Brake fluid: Dot 3 vs Dot 5

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LC Cnd
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Brake fluid: Dot 3 vs Dot 5

#1 Post by LC Cnd » Mon Oct 13, 2014 8:56 pm

Replacing 4LO brake lines cause the master cylinder diaphragm melted into the reservoir - a mess created fm 10yrs of sitting idle. A friend was suggested I use dot 5 instead of 3 because 5 repels H2O due to its siclicone base properties - an advantage(?). Research lead me to this Dot 5 comment: "Silicone based fluids are great for museum cars that are never driven, because the fluid is very non-reactive. The moisture that is bound to eventually get into the brake lines will not dissolve in silicone fluid. This water forms pockets that will boil off and become steam as the brake fluid heats up, and as a result it is virtually impossible to keep a silicone based system bled properly as there will always be gas in the lines." I don't plan making my 4LO a museum piece but I won't be racing it either. Are bike brake lines systems that vulnerable to moisture when garage stored; not in my experience. So, stick with Dot 3 or should one moderize to 5 as suggested.

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JonW
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Re: Brake fluid: Dot 3 vs Dot 5

#2 Post by JonW » Mon Oct 13, 2014 9:23 pm

use DOT4 and change it every year/few years. Ive used 3,4 & 5. 4 is best i reckon.
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Re: Brake fluid: Dot 3 vs Dot 5

#3 Post by Hooligan » Wed Oct 15, 2014 2:03 am

Yep, DOT 4 and change it every second year.
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two-stroke-brit
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Re: Brake fluid: Dot 3 vs Dot 5

#4 Post by two-stroke-brit » Wed Oct 15, 2014 1:49 pm

the best thing about DOt 5 is that it will not harm the paint if spilled !!
being silicon based
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Re: Brake fluid: Dot 3 vs Dot 5

#5 Post by subxero » Wed Oct 15, 2014 4:18 pm

on board with others, DOT4

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Re: Brake fluid: Dot 3 vs Dot 5

#6 Post by JonW » Wed Oct 15, 2014 6:02 pm

two-stroke-brit wrote:the best thing about DOt 5 is that it will not harm the paint if spilled !!
being silicon based
I agree with you but others (bare will chime in here soon) will tell you they have found it does, maybe it depends on the paint?
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Re: Brake fluid: Dot 3 vs Dot 5

#7 Post by waltmil » Thu Oct 16, 2014 9:06 am

The DOT5 just felt odd to me when I tried it years ago. The lever had a spongy feel and I couldn't bleed it out so I went back to 4.
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Re: Brake fluid: Dot 3 vs Dot 5

#8 Post by RuZty » Fri Oct 17, 2014 7:10 am

waltmil wrote:The DOT5 just felt odd to me when I tried it years ago. The lever had a spongy feel and I couldn't bleed it out so I went back to 4.
DOT5 is more compressible than DOT4, the sponginess is normal and why many don't like it. Only vehicle I ever had with DOT5 was an ex-military truck, I imagine they use it to avoid moisture problems on vehicles that may sit around for a long time and need to be ready to go on short notice.

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Re: Brake fluid: Dot 3 vs Dot 5

#9 Post by JonW » Fri Oct 17, 2014 8:03 am

That feel is what I didnt like when I used it, otherwise it worked ok... but DOT4 is the one...
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Re: Brake fluid: Dot 3 vs Dot 5

#10 Post by 75RD350rider » Fri Oct 17, 2014 10:14 am

I only use DOT 5 in my bikes.
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LC Cnd
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Re: Brake fluid: Dot 3 vs Dot 5

#11 Post by LC Cnd » Wed Oct 22, 2014 8:01 am

Asked the same question, on a UK form, and the consences hovered between Dot 4 and 5. Most votes went to Dot 4 - I'm sold. Thx 2 all who responded.

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Re: Brake fluid: Dot 3 vs Dot 5

#12 Post by heyjoe » Wed Oct 22, 2014 9:24 am

I put DOT5 in my race bike back in the day when I was racing. When it came time to restore my machine, the DOT5 had turned to jelly. Obviously it reacted with something.
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Re: Brake fluid: Dot 3 vs Dot 5

#13 Post by T.RexRacing » Fri Nov 28, 2014 12:25 pm

DOT 5 aerates easily and is hydrophobic. I use it in the clutch M/C but avoid it for brakes. I use it there because it never turns that nasty black due to the fact it's an excellent lubricant for seals in the master and slave cylinders. Methanol (DOT 3/4/5.1) based fluids are hard on seals that move more than .040"/1MM or so.


Motul 600 synthetic DOT 4 for brakes has been my go to for awhile. Hygroscopic so it gets swapped out every spring.
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Re: Brake fluid: Dot 3 vs Dot 5

#14 Post by sedsberg » Fri Nov 28, 2014 4:51 pm

heyjoe wrote:I put DOT5 in my race bike back in the day when I was racing. When it came time to restore my machine, the DOT5 had turned to jelly. Obviously it reacted with something.
DOT5 reacts with DOT4 (and DOT3 etc) and creates a mess. DOT 3, 4 and 5.1 are compatible. DOT5 is not compatible with anything.

And being hygroscopic is a good thing as it absorbs gets moisture out of your system when changing the fluid. A problem with non hygroscopic fluids is corrosion and build up of sludge. A common problem with older Citroëns using non hygroscopic LHM-fluid.
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LC Cnd
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Re: Brake fluid: Dot 3 vs Dot 5

#15 Post by LC Cnd » Wed Jan 07, 2015 5:30 pm

4 sounds like the way to go. My next issue is ceased caliper pistons - they are seated all the way in and there is nothing to grab on to. I was advised heat would be the last option followed by 100 psi to possibly pop them lose or soak everything in tranny oil. Solution: declined using any oil or heat. Found an old stainles steel braided brake line, attached it to @ calipers and blew out each piston with compressed air. It took a few minutes but fixed without an issue.
Last edited by LC Cnd on Thu Jan 08, 2015 4:17 am, edited 1 time in total.

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