The problem with Silicone dot 5, is that it is NOT hydroscopic. That would seem to be a useful thing, except that when you do get water vapor inside (and you will) it freezes when it's cold instead of being absorbed into the liquid. If your bike never nears freezing you are probably fine, but there is a very good reason the race stores don't sell any dot 5 fluids. I have always been warned to stay away from DOT 5 at all costs.

Check out this stoptech website whitepaper on brake fluid.

http://stoptech.com/tech_info/wp_brakefluid_1a.shtml

 

OK, I just read that article. It says that DOT 5 is NOT compatible but DOT 5.1 is. So I was correct the first time.

 

It seems actually odd reading this. I know DOT 5 was actually developed for racing,because of it's boiling points, and the side bonus was it didn't pit master and slave cylinders like the other brake fluids or damage paint. I converted my '62 Corvette to DOT 5, back in 1986, and my '73 CB 750 K3 about 3 yrs. ago. I so far have liked it so well I converted the Goldwing this spring and intend to do the same with the CBR 600 F4 over winter as I go through the bike changing all fluids.

 

They say the problem with DOT 5 fluids, is that being non-hydroscopic, meaning it doesn't absorb water... the water which does get in past the seals tends to collect at one point and pool and freeze up. Also the silicone can store more dissolved air.

This is the first place that I have ever heard of people using Dot 5... At least from the Honda car scene where I started, nobody that I am aware of ever used Dot 5. Stoptech is kind like the holy grail of brakes...

You would think if DOT 5 were a better fluid, more manufacturers would reccomend it. But according to AAA "DOT 5 fluids are all silicone based because only silicone fluid can meet the DOT 5 specs. No vehicle manufacturer, however, recommends DOT 5 fluid for use in its brake systems."

Just google dot 5 and you will see what I mean. Some people have reccomended it for cars that sit for a long time?

http://www.britcycle.com/Manuals/DOT5.htm
"DOT 5 does not damage paint like other brake fluids do, but is not recommended by AP Lockheed for use in their systems due to higher wear than with other type fluids.

Brake system contamination:

The single most common brake system failure caused by a contaminant is swelling of the rubber components (piston seals etc.) due to the introduction of petroleum based products (motor oil, power steering fluid, mineral oil, etc.) A small amount is enough to do major damage. Flushing with mineral spirits is enough to cause a complete system failure in a short time. I suspect this is what has happened when some owners change to DOT 5 (and then assumed that silicone caused the problem). Flushing with alcohol also causes problems. Brake systems should be flushed only with DOT 3 or 4.

If silicone is introduced into an older brake system, the silicone will latch unto the sludge generated by gradual component deterioration and create a gelatin like goop which will attract more crud and eventually plug up metering orifices or cause pistons to stick. If you have already changed to DOT 5, don't compound your initial mistake and change back. Silicone is very tenacious stuff and you will never get it all out of your system. Just change the fluid regularly. For those who race using silicone fluid, I recommend that you crack the bleed screws before each racing session to insure that there is no water in the calipers.

British Cycle Supply Company does not recommend use of DOT 5 silicone brake fluid on British motorcycles equipped with any AP Lockeed disc brake components."

It doesn't seem like there is much arguement for it, but it's very odd indeed, as I have been versed in exactly the opposite. I don't really care either way, but just curious this could be overlooked for so long by so many people. It appears I am in the minority with this one, but Google searches with just "Dot 5 brake fluid" seem to be on my side.

 

Certainly don't dispute all you said or the articles that you have. People in the old Corvette circle have been using it for about 30yrs. The disc brakes on the 1965 and newer cars were horrible in deteorating their calibers due to the DOT 3 & 4 brake fluids containing water and this water would collect in the calibers and pit them severly. The only recourse then was sleeving them. Then when DOT 5 came out, many people including me, switched to it. I certainly can't dispute the research that has been put into it, but I haven't had any brake problems since going to it in the '62 Corvette back in '86. I actually use the Dot 5 to flush the system. Bleed the brakes several times and do it occasionally as well after that to make sure any leaching from the rubber lines carrying the old fluid is purged of the DOT 3 or 4.

 

I think we're in agreement, that this is the first time we've heard of the other point of view. I will probably stick with DOT3/4 just because it came with it, and once you go DOT5 you can't go back. I think the DOT3/4 people are of the notion that you swap it out so often it pays to have cheaper stuff... where as over longer intervals the non-hydroscopic dot5 may be more beneficial for the majority of the braking system... I don't know, not really on the top of my list, I've been using ATE 200 and the BLue ATE

 

Silly question, but here goes:

Where does Synthetic Dot 4 fit into this equation? I thought that DOT 4 WAS synthetic to begin with. Is it just clever marketing by some companies (ie Valvoline)?

 

how should i drain the system any ideas ?