Brake fluid replace Problems 101

I have a big ride planned for tomorrow and since today was hot with chance of thunder storms - decided to replace the possibly 15 year old front brake fluid on my 79 / 650.

It has worked very well with some noticeable tight pad/brake noise when walking the bike.

Following the FSM, I drained the fluid (no problem). Filling up the brake line (J24), started and then stopped. It's at a point now that I can no longer drain the system. No pressure at the lever with the cap screwed down and the drain plug closed. I'm taking a dinner break and thinking I may have to get familiar with this brake system tonight.

HELP!!!!!!!!!!!!!!!!!!!!!!!

Where should I start? My guess would be to look at the piston unit (G24) first for debris and work my way down to the caliper?

You may have air in the system. When I bleed the front, I put it on the center stand open the fluid reservoir and trow a rag over it and slowly pump the fluid out the bleed at the caliper but DON'T LET THE FLUID LEVEL GET LOW ENOUGH IN THE RESERVOIR TO SUCK IN AIR. Then add fluid and just keep it up until it's flushed well enough. The times I have let the master cylinder suck in air, the handle goes spongy and it won't pump. Then you have to keep bleeding it until you get the air out.

Air is certainly in there. My thinking was I wanted new juice in there and decided to let the old stuff just drain out like an oil change. MY BAD.

I continued to bleed the system and at some point it just stopped doing anything. Going to let it sit over dinner and head back out to the garage to re evaluate.

What's my best option at this point or how should I proceed?

ty bountyhunter

I think you fill the reservoir and just pump the handle until it primes and starts pushing fluid through. Then keep pouring in the top and bleeding at the caliper until the handle feels solid again.

We've all been there, takes a while. Good to have a second person to open the bleed fitting and clamp it off after the fluid spurts to keep from sucking air back in.

BE SURE to keep the top of the reservoir covered with a rag while pumping so the brake fluid can't jump out and hit anything painted.

Bleed procedure doesn't seem to be taking effect. Tried with the cap on and off, no difference. I'm about to remove the master cylinder to look at the piston. There were flakes in the old fluid and my guess it's causing one of the rubbers not to fully seal and assert pressure into the reservoir from the level.

If that makes sense.

oh boy, plenty of debris in the reservoir, going to clean it out.

rephrase... sludge.

I normally just act like Im bleeding the brakes and just keep topping off the mc while till clean/new fluid comes out the clear hose om bleeder valve.
Sometimes you can leave the lever zip tied back to the bar for a while to force air out of system.

LineArtist wrote: oh boy, plenty of debris in the reservoir, going to clean it out.

rephrase... sludge.

Iso/rubbing alcohol works good for cleaning brake parts

Here are fine details, the master cylinder reservoir is/was caked with sludge on the bottom. The 2 openings at the bottom of the reservoir were also blocked. Pulled the piston out and more sludge. The 3 holes that lead to the outer cup by the spring were also clogged. I'm going to take my time on this. Once cleared everything should work. But I may have to repeat down on the caliper end.


that stuff on the paper towel was at the bottom of the reservoir, about 1/2 of teaspoon of plumbing goop.

Hello master cylinder piston, good to know you finally. Adding one more part to my knowledge base.


One of my best tools is that microwave plate that I use to clean all parts and contain liquids, small screws and springs from going missing. Going to make a ray gun with the rest of the parts from that microwave.

Yep that's some nasty stuff,brake fluid should be flushed every couple of years.

PLUMMEN wrote: Yep that's some nasty stuff,brake fluid should be flushed every couple of years.

+1 I change mine every 2 years. Those pictures show why that is not time wasted. Ed