silicone brake fluid

I know the boiling point is higher. I know it doesn't absorb any water.

other than it not playing nice with conventional fluid, and the price, what is the downside in collector cars? I swear I remember reading/hearing why its use was discouraged, but cant seem to remember the specifics.

reason I ask is that my best friend wants to use it in his 73 vette now that hes doing calipers, lines, master, etc.

Michael

Doesn't play nice with the old seals in old cars either. Something about the seal compound used in old cars aren't compatible with the newer silicone based fluid. If changing everything in the brake system and the lines and seals are silicone compatible then might be OK.

It can be difficult to fully bleed all the air bubbles out, so the brake pedal may be soft.

Also, you're going to get moisture in the lines over time anyway, whether you use silicone or not, and since the silicone fluid isn't hygroscopic the water will tend to collect in low spots in the line and cause rust.

And its near impossible to flush when u realize it isnt very good.

stuart in mn hit the real problem with it: if there's any moisture in the brake system at all it will not go into suspension, will collect at the bottom of the hydraulic system and cause rust. AFAIK the military phased it out years ago, about the only people who still use it is Harley since it won't damage paint. At one point some dirt bikes, most notably KTM, were going to mineral oil in the clutch hydraulics, don't know if that change made it to their brake systems though.

Curmudgeon wrote: about the only people who still use it is Harley since it won't damage paint.

I heard the same thing (or read rather) in this book.

Never had any practical experience with it though.

mostly what stuart said ... soft pedal

I just read last night a story about a guy who restored an old truck, tried to use silicone fluid, and despite everything being brand new couldn't get the system to function properly. Changed back to normal fluid and everything was fine.

I have never spoken to a single person who has gone to silicone fluid who didn't at some point return to the regular stuff.

It's also a somewhat compressible fluid, tending to give a slightly squishier pedal. It becomes more compressible with higher heat.

Easily foamed, and tends to hold that foam in suspension, which is a substantial part of the reason it's not recommended for abs systems.

Historically, it was developed for the military for long term storage. The theory being that all rust and corrosion problems would be eliminated. Turned out not to work nearly as well as expected, especially with the localized rusting problems mentioned above. Long abandoned by the military as a result.

Even Harley no longer uses it. They dropped it when they first offered abs.

My Harley does have it. Only vehicle I own with it. It works. That's about all I can say. Pedal/lever is a little spongy, but the bike is 10 years old with 50k miles.

DOT 5.1 has a similair boiling point to DOT 5 but is glycerol based like DOT 4 and 3.

I am changing all my clutch hydraulics over to DoT 5 as they get repaired. I think the stuff works fantastic. I pulled apart my rear brake on my bike after literally no so much as checking the level for 15 years. I expected the caliper and MC to be garbage. Light scuffing. Not a spec of corrosion. So far, I've done the Rolla, the RN Truck and the Locost.

Buy the Mil Spec stuff on ebay for a fraction of the price of the bike shop. Like $30/gallon delivered or so.

ddavidv wrote: I just read last night a story about a guy who restored an old truck, tried to use silicone fluid, and despite everything being brand new couldn't get the system to function properly. Changed back to normal fluid and everything was fine. I have never spoken to a single person who has gone to silicone fluid who didn't at some point return to the regular stuff.

why is it still on the market ?

It does a great job of restoring old, faded plastic. I just brushed a small amount on the switches on my Elan, wiped it off and they look like new.

Hungary Bill wrote:

Curmudgeon wrote: about the only people who still use it is Harley since it won't damage paint.

I heard the same thing (or read rather) in this book. Never had any practical experience with it though.

if i wrote a brake book, it would be that book.

I don't think not damaging paint had anything to do with the decision to run DoT 5 brake fluid by the MoCo. I would suspect it was more to do with not sucking water and corroding out the brake system. Harleys used DoT 5 from at least the 70's (that I know of) until the past couple years. The main disadvantage is that the brake can get a little spongy at very high altitudes, like >10K ft.

Now, as far as automotive applications, I have read of people that put them in race car brakes and had bad experiences with it on the track under extreme conditions (glowing rotor type heat).

Silicone brake fluid is used in kart racing.

I use it in my race car and will not go back. Granted I have not used the dot5.1 but it is a massive improvement over the dot4 that I was using. It's no fun sitting on a red for 10 minutes knowing your rotors are glowing, and then driving into the turn to find your brake going straight to the floor. I don't get that anymore and I kind of like it.