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General Category >> Rubber Side Down! >> Dot-5 brake fluid?
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Message started by SavageMan99 on 07/08/20 at 11:37:21

Title: Dot-5 brake fluid?
Post by SavageMan99 on 07/08/20 at 11:37:21

I use it elsewhere, no water absorbtion.
Any reason not to do a full flush and fill on the bobber when I swap over to the GS rim?

Title: Re: Dot-5 brake fluid?
Post by srinath on 07/08/20 at 12:32:10

0436213630321A36396E6E570 wrote:

I use it elsewhere, no water absorbtion.
Any reason not to do a full flush and fill on the bobber when I swap over to the GS rim?

I've used it, AND LOVE IT. Works well, and it lubricates the suction pump.
Cool.
Srinath.

Title: Re: Dot-5 brake fluid?
Post by oldNslow on 07/08/20 at 13:12:36

DOT 5 doesn't absorb water, but water still gets in. The water doesn't go into solution in the fluid but it still collects in the calipers and master cylinders over time as little blobs of pure water and can cause corrosion.

Harley used it for a few years in Sportsters and it caused problems when the owners didn't change the fluid often enough. I've got a 2004 XL883 that uses it and the owners manual recommends flushing and replacing the fluid every 24 months. HD switched back to DOT 4 sometime in the mid 2000s.

DOT 5 also doesn't mix well with DOT 4 so if you don't get whatever fluid is in there all out, that might cause issues too.

The only advantage to DOT 5 that I'm aware of is that it has a higher boiling point than 4. That could be important in race bikes that get the brakes really hot but I doubt that that makes much difference in most street bikes.

My opinion, which is just that, is that unless you get the system perfectly clean, and change the fluid regularly, using DOT 5 in a system that was designed for, and works satisfactorily with DOT 4 probably isn't worth the trouble it might cause.

Interesting side note:

When I bought my Sportster I had no idea what kind of maintenance the previous owner did so I immediately changed all the fluids. DOT 5 brake fluid is purple when it comes out of the bottle. The fluid that was in the master cylinders and that came out of the calipers when I started pumping it out was yellow. I thought "crap this guy put the wrong fluid in the bike. I went ahead and flushed and refilled the brakes with the DOT 5 and hoped for the best.

I did some internet research and discovered that DOT 5 fluid actually does loose the purple color over time. I haven't had any brake problems yet, so I assume the fluid that I took out was DOT 5, just old. I'd never dealt with DOT 5 before and I wasn't aware of that particular characteristic.

Title: Re: Dot-5 brake fluid?
Post by srinath on 07/08/20 at 13:31:57

Dot 5 also does not eat paint, and does not need to be new in a sealed can all the time.
It does absorb water and tends to make little chunks of deeper purple and turn the rest of it lighter colored.
You can suck out 90% of the reservoir, toss it, and put new fluid in and pump and bleed at the caliper bleed screw and be done every other year.
The not eat paint aspect is huge. It gets somewhere like wheel, frame, caliper .... meeh, no big deal.

Really .5 has no down side, IMHO, buy a big bottle and it will last forever.

Cool.
Srinath.

Title: Re: Dot-5 brake fluid?
Post by Armen on 07/08/20 at 14:12:06

Short answer, not a great idea.
Long, boring answer with personal experience and details if you insist.

Title: Re: Dot-5 brake fluid?
Post by Ruttly on 07/08/20 at 20:07:09

I found dot5 synthetic fluid just doesn’t have a solid feel to it , kinda mushy.
Dot 3 gives me a solid and consistent feel , grab a handful and stop , quick.
Don’t know about dot4 ain’t never tried it.

Title: Re: Dot-5 brake fluid?
Post by Dave on 07/09/20 at 03:05:29

Back in the 70's when I believe the DOT 5 fluid came out - it was supposed to be the "go to" fluid for collector cars that sat for long periods of time.

I really don't know why - but it never really caught on and became a popular replacement brake fluid.

Title: Re: Dot-5 brake fluid?
Post by srinath on 07/09/20 at 05:43:56

Dot 5 can be a bit mushy if you dont flush and clear out the system completely and let it dry completely. Sometimes it means running a contact cleaner through it, though I've had decent luck if the old fluid was not full of water.
The .5 silicone based fluid is slightly more compressible than .4 but in all other aspects it beats it.
The other thing is, the .5 will take on water if it enters the system but isn't hydrophilic like .4 or .3. It will fade a little, that bright blue gets paler when it takes up water. But unlike .4 it doesn't attract water.
I've run it in a lot of bikes, I frankly notice no negative over .4 and the lack of effect on paint is just a bonus IMHO.
Some bikes are built with .5 and sent that way from the factory. I believe ducatis. That should tell you no difference in the seals pistons lines etc.
Cool.
Srinath.