automec silicone brake fluid

[alan.gilbert_6384]

Hi All,

So at the beginning of the year I had trouble with a leaking clutch slave cylinder.  I replaced it with a new one, not long later that started to leak, got another new one from the vendor and replaced it.  All was well for a while then the clutch master cylinder started to leak, replaced the seals and now all well again (all with standard DOT4).  

Late on in the summer the brake master cylinder started leaking, so I have now decided to re seal this one.  I have dismantled it and found both the small and large seals have basically turned to mush, very odd.  The PO installed silicone brake fluid at some point many years ago.  I am really surprised it has lasted this long given the state of the seals.  

So the question is,has any one had experience of silicone brake fluid reacting with seals ???  Thought this stuff was supposed to be the bees knees ???

[PeteH]

Sounds like a reaction between the silcon and the DOT 4?. Maybe some traces left behind when the PO changed over. Or pehaps the Seals where not changed?. I changed a Vitesse back in the 80`s, but I did all the seals and new copper pipework too.

Pete

[dougbgt6]

Here is a very good article on brake fluid by our old friends Buckeye Triumphs

Selecting+Brake+Fluid.pdf (squarespace.com)

My understanding is that dot 4 and older "massage" and helps the rubber. Silicone does not do this. Deteriorating rubber can function in dot 4 but if silicone replaces dot 4 without changing the rubber there can be a sudden failure which is often mistakenly blamed on the silicone. So I think your rubber was decaying in dot4 originally, but not enough to fail straight away in silicone.

Anyway read the article it's all in there. I particularly like the bit where the guy mixes the two, they separate and a day later appear to have swapped places in the jam jar. What actually happened is they stayed separated, but one leached the colour out the other.

One of our guys at East Berks topped up with dot 4 not noticing the SILICONE ONLY label on his master cylinders, it braked fine for a month before he noticed the label. This is confirmed by Buckeye, they don't mix or interact, apart from the colour leaching. This makes replacement dead easy, you just pour it in and pump it out till the colour changes.

Doug  

[trigolf]

I've used Automec silicon fluid for twenty years with no problems. However, when I changed over from DOT 3/4 I replaced all the seals and flushed the entire pipe runs with meths, just to be sure. 

[dougbgt6]

Meths contains water so not a good idea, you don't want water in the brake system, but obviously OK now. You just pour silicone in and pump fluid out till it changes colour.

Doug

[PeteH]

1 hour ago, dougbgt6 said:

if silicone replaces dot 4 without changing the rubber

That`s likely why I had no problems then?. I changed everything seals, pipe, and all?.

Pete

[Mjit]

DOT3, DOT4 and DOT5.1 are by definition 100% compatible and Automec actually say on their bottles that it can be mixed/you don't need to replace anything when changing.

Of course being compatible is not the same as saying mixing them is a good idea, as you get the worst properties of each rather than the best.

The story of DOT5.1 is that the US military wanted something they could put in their millions of vehicles and just leave it there while they sat unused in a desert storage yard somewhere, not have to have people swapping the fluid every 3 years - but be able to top up with whatever came to hand in the middle of a war zone. And it's DOT5.1 rather than DOT5 or DOT6 because those numbers were already used by other specs.

[johny]

Not sure thats all correct Mjit as DOT5.1 is glycol based (so as you say mixes with DOT 3 and 4) but this means it absorbs water like the others so should be changed regularly. DOT5 however being silicone based doesnt absorb water so can be left in the system indefinitely and I read thats why it has been taken up by the military...

[ed.h]

DOT 3 & DOT4 are glycol based.  DOT5 is silicone based.

DOT 5.1 is glycol based like DOT 3 & 4.  It was numbered 5.1 because some of its physical properties are closer to DOT5 than to DOT 3 or 4.

Never heard of DOT6.

Ed

[Mjit]

Sorry, confused my silicon number. Should have been "DOT3/DOT4/DOT5 (silicone) can mix" and "DOT 5.1 number comes from other numbers already being used".

Main reason DOT5 (silicone) 'fell out of favour' is because it's not compatible with ABS. And of course DOT4 fluids got better (the standard just defines the minimum test point the fluid must meet while almost all far exceed them these days).

[Colin Lindsay]

4 hours ago, ed.h said:

Never heard of DOT6.

Ed

Used for racing, apparrently. I just had to look it up to see if it existed!

[Pete Lewis]

20 hours ago, dougbgt6 said:

Here is a very good article on brake fluid by our old friends Buckeye Triumphs

Selecting+Brake+Fluid.pdf (squarespace.com)

I love these  just adds to the Myth busting clear and controlled testing  .    you should all read Dougs  Link 

who remembers the millenium clock and leaded petrol Myths   E10 is next on the list 

its blamed when its  really   all the fake nasty hoses on sale anyone had their car dissolve overnight ???  

Pete

[Stratton Jimmer]

Both my Triumphs (Mk3 GT6 and Spit 1500 with GT6 engine) are on Dot5 with no problems whatsoever.

[johny]

I think the main question here is whether its recommendable to just whack in DOT5 without changing seals rather than it being a problem in its own right....

[alan.gilbert_6384]

Hi All,

So I have decided that new seals and flexes all round are in order.  Re seals on the callipers, the sectional view of the calliper shows an O ring between the two half's of the castings, replacing this seal is not mentioned in the WSM or Haynes, any thoughts ?  Also any recommendations where to source the seals and flexes would be appreciated, thanks.

[NonMember]

That O-ring isn't a moving seal so it's probably OK to leave it. You only need to touch it if you split the caliper, which isn't necessary for seal replacement (or even for a fairly extensive refurb).

[Mjit]

On 28/11/2022 at 11:50, johny said:

I think the main question here is whether its recommendable to just whack in DOT5 without changing seals rather than it being a problem in its own right....

Given you have to drain all the old fluid, the fact no seal lasts for ever, and the relative low cost of seal kits vs. DOT5 fluid I'd always recommend replacing the seals as part of a swap.  But you don't have to replace them.

If you only replaced them 6 months ago I'd probably keep them, but if you can't remember the last time you changed them probbaly worth doing it now rather than losing some of that blue liquid gold doing the job in 6 months time.

[Peaks]

All I'd add is that in my experience this is not the result of the use of silicon fluid, but is caused by another problem.

If I was a betting man I'd say poor quality rubber in the seals, but obviously difficult to say from.a distance.

I'm another one who's used silicone fluid for early 20 years with no problems either with component failure or with pedal feel. 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

[alan.gilbert_6384]

5 hours ago, Peaks said:

All I'd add is that in my experience this is not the result of the use of silicon fluid, but is caused by another problem.

If I was a betting man I'd say poor quality rubber in the seals, but obviously difficult to say from.a distance.

I'm another one who's used silicone fluid for early 20 years with no problems either with component failure or with pedal feel. 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Cheers, I can report that having now completely dismantled the callipers, there was definitely old brake fluid trapped in them ( this was also after needing them last spring when I replaced some old steel pipe runs), so you can’t just stick in DOT5 and expect it to be everywhere.  The PO changed to DOT5 in 2007 along with refurbished master cylinder, so this DOT5 was only ever in contact with new seals, really strange.  It was the first little seal on the plunger shaft, not the main compressor seal, although that was affected as well very soft, that turned to complete mush.  Like I said very strange but happy to replace all the rubber and start again with my own work, which I trust.

[SpitFire6]

On 26/11/2022 at 15:53, dougbgt6 said:

Meths contains water so not a good idea, you don't want water in the brake system, but obviously OK now. You just pour silicone in and pump fluid out till it changes colour.

Doug

Hi Doug.

 Meths does not contain water unless water is added.
Why do you think that?

Cheers,
Iain.

Edited December 21, 2022 by SpitFire6
Whey to Why

[Unkel Kunkel]

Methylated spirit will contain water - around 5% , but I don’t think that is an issue in itself but I question the need to use methylated spirit at all.

The main attraction of Dot 5 is not having to change it for a very  long time. Therefore it seems a very appropriate time  to do a full hydraulic overhaul before changing to it ie all  the seals  - and all the hoses.

Any Dot 4 : Dot 5 compatibility concerns  become irrelevant  and the bleeding process  will flush any remaining  tiny traces in the metal pipes.

This should give a thoroughly overhauled hydraulic system that should be fine - for many years to come.

[dougbgt6]

"does methylated spirits contain water?"

Interweb says

Industrial methylated spirits is comprised of ethanol (90%), methanol (5%), water (5%) and small amounts of pyridine and other coal-tar chemicals to make the liquid unpalatable. 

That's as much as I know

Doug

[SpitFire6]

37 minutes ago, dougbgt6 said:

"does methylated spirits contain water?"

Interweb says

Industrial methylated spirits is comprised of ethanol (90%), methanol (5%), water (5%) and small amounts of pyridine and other coal-tar chemicals to make the liquid unpalatable. 

That's as much as I know

Doug

Hi Doug.

I wrongly assumed you had mentioned Methanol.

Cheers,

Iain.

[68vitesse]

Have used Dot5 in my Vitesse for over twenty years, the instructions for the servo, Taiwanese copy of a Lockheed unit, said not to use it but so far so good.

Lot of don't use is just ass covering in my opinion.

Regards

Paul 

[johny]

Trouble is, although highly unlikely, if the insurer ever found out after a serious brake failure accident it would give them the perfect get out if they hadnt been previously advised...