Silicone Brake Fluid

[piman]

Hello all,
just reading about brake caliper problems in the Healey forum got me thinking about brake fluids.
I have used Silicone brake fluid for many years now and would use nothing else. In particular if your vehicle is not used a lot it helps stop brake cylinder corrosion. It does not need changing regularly (How many people actually do change their brake fluid as recommended?) and it doesn't lift paint when spilt (not if, when)
Some people say that it gives a softer pedal but I don't notice it. It is expensive but worth while I feel.
Anyone like to comment?
Alec

 

[61Alpine]

I switched to Silicone in my Sunbeam Alpine last year. I like it. I do have a question though.
I was ready some other threads lately and came across a line that said to fill the brake resevoir to the fill line. I can't see and particular line in my resevoir. Does it matter if I fill the tank almost to the top?

 

[Basil]

When my Jag EType was still running, I also switched to silicon. I like it over all, but I did notice some softening of the brake pedal feel.
But I like the anti-corrosion quality and will no doubt use it again when I get (if) my car back on the road.

Basil

 

[MDCanaday]

For ordinary street use silicon is the best compromise. It can and will fade sooner than LMA castrol under heavy use, but this is of no concern to most of us. Beats painting the firewall yearly.......
MD

 

[John Turney]

I have silicone in mine, and am very happy.

I've heard that the softness comes from silicone absorbing air. To keep air absorption to a minimum, don't agitate the fluid any more than necessary to get it into the master cylinder. I applied a vacuum to the silicone fluid I was using and did get a lot of air bubbles out. Between that and minimizing the runout on my disks (I have 4-wheel disks on mine now) I have great pedal feel.

The only other warning I have heard is that old rubber doesn't like silicone, but I feel if your brake rubber is that old, you should rebuild anyway.

John

 

[thegoodbeamer]

There is a debate on silicon in the sunbeam world. I have heard of many who say no way as it does cause problems regarding seals. First sign is the brake light switch isn't working or seems to be sticking.I have had the silicon in the Lister since it was built and the brakes are great. I did have to change a rear wheel cylinder at first as it was leaking. Since the cylinder was new I put it down to a faulty cylinder and never had a problem since.I do agree though if you have many miles on your car and years I would stay with regular brake fluid. On the other hand if I did do a brake rebuild I would switch to silicine.

 

[MGTF1250Dave]

Aloha All,

I changed to silicone brake fluid in my MG backing '85 and have noting but good experiences. The need for the annual bleeding and wheel cylinder clean up every spring went away (I lived in the Northeast then). I've not noticed a particular spongyness in the pedal pressure. I have not had a problem with rubber parts "being eaten", but I think this is only applies to natural rubber parts. I think most replacement parts are now neoprene. The only routine problem I've had is that every two or three years the hydraulic brake light switch fails. I don't know if this is related to silicone fluid or just normal wear and tear.

I'm rebuilding the hydraulics in my TR3A and will be using silicone in that car also.

Safety Fast,
Dave

 

[thegoodbeamer]

I just drained the brake fluid on the lister in preparation to changing the front end. All I can sy is like wow. The fliud is just as clear as the day it went in. This must be a good sign of its performance.
I do think that brake light switches are going to last more than a couple of years. I have never replaced the switch in the lister as of yet. Of course as I said it was all new parts put in the brake system. I haven't noticed spongy pedal either but then the great rebuild of the booster probably overrides any such sensation if there is one.

 

[Rick O.]

Just because it's silicone doesn't get you out of the periodic renewal exercise. Moisture still gets into the hydraulics, but instead of being absorbed and dispersed throughout the system, it'll pool. And where it pools the corrosion begins. The extra expense of this periodic renewal is the only real disadvantage of DOT5 in our LBC's.

 

[Super 7]

My understanding is that this "pooling" is worse for corrosion than the absormsion of water in glycol based brake fluid. I have not seen any documentation of this, however.


<blockquote><font size="1" face="Verdana, Arial">quote:</font><hr>Originally posted by Rick O.:
Just because it's silicone doesn't get you out of the periodic renewal exercise. Moisture still gets into the hydraulics, but instead of being absorbed and dispersed throughout the system, it'll pool. And where it pools the corrosion begins. The extra expense of this periodic renewal is the only real disadvantage of DOT5 in our LBC's.<hr></blockquote>

 

[John Loftus]

When I rebuilt my brake system a few years ago (the PO had use silicone fluid for a long time) I noticed corrosion in the wheel cylinders ... especially the lowest regions. I assume this was from water settling to the bottom. I remember reading that you can drain the silicone fluid into a clean metal container and then slowly boil the fluid over a burner for 10 minutes or so to get rid of any moisture that has found it's way into the system. Then pour it back into its original container,let it cool off, refill the system and bleed the brakes. This sounds like it would keep the water pooling corrosion at bay. I suppose you could also just replace the brake fluid at regular intervals. Anybody else hear of this or try it?

Cheers, John

 

[John Loftus]

I searched around a bit more on the www and found some advice that seems to make sense. If the water pools to the low spots in the system (eventually down to the wheel cylinders and calipers) it is best to crack open the bleed screws one by one and drain off a few teaspoons of fluid from each (using a pressure bleeder or assistant on the pedal). This should rid the system of the pooling water. I would guess once a year would be adequate, twice a year perhaps better. Then you just top up the system with fresh fluid. Sound good?

-Cheers, John

 

[Rick O.]

Annual sounds good. Revington TR catalog says to completely renew the silicone on an 18-month cycle.

 

[MGTF1250Dave]

Aloha All,

I found an interesting article on the internet regarding DOT 5 silicone brake fluid.

https://www.icbm.org/erkson/ttt/silicone.txt

The author sites over 16 years experience with silicone brake fluid in more than 50 cars. In addition to comparing DOT 3, 4 & 5, he also discusses conversion to DOT 5. Also, tips on the bleeding of the system after conversion.

Safety Fast,
Dave

 

[spritenut]

I switched to silicone fluid in my Austin A40 6 years ago. The only problem I have is pressure brake light switches don't last more than 2 months. so I fabricated a mechanical brake light switch.
I wish I would have used it in my Bugeye, I have since re-rebuilt all the hydraulics in just under 5 years. It seems I do this every 5 years using Castrol LMA. Next time, dot 5 for sure.
No to figure out a mechanical stop light switch for the sprite.

 

[Dale]

<blockquote><font size="1" face="Verdana, Arial">quote:</font><hr>Originally posted by spritenut:
I switched to silicone fluid in my Austin A40 6 years ago. The only problem I have is pressure brake light switches don't last more than 2 months. so I fabricated a mechanical brake light switch.
I wish I would have used it in my Bugeye, I have since re-rebuilt all the hydraulics in just under 5 years. It seems I do this every 5 years using Castrol LMA. Next time, dot 5 for sure.
No to figure out a mechanical stop light switch for the sprite.<hr></blockquote>
To what do you (or anyone) attribute the attrition on the pressure switches? The TR-7 has a pressure failure switch on the master cylinder. Would this present a problem like you're experiencing with the pressure brake light switch?

 

[MGTF1250Dave]

Aloha Dale

The MG TF has the master brake cylinder under the floor board and the brake lines run along the chassis. The brake light switch (stop lamp switch) is located on the bottom of the tee fitting where the line from the master cylinder branches to the front and back of the car. The switch is the lowest point in the hydraulic system. Any water intrusion is probably collected there and I think this is a factor in the periodic failure of the switch. The switch does not leak fluid, but fails electrically. Another possible reason for failure is that the membrane in the switch is made of a natural rubber that can be deteriorated by DOT 5 brake fluid. Lastly, it could be just a poor quality replacement part that just wears out after a few years.

Safety Fast,
Dave

 

[Dale]

Well I guess that explains it. The switch is actually being shorted out by the water which settles in the low spot because the DOT 5 fluid does not absorb it. OK so where does the water come from? I seems that 2 months isn't long for water to develope even in a high humidity environment such as you have in Hawaii. Any way thanks for easing my mind about the vulnerability of the brake pressure switch in the TR7s. That switch is high in the system and I'm not sure if it is even directly exposed to the fluid. BTW I wasn't able to find Kapolei on my map. Are you on the "Big" Island? I have relatives there that's why I ask.

 

[spritenut]

On my A40, it had an in line braske light switch fluid activated. It was not low like on the TDs so water was not the problem. Besides 60 days was the max any pressure switch would last. I even tried the specially made for silicone fluid switch, same thing.
I took apart the special silicone switch, the contacts were clean but I think the fluid coats the contacts and stops the electrical connection.
I letterally went thru a dozen stop light switches in 2 years. A mechanical switch solved the problem.

 

[MGTF1250Dave]

Aloha Dale,

I use a NAPA brake light switch and they last about 2 - 3 years for me.

Kapolei is the new "second city" on Oahu. It is located on old sugar cane fields outside of the now closed Naval Air Station Barbers Point near Makakilo. The City and County of Honolulu is trying to stimulate growth outside of Honolulu to try and slow the urban congestion.

Safety Fast,
Dave