I replaced my brake fluid last year, reservoir was was low, Don't think the reservoir cap was on tight, fluid all over the swingarm and exhaust. Anyway, I ended up using DOT5, well today I was out cleaning the bike up, and the reservoir looked a little low, so I grabbed a bottle of brake fluid off my porch. I put just a tiny bit in, maybe about a teaspoon full, not much at all. I looked at the bottle a little bit later and noticed it was DOT3. It's in the rear brake reservoir, will that be ok, or do I have to flush the reservoir, line and caliper?

Thanks, Jim

 

dot 5 or 5.1 was in there?

The higher the number, the higher the DOT rating was that the fluid can basically be contaminated (water/dirt,etc) and still function adequately.
Dot 3/4 is glycol based, 4 being the better. DOT 5 fluid is silicone based, and shouldn't be mixed with a glycol based fluid, they might react against each other.

Dot 5.1 fluid, however is glycol based , and basically has the wear/contamination properties of the silicone DOT5, but can be mixed.

If you just mixed glycol and silicone based together - I'd start flushing it all out.

 

It's DOT 5, silicone. I only mixed a very small amount of DOT 3 on accident. Probably even less than a teaspoon. Will that little bit have a major affect on the DOT 5? I guess I will be flushing tomorrow.

 

very bad... very bad...


the chemical reaction ends up making your fluid become gel like! it also will make your rubber seals swell, and it can/will cause brake failure through locking up (because of it gelling up) or because your seals swell to the point where they leak.

our braking systems use rubber seals, and they're not designed for a silicone based fluid. you should only use DOT3, DOT4, and (if you can find it) DOT5.1.

never use DOT5. its not good. it resists moisture (which means it (moisture) pools up in your system) which can cause rust (like in your pistons), but can also cause that little bit of moisture to evap under hard braking because of high temps which will put air into your system - brake failure. instead of a boiling point which goes up over time with glycol and ether fluids, you go from dry boiling point to exactly 100 degrees celcius. as well, the silicone based fluids are actually compressible, which causes a spongy feeling, that you can't get rid of.

the reason the guy at autozone or wherever you got it from said, "ya, a lot of bike guys use it" (which is what i was told) is because harley's come with it. the reason being that silicone brake fluid can't harm paint! and their systems are made to handle it.

i ended up using it once. i never got a firm lever feeling (even with braided lines). some would always seep out of the rubber seal at the top of the reservior. i looked into DOT5 more, found all this out and completely rebuilt my system before anything really bad happen.

but it is your rear brake, not as important as your fronts (which is what i had my DOT5 expirement with). its a big ooppss if your brakes fail.

 

I actually got it from a bike shop, and the kid that recommended it rides a Kawasaki 636.

Anyway, my next question then is, what do I need to do to replace the fluid? Will Draining it and putting in DOT3/4 and flushing it good work or am I in for a major overhaul?

 

If you only put a teaspoonful of DOT 3 in your brake reservoir I'd use a syringe to empty the reservoir and wipe it out dry with a lint-free cloth or paper towel and then re-fill with fresh DOT 3, 4 brake fluid and give the rear brake system a good flushing out and I should think that will be ok and no damaged should have been done to your seals, but do it right away!

 

i dont know if just sucking it up with a syringe and lint-free cloth is good enough... because if i understand it right.... you have a brake system with DOT4 (from the get-go). it was low a year ago, and you filled it up with DOT5. then just a little while ago, you refilled it with DOT3.... you never did a complete bleed, then right? that means its in your system, and like i said, its a chemical reaction. if you had just topped it off with some DOT5 recently, you'd probably still be able to see it and get it out, but because its been a year and what not, id flush the system.

then, what i'd do is take the caliper off. stick the end of the hydraulic hose into a cup or can (that you don't need again - an empty beer can with the top cut off works great) , and i'd run de-natured alcohol through your system (pour it into the reservior, and let it run out of the hydraulic hose into the can, by pumping the lever) a few times and blow that out with some compressed air after a few flushes of denatured alcohol. i'd take the caliper apart and clean it with de-natured alcohol as well. if the seals look good, i'd call it good. after everything is dried out, and i mean completely dried out, then put it all back together and run DOT3, DOT4, or DOT5.1 in the system, bleed it out a few times, run a good amount of fluid through it. remember when putting the pistons back into the caliper to coat them with brake fluid, it bleeds a whole lot easier then.

 

Actually, the reservoir was empty, I had no rear brake. I put the DOT5 in and bled the line and the caliper. I kept emptying the reservoir and refilling with the DOT5 a couple of times. I must have emptied and refilled it 4 times, then bled the line. Guess I will be taking my brakes apart today.