The Stovebolt Site Forums The Shop Area Engine Shop silicone brake fluid question

My buddy was working on the brakes of this truck this afternoon. He is almost sure he put silicone brake fluid in the system several years ago when we rebuilt his brake system. Silicone fluid is purple in the can but the fluid in his master cylinder is almost clear. The question is does silicone fluid lose it purple tint over time in a brake system? I would think it would remain purple in the system to keep from mixing DOT fluid with silicone fluid. Thanks

beltfed,

I don't think color would be an indicator of brake fluid type, but more of manufacturer marketing choice.

Dot-3 and Dot-4 are Glycol based fluids...they will eat the paint on your car! Dot-5 is Silicone based. Drip some of the fluid in question on a painted surface and watch for results. I wonder if a Glycol based product would be sweet if put it on your tongue.

Keep us posted, and call the para-medics if you have a negative reaction to the tongue test!

EDIT. If the Dot-5 was purple, it was obviously dyed. If the fluid in question is clear, and it truly was the purple Dot-5, wouldn't there be traces of the dye that has settled out on the interior components of the master cylinder.

Stuart

DOT 5 is required to be purple in color by DOT regulations. This is to provide quick identification. Unfortunatly, the dye can settle out. I had tried it in my '55, turned out it causes leaks in the system unless you use DOT 5 specific rubber components. When I removed the fluid from the system, it was a somewhat greenish color.
If you have any doubt, I'd suggest a complete flush of the system, possibly installing new cups in the cylinders, and start fresh with a known fluid type. Then mark the MC wiht what type is in it for future reference.

Several of the guys I run with use the DOT 5 for two reasons. One is they have mounted their master cylinder on the fire wall and the other fluids eat the paint in that area. Two is, as I understand it, Dot 5 doesn't collect or absorb moisture like the other fluids. These are rides that don't see a lot of miles per year, maybe 5,000 and they are highly detailed. So they do a lot of sitting.

Interesting point on the purple DOT fluid...it sure does stand to reason you need to be able to tell them apart.


Stuart

i'm planning on using sicone fluid in my '66 when it goes back together, my fender well paint got trashed when one of my lines leaked onto it and i'd like to avoid damage in the future from re-fill spills etc.

i seem to remember from shop class that you're supposed to use alcohol as a solvent to clean brake components. i've always used aeresol cleaners when working on brake systems, i've never 'flushed' a system. what's the correct procedure to flush before converting?

currently everything is empty ( all was disassembled for cab off paint ) and i'm running mid 70's brakes with power booster & master cylinder, front discs, rear drums.

thanks

I would use the brake clean aerosol to clean everything for brakes. Then dry with air.

I don't recommend it, but, to tell the difference, you could taste the brake fluid. Touch it to your tongue. If it stings, its DOT 3. If it tastes good....your probably addicted.

Yes, it loses it's color.

I use it in my Harleys, and as someone mentioned previously, it causes leaks so I have to refill the reservoirs occasionally. I noticed that when it goes in, it is purple, but when I open the reservoir to add more, it has become more of yellow color.

Bill Graham - Your best bet is to flush with denatured alcohol. However, you need to replace all rubber parts that have contacted the old fluid with new. That neans wheel cylinder and master cylinder rubbers and rubber brake hoses. I would start by draining the old fluid, flushing, then replacing the rubber and flushing again.

Also, if there is ever a possibility you will be painting in your shop, bleed the silicone fluid outside. It will cause fisheyes in paint, and you will never get it all out of the concrete floor.

fred,

thanks for the good point on the future bleeding and painting in the shop.

i'll have to keep that in mind.

thanks