Silicone brake fluid

[Pdv]

Hi All,

I have used sillicone fluid in my clutch which has new seals in the master cylinder and has a new slave cylinder.

I have reconditioned calipers that has had no fluid yet along with reconditioned master cylinder.

I want to use silicone for the brakes but not replace the rear cylinders as all seems fine .

It used to be said that all seals that had been using normal fluid had to be changed as they should not then be used with the new silicon fluid.

The fluid I purchased from Rimmers states that the fluid can be used in existing systems without any issues other than if you do not remove all the old fluid you would then be mixing the two and therefore reducing the effect of the silicone fluid.

Has the silicone fluid changed to make this possible or was it not the case years ago.

I will use a tube into a jar and apply light pressure with an airline to remove any old fluid at both rear brakes and when I bleed with the new fluid will expect to discard the first small amount that comes out and then bleed normally.

Any views or help appreciated.

Steve

 

[Badwolf]

When I replaced my dot 3 with silicone, I not only drained the system as best I could including pumping the old stuff through with a footpump, replaced all the rubbers and when bleeding the pipes made sure that I continued until the purple silicone came out. Silicone is a Marmite product in that you love it or hate it. I think it's good, especially when my re-rubbered clutch master cylinder gave up after a short time and fluid ran down the clutch pedal into the driver's footwell during the winter layup. No damage to the paint, just a mess to clean up. Do the brakes carefully, in my view do not mix, you may not be the only one to suffer from any mistakes!!!

[johny]

Just had a thought, does going to a non standard brake fluid have any insurance implications ie. does your company have to be informed?

[NonMember]

I've replaced mineral with silicon on several cars over some thirty plus years and never replaced the seals. I've had two seals fail out of about 70, neither of them particularly soon after the change.

[Badwolf]

My situation was normal paranoia. After all, I was refurbishing the whole brakes/clutch hydraulic thingie so did all the rubbers as a matter of course. Mind you, after 25+ years since they were last replaced I thought it the best thing to do.

[Pete Lewis]

a good site for all sorts of Triumph clues  is Buckeye Triumphs 

there some good spiel on fluids and so many things you need to know 

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

 

[dougbgt6]

Steve,

Mineral helps rubber, it "massages" it and failing rubber can still be OK. Silicone doesn't do this, so if you upgrade your rubber it has to be OK. My rubber was 3 years old, I upgraded to silicone and all OK. 

Doug

[Mjit]

All of the DOT3, DOT4 (mineral) and DOT5 (silicon) standards are specifically written to be interchangable and so mixable¹.  The only downside of mixing mineral and silicon is the potential to get the worst properties of each - though this is of course down to the ratio of the mix.  In practice draining all the old fluid/blowing through with a bit of air/pumping silicon through till it looks clean and purple out of each nipple will probably put you in the realms of 1 part in a million of mineral, so make no practical difference.  Also from this you don't NEED to change any rubbers BUT unless you only changed the rear wheel cylinders last year or something I'd say it's afalse ecconomy NOT to change them as part of the switch.  They aren't exactly expensive (~£4 for a seal kit/£9 for a brand new cylinder) while a bottle of silicon fluid will set you back more like £22/£38.  The seals are a service part that are expected to wear out and need replacing...something that always involves some loss of brake fluid (especially if you knock over your bleading jar for example).  How would you feel having gone to all the effort of swapping to silicon only to find one of the rear cylinders has started leaking in 12/18/24 months time and need replacing, and watching some of that expensive purple juice slipping away...?

 

¹ Worth noting that DOT5.1 is NOT compatible with any of DOT3/DOT4/DOT5, and probably the eason it's "DOT5.1" and not "DOT6".

[Colin Lindsay]

2 hours ago, Mjit said:

How would you feel having gone to all the effort of swapping to silicon only to find one of the rear cylinders has started leaking in 12/18/24 months time and need replacing, and watching some of that expensive purple juice slipping away...?

That is also one of the problems of the stuff; carry a quantity of it at all times as if it leaks whilst on the road you'll never find any for sale in local garages, so will either have to be trailered home or else top up with mineral...

[Peter Truman]

I get my silicone fluid from motor bike shops, dearer than Dot4 but not prohibitive.

Always carry 2/500ml containers on the shelf in case I need it in a hurry. I choose silicon as I had just. Re sprayed the bulkhead and wanted to avoid damage.

[Badwolf]

I carry a bottle of silicone just in case, but then I carry to many things, just in case. I did buy a bottle of dot 5.1 in error thinking that it was the next version of dot 5. Doh. The supplier changed it without question. I don't think that I was the first one who had got confused, but then, as you all know, I'm easily confused or just plain awkward.

[Pdv]

Hi All,

Thanks for all the replies, I have decided to replace the seals in the rear brake cylinders so all round now all new seals, forgot to say that new hoses fitted to the calipers and now new hoses to the rears so all rubber components replaced.

I also took the opportunity to dismantle the adjusters clean and grease them with copper grease, Little if any of the old fluid has weeped from the brake pipes but will blow it through.

Again thanks for all the replies will keep an eye on things as I go,will not be doing lots of miles but will carry a spare bottle of fliud.

Steve

 

[dougbgt6]

One of East Berks topped up his brake fluid with DOT4 not noticing the the SILICONE ONLY labels on his masters. A month later at the meeting he asked "What is this Silicone?" He paled as it was explained. What was to be done? He wanted to flush an replace all rubber. We pointed out he'd been running around with it for a month without brake failure all that was required was bled the brakes with which every you decide to use and keep bleeding till a consistent colour comes out.

Doug