Brakes: Is there a way to tell if brake fluid in a car is silicone or not?

[Bill Pressler]

The '66 Daytona I'm driving home this weekend had a body-off restoration in '98 or so. I asked the seller (not the owner during its restoration) if it had silicone brake fluid or not. He said he didn't think so. I asked if he'd ever had the fluid replaced in his eight-year ownership. He said he had a power brake booster put on '05, converting the car from non-power drum to power drum brakes, so new fluid would have been put in then, correct? Sorry for the basic-level questions. I figure I'd probably have the brakes bled and refilled not long after I get home, but would hate to mix DOT3 and DOT5. I had DOT5 in the '63 I recently sold.

Thanks.

[sweetolbob]

The '66 Daytona I'm driving home this weekend had a body-off restoration in '98 or so. I asked the seller (not the owner during its restoration) if it had silicone brake fluid or not. He said he didn't think so. I asked if he'd ever had the fluid replaced in his eight-year ownership. He said he had a power brake booster put on '05, converting the car from non-power drum to power drum brakes, so new fluid would have been put in then, correct? Sorry for the basic-level questions. I figure I'd probably have the brakes bled and refilled not long after I get home, but would hate to mix DOT3 and DOT5. I had DOT5 in the '63 I recently sold.

Thanks.

Bill

Put some Dot 3 in a small glass bottle and pour in some of the fluid in question. If it mixes Dot 3/4 if it separates Dot 5.

Bob

[Dougie]

Pour some on the hood and if it takes the paint off it's not silicone (JUST KIDDING!!)

[Bill Pressler]

Thanks guys (well, Bob anyway!).

[gordr]

Put a drop on your fingertip and taste it! DOT 3 is alcohol-based, and has a very acrid taste. Silicone is based upon a silicone oil, and has little or no taste, but will leave an oily feeling on your tongue.

One drop won't hurt you, but it wouldn't hurt to have a can of pop or some other beverage on hand to rinse your mouth out after the taste test.

[Gunslinger]

Silicone fluid is purplish in color...at least every silicone brake fluid I've seen. If your reservoir is all cloudy...you have mixed DOT 3 and DOT 5, so it should be completely flushed and replaced.

[wolfie]

Silicone fluid is purplish in color...at least every silicone brake fluid I've seen. If your reservoir is all cloudy...you have mixed DOT 3 and DOT 5, so it should be completely flushed and replaced.

If the two types have been mixed can the system simply be bled out or must it be completely torn down and cleaned? Thanks, Steve

[junior]

water dilutes dot3 brake fluid, it turns white in color....take some a small amount of fluid from the master cylinder resevoir, add some water to it and see what happens. silicone and water do not mix. I also like sweetolbob's suggestion...never thought about the density thang. junior

[whacker]

If the two types have been mixed can the system simply be bled out or must it be completely torn down and cleaned?

Flush the entire system with rubbing alcohol until it comes out clear. Then close the bleeders and refill with the new fluid. Re-bleed the system, and you should be good to go, er...stop.

[wolfie]

Flush the entire system with rubbing alcohol until it comes out clear. Then close the bleeders and refill with the new fluid. Re-bleed the system, and you should be good to go, er...stop.

Thanks. I will be tearing into mine Sun afternoon and building all of the cylinders. I am not positive it is mixed but I added silicone fluid and it immediately lost a wheel cylinder. I thought it already had silicone so it may have been coincidental that that cylinder blew at that moment. The fluid in the master cylinder is still clear (purplish). Steve

[Dougie]

Speaking of flushing the system, I'm working on my first Studebaker and noticed the bleed nipples are really small and kind of recessed. My regular wrench for brake lines is too large. Mine are tight and I'm afraid of stripping them trying to loosen them. Is there some special tool to use? Thanks.

[sweetolbob]

Speaking of flushing the system, I'm working on my first Studebaker and noticed the bleed nipples are really small and kind of recessed. My regular wrench for brake lines is too large. Mine are tight and I'm afraid of stripping them trying to loosen them. Is there some special tool to use? Thanks.

Dougie

A small 6 pt, deep 1/4" drive socket is what I use on all I can get to with it. It holds all 6 sides and is less likely to strip the hex.

Bob

[ROADRACELARK]

It would be best to disassemble the wheel cylinders to clean. The bleed screws are at the top and there is no guarantee you'll "purge" ALL of the DOT3 out. It's a little more work but.... Better to be safe than sorry. Hope this helps.

Dan Miller
Auburn, GA

[valleyguy]

I also think the longer style bleeders are available to replace those short ones; a little easier to get to..

Joe D.

[nels]

Does it really hurt anything if you do mix the two? I've done it and never had a problem.