Hot Rods silicone brake fluid

I just bought a 32 ford that has had silicone brake fluid in it for 25 plus years. I have had to remove a brake line for repairs. Now I have to replace the brake fluid and bleed. I have no idea of the brand of fluid in the car. Are different brands of silicone fluids compatible? I am thinking that I should just purge and clean the entire system and start over. I would prefer to just put Dot 4 in and be done with it. Any opinions appreciated.

 

25 plus years is a long time for rubber brake components, no matter what fluid is in the system. I'd be tempted to overhaul all the hydraulic parts, and then do as you say with dot 4 fluid.

 

so whats the condition of the brakes after 25 years? if no hydraulic issues in 25 years I know what Id be doing............if you go back to normal stuff flush yearly

 

yearly? how about every decade?

 

I am doing a complete mechanical going over including brakes before it is driven even though it was just driven 400 miles by previous owner. I didn't mean it hadn't been maintained. It has been using silicone fluid for that long. Are different brands of silicone fluids compatible was the question. Thanks.

 

if they meet the DOT 5 spec, they are supposed to be compatible with other DOT 5 fluids. That's what specifications are all about.

of course, there could be problems with some particular brands that I don't know about...

 

DOT5 is not hydroscopic and as such does not absorb water as it is silicone based, originally introduced to give higher temperature performance over DOT 4 fluid. DOT5 fluid also has another advantage, it does not damage paintwork.
Whatever you do, don't mix DOT 5.1 (Glycol-based) with DOT 5 (Silicone-based) or any other DOT fluid for that matter due. Different boiling points. The minimum boiling temperatures of brake fluid as per Department of Transportation (DOT) are:-

I had DOT5 but didn't like the feel of it so I flushed the entire system with methyolated spirits and replaced all seals in calipers and MC.

 

I flush the normal (hydroscopic stuff) yearly ..... if it sits and you don't it turns to goop and stuffs the system, generally it wont p*** a test after 12 months (over 3% water), this is normal cheap "brake fluid" not silicone . I was thinking stick to silicone if that's whats in there , don't go backwards.

 

Just to add a little real world information, I purchased an electronic tester that tells the percentage of moisture in DOT-3 and DOT-4 fluids. I have tested the fluid in my cars over the last several years, and it looks to me that it takes about 10 years for the fluid to absorb enough water to be of concern. Of course, these are cars operated under optimum conditions : stored in a climate controlled environment and not driven in bad weather.

 

mine get wet..........
Edit: they are cheap now the testers, you may find that half used bottle on the shelf is no good to use......

 

I had a restoration shop and ran silicone fluid in all my cars that had a complete restoration with all new components After a lot of years on these cars there were no failures from moisture. I have been using it in my 59 corvette for 20 years. I did change it at 10 year intervilles . It does change the feel of the pedal ever so slightly.

 

I have been using silicone for 25 years or so. Its awesome stuff. Rarely do I need to change wheel or master cylinders When one leaks, its the rubber piston gone bad. I dont find sludge or rust, no stuck pistons. The military uses it, they cant have brake failure.

Theres a myth that you cant combine DOT 3 and 5. They say it will jell. I poured both into a container on Dec 24 2015 and have been watching it. No jelling yet. Both are clearly separate

 

The OP wanted to know which 5 is compatible, but some members have brought up the issue of moisture absorption.

The OP in California has a less of a problem potential with that, than the Minnesota poster IMO.
I just repaired a local collect car that I replaced every brake cylinder/hose/flush/DOT3/, 10 years ago. The issue this time is the master was full of rusty fluid and "pouring" out the boot end. It changed my view on the potential benefit of DOT5 in our wet climate here. This car has a factory reservoir cap that can allow moisture to get in, versus a Chevy/Ford 60s-up cap with the expanding bladder under the fill cover that seals "airtight"
.

 

Thanks for bringing up the issue of bladder vs vented caps, that might have something to do with how long either type will stay fresh.

 

We install dot 5 in a lot of collector cars here at our shop. It has been a huge help with moisture issues since in northern Ohio cars sit many months out of the year. I've never had any issues with mixing of brands as long as it's dot 5 silicone.


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Because DOT 5 can't absorb water, the brake system is now subject to forming defined ice crystals
and causing full or complete braking failure when the temperature reaches freezing. If the MC breathes at all, it will condense moisture during heat/cold cycles. As long as the water is miscible in
a non-silicone system, it is protected from crystals.

 

what was the feeling you didn't like?

 

And if you do get moisture in a system with DOT 5, the water settles in the lowest points of the system where it can form rust.

For reasons I've read about but don't understand, and from experience in using it in a couple motorcycles, small air bubbles take forever to work their way to the top of silicone fluid, so in many cases, no matter how careful you are, there may be some air in the system, giving a slightly softer pedal. Just the act of pouring it quickly into the master cylinder can introduce bubbles that take forever to get out of the system.

 

I have DOT-5 in an O/T '68 Corvette. When I bought the fluid, the instructions said to heat it almost to a boil and then be very careful transferring it to the system. I did this, even buying a nice tea kettle that was perfect for heating the fluid and carefully transferring it to the master cylinder. I had a little more trouble than usual bleeding the system, but got it done, and it seems to work perfectly. I don't feel any difference in the pedal from any of my other cars. I quit using it because it was a pain in the *** to install, and the development of "Speed Bleeders" and brake fluid testers allows me to easily maintain my systems on the other cars.

Just about every time I see a thread like this I search the Internet trying to find any information about pre-heating the DOT-5 fluid, but have never been able to find anything. It kind of makes sense to me, as the heating would drive the air out. Does anyone else know anything about this? I may be imaging this, but I did buy the kettle and heat the fluid; why would I do that out of thin air?

 

Old thread... sorry. A friend of mine upgraded to Dot5 because it has a higher boiling point. He did not do it because he is a road racer and was overworking the rotors / calipers, but because his frame mounted MC is close to his exhaust system and he thinks Dot 5 is better because it can "take the heat" better while in the MC reservoir. Good or bad idea? Gary

 

In my opinion, which no one paid for, DOT 5 is only *possibly* suitable for drum braked cars which will never see any great change in al***ude.
Consider:
While it does not absorb water (see above), it DOES **** air, esp. in disc brake systems.
Said air bubbles then deteriorate braking, worse when the al***ude changes, as less air pressure leads to larger bubbles.
DOT 5 is NOT recommended for any ABS or TCS equipped cars (I know, not traditional, yet...), owing to the air ****age problem.
No OEM uses DOT 5.
Other than the paint peeling issue, what is wrong with DOT 4?? A funnel would cure most of the paint removal, and better aim would help in many more ways...

I'll definitely not use DOT 5 again (yes, I did once. Once.)

Cosmo

 

The manufacturers settled on glycol based brake fluid for a reason, I figured the fact that it is hygroscopic is for a reason, that's a feature, not a bug, or they would have used something else. If residual, small amounts of moisture were NOT absorbed, it would form ice crystals and the line could eventually freeze solid. Maybe I'm wrong, often am.

 

Seems no matter where I turn, Dot 5 gets rave reviews or giant boos. Still, I heard new Euro cars and even Harleys use it. But then it isn't recommended for use in ABS or other computer controlled braking systems or race cars (which is what I thought it was made for in the first place). I can find plenty of info on it on the web, but no conclusive trends. If it was me, I'd use the new 5.1 instead as it's not silicone based. Gary

 

Lots of good info.
My OCD training and experience in professional Motorsports, has made me a brake flushing fiend.
At my current city garage position, I flush all the cop car brake systems at least once a year. And/or each brake service.(Dot 4)
Most Foreign manufacturers suggest flushing annually, but for some strange reason it was never part of the domestic PM's
I do it myself with a bottle of brake fluid and a clear plastic hose
Attach the hose to the bleeder screw making sure it points in an upward direction and empties into a bottle. Crack the bleeder Proceed to pump the pedal two or three times starting from the furthest point.
This is the way we did it on a $300,000 Porsche race car it will work on your street car.


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It felt a little spongy to me and unlike conventional fluid, maybe it's me. Might try it out on the 46 Olds?

 

what the consensus for the best fluid to use?

just finishing up a complete brake rebuild with all new parts

 

Like oil, there is NO consensus.
I use DOT 4. Most manufacturers use either DOT 4, or DOT 3 as factory fill, none use DOT 5 (Harley DID use DOT 5 in the past, but no longer, as it is incompatible with ABS and TCS).

If you're worried about spillage stripping the paint - don't spill (duh).
If you're worried about water absorption, change the fluid annually as recommended.

Cosmo