Brake rebuild problems

[JIM77]

So I've rebuild the caliper and Master cylinder on my 96 cr 250 and can't get any feel what so ever. Have bled the normal way and reverse bled with a syringe. I've even pulled the master cylinder apart again thinking that I might have damaged the seals when fitting to the piston but they look fine.

I got no more bubbles when feeding the fluid in from the bottom with a syringe, but after closing the bleed nipple can get a small bubble or 2 in the bottom of the MC when pumping the leaver.

Is my MC buggered? Any ideas?

I'm using a new Hel braided line as well, if that helps.

[OverTheHill]

i woke up 'full of ideas' but think you've covered them--damn. no chance you're using another non original master of smaller size!!--maybe not. First thing i'd try [now] is block it off at the master with a bolt [fine thread i know but], loosen it to bleed a bit by pulling lever in then quickly lock bolt while it's not quite stopped moving, should only take a couple of pumps doing this to bleed it up to test the master. if that's ok then add the line & do something similar. After that, i dunno. Had a bmw at work many years ago [traffic cop one] where the pads were worn & the caliper seals were holding the pistons so tight that they were stretching with the pistons then pulling them back so far that the brake had most of a lever movement just to get them out there. Anyway, back bleeding always works if it's reluctant to start. I just use a clean oil can of fluid & pump away through the bleed nipple. Never fails to get the ball rolling to the point of bleeding it properly via the lever. Have had LTF suzuki quads where they've probably been low on fluid up top & the boot thing under the cap has followed the fluid down in the level then [trying to think] maybe dirt has sealed around the cap so the rubber thing has created a vacuum above it and pulled the wheel caliper pistons back when lever released. Something like that & was 20 years ago but--might be relevant, or not lol. Cheers & good luck.
ps, piston in master not returning fully? so can't get another mouthful. Pirate new lever not letting piston come right back etc.

[JIM77]

Your right I should have had some sort of feel by now, I tied the lever back overnight, so will see what happens with that. I think you might be onto something with the piston not returning all the way, might have a check of that.

 After doing some more reading last night. Apparently the small bubbles in the bottom of the MC when pumping the lever is pretty normal?

I used all honda parts on the caliper and moose for the MC, I compared the old MC piston with the moose one and I can't see that they are any different  the old Honda one is well worn though.

[JIM77]

Finally I have feel in brake, tying it back did the trick, although it's still spongy so will do it again.

It is leaking fluid from the bleed nipple though, any ideas for getting a better seal on the bleed nipple? The bleed nipple is new OEM.

[Mike52]

Jim.
Unbolt the master cylinder [ from the handle bar ] and tie it up to a roof rafter or something so as the hose is straight.
Leave overnight.
May help.

[pancho]

 Any motor mech. who has had bleeding problems with the old pommy Girling stuff knows the frustation. Try bleeding old series Landrover brakes. Pressure bleeding is usually effective with problem systems where you need to devise a method of applying pressure to the fluid in the master cyl. with a specialised pressure bleeder, or carefull use of compressed air through a bleeder hole. Dont splash fluid in your eyes or on paint.
 Even this doesn't get an instant result sometimes because with any method used it is possible to get the fluid aerated with fine bubbles. This is why sometimes you give up only to find that overnight the fine bubbles come to the top and bingo full pedal.(or lever)
 good luck. pancho.
 P.S. Just remembered another trick.
 Bleed it as normal, then force the piston back into the caliper. (fluid overflows out the reservoir) this forces all the aerated fluid back up to the M.C. Then SLOWLY pump and release the lever forcing fresh fluid down to the caliper pushing the caliper piston out to the disk. Keep the reservoir full all the time while pumping, and be carefull to release the lever SLOWLY after each stroke other wise air can slip back into the master cylinder past the seconderry cup.Squeeze the lever only halfway each stroke.

[JIM77]

Aerated brake fluid sounds right as the last bubbles coming out when tying the lever back are micro. What about the bleed nipple got any tricks to seal them?

 
Using the pistons to help bleed is a good idea.