Bleeding the Brakes

[Gpaws1968]

So, I did a full rebuild on my front brake, I got it all assembled and now I'm starting to bleed the system and it's taking forever to get the fluid through the lines, is there a better way than pumping the lever?

1981 XS 650

 

[XSTime]

Pumping the lever does work.
Keep the master cylinder level.
Tap on it lightly with something to help the last bubbles rise out.
Be patient and feel the fluid fill the spaces.
Bleed the calipers when that feel is good

 

[Melnic]

if you have a compressor, get a vacuum bleeder from Harbor Freight.
I just finished rebuilding calipers and putting in new pads and steel braded brake line on my 82 XJ650.
Bleeding takes less than 5 minutes. with that thing, I bleed more than I have to since a bottle of brake fluid is enough to do several bikes worth and I toss it after doing one bike.

They also make pump vacuum bleeders but never used one.

 

[5twins]

I have a Mityvac vacuum pump just like this one .....

https://www.ebay.com/itm/3951868210...MI4_29zO-ihAMVlXNHAR2XUgZ0EAQYCCABEgIXAvD_BwE

It makes short work of filling an empty system. Once full, I finish the old fashioned way with a few pumps of the hand lever or foot pedal.

 

[Its been a long time]

I recently rebuilt the front brake on my 77 650 too. I was surprised how difficult it was to bleed given it has only a single piston caliper. A bit less sophisticated than above, I used a plastic syringe and a short piece of plastic tube to suck the fluid from the bleed nipple. Draw the fluid though until the bubbles are gone. Takes a few attempts but it works.

 

[Max Midnight]

IA bit less sophisticated than above, I used a plastic syringe and a short piece of plastic tube to suck the fluid from the bleed nipple. Draw the fluid though until the bubbles are gone. Takes a few attempts but it works.

A variation on the above is to reverse bleed, i.e. push the fluid back up into the reservoir. That way you are pushing the air upwards rather than trying to pull it down. Source some silicon hose for the syringe as this is flexible and gives a good seal over the bleed nipple.
You do need to keep an eye on the reservoir to make sure it doesn't overflow - some cling film over paint is a good precaution.
When done tie the lever back over night to remove any remaining air.

One other thing to do is to put a couple of wraps of PTFE tape around the bleed nipple thread to ensure you aren't pulling in air. via the threads.

 

[Its been a long time]

A variation on the above is to reverse bleed, i.e. push the fluid back up into the reservoir. That way you are pushing the air upwards rather than trying to pull it down. Source some silicon hose for the syringe as this is flexible and gives a good seal over the bleed nipple.
You do need to keep an eye on the reservoir to make sure it doesn't overflow - some cling film over paint is a good precaution.
When done tie the lever back over night to remove any remaining air.

One other thing to do is to put a couple of wraps of PTFE tape around the bleed nipple thread to ensure you aren't pulling in air. via the threads.

Yes. I actually filled the brake caliper with fluid and pressed the caliper piston in with a G clamp. Went in very easily. By pushing the fluid up into the master cylinder, I was hoping it would then need minimum bleeding. The system filling worked just fine, minimum to no fluid spillage. But the system did then need bleeding properly. Hence my using the syringe to suck at the bleed nipple. I have found that putting some grease on the nipple thread, then only loosening it just enough to suck fluid is a pretty good way to not draw air down via the nipple threads.

 

[bosco659]

Yes. I actually filled the brake caliper with fluid and pressed the caliper piston in with a G clamp. Went in very easily. By pushing the fluid up into the master cylinder, I was hoping it would then need minimum bleeding. The system filling worked just fine, minimum to no fluid spillage. But the system did then need bleeding properly. Hence my using the syringe to suck at the bleed nipple. I have found that putting some grease on the nipple thread, then only loosening it just enough to suck fluid is a pretty good way to not draw air down via the nipple threads.

I’ve also used a bit of Teflon tape on the bleeder nipple threads to minimize air intrusion.

 

[Its been a long time]

Yes. I actually filled the brake caliper with fluid and pressed the caliper piston in with a G clamp. Went in very easily. By pushing the fluid up into the master cylinder, I was hoping it would then need minimum bleeding. The system filling worked just fine, minimum to no fluid spillage. But the system did then need bleeding properly. Hence my using the syringe to suck at the bleed nipple. I have found that putting some grease on the nipple thread, then only loosening it just enough to suck fluid is a pretty good way to not draw air down via the nipple threads.

Spoke to soon. Removed the front brake when I was having a new tyre fitted (pushed the caliper piston back in fully to give more clearance). After refitting the wheel, the front master cylinder has no pressure. Zero.

So, as per this thread from earlier ( https://www.xs650.com/threads/faulty-master-cylinder.66098/post-835895 ) here's what I have tried. I am completely out of ideas and I'm amazed such a simple front brake has become impossible to bleed.

I have - Emptied and refilled the front brake (actually tried it twice) by reverse filling with a syringe through the bleed nipple. If fills easily and fluid runs freely if the nipple is left loose.

Attach a hand vacuum bleeder and ensure a solid vacuum is held. As a precaution I have put a generous wind of ptfe tape on the bleed nipple thread.

Crack the nipple and flow fluid under vacuum. Top up the master cylinder as required. Fluid runs free of air under vacuum.

Close the nipple fully. There's zero resistance at the brake lever. Nothing.

I have tried this start to finish 2x and used about 1 litre of fluid.

I'm struggling to say what on earth has happened between removing the front wheel and refitting it. But I have zero front brake.

I'm out of ideas. What's the likelihood that the new EMGO master cylinder is faulty?

 

[Jim]

I'm out of ideas. What's the likelihood that the new EMGO master cylinder is faulty?

Sounds like that's the problem from your description of what you've done and what it does.

EMGO stuff appears to be a bit hit-n-miss. Some stuff is OK... some not so good.
I bought a set of EMGO Commando mufflers for my bike. The baffle in the left one broke loose in less than a thousand miles of use. The rattle is very irritating.
I'm VERY Leery of their stuff now.

 

[Its been a long time]

Sounds like that's the problem from your description of what you've done and what it does.

EMGO stuff appears to be a bit hit-n-miss. Some stuff is OK... some not so good.
I bought a set of EMGO Commando mufflers for my bike. The baffle in the left one broke loose in less than a thousand miles of use. The rattle is very irritating.
I'm VERY Leery of their stuff now.

Thanks. I think so too.

The seller does have a good reputation in the UK and I do actually believe them when they say they have sold hundreds and not had one return.

I am going to try vacuum bleeding one more time tomorrow. If it's still the same result, I don't think I have much option except returning the master cylinder. Seller has agreed and will give me a returns number if I decide to return it.

 

[Jim]

Thanks. I think so too.

The seller does have a good reputation in the UK and I do actually believe them when they say they have sold hundreds and not had one return.

I am going to try vacuum bleeding one more time tomorrow. If it's still the same result, I don't think I have much option except returning the master cylinder. Seller has agreed and will give me a returns number if I decide to return it.

I think the only other thing I'd dry is cap the outlet or the line and see if it'll build up pressure when you take the caliper out of the equation.
If it still won't build up pressure, then there's no doubt the master's faulty.

Maybe disconnect at the caliper and block the line/banjo fitting with a 10mm bolt and nut.

 

[Its been a long time]

I think the only other thing I'd dry is cap the outlet or the line and see if it'll build up pressure when you take the caliper out of the equation.
If it still won't build up pressure, then there's no doubt the master's faulty.

Maybe disconnect at the caliper and block the line/banjo fitting with a 10mm bolt and nut.

Good idea. I'll have one more try tomorrow, then if I fail again, that'll be what I do before removing the master cylinder. Thanks for that suggestion, I hadn't thought of that.

 

[JOHNDADDY]

On cars I've owned when the master is going/gone, a fast stab or a few at the brake will give pressure
but it you ease off it will fall through. A slow push will simply fall through.
I'd try brake lever a few times as fast you can and see what you get.
Might help diagnose without having to take anything apart. Good luck with it.

 

[Its been a long time]

On cars I've owned when the master is going/gone, a fast stab or a few at the brake will give pressure
but it you ease off it will fall through. A slow push will simply fall through.
I'd try brake lever a few times as fast you can and see what you get.
Might help diagnose without having to take anything apart. Good luck with it.

Pulling the lever quickly or slowly makes no difference. I can get no resistance on the lever at all. I think the new master cylinder is faulty. But I'll try bleeding one more time tomorrow.

 

[5twins]

That's why I like to use old, used MC's from other Yamahas. Most are the Nissin brand and the quality is good. And all they needed was a good cleaning. The only thing I replaced were the screws in the lids, lol.

 

[Wingedwheel]

I’ve had Emgo rebuild parts that I used in an MC that would lose pressure, sometimes out of the blue. A quick pump and it would return but I was nervous that wouldn’t work one day so I just cleaned up the OEM guts in another MC I had and problem solved so yeah, I don’t trust their MC parts.