Morris Minor Owners Club

I have a question for any budding chemists here. After removing the plate covering the master cylinder, I noticed the Chassis leg below looked a bit wet. It’s covered in Waxoyl from years ago but it could be the wet appearance is caused by silicone fluid that may have found its way into the leg whilst pressure bleeding the brakes. It’s not swimming in it but there looks like a film of it.
Is silicone brake fluid likely to cause corrosion or rust or is it simply oil? Any info would be helpful.

Silicon brake fluid can cause the rubber seals in the master cylinder to perish after a while.

newagetraveller wrote: ↑Wed Jul 03, 2019 9:45 pm Silicon brake fluid can cause the rubber seals in the master cylinder to perish after a while.

Surely that only happens if some glycol fluid is still present in the system?

From what I’ve read that does not ring true, also my experience of 20 or so years of use does not bear that out.
It’s Recommended that the system is clean to start with.

It won't cause any rust problems Les, it is used to protect metal from corrosion it is often found in spray on lubricants. The only problem I know of with it is if you get it on the paint work it can cause silicon spots when painting over, you often have to sand the paint down to the metal to get rid of it.

I would have thought Dot4 leaking into the chassis leg would be more of a problem as it's hydroscopic..

John

Indeed, silicon oil won't harm the steel significantly.

Though, I would still clean it out and make sure you don't have a leak by checking after a good drive or two.

Opinions are divided on benefits of silicone fluid, I recently replaced just about everything, but decided to refill with dot4. Why? Well, no OEM fits it, they all use dot4, so it must be OK for an old minor.

Yes, change every couple of years, but that is no real hardship.

Thanks for all replies, I would normally clean it up but the position of the master cylinder makes this unrealistic, hence my query about the possible harm.

I have used silicone brake fluid for twenty years or more without a problem. I have never changed it in all that time. Some had spilt or leaked into the cassis leg a long time ago. It dribbled out of the drain holes but the metal is unharmed. If it is good enough for Rolls Royce and Harley Davidson then its good enough for me. The biggest benefit is no more seized rear cylinders. Fit and forget.

I really don't understand why it's not more widely used. I filled my Minor with it 10 years ago (into a fresh system) and haven't experienced any problems.
If I were replacing/rebuilding braking components on our other vehicles I wouldn't hesitate to use it in them.
To me it's a bit of a no brainer.

Alan

It is all down to cost. Silicone brake fluid costs about four times the price of ordinary fluid. Times that by how many cars are produced ant it will add a huge cost to the manufacturer. Plus. the benefit won't be felt until the car is over four years old and probably passed to the second hand market.

Add to that the dealership service losses. Now that BEVs are steadily taking over, dealerships will want to retain as much servicing as they can. Many now check the moisture in the fluid and frighten the customer into an expensive fluid change added to the bill. I reckon some of them simply change the bulk of the master cylinder contents and await the next moisture check!