dot 5 dot 3
Seasoned HDF Member
Joined: Aug 2007
Posts: 8,202
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From: NW AR
Flush it really well. "They Say" the best way to flush it is to use denatured alcohol, which is cheap because the alcohol is cheap ethanol, but the "denatured" part is methanol so that if you drank it, you'd die (or go permanently blind first.) Otherwise it would be expensive ethanol. (Side note: In Poland, the "denatured" part has to be non-toxic, by law, because, you know, people will drink it anyway...) Anyway, flush with the denatured alcohol, then open the nipple and blow down the line with compressed air from the MC side, refill with DoT 5. I have used a can of brake cleaner instead of the denatured alcohol when I changed my hydraulic clutch on the Rolla from 3 to 5. That was over a year ago and everything is just fine. Do not mix the 3 and 5 and leave it like that. "They Say" bad things will happen. A can of brake cleaner is a lot cheaper than a bottle of DoT 5 (except the MIL SPEC stuff on ebay).
Elite HDF Member
Joined: Sep 2007
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From: Bluffton, South Carolina
I do believe the good Doctor has this one diagnosed properly!! Note: "They" also say that the internal rubber parts are slightly different between DOT 5 and DOT 3 systems, but I don't know for sure.
Club Member
Joined: Jun 2007
Posts: 45,429
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From: Bedford UK
I have long and bitter experience of mixing DOTs, on my 1990 bike which I bought new. The significance of the difference flew over my head during my early years of ownership, so I used whatever I could get easily. Forget about the supposed differences in rubber parts, there are far more serious things to consider!
What happened to my brakes, by the time I realised something was wrong, is that both master cylinders became filled with a jello like stuff that contaminated new fluid. In addition the insides of the precision parts of them both, as well as the insides of the calipers, became seriously eroded. By that I mean that corrosion had created pits and hollows in what should be smooth highly polished parts. I stripped everything to realise that none of them were fit to rebuild, so it cost me an entire new brake system!
So IMHO, if you establish that you have mixed fluids, dismantle and clean. Don't rely on a simple flush.
Last edited by grbrown; Apr 7, 2012 at 09:52 AM.
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From: TOAK western branch
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Road Warrior
Joined: Dec 2007
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From: SoCal
Dr. Hess and MIACYCLES know their stuff so flushing is probably okay if you really flush it well.
Myself, I'd be so stinkin' worried about it that I'd take everything apart and clean it out as Mr. Brown suggested.
Myself, I'd be so stinkin' worried about it that I'd take everything apart and clean it out as Mr. Brown suggested.
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Club Member
Joined: Jun 2007
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From: Bedford UK
I would guess it has had mixed DOTs in there for quite some time. Best to clean it out as best you can.