Bloody bleeding problems.... need ideas, I'm out.

[Guest]

To make a long story shorter:

'84 GS750ES/EF

Thought I had a bad master cyl so rebuilt the spare. Thought the problem was solved...but it was late that night and I must have been dreaming early.

Hoses are all fairly new.
Calipers, anti dive units and anti dive actuators all rebuilt.

Bled the brakes. and bled. and bled. and bled. and bled.

Spongy lever.

Bled some more.

Spongy lever.

I've bled by pumping the level a few times, opening the bleeder, pumping, closing, pumping, opening ect.

I've bled by using the submerged hose and open bleeder method.

I've bled on the centerstand with the wheel straight.

I've bled on the sidestand with the wheel turned because I thought I might have had air stuck in the pipe/manifold that divides the fluid between the sides. Its flat when on the centerstand so I thought I'd try it with one side higher.

I tried bleeding in reverse with pressure. In other words from the bleeder up but for some reason I can't get it to take fluid that way?! I has normal bleeders, not speed bleeder...no check valve anywhere in the system that I can see.

I'm going out of my freaking skull here... any clues? Any glaring errors on my part?

The factory manual says to bleed the L anti dive, the L caliper and then the R anti dive, R Caliper. I did this, I also removed the anti dive actuators as per the book to get the air out of that line.

GAH!

/\/\ac

[Jethro]

I found success by using the banjo bolt on the lines as a bleeder screw, and bleed from there before the caliper iteself. Also make sure there isn't a blockage in the return hole in the master cyl resevoir.

[Macmatic]

I found success by using the banjo bolt on the lines as a bleeder screw, and bleed from there before the caliper iteself. Also make sure there isn't a blockage in the return hole in the master cyl resevoir.

Thanks, I'll give the banjos a shot in the morning. The master cyl is 100% good unless I got defective parts, but it "pumps up" so I don't think thats it.

/\/\ac

[Rocketjock]

My previous owner had everything replaced except for the master cyl. on the advice of those friendly guys at the bike shop and still same problem. I took the master apart and found that little (and I mean little) hole for the return was blocked. That fixed it. Make sure you can see fliud movement out of it and not just the main hole. I cleared it with a welding tip cleaner. you could also pluck a wire from a wire brush.

[Jared]

If You've checked everything already mentioned...and it's not fixed...Double check how the pads are seating... I recently had a similar problem on a Gs500e (dunno if the brakes are laid out alike on the older ones yet..as I haven't had my Gs850 apart yet..).

The inside pad was sitting out and not seated in the caliper correctly and it gave the same soft lever feel tho I had bled the hell out of it....It came unseated when I was putting the caliper back on....

Once I got the pad in right it worked and felt fine....

Good luck...

[KEITH KRAUSE]

Follow your manual procedure, make sure return holes are clear, etc, then try this first before completing bleeding at the caliper fittings.
Remove banjo at the master cylinder, lots of rags.
With a full reservoir and a re-fill within reach if needed, squeeze the lever fully allowing fluid out, hold it, place your thumb hard on the cylinder end, release lever, keep thumb on tight, squeeze again while removing your thumb, hold lever, place thumb again tightly against cylinder, release lever, repeat until no air spits out other than what your thumb has allowed. You can tell the difference. Won't take very many cycles of this.
This will remove most of the air trapped in the MC. Now you should be able to complete the bleeding at the caliper fittings without pumping too long. Works for me every time.

[Macmatic]

Thanks for all the ideas everyone!

This is my first bike so I don't know how hard the lever should be, when I tested the master cyl by plugging the output port with a 10x1mm blot it was hard as a rock. I tried it in several areas of piston travel by cracking the blot loose with pressure on the lever and it was solid everywhere.

I put the main hose back on and rebled the MC and banjo that way, cracked it loose and squeezed, locked it down and released. I repeated that until I got nothing at all but a stream of fluid several times in a row, about 8 times total.

Next I did the same thing at the banjo on the left (from the seat) of the splitter pipe. That thing has a huge ID, around 1/4in so I can imagine a pocket of air staying there. I tuned the wheel so that the left side was higher and repeated the bleeding, same with the calipers.

This might be a clue

In short I got no air out anywhere other than the MC until I removed the calipers and pushed the pistons back with a c-clamp. I did that and bled at the anti-dive units again and got a few bubbles out of the left side but that was it. This was with the anti-dive units removed and held with the bleeder highest.

With the pads/piston fully retracted the lever feels harder than it does with the caliper mounted and the pads/piston out. The pads are not new but they all have 5-6mm of friction material and are flat and clean.

So the brakes feel much better, much much better. I can now chirp the front tire if I really get on the brakes at low speeds...haven't tried to do that at higher speeds!

What I'm feeling now could be flex in the calipers and flex in the hoses....if there is still air in there...*#$@* if I know where it is.

Thanks again!
/\/\ac

[duaneage]

After I flushed the fluid and re-bled my 650 brakes I was able to lock the front wheel and lift the back up. I'd say the GS650G has pretty damn good brakes for what it is.

I don't have the anti-dive. Some on this site have advocated removing it for better performance, ask around about doing that.

[DaveDanger]

It sounds like you've tried every method known to mankind, but I'll toss my variation in for others to evaluate as well. I connect a length of clear vinyl tube of an appropriate inside diameter (snug fit) to the bleeder nipple of whichever caliper I'm working on, and run the other end all the way back to and INTO the reservoir. I then open the bleeder nipple and begin to pump the lever. Keep a refill can of proper fluid on hand for keeping the reservoir fairly full the whole time. Any air that is inside the system will sooner or later circulate through the clear tubing and you can see it as it disappears in the reservoir. Keep pumping till no more air bubbles flow through. Close the bleeder and remove the tubing.

If there's an oddity to the system that's trapping air in a weird place, this won't necessarily solve it. But for a normal system that's simply gotten air bubbles in it from opening a fitting or caliper, this works quite well. It works well on any brake system that I've ever attempted, automotive, bike, aircraft... you name it.