silicone Brake fluid?

[Ray G.]

Hello;
Share your experience w/ the Pros & Cons of Silicone brake fluid.
Thanks
Ray

[Frank C.]

Re: silicone Brake fluid?

Hi Ray....I have no cons on DOT 5 silicone brake fluid. I have been using it for about 15 yrs and have never seen any adverse effects from it. It's in all 3 of my C2s and my '57-and 2 '66 full size Chevs. The main thing about it is, it doesn't attract moisture or remove paint if you accidently get a drip on the fender. I'm sold!!!...Regards Frank

[Joseph E.]

Re: silicone Brake fluid?

Good Morning Ray,

I've got silicone fluid in my '66 and and have had no problems with the system whatsoever in that application so I intend on converting my '65 and '67 over as well. It's biggest benefit is that it does not attract moisture and alleviates the problems associated with DOT 3 fluid. With that being said, I did have a problem with silicone fluid when I converted my snowmobile over from standard DOT 3 to DOT 5. I thought the silicone would be better in this application than the standard fluid, however, I found out I was wrong. Apparently, in these small, single reservoir master cylinders the silicone causes the seals on the piston in the bore of the master cylinder to shrink slightly over time which allows a leak to begin. This just happened to me when I was riding about two weeks ago. I was running my sled on a frozen lake going about 120mph and found when I squeezed the brake lever that it was spongy. Once stopped, I saw that the master cylinder was leaking fluid past the seals on the piston in its bore when the handle was squeezed. Fortunately, I was able to get the sled stopped safely. I limped back to my hotel, packed up my belongings and headed for home early. Repairs could not be made on site so they were done when I got home. The entire system had to be cleaned, flushed and filled with standard fluid. I know this information is not directly related to your question, but for those out there with sleds thinking about converting them to silicone brake fluid-DO NOT DO IT!!

Joe

#45420

[Terry M.]

Re: silicone Brake fluid?

Joe I am surprised at your experience since Harley Davidson uses DOT 5 in their bikes.

[Joseph E.]

Re: silicone Brake fluid?

Terry,

I was surprised as well but I talked to three snowmobile technicians and told them of my dilema. Once I informed them that I had installed silicone fluid, they all said to remove it by flushing the system and install the standard DOT 3 fluid and new seals on the MC piston. Each of these individuals told me the same thing-that the silicone fluid causes the seals to shrink and leads to leaks. I checked the master cylinder when I installed the new seals and there were no scratches or gouges in its bore that would lead to such a situation. The sled had standard fluid in it when I bought it and it remained that way for a few years until I thought it necessary to clean the system (even though I had no problems with it) since I did not know when it was done last. At that point, I installed the silicone fluid and in short order the system began to leak. I'm not familiar enough with motorcycles and the use of silicone fluid in their system to have an opinion on it but with my experience with my sled and on the advice of snowmobile technicians, I would not use silicone in it again. Thanks.

Joe

#45420

[Eric J.]

Re: silicone Brake fluid?

As others have stated it is good for older less driven cars but the cons would be: Sometimes it is difficult to find, I had to go to 3 major autoparts stores to find some. Ended up at NAPA. It is relatively expensive $8 a pint versus about $4 for dot3. Harder to bleed. DOT5 bubbles easy (that's why you can't use it in ABS applications). Bleeding takes longer. Bleed, wait a few hours, bleed again. Don't mix DOT3/4 and DOT5. TO quote Egon from the movie Ghostbusters "That would be bad" Make sure you label the MC "DOT5" so you remember. The good new is once you convert over you almost never have to worry about it again. Eric

[Jim T.]

Re: silicone Brake fluid?

I have been using silicone brake fluid in my 68 and 70 for over 20 years. Not at home to check out my maint logs. My 70 with power brakes still impresses me with its stopping ability and never experienced any problems with using silicone.

[Larry L.]

Re: silicone Brake fluid?

On my 66 with few miles. I was driving the car a few 100 miles each year. Each spring I rebuilt the brake system because of leaks. The last straw was in 71 on a very cold day I left work and put my foot on the brakes and no brakes. Took it home and disassemble a front brake and there was ICE in between the boot and around the perimeter of the piston.

In 72 I dismantled the the brake system and cleaned it. I must have been one of the first dozen customers of SS Brakes and I told him I wanted the 1st design pistons guides left in place and the bores perpendicular to the rotor. He told me that several others wanted the same thing. After about 3 weeks I got my sleeved calipers back. They were perfect and incredibly clean.

I used SS bleed valves because I was tired of removing calipers and machining the bleed valves out. After about the 3 rd time I took my Craftsman sockets out and put in trash. Bought a new set of Snap-On single hex and was able to remove some of the rounded bleed valves.

Rebuilt dual circuit master cylinder
In 1972 in perfectly clean system I used silicone brake fluid and in 2005 and 30,000 miles later.(41K miles) I did an inspection of system and it is still perfect.

Other troubles I have encountered.
Some sleeved calipers are not machined properly and I have seen a number that weep brake fluid around the sleeve. Or bores are not perpendicular with the rotor centerline. To fix the weep a locktite (blue) bead was put around the bottom of the bores left to dry for a few days. Wipe excess out with mineral spirits and dry. In 5 Years we have seen no evidence of weep or any other brake problem. The problem brake systems have remained dry.

Its buyer beware as always.

The main cause of brake problems is rotor run out. I trued mine on the car and they are + / - 0.001. The orig. Delco lining is perfect and the rotors are evenly polished. The person who drills out the rivits and puts on a new rotor is asking for touble and bad brakes. The rotors were rivited and then turned to make the spindle and rotor run ture.
Replacement rotors may be machined true but the hubs front and rear my be out +/- 0.006 so rotors at the outside would wobble as mush as 0.012 - way beyond factor spec.
On other rebuilds I turned spindle front or rear to make it ture. Rivet the rotors and turn the rotors. The assembly is + / - 0.001.
Brakes work perfectly.

It a lot of work but so is rebuild the front end if you can't get it stopped.

[Bruce B.]

Re: silicone Brake fluid?

On my modified 62 Corvette I rebuilt the stock brake system, used stainless lines and filled with silicone fluid. Over a 18 mont period I drove the car around 8000 miles and never had a problem. No leaks, good pedal and the silicone fluid will not harm paint. I have just put it in a 57 that I am building and it was easy to bleed and the pedal feels fine. After any brake system rebuild I will refill with silicone fluid.

[Joe L.]

Re: silicone Brake fluid?

Joe-----

Keep in mind that the "DOT" in DOT-5 silicone brake fluid represents "Department of Transportation". In order to be DOT-rated, a brake fluid type has to be compatible with components used in automotive braking systems. If a type of fluid were not compatible, then it would not be DOT-rated. If a container of brake fluid specifies a DOT rating, then the fluid in that container has to meet the DOT specifications for that rating number.

It may be that the components, particularly the seals, used in the brake systems of snowmobiles are not the same as those used in automotive brake systems. That would surprise me, but it's possible. If so, these seals might not be compatible with DOT-5 brake fluid. However, if they are the same as those used in automotive brake systems, then I do not understand why the DOT-5 fluid would be a problem.

[Ray G.]

Re:Thank you, everyone. Ray *NM*

[Chris Patrick]

Re: silicone Brake fluid?

Never spill it on bare fiberglass.

Don't use it in competition driving.

Use it in long term storage cars.