Topic: AAAAUUURRGGGHH!!!!!!!!!!!! Brakes won't bleed!!!!! FIXED!

[Blaize]

So I have been in the garage going slowly insane and decided before I shoved the damn thing into traffic I would take a little time away and think things over.

 Here is the deal- Its a 74 750k. I am finishing the overwinter rebuild and in the proces a dual disc conversion. I have rebuilt the calipers (very clean inside) all new stainless lines, still using the orig metal end sections but they are clean inside. The Master cyl is (I think) from an f3-4 cb750 from the early 80's. I had it on the bike before all of this and it was working fine. But now nothing will bleed. I also replaced the bleeders with speed bleeders. I tried just cracking the speed bleeders one at a time and pumping. No dice. Tried replacing the orig bleeders and doing it the old fashioned way, Nada. Tried a mitey vac on both the orig. and new bleeders, nope (by the way you cannot pull vac thru speed bleeders). then I pulled off the master and tried an old std. round resevoir unit I had laying around, still no good.

 So after checking every damn thing I can think of the only odd thing is this- When I hold either M/C in my hand with a finger over the output wearing rubber gloves it make press (a little) on the pull stroke, and a fair amount of vac on the return stroke. And the vac will hold for over a min. so long as I keep my finger there. Should it make this vac?! seems to me pulling vac on the return stroke would be a bad thing.

 Any ideas?

[pddpimp]

I just had this same problem doing my mc. I spent 2 days trying to figure it out. The only thing that worked was to crack the bleeders with the mc cap off and let it gravity bleed. It only takes a few hours for the mc to become empty so becareful. I let it bleed for a whole day, filling it 3-4 diff. times. I was then able to pump pressure and bleed it the standard way. Give it a try, and good luck.

PS- make sure your lines are not leaking, I had that problem and didn't catch it at first.

[Blaize]

Alright, it is spending the night with three foot long hoses on the bleeder nipples hanging from the ceiling, and a full M/C. I will check/fill it in the morning and try the whole dance again tomorrow night. Any other ideas feel free to chime in.

[Magpie]

This has worked for me - tighten everything up so it's in it's normal positions, tie, bungie, or cable tie the brake lever to the handle bar so it's in it's hard braking position and leave overnight. The bubbles will work their way up to the mc and because it's pulled to the bar they will go into the mc.
Try it.
Cheers,
Cliff.

[Blaize]

Yeah thats my other problem, I have clubmans so I have to do all of this with the M/C unbolted. I may come up with another method to hold the handle back if this doesnt do it tonight, sounds like good thinking.

[FunJimmy]

Keep us posted.

I too have bleeding issues with my bike and your solutions are sounding good.

[stueveone]

Yeah, me too. I just rebuilt my front end, and for the sake of this thread, the only braking issue that I changed was the rotor. I scraped together an old one and had it cross drilled. I'm rocking stainless lines, rebuild caliper and master. The brakes were very firm before and now they are very spongy. I DID have to open the bleeder on the caliper to relieve pressure on the piston to get it back in bore to get the caliper back in. I figured that wouldn't be such a big deal, and that I'd simply bleed it and I'd be good. Not the case.
I'm going to try the over the night hard brake/handle bar suggested by Magpie. Thanks!
I'll let you know what happens.

[Blaize]

Well it sat ovenight with the cover off of the M/C and the bleeders open. Did nothing. Resevoirt still full this morning. I have wedged the handle back and gone to work, hop for better results this way

[Tim2005]

Are you sure it's a bleeding issue? So that master cylinder worked fine with 1 caliper but now you have two calipers it doesn't? That would indicate that you need a bigger master cylinder.   

[GammaFlat]

One thing I have found with bleeding problems is that very clean or new parts will get bubbles to stick inside.  To get around the problem, rap your part with the handle of a screwdriver to "un-stick" the bubbles.  I had this problem on the master cylinder of a car and went through three un-sticking cycles until I had a firm brake.  Hope this helps.

[Bido]

I had the same problem with my 78 750 Supersport after a couple of days I found that there were two holes in the master cylinder the very small one that I thought was clean was still clogged I used a super fine wire on it and that was the problem. Still took a while to get the air out but cleaning the fine hole made the difference. Good luck.

Bido

[ProTeal55]

If u guys remember I had a #$%* of a time trying to bleed the brakes when I first got my dual-discs put on my CB750. First the master I had got froma buddy was leaking air (so that didnt help). Then pretty much ALL my lines were leaking (that didnt help).

So once I got the proper lines and a new master I was in the show.
Do yourself a favor ad get a mighty vac, and suck the air outta the system (works so good)..

[mick750F]

   When I rebuilt my system a couple of years ago it took forever to bleed the system but it eventually bled using the age old technique described in the Honda Shop Manual. The system being completely dry I think, causes the bleeding process to take a long time. I also suspect that air bubbles get caught up in the splitter of the dual disc system.
 
   A word of caution from the Honda Shop Manual..."To prevent piston over travel and brake fluid seepage, keep a 20mm space to the handlebar grip when bleeding the front brake system."

   I might as well post their recommendation for bleeding...

"Pump up the system pressure with the lever/pedal until there are no air bubbles in the fluid flowing out of the reservoirs small hole (until the lever/pedal becomes hard).

Pull the brake lever back. Screw out the bleeder valve 1/2 turn, and retighten.

Note...Do not release the lever until the bleeder valve has been closed.

Release the lever gradually and wait for several seconds after it reaches the end of it's travel. Repeat the above steps until air bubbles cease to appear in the fluid flowing out of the bleeder valve.

Fill the reservoir up to the UPPER FLUID LEVEL.

Check the entire system for leaks by operating the lever."

So says Honda...Mike

[mic-57]

Did you bleed the master cylinder when you installed it? If not you should do this before moving on.
This process has allways worked for me

1.  remove the upper bake line from the spiltter
2.  put the end of the upper line into the M/C resevoir (make sure it is covered by the brake fluid)
3.  pump the brake lever until no more air bubbles come out of the hose. ( make sure to keep the fluid level abve the opening in the hose)
4.  The M/C should now be bled, when you lower the hose to reconnect it fluid should run out be sure not to let the M/C run dry.
5.  now you should be able to bleed the brakes.

[Blaize]

Jesus!!! This damn thing is making me crazy. Well when I got home from work nothing had changed. Still a full resevoir, no fluid at all in the bleeder hoses. So I pulled the M/C again, and took it apart again, and blew brake cleaner thru all of it, little hole and all, again, and upon assembly, still no go. tried the mitey vac at the caliper again, nope. shoved its hose into the output of the master cly and cant draw any from there either. Then tried mic-57's suggestion and ran clear line from the output of the m/c in a loop onto the resevoir, and nothing. So I poured some fluid into the loose end and resubmerged it, and I can pump it out, but when I release the lever it draws it right back in.

 I tried the loop method with my other m/c and got the exact same results. So I dont think either one is faulty and as I said it was all working before. Of course during all of this I got brake fluid all over the calipers and ruined the paint (for the 3rd time!!!) and I have pulled them off and apart to strip them. I am not going to bother painting them a 4th time, they will go on naked and maybe I will polish them in the future.

 And of course I am now so pissed at it all I am getting diminishing results so I have given up until tomorrow.

 The big question is, why cant I draw fluid from the m/c (either one of them) with the mitey vac. I can max the vac gauge at 30Hg but still not a drop?!?!?!

 and if nobody has any ideas on any of this, Where can I get a decent aftermarket m/c with a built in brake light sw?

[stueveone]

Ok, so I tried the overnight hard-brake-hold, and it didn't seem to help much. How much play should there be in the lever? Meaning, besides the gap between when the lever arm is all the way out and just hitting the MC piston, I still can push the lever in a little bit before the caliper engages the rotor. How much is normal? Maybe in mm? Does the piston have to have play plunging in to the bore before the caliper is engaged? A small amount, of course. But again, how much?

[Jv550]

I'm so feeling your pain - been bleeding mine for three days now. (Do all motorcycles have periods or just the girl ones? ) I'm trying the "hold the brake halfway open with electrical tape all night" method now.

[bryanj]

Yes there will be a bit of movement before the brake comes on otherwise it would drag all the time. With the lever pulled hard in there should be at least 1/2 inch gap to the throttle grip

[Blaize]

Ok So I got pissed at it and left it alone for a couple of days to calm down. I have found that one of the caliper seals it swolen so I have ordered a new pair of those, and I polished the calipers because I was sick of painting them over and over again once I got brake fluid all ovber them.

 But, I still cannot get the M/C to even bench bleed, so my problem is obvously there. Anybody know what function the little and big holes have in the resevoir so I can stare at it, understand how it is supposed to work, and with any luck figure out why, after 3 cleanings, it still doesnt. I cant pull anythiung tru it at all. I hooked my mitey vac straight up to the output and pumped away and the vac gauge went all the way around. completly airtight.

[Blaize]

Well it works!! I ended up with the following problems- Leaking banjo washers, One bad seal on a hard line (though it was minor and I found it after I had it all working) and the damn M/C is bad. I suppose the seals have swolen or somthing. Dunno for sure but the long and the short of it is the little hole never opens up to the lines. So I couldnt draw any fluid thru to the calipers. Instead I could draw air in thru all the leaking banjo washers. I have #$%*canned the modern M/C and reinstalled a year correct one I had in the shop. It works now but the lever throw is a little long and I have no brake lights on the front lever. I had wired it to the M/C switch and deleted the press. switch.
 But it is good enough to ride and I will ride it over to the bike breaker once I get the tank back from the painter and buy a better M/C with a switch in it. Thanks for all the ideas, as you can see about half of you were right.