Bleeding brake systems

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bigstu

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Jan 2, 2009
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Can anyone give me advice on bleeding brakes.
I am setting up a master cylinder of 11mm piston diameter on the front end of my 850, which is running with an RGM big disc and Grimeca twin pot caliper.
I have pumped the piston and connected a tube to the bleed nipple at the caliper, running down into a glass jar with some fluid in. The tube fills with brake fluid up to the point where it turns downwards towards the glass jar, when I pump it just runs away down towards the jar. The system still allows the lever to touch the bars without too much resistance.
Has anyone got a good method of bleeding I don't know about. I always seem to struggle here...
Stu
 
Pump the brake with the bleeder valve closed. Then hold the brake on and crack the bleeder valve. If air bubles escape, close the bleeder and release the brake handle. Pump again and repeat until no bubbles escape when you crack the bleeder. If you still have no brake or a spongy feel, you can remove the master cylinder from the handlebar and raise it until there is no bend in the fluid line and pump again. Be careful not to spill brake fluid on the paint! Sometimes getting that last bit of air out of the line can be frustrating.
 
Some people prefer an "up bleed" method. Using a plastic syringe filled with brake fluid, inject it into the caliper bleed nipple slowly and force the fluid (and bubbles) up toward the MC.
 
maylar said:
Some people prefer an "up bleed" method. Using a plastic syringe filled with brake fluid, inject it into the caliper bleed nipple slowly and force the fluid (and bubbles) up toward the MC.
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This is how I've done it for years on mountain bikes with disc brakes. It works well.

Syringes are a great tool to have around, especially for bleeding brakes, measuring and injecting fork oil ect.
 
The hand-operated brake bleeding pump kits are invaluable.

You can use both the pressure and vacuum features to ensure ultimate success.
 
Some people prefer an "up bleed" method. Using a plastic syringe filled with brake fluid, inject it into the caliper bleed nipple slowly and force the fluid (and bubbles) up toward the MC.
Click to expand...

When using this method make certain that you have a tight sealing hose on the end of the syringe and teflon or other sealer on the threads of the bleed nipple. Don't use too much pressure or you can blow the tubing off the syringe or bleeder making quite a mess. DAMHIK!!
 
I made a power bleeder from a small weed sprayer. It does need a master cylinder reservoir cover with a hose nipple. It worked great on the BMW ABS brake. In fact, they must be bleed that way. I've yet to try it on my 11mm master and Grimeca 2P caliper for my Norton.
 
JimC
I got an 1mm master cyl for £10 off a mate..as you suggested...think its a Lockheed...it says 'ap' on it..this is what I am trying to sort.
Handle still pulls back to the bars so far....
Stu
 
I assume you meant 11mm. You stated you are using a Grimeca 2P caliper. This will work great. I have that exact same setup. You may have air in the line. If not, maybe the £10 master cylinder needs some work. If the seal is shot the lever will go to the handlebar without building any pressure.
 
11mm yes.
I can't see any leaks, it must be air in there but I can't seem to get rid of it. Must have pushed half a can of dot4 through it last night..
Stu
 
You won't see any leak if the m/c seal is shot. Fluid will pass by it, but still be contained within the m/c.
 
JimC
Bugger, coz I don't know what the thing is to buy spares.
If I blank off the line to the caliper it should be hard as a rock if good and still soft if bad....yes?
Stu
 
bigstu said:
Bugger, coz I don't know what the thing is to buy spares.
Click to expand...

List of UK AP parts distributors: http://www.apracing.com/info/distributor.asp (Andover Norton is one)




bigstu said:
If I blank off the line to the caliper it should be hard as a rock if good and still soft if bad....yes?
Click to expand...

= Yes, depending on where you blank it off? If air is still trapped between the master cylinder and wherever you blank it, then could still be the same?

You could try tying the brake lever back against the handlebar and leaving it overnight ? This seems to work for many people.
 
Try cracking open the banjo bolt that holds the brake line to the m/cyl while squeezing the brake lever(cover all paintwork 1st!) because if the bolt end of the cyl is higher than the hole in the reservoir the air can't escape.
 
hi bigstu,you mentioned everything but the flexible rubber hose,i had a similar problem and it turned out to be the hose had collapsed inside
 
chris plant said:
hi bigstu,you mentioned everything but the flexible rubber hose,i had a similar problem and it turned out to be the hose had collapsed inside
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Older hoses have a tendency to delaminate, where the inner lining cracks and pulls away from the wall of the hose. Fluid pressure makes this lining flap over like a valve, and cut fluid flow. A hose like this is hard to bleed and makes for spongy or dead-feeling brake action. If the hose has any signs of cracking on the outside, this is a real possibility on the inside.
 
When I first reused this hose on rebuilding, it was blocked and I had to force the blockage free by use of the master cylinder to blow it through. It is not in great shape. I think it may have delaminated as you describe.
I will replace it with a braided hose if I can.
I have no problem bleeding the system with the other master cyl (off a Suzuki GT750), and I also have no problem with the new master cylinder if I just block off the banjo exit on the master cylinder, so it is not leaking internally.
I need to make up a flexible hose that is m10 x 1 pitch at the master cylinder and whatever the thread is that goes into the caliper (Grimeca 2 pot from RGM). Then we will try again.
I am running again with the Suzuki master cyl until then.
By the way, can you knacker your pads by contamination with brake fluid?
Stu.
 
bigstu said:
When I first reused this hose on rebuilding, it was blocked and I had to force the blockage free by use of the master cylinder to blow it through. It is not in great shape. I think it may have delaminated as you describe.
Click to expand...

Good information to know when you first described the problem. :|

By the way, can you knacker your pads by contamination with brake fluid?
Stu.
Click to expand...

About as ideal as the crappy hose. Maybe worse.
 
As far as brake fluid contamination on pads it can often be removed by washing the pad with soap and water to get rid of excess fluid and sanding until clean material shows. One time that did not work for me on porus pads but it usually does.
 
Hi JimC
Finally got the 11mm master cylinder bled with the help of another set of hands. Also used a braided hose.
Tested last night. You can pull the lever almost back to the bars at standstill if you try, just like a modern system.
On the road you need one finger to pull the bike up.
Now I need a fork brace!
Thanks Jim, if it wasn't for your advice I would have gone for 13 of 14mm piston diameter as per RGM advice.
Stu.
 
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