I just replaced front and rear calipers on my 1972 with stainless and new rubber hoses. I have gotten mixed feelings as to what fluid I should use - silicone or (regular brake fluid castrol GT LMA). Multiple opinions are appreciated.

 

Silicone but boil it

 

Used silicone in my last 65 with good results in general. While silicone does not absorb water like Dot3, it does absorb air. These caracteristics make it great of our cars in that it prevents caliper bore rust and subsequent leakage. There is no free lunch however. I found the stuff hard to bleed fully. The boiling trick may work for opened or old silicone, but I would suggest only using fresh silicone from unopened containers. Minimize its exposure to the atmosphere....

As you are probably aware, do not mix Dot3 with silicone. Stuff is like oil and water, it doesnt mix! System must be totally clear of Dot3 before going with silicone...

 

Even new silicone fluid right out of bottle seems to release air when temp gets to aprox. 200* ? Water boils 212* Is it because this air has moisture in it ? I know after I boil silicone(and let it cool) it bleeds just fine otherwise the pedal is spongy.Boiling is recommended or OKd by manufacture.

 

I used silicon in my '82 and really don't like the feel of it much. It seemed to get better afterawhile, but as others have said it feels a little spongey. I bled my brakes a million times before it finally got hard.

 

I go by the Stainless Steel Brakes book when it comes to swapping into silicone brake fluid. You might want to get a copy to avoid the mass confusion regarding this subject. I have had good results in other cars doing it this way so I put it in the Vette too. Bleeding was problematic with the Vette but the Motive Pressure bleeder worked great. Cook the air bubbles out of it before you use it using a stainless steel pot on the stove top. It gets air trapped in it from shaking during transit.

You will need to replace all the rubber parts on the brake system as they have absorbed moisture laden DOT 3 fluid over time and it can leach out later after you put the new fluid in.

Once the system has new rubber parts you can flush the system with a fresh quart of DOT 3. This fluid will not be in the system long enough to absorb into the new rubber parts and it does not have any moisture in it yet anyway. This procedure is only to flush out the hard lines. Flush the new DOT 3 out of the lines before you start to add the DOT 5.

Bench bleed the new master cylinder with the DOT 5 and install it. Hook up the Motive Pressure bleeder and add a big C-clamp to the top of the M/C adapter along with a block of wood to distribute the clamping load. Keep in mind that you want to bleed the rear inner screw before you bleed from the outer rear screw on each rear caliper or it will take a long time.

Hope this helps.

-Mark.

 

my main reason for using dot 5 was that it does not harm paint. I would cry if dot 3 got on my newly painted frame

 

I use silicone because it doesn't take the paint off everything it touches.

 

I'm in the process of doing my brakes as we speak, new rotors, calipers, pads, master cylinder, and rubber hoses. What's anyone's take on this stuff vs. conventional Dot3? http://www.valvoline.com/pages/produ...asp?product=51 Sorry, didn't mean to hijack this thread.

 

I use DOT3 on all my vettes. Use a fender cover, be very careful when using it, use a Motive bleeder and bleed the system every 2 years when you pull it from storage or every 3 years if you drive it daily.

 

Yes, conventional DOT 3.

 

I am throwinig a wrench into this. I use DOT 4, with a higher boiling point. And it mixes with DOT3.

 

I did the same job about 8 months ago. Went with DOT 5. Gravity bled the system 2x. No problem and a firm pedal. Since my 79 gets only occasional use, I didn't want to worry about moisture in the new brake system and go through this again in a couple years.

 

100% I gravity bled 2 or 3 times and have a very hard peddle.

 

Going To My Brakes-explain Gravity Bled ?

 

Having once spilt Dot3 fluid on my bike (it removes paint quicker than stripper does) I swapped to DOT5 silicon. This was sometime in the mid 80's. I cleaned out the system with alcohol & then compressed air to remove all the old fluid, changed the seals & then carefully poured in the silicon fluid. You need to carefully pour it to minimise air bubbles. Even though I've got a "self-bleeding" system where aeroquip hose runs vertically up from the calipers to the M/Cs, it was still a nightmare to bleed all the air out. DOT3 fluid bleeds itself as the bubbles just rise to the top, but the bubbles in the silicon fluid seem to take forever to rise. DO NOT pump the brake while bleeding as it creates more bubbles or, more dangerously, breaks up existing bubbles into even smaller ones, which then take even longer to get rid of. Very slow movements on the brake pedal should be used to bleed it.
The brake system (cast iron callipers, but with none of the problems of stock Vette calipers) was dismantled for a cosmetic tart-up within the last 5 years & the internals showed no signs of corrosion. Silicon fluid has never given me any cause for concern, it was truly "fit & forget". The brake pedal & lever feel slightly spongy compared to identical systems using DOT3/4 (some people prefer this for the reason that the lever/pedal don't feel as "wooden" & there's more "feel") & it doesn't seem to be affected by abuse of the brakes & excessive heat. No doubt if I was using all the stock rubber hoses in the system then the feel would probably be a lot more "spongy", but with aeroquip lines throughout it's got a nice progressive feel to braking, ie ditch the rubber hoses on the Vette & it could work out well.
Personally, I haven't bothered with silicon fluid in the Vette & would only consider it if the entire system was new. I can't see what advantage would be gained in taking an age to clean out the existing system so that silicon fluid could be used. I use DOT4 fluid & change it once a year. The way I see it is that on my bike I can see every part of the brake system & regularly get a close look at it when I clean/polish it. The brake system on the Vette is hidden away so I wouldn't be aware of any developing problems with it. By replacing the fluid every winter, bleeding it & stamping down hard on the pedal frequently, I'll hopefully spot if there's any leaks/problems with it before I find out when the brakes fail on the road.
The advantages to me of silicon fluid are purely that if I do spill it then it'll actually put a nice shine on the gas tanks paintwork, instead of lifting it off, & that it doesn't need regular changing. I don't think these advantages warrant the amount of hassle to change the Vette's system over to it (unless it was all new) as I haven't got an expensive paintjob right beneath the MC.

 

Just completed brake job on my 73, cost to convert and hassle didn't seem worth the time and effort. Made a brake bleed so I can bleed my brakes anytime I want to or just flush the system with fresh fluid. NO big deal!

 

With an all new brake system in my 68: lines, master cylinder, and calipers, i dumped in silicon (dot 5). Brakes work fine.

(Well OK, ...I used gravity flow to fill the lines with silicon and to eventaully get rid of air bublbes. It was tedious, tedious)