No brake pressure

David Toll

David Toll

Reliving my youth?
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OK before I get subjected to possibly warranted abuse I would like to say that I have read the 7 thousand or so threads on this topic but I would still like some advice before I dismantle the MC. Went to bleed the brakes yesterday and everything initially went according to plan. In October last year I posted a thread about how I replaced the MC with one from a Yamaha Virago. Rebuilt it entirely along with the calliper. All bright, shiny and new in the right places. New stainless brake line, new banjos, copper washers, pistons, seals and rubbers. Used the Banggood kit and it seemed to fit and function properly. Put it all back together and assumed it would be a case of filling it with fresh fluid and looking forward to a lifetime of collision avoidance.
Attempted to bleed it today and could not seem to build any significant pressure. Achieved no air coming from the bleed screw but no hardening of the brake. Took the calliper off and checked the function of the piston and state of the seal - all good. Applied air to the bleed screw and covered the ceiling with brake fluid, (careless I know). Removed the banjo at the MC and covered the hole with my thumb. Seemed to have pressure there and didn't get any bubbling to indicate air trapped in the MC. Put it all together and pumped the air out again using about 3 cylinder refills. Still limp. There were signs of leaking around the banjos but I have tightened them up and now it's all dry.
Do I strip the MC and check that I have fitted the new piston assembly correctly or do I continue pumping??
 
David,
Having bled many MC's, I'd like to offer some advice:

Be very patient with this process, as it can take quite some time.
I have never needed to use any fancy techniques.
Make sure your MC is perfectly level.
Pump the lever VERY slowly.
You might have to depress the lever a few hundred times.
Took 20 minutes of pumping a few weeks ago on my '82.
Eventually, tiny bubbles will surface in the MC.
Tap the MC gently to move the bubbles.
Consider "borrowing" your wife's vibrator :) to press against the MC to move the bubbles.
Pressure will build very gradually.
Jeff
.
.Let's all sing this one together;

.
 
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I'm my wife's vibrator Dude and I don't need batteries! Thanks for your interest and patience folks. I know this is a heavily commented topic. I wondered if there was something I was missing in the bleeding or reconstruction processes. It would appear to me that if there was no pressure buildup, there must be a leak. But then, a leak would be indicated by dripping fluid. Will try the "Modified Gary" technique.
Cheers
 
Jim said:
1+ on what Lakeview says. Have a read here David.
Click to expand...

I totally forgot about that post. The other day when I spent hours trying to bleed my front brake, I should’ve tried that. As I said then, I eventually got the system bled, but the lever still felt a little soft. Over the last few days, every time I go out into the garage, I squeeze the lever a few times and there must’ve been micro bubbles in the system that have worked their way out because now that lever is rock solid!
 
Mailman said:
I totally forgot about that post. The other day when I spent hours trying to bleed my front brake, I should’ve tried that. As I said then, I eventually got the system bled, but the lever still felt a little soft. Over the last few days, every time I go out into the garage, I squeeze the lever a few times and there must’ve been micro bubbles in the system that have worked their way out because now that lever is rock solid!
Click to expand...
OK, OK, they're tiny MICRObubbles :D;)

...but there's no song called Tiny Microbubbles.
 
YamadudeXS650C said:
OK, OK, they're tiny MICRObubbles :D;)

...but there's no song called Tiny Microbubbles.
Click to expand...
If Don Ho is a sample of your musical taste Dude....... Thank God!
Yes, there are 2 holes in the bottom of the reservoir Skull. One appears to have a ball bearing which, I assume is some type of pressure closure. The other is open. When I hooked the compressor up to the bleed nipple, a 10' stream of brake fluid was jetted across the room. Figure that hole might be clear. Went back to it again last night. 30 mins of pumping the handle and bleeding and still virtually no response. I would try Gary's trick but I can't see how air could be the problem as I have a steady "bubble less" stream coming from the nipple. Must have something wrong in the way I rebuilt the piston assembly but the Banggood kit comes with the plunger rubbers in place - I would have to put the entire assembly in back to front! Am I that stupid?...... I'll strip it down.
 
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One more question, the calliper piston doesn't seem to be moving. When I rebuilt that piece yesterday, I used assembly grease to lubricate it and it slid in nice and smooth. Should it be showing some sign of operation without handle pressure if the fluid appears airless?
 
OK. I'll pull the calliper off, remove the piston, clean off any grease, (it was a light coating in consideration of the proximity to the pads) and re-install it with a brake fluid garnish.
Jim, when I pull the handle in the piston doesn't appear to move. That's part of the reason why I gave it a touch of grease. This morning, I also appear to have a leak but I don't know if it is simply coming from the tube on the nipple. I put a small cable tie on the nipple end to see if it improved. Will pump it up and leave it for a couple of hours.
 
If you pull the piston out of the MC, make sure the seals are facing the right way. They should flare open towards the spring and line end of the MC, not the handle end .....

8TBKDbV.jpg


xRADk6x.jpg


It's not unheard of for them to come installed backwards. Then they won't flare out, seal to the bore, and push fluid when you pull the lever. In fact, I'm pretty sure the two pics above show the springs installed backwards, lol.
 
Pondering all my options before a weekend dismantle. I left the MC full and "pumped" up as much as possible overnight. In the morning there was a patch of fluid under the calliper - seemed to be coming from the bleed nipple thread which was only finger tight. As I tightened the nipple, I noticed that it "wobbled" in the thread. It was firm when tight but it wobbled alarmingly when loosened. I inspected the rear calliper and found the same thing happening. The nipples are replacements from Mikes, (or his Aussie equivalent). Is this the norm? Could the threads in the calliper be worn, (they look OK), or maybe they are the wrong bleed nipples for this model. Reaching, I know but I am trying to consider all possibilities.
 
Here in the States David, you can get the bleeder nipples at any hardware or auto parts store for next to nothing. Perhaps over there too?
 
Yes, I'll try some new ones - see if they come in different sizes. Would have thought that Mike's would have been OK. As I say, I know I'm reaching here but I'll give it a go.
Cheers Jim
 
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