Talk Morgan Forums Morgan Sports Cars Maintenance & Servicing Silicone Brake fluid - Holy Grail

Currently I have the standard DOT4 hydroscopic (absorbs water, damages by rust brake components etc) also damages paintwork!

I've the opportunity to upgrade to Silicone which has so many advantages so it looks they way to go

Any advice TMers?

Some more reading reveals that it has some serious cons to think about

It is more compressible so not as hard fell on actuating brakes
It is more viscous so bleeding is more difficult
Due to being more viscous the pads have a delayed 'on' braking effect as the fluid vacates the cylinder after brake release.
So lots to think about...

This topic, like waterless coolant, has been discussed a number of times.
If I recall correctly silicone fluid can only be filled into an all new system, it cannot be used to replace DOT 4 fluid. It is also incompatible with some older rubber materials and doesn't lubricate as well as DOT 4.
It is also expensive.
In my opinion it is better to change the DOT 4 brake fluid every year!

Any other thoughts, team?

And DOT 4 (like 3) is hygroscopic not with a "D" - a common mis-spelling.
As Peter says, just change fluid on a regular basis...

Yes agree looks best option is to stay glycol based and change every year see my other edit in earlier message

Here is the reason for my not liking corrosion on a morgans rear brake cylinder, it has 2 pistons only one side working ...so it passed its MOT with this...

DSC_0339 by Robert & Ali Davies, on Flickr

Agree with everyone else on this. Dot 4 changed regularly.
As far as rusting is concerned, I don’t think that the hygroscopic fluid is totally to blame. When you go through a puddle, water is easily able to enter the brake drum. Many people who have suffered corroded cylinders seem to have it most commonly on the nearside (where puddles are most prevalent on the roadside. )
Also, when parked up, moisture can condense inside the drum as it cools. If not driven for a while, I sometimes hear a rear brake squeak going down my driveway but it soon disappears as surface rust rubs off.
For longevity, when fitting new cylinders best to peel back the rubber boot and pack with Ceretec grease or similar, something manufacturers often fail to do.

Rob,
I agree with DOT4 changed annually with greasing of the rear pistons. If Belle is parked up for a long time in the garage I also chock the wheels & let off the handbrake.
John

Bob

As a chemist involved in brake fluid production for a few years (admittedly about 20 now!) please don't use silicone brake fluid in an old system.

It does have applications in brand new systems, but the two fluids are totally incompatible, and the smallest trace of old glycols/glycol ethers/glycol ether esters are going to render the silicone system very compromised.

It really isn't a big job to change brake fluids regularly, so that it is by far the best option for us.

Yes , there are several disadvantages with the glycol etc based systems , only some of which you have highlighted, but silicones are also not without their problems.

Although DoT 4 is hygroscopic (thank you Graham), it should last at least 2 years in our applications, although an annual change won't hurt anything (except your wallet)

DoT 3 fluid is less hygroscopic, but the boiling point is lower, however for light cars like Morgans it is probably more than good enough, but DoT 4 is a good compromise between the cheaper DoT 3 and the much more hygroscopic (but even higher boiling) DoT 5.1

Thank you...so what to use for the caliper and lubrication to rubber parts on the pistons please? any recommendations

I had silicone in my old+8 , done by the previous owner. I owned the car for 18 years. Never had any problems with the brakes apart from wear to the pads.approx 4000 miles a year.

Another comment, dragged out of my bike days memory, is to replace all the flexible hoses with Aeroquip or similar high spec lines: it was believed that most of the moisture got into the fluid through the hose walls.. No idea if it is true, but on a bike braided hoses with nicely anodised couplings look so cool...