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Bleeding brakes

  • Thread starter Thread starter Dave W
  • Start date Start date
D

Dave W

Guest
Decided to rebuild my brakes in the off-season on my '79 GS 850. Got a big trip coming up this summer. Rebuilt the calipers (all 3), both master cylinders, new pads, all with new cups, seals, etc. Now I can't get the @%*(%%** to give me a good, tight brake. I can pump up the front lever/back pedal to get pressure, but after I leave it a minute it goes all the way down again. Started at the top banjo fitting, working my way down. Pushed a bunch of fluid through it, no more air coming out. Tried everything I can think of, but to no avail. Any ideas???
 
I usually just use a short length of clear hose Attach it to the bleed nipple and into a empty water bottle with an inch or two fo brake fluid in the bottom . Open the bleed nipple, slowly pump untill no more air comes out
Close the nipple - done.
 
Re: Bleeding brakes

Dave W said:
Decided to rebuild my brakes in the off-season on my '79 GS 850. Got a big trip coming up this summer. Rebuilt the calipers (all 3), both master cylinders, new pads, all with new cups, seals, etc. Now I can't get the @%*(%%** to give me a good, tight brake. I can pump up the front lever/back pedal to get pressure, but after I leave it a minute it goes all the way down again. Started at the top banjo fitting, working my way down. Pushed a bunch of fluid through it, no more air coming out. Tried everything I can think of, but to no avail. Any ideas???
Click to expand...

I can pump up the front lever/back pedal to get pressure, but after I leave it a minute it goes all the way down again.

Help me out here, are you saying they don't work at all or you have to pump it to work? When you grab the lever and squeeze once, what happens?

Started at the top banjo fitting, working my way down. Pushed a bunch of fluid through it, no more air coming out

Close up everything and bleed from the caliper bleed valve. Leave the banjos alone. It is best to replace the copper washers with new ones, any auto parts store should have them.

Are you sure you rebuilt the master cylinders correctly?
 
If they are bled correctly and do not grab when you squeeze them on the first pull or if the lever slowly fads in while applying them then it sounds like you have a leak somewhere or your master cylinder rebuild didn't go as you had hoped.

If it was a leak, you would see it, unfortunatly that only leaves the other thing :(

I can't imagine what else would cause that?
 
Sounds like your master cylinder is bypassing, that is fluid is getting by and returning to the resevoir.

Open the lid and squeeze. If you see fluid bubbling up your bypassing and that means take it apart and see what is up.

Replacement cylinders are cheap on eBay ( i just sold one 2 minutes ago for 10 dollars) and that beats monkeying around with rebuilding them. Brakes are important, i would not try and fix a broken master cylinder on a motorcycle.
 
Re: Bleeding brakes

Dave W said:
I can pump up the front lever/back pedal to get pressure, but after I leave it a minute it goes all the way down again.
Click to expand...

Do you mean, you pump the brakes up and get a good pedal (or lever), and while holding presure they go down? Or, do you mean you pump them up to get a good pedal, but after a minute of sitting with them in the released position there is no braking on the first re-application?
 
Bleeding brakes

I rebuilt a master cyl that I got used, it did as I said. Bleed the air out, pumps up fine, let it sit a while, pull the lever, it goes all the way back. Put the old one back on (it worked fine when I took it off), bleed it out, it does the same thing. So I don't think I did the rebuild wrong. The cups I used came new from Suzuki. Also, both the front and back brakes are doing the same thing. Can't really see making the same mistake on both. I spent 25 yrs as an auto mech, so I've got a pretty good idea of what to look for. Just looking for ideas of something I might have overlooked. I realize I'm not perfect, and I do make mistakes.
 
brakes

brakes

you still have air in the system, if you have to pump it up thats a dead give away, you can take the lever off and push the master piston to bottom with a wood dowel (only), by hand, this will push out any air that the lever is unable to get out due to lack of stroke, you bench bleed a car master the same way, other wise you will not get all the air out
 
I'm gonna head out to the shop and try these brakes again. Wish me luck.
 
Well, I've gotten some improvement, but not a lot. At least I have some pressure now and I don't have full lever travel when I pull on it. I can feel the calipers move when I pull the lever. (Or push the pedal). I think I'll get the battery in and get it ready to run and try it in the driveway and see if bedding the pads in helps. I live in the country and I can get some distance without having to deal with traffic, so if the driveway test goes reasonably well, I can go to the corner and back. Maybe, too, the motion will shake some air loose.

I'm running out of ideas. (Actually ran out a long time ago).
 
Dumb idea but here it goes

Are you sure, absolutely sure, you have the correct brake pads? If they are not the same they might be causing a problem with travel in the calipers.

Just an idea.
 
Yeah, the pads are the same as the ones that came out. Made sure the slides in the caliper were free, calipers mounted correctly, etc.

Still think it's air, but I've put about a half pint of fluid through each system.
 
the angle that the mastercylinder is mounted at traps air in a corner.
you need to adjust the angle of the master cylinder up and down and slowly work the lever to get that last bit of air out.
 
focus frenzy said:
the angle that the mastercylinder is mounted at traps air in a corner.
you need to adjust the angle of the master cylinder up and down and slowly work the lever to get that last bit of air out.
Click to expand...


Top advice! That explains a lot. I didn't think of that. Thx Leon :)
 
Master cylinder angle, hadn't thought of that. I'll give it a try. What about the back? It sits vertical and I've got the same problem there.
 
Re Brakes

Re Brakes

After rebuilding the master cylinder on my 450, it would not bleed no matter how many times I pumped and opened and closed the bleeder. Went down the street to my mechanic buddy, we used his vacum cannister to draw the fluid down through the lines. Seemed to be the only way to be sure the air was out. Took about 2 or 3 pumps on a pretty large vacum tool. Once that was worked out, the front calipers wouldn't release the wheel. So then I had to re-build the calipers and they were pretty gunked up inside. Then went back to mechanic buddy to vacum bleed again. Now the brakes work like new.
 
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