I installed silicone fluid in my 68 and 70 over 20 years ago. I am still impressed with the stopping ability of my 70 with power brakes, very solid pedal. I did the changeover. The 68 has manual brakes and has always had a firm pedal, just takes more aggressive application. Still have this memory of a little sweet thing that was not buckled up in 1971 and a unexpected abrupt application of the brakes in my 70. She ended up sliding off the leather seat onto the floor. She did not thing it was as funny as I did.

 

I put silicone in my 72 about 10 years ago. I just put jars with hoses at every bleeder opened them up and kept filling the master cylinder until I could see the silicone at each caliper. I’m sure all the regular fluid didn’t come out, but I haven’t had any problems. My pedal is still rock hard and don’t have any discoloration. I highly recommend it.

 

I have heard that silicone brake fluid is more "runny" than conventional brake fluids and leads to more leaks.
My system has been changed to stainless steel sleeves in the pistons so it should not rust.
What advantage is there to change and how far do I need to go???

 

All fluids is compressable. if you have a tank filled with oil the compressible factor is : (bar x l) :20000 = fluid in l needed to get pressure x pressure in bar
The same tank with water will be (bar x l) :21000 = fluid in l needed to get x pressure in bar


When you pressure on the brake pedal you are compressing the fluid in the system to make the pressure that moves your pistons in the calipers.
So the more compressable the fluid is in your system, the longer you will have to push your brake pedal to get the same pressure.

Bottom line is: Water is less compressible than oil. So a water based hydraulic oil will get you better responce than a oil based hydraulic oil.

To make tings even more difficult the compressibility will cange some with temperature. at high temperature you will need sligthly less volume to get the same pressure. (the same with air. that is why the tire pressure is lower when it is cold ouside, than it is when the car has been in the sun all day. ore if you have been burning rubber.)

 

I've been using DOT 5 silicone in my older cars that don't get driven frequently. Never had problems with soft pedal, air bubbles, or issues with bleeding. I've also never had to worry about the fluid absorbing water and the brake lines and brake/master cylinders rusting, pitting, and freezing up since I made the change. Since I don't road race these cars, I can't say how the DOT5 performs compared to how DOT3 would perform at the extremes. In normal driving, I've never noticed a difference.

A friend of mine swears by DOT5. After detailing the engine compartment and chassis on his '69 Z28 he filled and bled the brake system with DOT3. He didn't realize that his newly rebuilt proportioning valve was weeping brake fluid--not enough to cause the brakes to be spongy or ingest air but enough to slowly leak brake fluid onto his nicely painted sub frame and suspension parts. After a couple weeks he went to work on the car again and found the leaking brake fluid had ruined his nicely detailed chassis. I wasn't there to witness the cussing that ensued when he found this, but I did help him pull the front clip, engine, and subframe/suspension again so he could re-do all of his hard work by re-painting everything.

He uses DOT5 brake fluid now and is quite happy with it.

The only time I wouldn't recommend DOT5 fluid is for cars with anti-lock brakes.

 

Vette calipers leak.....and not having it strip paint,causing rust etc....and bleeding can be messy....but with silicone, you don't have to avoid touching anything like the plague as you do with conventional. I've had it in my manual brake big block for 10 years.

 

I just replaced all the brake lines with stainless steel, the rubber hoses were replaced, drained the MC and all 4 calipers. Is that good enough to replace with silicone or should I stay with DOT 4--wondering because I can't be 100% sure that there is no DOT 3-4 in the system. I am going to use he Motive bleeder. Thanks

 

I've used silicone fluid in my '58 for the past twenty years and I love it. On the other hand I won't let it near my race car.

There is a different pedal feel with silicone - no question.

I'm still up in the air with the DOT 5 stuff. When it comes to conventional fluid I like the Ford stuff - or Wilwood.

3 years without flushing the fluid? You're asking for trouble. Flush the fluid every two years - at least. I flush the fluid in every one of my cars on an annual basis. The race car gets bled every month.

Richard Newton

How to Restore and Modify Your Corvette, 1968-1982

Autocross Performance Handbook

 

I put DOT5 in my '70 about 8 years ago when I rebuilt the brakes, and never having messed with C3 brakes discovered like y'all that you can't bleed them w/ pedal pressure alone. I used my Mityvac and everything's been fine since with the exception of a couple leaky front calipers which I replaced with sleeved AutoZone units and now they're fine. I can easily lock the brakes with a good stomp on the pedal and pedal height has always been good with no sponginess or mushiness and NO, I didn't get every last molecule of the old goopy DOT3 out of the system, just a decent flush. I just use organic pads- it's not a race car so I don't drive it hard enough to heat the brakes significantly, but they're there when I need them.
I do have a friend that had a Shelby Mustang that he used DOT5 in for nearly 20 years and did find pitting in the caliper bores when he disassembled the system, which provoked him to return to DOT3.
Personally I used Wilwood or Motul DOT4 in my own vintage race car on the recommendation of numerous other racers-it was good for 550 degrees and I really didn't want to find out what boiling brake fluid did at 140 mph. I did witness one other guy making this discovery and the result was not pretty to say the least.
IMHO DOT5 is great for street use as long as your system is in good working order and since many of us can be included in the category of People Who Care What Their Car Looks Like Underhood the fact that it doesn't eat paint is a real plus.