Classic cars forum & vehicle restoration.

[ukdave2002]

I think that technically all glycol brake fluids must be synthetic? the brake fluids that you shouldn't mix are silicon and mineral.

Dave

[Ray White]

[ukdave2002]

Ray

Mineral fluids are all synthetic, there has never been a "natural" brake fluid, the word synthetic is probably added to the can by marketing folk!

synthetic does not equate to silicon

Dave

[Ray White]

[Miken]

In my experience ,if you want to know about oils and lubricants, the best people to ask are the people who make the stuff.
Choose a manufacturer and ring up their technical department. They are always very pleasant ,knowledgeable people who are always seem happy to answer your questions. A couple of Weeks ago I wanted to know which oil to run in my Devon pick up so I called Morris oil, Penright, Castrol and Miller oils. All very helpful.

[lowdrag]

I have never had a problem with glycol-based fluid - no bubbles, no water, no rust, and the only difference between DOT4 and 5.1 is the boiling point. For spirited driving use the latter. I have used 5.1 for years, and always keep a couple of sealed litres on the shelf.

[Richard H]

In addition to the drawbacks of silicone fluid mentioned above, it is also thinner, so in certain cylinders where the seal tolerances aren’t great anyway, you can get leaks.
Examples of vehicles to avoid silicone fluid with:
Anything Italian, using ‘donut’ seals in their braking systems.
Anything with o-rings in the braking system (not the best seal in the world!) French Record master cylinders commonly do, but apart from those they’re rare.
Anything with a remote servo, especially some of the older models. One major servo reconditioning company goes so far as to say you will void your warranty if you use silicone.

I would imagine on a car like Keith D’s Devon, which has decent cup seals in the wheel cylinders and seals with good tolerances in the master, you will have no problems at all.
_________________
Richard Hughes

[Keith D]

Finally, after a mere 34 years, my silicon filled hydraulic brakes have failed. I found a puddle of fluid under a wheel this morning and an almost empty reservoir. The car is now jacked high on axle stands and minus the brakes.

By the initial check of the cylinders, it would appear all I need do is to replace the rubbers, however I will check the cylinders thoroughly first.

One thing is for sure, silicon fluid will definitely be used in the repaired system.

In the whole 34 years, I have experienced NO PROBLEMS WITH BRAKES AT ALL and the car has often been unused for months while I do my globe trotting.

I was 47 years old last time I fixed the brakes. It this repair lasts as long as the previous one, I'll be 114 years old when they need doing again. Somehow I don't think I'll be worrying too much!

Keith
_________________
1926 Chrysler 60 tourer
1932 Austin Seven RN long wheelbase box sedan
1950 Austin A40 tourer
1999 BMW Z3
Its weird being the same age as old people.
You are either part of the problem or part of the solution

[Keith D]

A40 is now back on the road again.

I had the 4 brake cylinders resleeved (again) and new rubbers fitted. Master cylinder is still fine. Assembled everything, bled the brakes with Silicone (of course) and now have very nice braking again.

Keith
_________________
1926 Chrysler 60 tourer
1932 Austin Seven RN long wheelbase box sedan
1950 Austin A40 tourer
1999 BMW Z3
Its weird being the same age as old people.
You are either part of the problem or part of the solution