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Discussion Starter · #1 ·
I have just read an article on silicone brake fluid and at first glance it appears too good to be true,no more changing every couple of years and no more siezed calipers,however the first problem seems to be that it is not recomended for ABS systems,anybody know why? And is anyone using it?
 

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Hi MikeH

DOT 5 isn't compatibly with DOT 4, the normal fluid in the brakes and clutch of the SAAB.

DOT 5 is different to DOT 5.1, 5.1 is compatibly with 3 & 4.

If you were to use DOT 5 you would need to flush all the old fluid from the system.

I cant take the credit for this,
have a look at:

http://www.norseperformance.com/diary6-11-04.htm

It was suggested to me on a question of the rear brake pipes, I found the site very helpful.

I suspect this may not answer your question on suitability for ABS, but wait, someone will come along and give you an answer.

cheers

David
 

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If you ere to use DOT 5 fluid, it's not just a case of flushing the system- to be safe you would need to replace all the seals as well.

"DOT 5 fluids are silicon based and are non-hygroscopic, which is good. They are also subject to frothing from high frequency vibration, which gives a soft pedal. Soft brake pedals may be OK in non-high performance cars (in fact, most drivers accept mushy brake pedals as normal) but they are not acceptable in any situation where the driver intends to modulate braking at high force values." (more on braking here)

The particular property of frothing does make it unsuitable for ABS systems.

Although not hygroscopic (i.e. does not absorb water) the fact is that water does get in to brake system from various routes, and whislt it is absorbed in to regular fluid, which can then be easily changed, it collects in pockets in a DOT5 system, and can lead to corrosion and poorer braking. Regular, thorough flushes are therefore necessary.

PS moving to Performance....
 

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Discussion Starter · #5 ·
The article I read made no referance to "Frothing" and as for mixing with mineral fluid,that sounds a dogs breakfast.In my experience normal fluid pools anyway and causes corrosion,rear calipers and wheel cylinders been the obvios examples.
If changing to silicone the article states you must flush aggresively to create as much turbulance as possible,this enables the SLURRY caused by the mixture of Dot-5 with the residues of Dot 3or4 to be carried away , together with rust,water&dirt.
I have no intention of using Dot 5 in any of my old ladies ,but it does sound to be an improvement long overdue
 

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We've been using DOT5 for years, in Morris Minors And I have it in my 99T. No ABS on any of those of course. The method for removing any water in the system is to bleed out roughly the volume of each caliper each year as the water should sink to the lowest point in the system.
 

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At the meeting of the local branch of the Morris Minor Owners Club we had a talk from a man from Castrol. He said that they did not make silicone based brake fluid because it allowed water to pool rather than be absorbed. Castrol were concerned that if the pool of water was at the lowest point (probable) in the brakes it would turn to ice in cold weather and could seize the piston.

This was about 5 years ago, maybe things have changed since then?
 

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Can't say I see any truth in it, I forget how long our Minors have had it in there, but it's measured in decades and we've never ever had a problem. Discs brakes are slightly different in that they have a much larger volume of fluid in the caliper bodies rather than wheel cylinders, hence bleeding a little out every year or so to lose any collected water.

I believe the US military use it in all their vehicles. And apart from an unrelated problem of the odd shot in the wrong direction I don't think they have any problems with it.
 

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Discussion Starter · #11 ·
Nutcase is correct as far as the US military is concerned,it was at their behest in the late 60's that the stuff was developed,prior to Dot 5 they used 3 kinds of fluid,one for the tropics,one for temperate and arctic,and one for storage.The Only manufacturers are Yanks.
mike
 

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I've used DOT 5.1 in all my modern cars with Goodridge hoses to firm the pedal up and i have had no issues at all ABS or not.

Zippy
 

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A couple of points.

1) The bleed valves on brakes are at the top of the calipers/cylinders etc. This is to let air out. I do not know what the density of DOT 5 fluid is, but if it is less than water, you will never get any accumulated water out of the bleed nipple.

2) Some years ago, I too decided to use DOT 5 in a classic car, albeit one somewhat faster than a Minor. I was able to blow out all the lines with compressed air, and generally did what I thought was a good job at cleaning the old fluid from the system. Initially everything worked well with the new DOT 5 fluid in, but soon it all went horribly wrong. The pedal became sprongy and I was having to really stand on the pedal to get any effect. I commented on this in my local motor factor, and they instantly produced a kind of technical warning letter (from Castrol, I think) listing the problems that can result from using DOT 5 in a system previously run on DOT 3 or 4. I seemed to have most of them, the main one being swelling seals causing everything to stick, and requiring vastly increased pedal forces.

So if I can give one word of advice: DON'T!

In a brand new system with all new components and seals, maybe. In an existing sytem, NO.
 

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Zippy,

just to clarify: DOT 5.1 is the natural successor to DOT 3 and DOT 4. They are compatible and miscible. DOT 5.1 has a higher boiling point, but also must pass a low temperature low viscosity test to ensure that your ABS will work properly in winter (this is not part of the DOT 3 or 4 spec).

The silicon based DOT 5 is not compatible with DOT 3, 4 or 5.1, and does not pass the low temp low viscosity ABS test.
 
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