how to change brake fluid

[greg]

roketa 150cc catalina. front and rear discs. 2 reservoirs. one on each side of handlebar.

i bought some cheap dot3 fluid. would dot4 synthetic be better?

whats the best method to change the fluid. i have no vaccuum tool. gravity?

[medman1952]

here is a thread on bleeding the brake, pretty much the same thing as changing the fluid out.

scootdawg.proboards59.com/index.cgi?board=general&action=display&thread=1578

[xs650]

Any brand name DOT3 or 4 is good enough. I prefer better than "good enough" but don't expect you will have any problems.

There are several ways to bleed brakes, an old one that works about as well as any is the pump and hold method.

I lifted this from Wiki to save typing.
en.wikipedia.org/wiki/Brake_bleeding
Substitute scooter part name for car part names.

Pump and Hold Method: One person pumps the brake pedal to compress the air, then holds pressure on it. The other person opens the bleeder valve to let out fluid and air, then closes the valve after the pedal has landed (to prevent air being sucked back in through the valve on the upstroke). The process is repeated, sometimes many times, for each wheel. Usually a length of clear tubing is connected to the bleeder valve and run to a container during the process, both to collect the toxic brake fluid and to better view the fluid and bubbles. The master cylinder reservoir must be replenished frequently, for if it goes dry the entire process must be redone. The cover must be left loose so that the fluid may be drawn, but should be in place so that fluid does not squirt out on the return stroke. A block may be placed under the pedal so that it does not bottom out during this procedure, as the master cylinder seals could be damaged by encountering accumulated sediment and / or corrosion.

[greg]

thanks for the replies i went back to the store and bought prestone dot4 synthetic. did the front brake about 60 times! some air came out..i noticed a difference in the feel. tomorrow i'll do the rear and im betting there is more air in that line. never was firm.