Squishy front brake lever- not air.

[chuck hahn]

New green dish scrubbie and relieve the seals a bit..refit and see how tightly they go back into the piston wells. They should go in snuggly but not to the extent you need to lean your body weight on them to get them to go in. Some decent finger pressure, but they should readily slip in.

This was covered not all that long ago to another member that had spent 6 months trying to get the sponginess out

A few thousands makes world of difference!!

 

[chuck hahn]

The fluid must back flow when the lever is released and be able to create enough vacuum to suck the piston back. If the piston doesnt move well enough, then the fluid is basically hydrolocked and it cant return back to the master to allow the maser piston to develope the proper pressure..see what I mean?

Squishy feeling is the result.

 

[Wayne]

This was covered not all that long ago to another member that had spent 6 months trying to get the sponginess out

Sorry about that then, I did laboriously search through the forums but obviously missed it.

 

[chuck hahn]

I did too but couldnt remember the thread name..I think it was Steve that went and unlocked the puzzle. The scrubbie to relieve the rubber on the seals was what the fix was.

 

[chuck hahn]

Wayne..by hydrolocked picture this.

Take a pencil and hold it in both hands..the lead side is the master cylinder piston and the eraser is the caliper piston. Your fingers on one hand represent the brake line. The shaft of the pencil represents the brake fluid

Now slide the pencil thru your fingers and note that the eraser (caliper piston ) follows at the same speed as the lead ( master cylinder piston ) does...and does so both ways. AS does the brake fluid.

Now grip each end of the pencil hard and try to push the ends together or apart..nothin will move either way..right? Well thats basically what hyrolocked brake lines do. If the piston in the master cylinder is trying to move toward the caliper and the caliper piston is too tight..you get nothing.

If the piston in the master cylinder is moving back toward the brake level, but the piston in the caliper wont retract..you get nothing but a spongy unresponsive lever.


Does this analogy seem like what your brakes are doing?

 

[Wayne]

Thanks Chuck. That's an interesting illustration for future diagnosis. Sliding the pencil around, I see how you could have sponginess with a hydrolock in that manner.

But it doesn't apply to the bike since I took the advice of removing the caliper and squeezing the pads together as much as possible. Since doing that I've done about 140 miles on it and the brakes now work to an acceptable level but are still not as firm as my other GS.

The overnight test involving pressurising and cable tieing the brake lever to the grip also really illustrated that some of the sponginess is in the lines. Now that I've moved the pistons in, the brake is still a bit spongy but nowhere near what it was and it's at least rideable. Once I get the new lines on I think it will work 100%.

 

[chuck hahn]

You can squeeze the piston in..BUT..after you use the lever and the piston comes back out against the pads and rotor, guess what. Your right back at the SAME point you were before you manualy pressed the psiton back.

Granted it may be "better" but its not as good as if you relieve the seals of a bit of rubber with the scrubbie. A few thousand of an inch is like a world of difference.

Yes the new lines are needed regardless.

 

[Guest]

"the brakes now work to an acceptable level" The brakes either work or they don't "acceptable" is not worth putting your life at risk.

 

[chuck hahn]

You said it more directly than I did Bill. But thats the jest of me prodding to at least give the relief a try. Its a pain taking the caliper on and off and rebleeding to try the lever, but at least you HAVE fully reliable brakes when you are done.

Few hrs at the brakes is worth more than a few weeks in a hospital bed..or god forbid dead.

 

[jpaul]

On my 1980 750, which had the rectangular front master cylinder, there was one air bubble that just would not come out. What I ended up doing was taking my Mityvac, along with the narrowest nozzle it came with. When I stuck that down into the master cylinder by the bottom hole, and pulled in the brake lever just a bit so the tip could get a little further in, I pulled out one air bubble that was trapped in a small high spot there. The brakes firmed up immediately after that. Except for that one application, the Mityvac has pretty much been a waste of money. I find it easier to bleed the brakes with a clear tube running into an old water bottle.

 

[chuck hahn]

I take it that you were doing the "wiggle the brake lever oh so slightly" trick to expell air out the return hole. Often that does do wonders to get the master reprimed, but like you said, that one bubble wouldnt come out.

Another trick that will SOMETIMES (empasis on sometimes) work is to mighty vac them and then press back on the caliper pistons as hard as you can with a big heavy duty flat tip. Pry between the rotor and the pad. The fluid being squeezed back into the master via the return hole will "sometimes" flush that last bubble out.

 

[Wayne]

I'm reluctant to do the seal relief just yet. I like to be really methodical and step by step. When I know that I have a definite problem with the hoses, I'd like to replace those first and see the effect (they're on the way). And I'll admit a tad lazy, not keen to pull the pistons again if I don't have to but will if the hoses don't fix it completely.

I sometimes ride with half a dozen bikes of the same make, model and year. All the brakes (legally) work, but they're not all the same effectiveness. Why ? Pad material, fluid choice, hose age (even if they are all within 2 years old) and perhaps other things as well. I don't go with the black and white of them either working or not but appreciate the sentiment. Thanks.

Nevertheless, all the suggestions are in the mental "archives" for this and many more future rebuilds. Much appreciated and very useful. A great help.