Trouble filling/bleeding brake system

I use a different technique for every bike I've done, you'd think I'd have it solved after so many bikes. Well, I sort of do, but it's a pain. Most times I bench bleed the MC and push fluid up the line till it spills out with a syringe. Then join them quickly with lots of rags on hand, and twiddle the lever for bubbles. Seems to work best. Some MCs work with a syringe all the way up. Some don't. Some systems I've elevated the caliper above the MC with a block between the pads. Some work just normal, I put grease around the bleed screw threads, and also use a small sturdy zip tie on the clear hose attached to the bleed screw, really tight. Recently I had a lever travelling too far before engaging, bleeding didn't help, but pulling the caliper off, putting in a block that's narrower than the disc in, and pumping up and cleaning around the outside of the exposed piston fixed it. The pistons were retracting a lot when releasing the lever.
 
BrianK said:
PS, Concours, I have one of those pressure bleeders but have never found an adapter that fits the Norton reservoir. If you can point me in the right direction that would be great!
Click to expand...
The pressure kits are excellent. I have a Gunsons Eazybleed kit which makes filling & bleeding so easy it turns a hassle into a pleasure. I had to use a spare reservoir cap and adapt it for the hose fitting, as the kit didn't come with a suitable cap. I also made a larger brake fluid container so I don't have to keep such a close eye on the fluid level going down while I'm using it. Just fll it up, connect the air line from an infated tyre, open the bleed screw and watch those air bubbles come out until they're gone.
 
Tigernut said:
The pressure kits are excellent. I have a Gunsons Eazybleed kit which makes filling & bleeding so easy it turns a hassle into a pleasure. I had to use a spare reservoir cap and adapt it for the hose fitting, as the kit didn't come with a suitable cap. I also made a larger brake fluid container so I don't have to keep such a close eye on the fluid level going down while I'm using it. Just fll it up, connect the air line from an infated tyre, open the bleed screw and watch those air bubbles come out until they're gone.
Click to expand...
Are you on commission from Gunsons ??

You’ve made that sound very appealing. Bleeding brakes is something I hate !
 
From my experience modifying a factory cap doesn’t always work. A lot of times they vent to the atmosphere on the outside of the rubber gasket.
I am a fan of pressure bleeding, especially cars, because it becomes a 1 person job. Pressurize the system and just go from wheel to wheel and open the bleeder. I have a Motion system, but don’t bother filling the container. I fill the master cylinder and bleed til the level gets low, but not empty. Then I refill it, caution, don’t let it go empty or you will force air into the line.
My go to for motorcycles is still a syringe, unless it’s my yearly bleed to replace the fluid. Then I just use the lever/pedal system.
 
The way I’ve always successfully bled bike brakes is to fill the reservoir, then pull in the brake lever a tiny amount (max 1/2” to uncover the small bleed port in the master cylinder) until you see bubbles rise. Hold it there a few seconds, release then repeat. You may have to do this quite a few times until you start to feel pressure build. Once you do feel pressure you can attach a hose to the caliper nipple and bleed in the normal way.
 
Well, the pistons in the caliper are in proper orientation. The inner one is in only far enough to permit the pad to fit in, not blocking the inlet port.

I have teflon tape on the bleeder screw threads.

Got a syringe and tried to reverse bleed - just seemed to pressurize the caliper, resulting in fluid spraying out when syringe pulled out.

I had let the brake line self-prime via gravity, so the line doesn't seem obstructed.

Still can't get any pressure. No more bubbles coming out of holes in reservoir or bleed screw. Not much fluid from the latter, though. Starting to wonder if MC needs a rebuild.
 
Good point on the old hose swelling up. Usually it inhibits the flow LEAVING the caliper which means the brake wants to stay on.

I have always had a tough time getting fluid into the inboard piston. The fluid does not want to go there and it would have been better to have the bleeder at the far foreword end of the caliper. My method is to have the caliper on the bench tilted so the fluid wants to go to the inboard puck. Then, with an eye dropper, I dribble it down the bleeder hole. Next I use a thin wire down the hole to the inboard side which allows an air bubble or two to escape. Repeat several times until the air is gone. Then it works properly.
Of course there must be a little bit of room behind the puck for brake fluid in the first place.
 
BrianK said:
Well, the pistons in the caliper are in proper orientation. The inner one is in only far enough to permit the pad to fit in, not blocking the inlet port.

I have teflon tape on the bleeder screw threads.

Got a syringe and tried to reverse bleed - just seemed to pressurize the caliper, resulting in fluid spraying out when syringe pulled out.

I had let the brake line self-prime via gravity, so the line doesn't seem obstructed.

Still can't get any pressure. No more bubbles coming out of holes in reservoir or bleed screw. Not much fluid from the latter, though. Starting to wonder if MC needs a rebuild.
Click to expand...
If applying pressure from the caliper end only forces pistons out, something is certainly inhibiting flow up to the MC....obvious thing is an internally collapsed section of the hose. Easy enough to remove and test it directly. Your reverse bleed attempt makes no sense for a MC issue...there is nothing btwn the reservoir tiny ports and the cylinder bore when the lever is not pull in...so fluid should immediately flow up to reservoir and begin filling up the reservoir when reverse pressure applied.
 
Good suggestions, but....

With caliper and brake line removed, fluid injected into bleeder port flows readily through caliper, through line and out other (MC) end of line.

Attached, the MC does pump fluid out when lever pulled in.

I'm at a loss.
 
AND with line attached to MC, fluid is having a problem getting into the reservoir - seems to take what is to me excessive pressure, and its coming in through the feed hole, NOT the compensating port.

And brake fluid squirted into the ports gathers in the reservoir. That from the comp port initially was blackish (like contaminated by deteriorated rubber seals, mayhaps) but is coming out clear now.

Working on mysteries with increasing numbers of clues....
 
Last edited:
Looks like a blockage between the M/C and reservoir. That would stop you pumping fluid out of the reservoir when bleeding and prevent fluid being pushed up the system (by the syringe) into the reservoir, when reverse bleeding.
 
I think it's time to rebuild that MC, which however was modified by Fred Eaton/Old Britts - resleeved to 13mm in a way that I'm under the impression makes the rebuild "non-standard" in some way.

Can anyone educate me, including where to get an appropriate rebuild kit?

Thanks for your continuing support (and patience! - my own is wearing thin I must say.)
 
BrianK said:
I think it's time to rebuild that MC, which however was modified by Fred Eaton/Old Britts - resleeved to 13mm in a way that I'm under the impression makes the rebuild "non-standard" in some way.

Can anyone educate me, including where to get an appropriate rebuild kit?

Thanks for your continuing support (and patience! - my own is wearing thin I must say.)
Click to expand...
Brian, personally I don’t think it’s the master cylinder. As suggested earlier, with the hose disconnected from the caliper try reverse bleeding with a syringe. If you can’t get fluid through it, there must a blockage.
When you rebuilt the caliper, did you clear all the passageways?(with a drill bit for example)
 
cliffa said:
Brian, personally I don’t think it’s the master cylinder. As suggested earlier, with the hose disconnected from the caliper try reverse bleeding with a syringe. If you can’t get fluid through it, there must a blockage.
When you rebuilt the caliper, did you clear all the passageways?(with a drill bit for example)
Click to expand...
See post #31
 

Similar threads

robs ss
Bleeding brake (and clutch)
Replies
8
Views
226
Tornado
Tornado
uneasy rider
rear brake system bleed
Replies
3
Views
783
uneasy rider
uneasy rider
J
  • Locked
Trouble bleeding madass 140 master cylinder setup
2
Replies
32
Views
7,920
concours
concours
swooshdave
  • Locked
Bleeding Front Brake
2
Replies
29
Views
4,452
cjandme
C
tban52
  • Locked
Front brake bleeding help
Replies
17
Views
4,914
Matt Spencer
M
Back
Top