Brakes: Brake fluid contamination

[Warren Webb]

Well, my master cylinder went south after only 5 years. When I drained it I was surprised to find the once clear fluid had become amber in color with fine particles of rust. This caught me by surprise due to the truck being in So. Cal. with it's very dry & low humidity climate. It made me wonder about many of you where humidity is high. Dot 3 sucks moisture out of the air so the advise we get for flushing our brake systems every 2 years is wise. I certainly will adhere to that from now on for sure!

[unclemiltie]

I live in the midwest and that is why I now run Silicone in all classic cars. I got tired of rebuilding the systems.

You probably should also check your wheel cylinders also. While flushing the fluid will get crap out of them, that crud could also cause one side to stick thus affecting braking

[Bud]

I live in So Cal and I still flush the brake systems on my vehicles every couple of years because of moisture contamination. I have an air compressor powered vacuum brake bleeder, so it makes the job of flushing out the brake system fairly easy. Bud

[Warren Webb]

While unpacking from the move I found I have 2 of those Bud. Guess I need to use them more often!

[Paul Keller]

Two points:
Test strips are available from many auto parts store. They show if water is present in the brake fluid.
Silicone brake fluid (DOT 5) is NOT recommended for street use by several of the brake fluid providers (it is useful in racing use). The reason: although silicone fluid does not absorb moisture - It does NOT eliminate contamination due to moisture. The water sinks to the lowest part of the system allowing rust and (more seriously) boiling at the calipers. Why used in racing - The fluid is changed often due to regular changes made in the brake system. Each time the system is reconfigured, the system's fluid is changed eliminating the moisture before it can cause a problem.

Check out a few fluid manufacturers sites for their point of view.

PaulTK

[Mike Van Veghten]

DOT 5 fluid IS NOT used in any forms of real racing in ANY form.
And yes, most brake manufacturing companies DO NOT recommend DOT 5 fluid. I know a couple of people that tried it years ago, when it first came out. All switched back to "normal" fluid within 6 months to a year.

Though DOT 5.1 (a more normal glycol based fluid) is sometimes used.
ALL (99.9 %) road cars, motorcycles change their brake fluid for EVERY race. Drag racers, depending on the class, will refresh their brake fluid four to five times a year.

It (DOT 5) works best at sea level and the higher the altitude, the more compressible (a bad thing) it is, fact.
It (DOT 5) is more compressible than normal based glycol fluids at "all" altitudes, which makes it a bad fluid. Brake fluid should NOT be compressible.

Although some seem to be happy with it...so be it..!

Mike

P.s. - For glycol based fluid to work its best, it should be refreshed as soon as it turns an amber color. Best not let it turn brown..! It does make a difference in braking action.

[TWChamp]

I just went through the brakes on my 1950 Land Cruiser, and I switched to DOT 5 silicone. Now this car has the best brake pedal of any vehicle I've ever owned. Just push the pedal and within an inch it's rock solid. In the early 80's I also switched my 49 Chevy 1 1/2 ton truck and my 71 Scout to DOT 5 silicone, and have had no problems.

[bensherb]

I've used DOT 5 for four decades and never had any problem with rust or any other problem with it.

Harley Davidson has been using DOT 5 at least 22 years. (I don't know exactly when they began) New bikes come from the factory with it and the master cylinders state use only DOT 5 fluid on their tops.

[Mrs K Corbin]

I use silicone as well.

[Jeffry Cassel]

Used to use silicone, but decided that it was important to have brake lites and it tends to soften up rubber parts. Much happier with Valvolene fully synthetic brake fluid. I does not adversely effect brake lite switches and does not soften rubber parts and it is far less hydroscopic than Walmart stuff. I check brake fluid quality with a little electronic gizmo that you dip in the fluid and push a button. It will show a green light if less than 1% water to a red light if 4% or more. They are not too expensive and seem to me to be really worth it.

[62champ]

I became a Dot 5 convert after a friend pulled his '64 Hawk from its storage back in 2014. It had been parked in about 1986 with Dot 5, and after refilling and bleeding the system, the master cylinder and all the wheel cylinders worked and did not leak. I am not going to park any of my vehicles for 28 years, but if I do, I know a brake job will not be needed when it sees the light-of-day again...

[bensherb]

I have several vehicles using hydraulic brake light switches with DOT 5 fluid and have never had an issue with any of them, or with "softened" rubber parts. In fact, I built a four wheel disc system for a car in 1984 using Ford 4 piston calipers from 1965 and a 1963 Corvair master. It uses a hydraulic switch and DOT 5 and has never had any issues with anything and has never needed rebuilding.

Will your "Valvolene fully synthetic brake fluid" damage paint?

[Buzzard]

My '83 Avanti came from the factory with Dot 5 fluid (labelled on the cover). When it was still my father's car, some garage topped up with Dot 3-What a mess we had to contend with! We replaced EVERY single rubber component in the whole system due to distortion of the rubber and ultimately brake system failure. It had a very hard pedal but the caliper and cylinder pistons were barely moving. After thorough flushing I returned the system to Dot 5 to keep it original. However, every other vehicle I have has Dot 3 and work just fine.
Just my take.
Bill

[StudeNorm]

My '63 Avanti had DOT 5 in it when I got it in 2013. It is my understanding it was changed to that in 1985 when it had a major overhaul. It only had 5K miles put on it since then and the brakes worked fine on my 1000 mile drive home. I pulled the MC to change an exhaust manifold and refreshed the fluid when I re-installed the MC. I actually bought EBC yellow pads for it but they have been shelved for now because the brakes work super as they are. No plans now to change anything. Just sayin'.

[Jeffry Cassel]

Synthetic will damage paint, alltho it is not as good at sripping paint as DOT-3.