Brake fluid overfill [Archive] - Triumph675.Net Forums

: Brake fluid overfill


plexwang
05-17-11, 20:18
Today I change the rearset to SV racing part, and bleed the brake system. Just found the brake fluid level for the rear brake is a bit above max line, can I just simply open the reservoir cap and drain some out use pipette, or I have to go over the bleed procedure again? What will happen if the brake fluid overfill.

Thanks!

MGFChapin
05-17-11, 20:23
It's fine to suck it out the top with a pipette or something, you're not introducing any air into the system. If there's enough room at the top for reservoir cap to go on without spilling brake fluid everywhere though, I'd call it job done and not worry about it.

MacBandit
05-18-11, 00:06
Agreed. If the cap will go on you're fine.

mikereiser
05-18-11, 00:11
I trust mac bandit, but, and not to thread jack but my back brake seized up and i think its from overfilling by resevoir.

MGFChapin
05-18-11, 02:09
I trust mac bandit, but, and not to thread jack but my back brake seized up and i think its from overfilling by resevoir.
How do you figure? Pics?

plexwang
05-18-11, 10:15
Thanks, guys,

my concern is if it comes to hot, the brake fluid may expand and cause a brake drag, so I just top off about 1 ml fluid, and it is a 30 seconds job, no panic.

MacBandit
05-18-11, 10:23
Brake fluid does not expand but very very little. If there is water in the fluid (old fluid) it will expand. The only times I've seen caliper lockup with excess fluid was when someone put new pads in after topping up the fluid and pressed them out and put them over the disc which then caused them to drag and get too hot causing the old fluid to expand.

dtrides
05-18-11, 10:56
..or when someone uses brake fluid intended for cars..Saw it happen to my buddy when he mistakenly grabbed the wrong bottle from the shelf and filled her up. We were on a steep down hill when I saw him very quickly slow down and stop. I had to grab a wrench and open the bleed nipple to release the pressure and get him rolling again..
DT.

timwu12
05-18-11, 11:01
you can't use car brake fluid? I don't see why it'd make a difference.

NewShockerGuy
05-18-11, 11:13
you can't use car brake fluid? I don't see why it'd make a difference.


That's what I am wondering as well. You can't use DOT 4 or DOT 5?

I am looking at my motul brake fluid and it's DOT4

I am looking at my ATE Super Blue for my STi and it's DOT4...

-Nigel

Pathos
05-18-11, 13:43
you can't use car brake fluid? I don't see why it'd make a difference.You can but it won't be quite as firm as the fancy stuff. It won't hurt the system or anything, just less performance (in my subjective opinion).

MacBandit
05-18-11, 22:24
There is no such thing as car specific brake fluid. Our bikes are spec'd for DOT4. The glycol based brake fluids are DOT 3,4, & 5.1. I use 5.1 in my bike. Unless you are racing you don't want to use DOT 5 which is synthetic. DOT 5 does not absorb moisture (hydroscopic) and has a high boiling point. Both of which sounds like a good thing but.. Unless you change your fluid very regularly you want your brake fluid to absorb moisture. The reason is no matter what over time if you ride in the rain or wash your bike or however you get water on the brakes it will work it's way past the seals. Once in there if you have glycol fluid this moisture will be safely absorbed and diluted so that it does not cause corrosion. If you use DOT 5 this moisture will actually pool and start causing corrosion. So yes it sucks that brake fluid absorbs moisture and therefore lowers it's boiling point over time but you want it to do that so when you flush the fluid the moisture comes out too and you have a fresh clean system. So change your fluid often.

Also if you have a vehicle with ABS use the fluid specifically specified for it. The reason is different brake fluid ratings DOT 3, 4 etc. have a different viscosity (thickness) and the ABS system was designed specifically with a specific viscosity in mind to work work properly.

Here is the wikipedia entry on brake fluid. It has more technical information but not as much of the application info as I just provided.

http://en.wikipedia.org/wiki/Brake_fluid