Silicone brake fluid
228B
Brake Fluid - corrosion in the hydraulic systems

Note from Georg Muller. This note should be read with V8NOTE228A. (Mar 05)

Who of us hasn't thought about spare parts for the brake and clutch hydraulics, especially as some of the parts are no longer available. There are good reasons for this too because over time, corrosion in the hydraulic systems is something we will come across more often. Even regular and good servicing and changes of the brake fluid every year will not avoid this. So what is the reason?

Conventional brake fluid is hydroscopic and leads inevitably to corrosion and rusting. Hydroscopic products are those which readily retain moisture based on temperature and humidity. Over the years the seals will become hydroscopic as well. For this reason you will find corrosion and rust close to the seals even with regular changes of the fluid. So what can we do to avoid these problems? The only way is not to use the conventional glycol based brake fluid. There are silicone brake fluids on the market, which are not hydroscopic. Some weeks ago I spoke with Mike Sander who is well known for his Rust Prevention Grease (Winner of the Motorklassik 3 year long term test). He sells a silicon based brake fluid as well and we discussed the pros and cons about the product. He has used the product in his MG TA since April 1984 and he has never changed the brake fluid again.

So what are the pros and cons of silicone brake fluid?

Pros:
o It's not hydroscopic - so no corrosion and rust.
o Fulfils DOT5 specification. Minimum wet boiling point of 260°C (500°F).
o No need to replace the fluid again - maintenance-free hydraulics.
o No paintwork damage.

Cons:
o More expensive but this os short term one as you have only one replacement.
o It's more difficult to bleed the hydraulic system (higher viscous).
o Very little elastic.

So finally I decided to use the silicon based brake fluid. Last Saturday I went for the procedure as follows:

1. Draw off the brake fluid out of the expansion tank.

2. Refill with the silicone brake fluid.

Such refill system can be used to automatically refill the expansion tank, which will avoid new air coming into the brake system during bleeding

3. Bleeding the brake system. As the conventional brake fluid is heavier you may dismount the callipers and put them up side down for a first bleeding. After re-mounting go for a second bleeding.


Bleeding system with non-return valve - using such or similar system will make bleeding less difficult

4. Redo the bleeding after some days.

Even though my brake system worked very well, I identified one piston which was seized up. I was able to clean the piston and make it work again. So my decision for the change was just in time. After the change I did some test driving. The brake system performs very well. As the silicone brake fluid is a very little more elastic I did expect, that the braking would be a little soft. But this is not at all the case, it's even better than before. So overall this is a change I can recommend. Everybody who wants to keep their brake and clutch hydraulic system in good condition should think about this. If you have any question please feel free to contact me by email at georg.muller@g-concept.com.

Contacts:
Mike Sander http://mike.british-cars.de/english.htm
FROST restorers equipment http://www.frost.co.uk
V8NOTE228 - servo failure & brake fluid.

V8NOTE228A - additional notes on the debate - silicone or mineral brake fluid for V8s?

V8NOTE228B - extra note with the views of Georg Muller on silicone fluid.

V8NOTE398 - comprehensive review of brake fluids by Bob Owen
V8 Register - MG Car Club with support and services for MGV8 enthusiasts