well short story.... i put in dot 5 but the guy that had the bike before me had dot 3/4 in it......Soooo can i just keep flushing it out and be ok?

 

What does your bike call for?

 

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).

 

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.

 

how do you know the previous owner was using dot 3?

i hope you didn't come to this conclusion based on the color

 

Agreed! Let's get to the bottom of this first. You need to be confident of your facts before acting.

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.

 

If mixed and left alone the seals will swell so flush good!

 

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.

 

ya it turn to jello... i was just going what it sayed on the top of my master cylinder... so i guess i will just pull the system and rebuild...

 

Ironically I was preparing my bike at the time for shipping it from the UK to the USA for Harley's Centenary! We rode 3,500 miles on 'foreign shores' and the last thing we needed was a brake failure in our bike's homeland!

I would guess it has had mixed DOTs in there for quite some time. Best to clean it out as best you can.