Clive Posted January 8, 2019 Report Share Posted January 8, 2019 My point is that silicone fluid is hydophobic, so won't absorb water/moisture even from moist air in the mater cylinder. Not so with hydrophilic conventional fluid. Re fully synthetic oils, Kipping used to offer the advice that mobil1 was THE biggest factor in 1500 longevity, and they rarely changed the oil. Mind you, his fleet of cars were exceptionally well set up, and conversely driven like they were stolen by the assorted people who worked there. Poor combustion down mainly to poor setup, and short journeys on choke. Again a common symptom of cars that are not used enough. Link to comment Share on other sites More sharing options...
NonMember Posted January 8, 2019 Report Share Posted January 8, 2019 25 minutes ago, johny said: I believe moisture can get into our systems via the breather hole on the master cylinder. This allows air (and any moisture it holds) in as the fluid level goes down due to operation of the pedal or even liquid volume change due to temperature. Yes, but there it stops unless... The point is, silicon fluid doesn't absorb water, so the airborne moisture (which, being a vapour, is lighter than the fluid) stays in the air, where it's harmless. Conventional fluid can, and absolutely does, absorb that moisture straight out of the air and sucks it into the brake system. Link to comment Share on other sites More sharing options...
johny Posted January 8, 2019 Report Share Posted January 8, 2019 as we all know moisture can and does regularly precipitate out of the atmosphere without being near anything hydroscopic but yes we're talking about miniscule amounts in a brake system. However Ive never understood why the main car manufacturers have never supplied their vehicles with silicone from new.... With non synthetic engine oil my engine, which runs pretty well, comes out black n smelly so I wouldnt want to leave a synthetic in there any longer. Link to comment Share on other sites More sharing options...
Colin Lindsay Posted January 8, 2019 Report Share Posted January 8, 2019 34 minutes ago, johny said: However Ive never understood why the main car manufacturers have never supplied their vehicles with silicone from new.... ...which wouldn't be either a cost or production issue, so they must know something... Link to comment Share on other sites More sharing options...
dougbgt6 Posted January 8, 2019 Report Share Posted January 8, 2019 6 minutes ago, Colin Lindsay said: ...which wouldn't be either a cost or production issue, so they must know something... Which is...... You must NOT use silicone in a an ABS system. It's all in the Buckeye Triumphs document, it's there, waiting to be read, all you need to do is, read it! Doug 1 Link to comment Share on other sites More sharing options...
johny Posted January 8, 2019 Report Share Posted January 8, 2019 apparently it depends on the ABS system but some can definitely use silicone fluid so it comes down again to the manufacturer deciding to design their vehicles to use it or not..... Link to comment Share on other sites More sharing options...
Clive Posted January 8, 2019 Report Share Posted January 8, 2019 This is an interesting clip, and explains why silicone shouldn't be used in ABS systems, and probably why it compresses a tad (if even measurably in real life) than other fluids The "boiling" is done not by heat but by vacuum. Link to comment Share on other sites More sharing options...
johny Posted January 8, 2019 Report Share Posted January 8, 2019 wont any liquid do that though if its got air in it and then is subjected to a vacuum? Link to comment Share on other sites More sharing options...
Clive Posted January 8, 2019 Report Share Posted January 8, 2019 Only if it lets air dissolve in it. I suspect silicone fluid does that far more than conventional fluids, hence it causes frothing/brake loss in ABS systems. Link to comment Share on other sites More sharing options...
johny Posted January 8, 2019 Report Share Posted January 8, 2019 hmmm if its that much of a problem there should be very prominent warnings on the containers of silicone..... Link to comment Share on other sites More sharing options...
Clive Posted January 8, 2019 Report Share Posted January 8, 2019 This is from Opie's site. It implies silicone fluid is not a great lubricant for the ABS pumps. They also state not suitable for motorsport... But I assumed it was on the bottles that it was not suitable for modern car braking systems? Or maybe it doesn't meet the same stds? Either way, in a simple braking system it should be fine (though I maintain that if using, ALL the rubber seals should be changed as they will have absorbed mineral brake fluid, and they don't mix, and gut feeling says that is bad news) SILICONE BRAKE FLUID (DOT 5) Silicone based DOT 5 was originally introduced to give higher temperature performance over glycol DOT 4. Silicone fluid also has other advantages, it does not damage paintwork and it does not absorb water. However, silicone fluid is a poor lubricant and does not lubricate ABS pumps as well as PAG fluids. It is also more compressible than PAG fluids, which can result in a sluggish or spongy pedal. It therefore requires special design considerations in braking systems. Further, because it does not absorb water, any water remains as globules, which can pool in low spots in the system and cause corrosion. This water can vaporise when heated under heavy braking giving a disastrous effect on braking efficiency. DOT5 fluids are not recommended for motor sport applications. Link to comment Share on other sites More sharing options...
Colin Lindsay Posted January 8, 2019 Report Share Posted January 8, 2019 2 minutes ago, clive said: However, silicone fluid is a poor lubricant and does not lubricate ABS pumps as well as PAG fluids. It is also more compressible than PAG fluids, which can result in a sluggish or spongy pedal. It therefore requires special design considerations in braking systems. I'll stick to the original recommendation; silicone has not so far been sold to me as a worthy replacement. 1 Link to comment Share on other sites More sharing options...
dougbgt6 Posted January 8, 2019 Report Share Posted January 8, 2019 Clive, Yes it does retain air, I had to bleed my clutch 3 times over a period of a week until I was happy with it. Is this a problem? No. Dot 4 and the rest lubricate the system and to an extent will mask failing rubber. Silicone is not a lubricant which is why rubber should be checked/replaced before installation. Doug Link to comment Share on other sites More sharing options...
Chris A Posted January 8, 2019 Report Share Posted January 8, 2019 Interesting debate on modern version versus traditional item. Much in the style of points v electronic or mechanical fan v electric. As far as this debate goes on the brake issue I'll carry on as normal - not using brakes. Saves all this worry. 🙈 Link to comment Share on other sites More sharing options...
dougbgt6 Posted January 8, 2019 Report Share Posted January 8, 2019 As far as I'm concerned it IS a worthy replacement, the only thing against it is Clive's point about availability. However, it wasn't actually sold to me, I won it in the Courier picture caption competition. Doug 1 Link to comment Share on other sites More sharing options...
johny Posted January 8, 2019 Report Share Posted January 8, 2019 dont think theres an inherent problem having silicone and mineral oil mixed but of course you would be missing out on the advantages concerning moisture retention and paint damage.... Link to comment Share on other sites More sharing options...
Clive Posted January 8, 2019 Report Share Posted January 8, 2019 The point is they do not mix. At all. Like oil and water. So seals that have absorbed mineral fluid, will not absorb silicone. Where as fresh seals will, which is what is meant to happen. That is why it seems wrong to just change the fluid. But either works in our cars. Pro and cons to each. 1 Link to comment Share on other sites More sharing options...
johny Posted January 8, 2019 Report Share Posted January 8, 2019 Cant see a problem with them not mixing but I have seen (expensive) recommendations to flush the system with silicone fluid before the final fill so as to minimise the amount of mineral oil contamination. Not heard of seals giving problems and wonder if there isnt some vested interest from a few companies in this field..... Link to comment Share on other sites More sharing options...
daverclasper Posted January 8, 2019 Report Share Posted January 8, 2019 I have heard that disk calipers ideally need to bled (by sqeezing the pistons in) after running new fluid through to remove water that stays there, but did not know that applies to removing wheel cylinders for the same issue. What a faf !. I have always changed fluid every 2/3 years without doing the above, but this implies it's maybe a waste of time?. Thanks, Dave Link to comment Share on other sites More sharing options...
dave.vitesse Posted January 8, 2019 Report Share Posted January 8, 2019 I agree with Clive. From experience seals that have absorbed mineral fluid can loose their form when they subsequently come in contact with silicon fluid. The same goes for some engine oil seals. It's best not to mix the stuff. Dave Link to comment Share on other sites More sharing options...
Colin Lindsay Posted January 8, 2019 Report Share Posted January 8, 2019 Weren't we all advised way back in the day to change rubber seals before switching to silicon? (Anyway Dave I've no intention of changing my engine oil for silicon.) 1 Link to comment Share on other sites More sharing options...
johny Posted January 8, 2019 Report Share Posted January 8, 2019 I think what we need is some first hand info. Can anyone who's actually changed over to silicone without replacing all the system seals give us some feedback please? Link to comment Share on other sites More sharing options...
dave.vitesse Posted January 8, 2019 Report Share Posted January 8, 2019 19 minutes ago, Colin Lindsay said: Weren't we all advised way back in the day to change rubber seals before switching to silicon? (Anyway Dave I've no intention of changing my engine oil for silicon.) Yes, re the seals. Me neither re the oil, Colin. I do use silicon brake fluid but I have to draw a line somewhere! Dave Link to comment Share on other sites More sharing options...
dougbgt6 Posted January 8, 2019 Report Share Posted January 8, 2019 Johny, I replaced my brake and clutch master cylinder rubbers a year ago, replaced the clutch slave cylinder and put in DOT5.1 . 6 months later, 200 miles, I swapped the clutch hydraulic pipe for an armoured version and upgraded the clutch fluid to silicone. No problems so far. When the weather warms up the brakes will be changed to silicone. I replaced my rear brake cylinders about 5 years ago and I will change the rubbers. Repair kits are £8 each from Rimmers, probably cheaper elsewhere. I shall check the master cylinder rubber but I don't think 200 miles of DOT 5.1 will matter. Incidentally although silicone doesn't eat paint it does make it go dull, not a problem on the bulkhead really, but don't spill it on the wings! Doug Link to comment Share on other sites More sharing options...
NonMember Posted January 8, 2019 Report Share Posted January 8, 2019 4 hours ago, johny said: I think what we need is some first hand info. Can anyone who's actually changed over to silicone without replacing all the system seals give us some feedback please? I've lost track of when I changed the GT6 to silicone. Probably mid-1990s. It developed a leak from the master cylinder about three years ago. Link to comment Share on other sites More sharing options...
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