Silicone brake fluid - good or bad?

I dislike the pedal 'feel' with silicone fluid. And no manufacturer that I'm aware of uses it, so I'd say there are other disadvantages.

Well on a possibly 30 year old car, what do you expect? Or are you saying you've had corrosion problems after replacing them and changing ordinary fluid every two years or so?

What often happens with an old car like this is that the cylinders get replaced only when they start leaking. After possibly never having had the fluid changed in many years of low usage. And with six, it can happen seemingly every time the car is used. ;-)

It's often the same with cooling hoses.

In news: snipped-for-privacy@davenoise.co.uk, Dave Plowman (News) decided to enlighten our sheltered souls with a rant as follows

Never tried silicon brake fluid in the cooling system...

In message , Asolepius writes

I've had silicon fluid in my car for the last three years. Found it best to use a Gunsons Ezeebleed to bleed the system, otherwise it's difficult to completely remove all of the air bubbles - silicon fluid seems to hold very small bubbles of air within the fluid making it more difficult to expel than with other fluids.

Having done so though, I can't say the pedal is any less firm than it was beforehand. I suspect its the possible retention of those minute bubbles of air that leads to the spongy pedal complaint.

Phil

When I bought my PI, it had silicone fluid, so I have kept it like that. My

2000 has always had the ordinary Girling stuff.

I haven't noticed much difference between them in normal use, but the 2000 pedal feels slightly firmer. I had not considered micro-bubbles, but I suppose it is a possibility. But I also know that the front hubs are adjusted slightly differently. When I turn the castellated nut back to line up with the split pin hole, it is virtually no distance for the 2000 but almost an entire flat for the PI, which makes a difference to how far the pads get pushed back when cornering. In an emergency stop I have to tread harder on the pedal in the PI for maximum braking. It could be differences in the pad material though, and not a feature of the fluid.

By all means switch to silicone if you want to, but I haven't found it makes a great deal of difference, and I wouldn't have bothered with silicone for the PI if the previous owner hadn't used it..

Jim

seal catalogue there is a full page of text on why you should not use silicone brake fluid with their components. steve the grease

I've also been using it for 3 or 4 years. I had no trouble bleeding the system and have no complaints at all. There's no servo fitted, so the pedal needs a bit of welly and I don't notice any sponginess. I had replaced all the rubber seals and hoses before switching to DOT 5, which I understand gets around some of the alledged problems with it.

There are some problems

1 You must replace all the rubber seals and hoses before switching to DOT 5 or old ones used with older fluids may swell and sieze up ocking brakes on - particularly with the Master cylinders it seems..

2 Pedal Pressure needed may increase (No idea why it just has on some cars Ive converted to silicone.

3 Traditional fluid absorbs some water, silicone does not. When water gets into the system and it does -- it settles at the low point and in severe weather of UK Winter type can then freeze and block the brake line with predictable results

- ie none when you try and brake! Not a frequent occurance but you must change the fluid every couple years.

4 Any silicone fluid on bodywork makes paint touching up a truenightmare

Its prime advantage would seem only to be that it wont damage the paintwork like old fluid can

I've now gone back to non silicone!!!

Regards

Clive

disadvantages

sticking

cylinders.

ordinary

happen

So how does the water get in? This claim has been made on this group before without any reasoning to back it up. I've yet to see _any_ water get into the system on my car. Even if it's true, then surely bleeding a few drops of fluid out at the callipers/cylinders would sort out the problem. As water doesn't mix with silicone fluid you don't need to change the whole lot and can even return the bled fluid to the reservoir if it looks clean.

True, but many waxes also contain silicones which cause exactly the same difficulties - and not just when they're accidently spilt.

The reason I use it is that it won't encourage corrosion within the braking system by absorbing water from the atmosphere. I've thrown away far too many corroded brake cylinders over the years.

: The reason I use it is that it won't encourage corrosion within the : braking system by absorbing water from the atmosphere. I've thrown away : far too many corroded brake cylinders over the years.

I wonder why more manufacturers don't use oil in braking systems like Citroen/LHM. It's so much easier to work with than normal brake fluid.

Ian

Thanks folks - but I'm not sure if I am any further ahead with this! Just to clarify, almost everything in the system is new - except for the cylinders which have been honed and polished. All new seals, pipes, and hoses. The Automec blurb says that DOT 5 never needs to be changed, and has been US Army standard issue for 15 years. That sounds mission critical to me. Despite what some posters have said, water does get into the system, at least when using DOT 4 which is my only experience so far. Also, I find with DOT 4 that the water settles out even though it's supposed to be miscible with the fluid. Hence the corrosion at the bottom of the master cylinder bore. This is not funny when a new master cylinder is £179. So we have this conflict between the seal manufacturers who say DOT 5 is rubbish, and the DOT 5 manufacturers who naturally say it's the bee's knees. On top of that, there are very variable opinions in this NG, so I'm still undecided.

If you drive a tank, maybe.

Don't you wonder way car makers don't use it from new? Plenty are moving towards 'lifetime' coolant and gearbox oil etc, so them wanting the servicing costs doesn't really wash...

Dave Plowman (News) ( snipped-for-privacy@davenoise.co.uk) gurgled happily, sounding much like they were saying :

Because DOT5 is silicone, and if any gets on the paint, it's an absolute bastard to get off if you need to do any accident repairs. It's also an absolute bastard to bleed properly, as it tends to suspend tiny bubbles in it *very* well indeed.

As has already been asked, what's wrong with a non hygroscopic, non silicone fluid like LHM?

Easily explained. As the brakes are operated, air moves in and out of the master cylinder reservoir, as it is vented to atmosphere. Any moisture in this air, will condense if the car is parked overnight and the temperatures drops.

This claim has been made on this group

Try looking at the engine oil filler cap, first thing on a cold morning. Chances are you will see droplets of condensed water on the inside of the cap. The same process as takes place within the m/cyl reservoir.

Even if it's true, then surely bleeding a

That might work, if the bleed nipples were at the lowest point in the callipers, or wheel cylinders, but if they're at the top, you'd probably only bleed some silicone fluid off, as any water would be at the bottom.

Better IMO that water is absorbed by the fluid, rather than puddling in the lower parts of the system, which is what you get with silicone. Mike.

Or if you drive anything in temperatures of 40 below. That, as far as I can ascertain, is why the US Army use it.

There's some blurb out there suggesting that DOT 5 shouldn't be used with ABS systems because of the likelihood of minute trapped air bubbles messing up the sensors, so that could rule it out for modern car makers.

You have to admit though that it's very hard to find any proper, unbiased information about the pros and cons of DOT 5 fluid. Everything on the web about it seems to be anecdotal rather than scientific.

OK, that makes sense, but how long would it take to build up to any real quantity? After all, we're not talking about pumping vast quantities of air in and out.

Only if you're bleeding at low pressure by opening the nipple and letting gravity do the rest. I'd find it hard to believe that any water would be left when bleeding under pressure by pumping the brake pedal.

It's about time I had a look at mine, so when I have the time I'll see how much water comes out of my car's brake system after 3+ years of DOT

5 and report back. I could be in for a nasty shock, but I'll bet there's none there...

We're not, but during a year there will be many times when the humidity and the difference between day and night temperatures will mean condensation will occur in the reservoir. I have no idea of how much water is still regarded as safe. Probably well in excess of the amount one would expect after 2 years. No doubt the recommended 2 year change, is erring on the side of caution. I don't imagine there's anything scientific about it. Mike.

Thanks again folks. For the record, I am taking the conservative route and sticking to DOT 4. This is mainly because I have it on the shelf and I'm too lazy and mean to buy some more!

I read a little of what I could find on the subject last night, and one anti-DOT 5 site suggested that while in use, conventional brake fluid absorbs water to about 3% of its volume and stabilises at that. They claimed that corrosion inhibitors within the fluid were quite capable of dealing with such quantities while mixed with the fluid whereas silicone fluid doesn't contain corrosion inhibitors and they'd be ineffective anyway because the water stays seperate. Of course if the first part of that was true, we'd never come across rusty brake components where conventional fluid has been used. I've a pile of Morris Minor brake cylinders that prove otherwise.

That is, unless the insides of the cylinders were being protected and the rust started on that part of the bore outside the piston, where small seapages of brake fluid combined with damp air to absorb higher concentrations of moisture than the corrosion inhibitors could handle.

Hope it's never been opened. Some say a half full tin shouldn't be used after a while because of it absorbing water... ;-)