time. Either liquids mix and migrate down a long narrow tube or they don't. Yes/No?

My guess is that there is a good deal of migration over a month or two, after all liquids aren't stable entities, their molecules are buzzing around like a swarm of flies if I remember my physics correctly.

My feelings too. However, changing fluid with a pressure bleeder is so painless it seems silly to faff about with any other method.

The message from "Dave Plowman (News)" contains these words:

Except with these fancy silicone fluids the boyracers like. Then again - I've taken calipers apart and found some very unpleasant sludge at the bottom.

The message from "DougP" contains these words:

You're not the "copper topped one" that keeps on going are you?

The message from "SteveB" contains these words:

Why not? If you introduce water to the master cylinder it's quite normal to assume that it'll diffuse along its concentration gradient until it's quite well mixed. OK, if you strip out the dirty fluid from the top it may difuse the other way as well - but it's a slow process.

The purpose of replacing fluid is to remove two years of accumulated crud and absorbed water. Using your method could take around two years to accomplish this.

I changed my brake fluid when I changed the pads, I had to take the calipers off and hammer the pistons about because they had both siezed up. It's probably worth doing , although there seemed to be a lot of what was possibly greese that was washed out with the new fluid ? I dont know if you are meant to re-apply greese to the piston seal inside the caliper ?

I broke a bleed nipple once, not sure how but at least it did not leak, so I guess if you were that unlucky you would just abort the job and forget about it ( and maybe try to find a new caliper from a scrappy !)

Maybe that's the answer,, get youself a standby caliper in case you break it ! ( talk about tempting fate though !)

Simon

What floats on what - oil on water or water on oil?

What sinks into what? - water into oil or oil into water

You can experiment with brake fluid and see...

What's the safe option?

What's the impact of saving a few quid and turning out to be wrong? - a bit of a fright, or a few lives perhaps?

Where's your sense of responsibility?

I don't think clean brake fluid causes any corrosion to steel or ally. Some time ago I came across a part used tin of brake fluid in the garage that must have been at least 15 years old. No sign of corrosion inside the tin at all.

- after all

Apart from new discs, pads, and brake shoes, everything on my '85 Vitesse is original. I think I've only changed the brake fluid about 3 times since I baught it in '88. Before I baught it, I had a 2600, which I had intended to convert to Vitesse brakes. IMO the std brakes faded too easily. The Vitesse was baught before they were fitted. Consequently I still have a brand new pair of calipers. An almost unworn pair of OE discs. A master cylinder and servo. A r/brake compensating valve, both it and the m/cyl reconned with new seals etc. All I'm lacking is the rear cyls to do a complete brake overhaul when the time occurs. Which hopefully will not be too soon.

"The answer my friend is blowing in the wind". :-) Mike.

The message from " snipped-for-privacy@lycos.co.uk" contains these words:

If they're that bad I reckon I'd rather strip the caliper down and fix it rather than just belt it one with a hammer. Or fit a recon.

If a caliper has seized, the pair should be stripped, examined for scoring and damage, and assembled with new seals. Most decent motor factors will sell repair kits. I use rubber grease at assembly time. Again, a decent motor factor will sell a tube of it. *Do not* use ordinary grease - it can attack the seals and contaminate the fluid.

I'm sure the designers of hydraulic brake systems are well aware of fluid dynamics - the manufacturer's say that the brake fluid should be changed every two years regardless of mileage. If you have an accident due to the car not being serviced properley (i.e. according to manufacturer's guidance) then your insurance co. probably wouldn't pay up...

Darren

ok thanks for that,.. i think it's siezed up again actually