Front master cylinder question

I have rebuilt a lot of calipers and masters. I noticed early on during final assembly that if you push the inner piston too deep into the bore that you may actually be sealing the transfer port. Before I commence hydraulic bleeding and before I attach the brake line I give the caliper a shot of compressed air, while it is mounted and populated with pucks. To check that the pistons are moving I get the wheel moving at good speed by hand and hit the caliper with air, the wheel should stop instantly. Once I am satisfied that both pistons are moving then I bleed the system hydraulically according to the protocol(s) listed above.

These are the instructions that I got with the master cylinder.
Bleeding the Brake Assembly
If the brake assembly is to be bled from the top down (not recommended) add brake fluid to the reservoir prior to bleeding. The brake may be bled with the use of a vacuum bleeder or by the more traditional method of repeatedly actuating the brake lever while the bleed valve is open and letting the lever return with the bleed valve closed. The most efficient method: fill the system from the bottom using the syringe provided. No brake fluid is required in the reservoir prior to bleeding as the reservoir is filled from the bottom up. Make sure the reservoir cap and seal are in place as the hole at the bottom of the reservoir has a tendency to squirt fluid. slip a 1/4" box wrench over the bleed valve of the caliper. Attach the short length of vinyl tube (found inside the syringe housing) to the end of the syringe (provided). Draw fresh brake fluid into the syringe until the syringe is full. Force the open end of the vinyl tube over the bleed valve. Make sure there are no air bubbles present at the open end of the vinyl tube. If air bubbles are present, remove the syringe with the vinyl tube attached, squirt a little fluid out of the syringe and then reattach the syringe and tube. Open the bleed valve slightly. Slowly inject brake fluid into the caliper. Do not fully depress the plunger of the syringe. Stopping the plunger early will prevent injecting the always-present air at the end of the plunger. Leaving a little fluid in the syringe insures against injecting air bubbles into the caliper housing. When almost all the fluid is gone from the syringe, close the bleed valve. Remove the syringe with the vinyl tube still attached. Reload the syringe and repeat the above operation to insure all bubbles have been displaced. The syringe holds 12cubic centimeters of fluid. The reservoir will comfortably hold 24 cubic centimeters. If it becomes necessary to bleed beyond two full syringes, some of the fluid may need to be removed from the reservoir. The syringe may also be used to capture brake fluid at the bleed valve if the aforementioned traditional bleed method is used.
Regardless of which of the bleeding methods is used, when the brake handle "firms up" set the bike on the side stand or lean it to the left and turn the handlebars to the to the extreme left. With the brake cylinder in this "up hill" position, the last remaining bubbles will have risen to the reservoir port and will be ejected with several slow and deliberate actuation's of the brake lever. The lever should be actuated slowly to about half way to the handlebar and then release slowly. Never pump the lever fast this action only moves the bubbles up and down the line. Remember you are trying to entice the last few bubbles from the system. At completion: test the brake, if it feels spongy or the handle travel is excessive, repeat the bleeding procedure. When bleeding is complete add fluid to the reservoir as required, then replace the and tighten the reservoir cap. Test the brake prior to sliding the rubber sleeve up over the end of the exit ports.

This is what I got! No holding the master cylinder vertical no turning nothing.

I have tried to contact tech support but as of now haven't received a return call. To say that I am a bit PO would be an understatement.
When I work the brake lever I don't see any bubbles in the reservoir which makes me think the master cylinder might be defective. Again, I am waiting a return call from tech support. So much for me going riding this weekend!

Sorry to vent but this shouldn't be this hard. I have rebuilt many master cylinders and calipers and have never had this much grief. Why do they make it so much harder than the OE system?

John in Texas

Try this:

Put the bike on the side stand.
Turn the bars all the way to the left.

This should have the master cylinder inclined to the left. This allows air bubbles to travel up into the MC.

Leave it half an hour.

ENSURE THE MASTER CYLINDER IS NOT TOO FULL BEFORE REMOVING CAP.
If it is full, return the bike upright before removing cap take out some fluid until the level is low enough that the bike can be leant over on on the side stand again.


Take off the MC cap carefully ensuring you don''t spill any fluid and gently move the brake lever back and forth GENTLY .

You should see bubbles coming up in the MC.

Continue until no more air comes out.

The crucial bit of this is that the master cylinder must be the highest point of the system and it must be leant over so air will travel up into the reservoir. Often when a MC is mounted on the bars, the highest point of the system is the elbow or banjo on the end of the MC and this is where air accumulates.

N0rt0nelectr@ said:

These are the instructions that I got with the master cylinder.
Bleeding the Brake Assembly..................

This is what I got! No holding the master cylinder vertical no turning nothing.

Click to expand...

Which doesn't work, does it? And why two people have suggested you follow the Old Britts instructions.

N0rt0nelectr@ said:

When I work the brake lever I don't see any bubbles in the reservoir....

Click to expand...

I already suggested the probable cause, that the holes in the sleeve often don't line up with the holes in the master cylinder, so air can become trapped inside the sleeve unless the cylinder is rotated as it is bled, but it's also important to make sure the brake lever isn't preventing the piston from fully retracting.

pommie john said:

Try this:

Put the bike on the side stand.
Turn the bars all the way to the left.

This should have the master cylinder inclined to the left. This allows air bubbles to travel up into the MC........

Click to expand...

Yes, fine, when bleeding a standard master cylinder, however, it won't always work with a sleeved cylinder for the reasons stated above.

The Madass sleeve is not drilled until after its inserted, so the holes are always in line with the original holes, so less risk of a difficult bleed.

I spent most of yesterday pushing fluid through the caliper drawing fluid from the MC and doing it again and again.
I even watched youtube videos on how to do the reverse bleed though not on a Norton. Went out and tried it again. With the same results.
I even removed the lever and put on a spare which was exactly like the old one just in case.
Still waiting for a reply from Tech support.

I am going to vent here.
The idea that to bleed the master cylinder you have to hop on one leg while rubbing your belly and patting yourself on the head is just wrong!
It should be as simple or simpler as the original set up, not harder.

John in Texas

I would suggest that you not draw the fluid out of the MC unless you can transfer it to a clean, sealable container so that air can settle out. I draw it from the new bottle of fluid, then point the syringe straight up an hit it with a screwdriver. You can see the tiny bubbles work their way up and out. Clear the last with a small movement of the plunger, invert it, attach to the bleeder whilst expelling a bit of fluid, open the bleeder, hold the MC in one hand whilst pushing the plunger in fairly rapidly moving the MC with the other hand so that bubble of air that's so frustrating can find its way out.

Do you have the MC off the switch gear and standing straight with the lever pointing at the sky? The idea is to have a straight line from the caliper to the reservoir.

With a 60cc syringe and a longer hose it's a one shot deal. I was able to do it with the small syringe and short hose supplied but it took several attempts. I have no qualms now opening the system as I know I can bleed it fairly quickly.

It can be a frustrating task, I know. My first attempts before reading and following the instructions resulted in failure. I've bled countless brake systems but only ever been stymied by this one.

Yes order in the SS pistons and seal kit. The stock pistons rust-up and can get stuck or maybe rust has entered or blocked a flow hole too. Or old brake fluid can go crusty and block holes or compromise seals. Use a penetrant and force to open up the end plug (you can make the special tool yourself) and knock out rusty old pistons by whacking on a chunk of wood (caliper can take it). Clean meticulously. BTW , 06-2185S/S is one good looking Stainless end plug instead of the rust prone original. :wink:

I too am having difficulties getting pressure on the sleeved Norton M/C. I have used the syringe and filled it from the caliper, as well as 2 different vacuum bleeders. No joy. I have bled 100's of motorcycle calipers in the past but this one has been a challenge. I put it aside for a while and tackled a Brembo that I got from CNW, on another Norton. The Brembo didn't bleed well either...I was starting to get a complex. Many older BMW's in their manuals ask you to remove the caliper and shim the pads when you bleed the system. I did this on the Brembo, and lo and behold I got some pressure on the lever. I re-bled it and got more pressure, then I installed it and had a great functioning brake. The Brembo is a very nice addition!
On both of these brake jobs all the calipers were dismantled, checked out, cleaned, and had new pistons and new seals installed.
I haven't gone back to the sleeved M/C, but I will soon, and will use the shim method. Please keep us posted on your progress

See my previous posting here, it may be of some help..

brake-calipers-t26832.html

(Apologies for using the word "Once" more than err, once in that).

I have a sleeved M/C and found no issues bleeding it after reassembly and with everything in place.

These are the steps I followed on my MK2a (MK3's may be slightly more challenging):
1) Cover all your paintwork with towels, and wrap an old flannel around the master cylinder.
2) Make sure both pistons are as far back as they will go, (this reduces the amount of air in the system to start with, ((and will not block the ports)).
3) Open the bleed nipple max one turn, and attach your bleed tube which has it's other end immersed in clean brake fluid in a jar.
4) Fill up the master cylinder, then just holding the ball end of the lever between thumb and forefinger use very short and fast "pulses" on the lever watch and as air begins to rise out of the intake & bypass ports. Obviously keep topping up the fluid.This stage may take 5 - 15 minutes, but eventually air will stop coming out, and you will start to see spurts coming up through the fluid as the master cylinder is purged, and begin to feel a bit of pressure building up. At this stage you may also see some air bubbling up in the jar
5) Start using longer strokes on the lever in order to move more fluid down the hose (topping up all the time).
6) When you see air bubbling up in the jar, depress the lever all the way, hold, then close the nipple, let the lever out, open the nipple, depress the lever, repeat process until the lever starts to firm up.
7) Once you have as much air from the system as you think you can get, pump the brake lever until it's at it's firmest, hold it there then use a ratchet luggage strap or cable tie to hold it under pressure.
8) Come back in 24 hours to a lovely firm lever.


Hope this helps,

Cheers,

cliffa

I finally got a reply from tech support yesterday but haven't had time to do as he said but I will relate his instructions to you.
First, I shouldn't have rebuilt the caliper until after fitting the new master cylinder. As he explained it and other have mentioned air get trapped in the caliper and can be a pain to get out. I am getting SS pistons and a new seal kit to rebuild the caliper once I have this sorted out.
He recommended that I remove the MC and disconnect the caliper, force fluid into the caliper first then continue working my way up as I connect the short steel pipe force more fluid, hose more fluid. When I have fluid coming out of the SS hose reattach the MC. He says that at this point the only thing that hasn't been bled will be the MC. Right now the bike is on my lift so I will get it off so I can set it on its side stand when I get to this point.
Instead of threading the hose into the MC I will have to thread the MC onto the hose. He mentioned that I might remove the lever as this might be holding things open and making it hard to bleed. I have to wonder about that and why it would make a difference while bleeding but not later, but I will try that too.
Then I will again force brake fluid into the caliper and back up into the MC. Set the bike on its side stand and let it sit and hopefully allow the last of the trapped air work its way out on the MC. Re fit the lever give it a try and report back on my progress.
After all of this I hope the news is good. I do think I will go into town and get a larger syringe before I start.

John in Texas

N0rt0nelectr@ said:

He mentioned that I might remove the lever as this might be holding things open and making it hard to bleed. I have to wonder about that and why it would make a difference while bleeding but not later,

Click to expand...

It certainly can cause problems later.
If the M/C piston does not retract sufficiently to uncover the vent port then a build-up of pressure within the system can cause the brake to drag or even lock on under certain circumstances and why I already mentioned about making sure the lever wasn't preventing the master cylinder piston from returning to the fully 'off' position.

N0rt0nelectr@ said:

I do think I will go into town and get a larger syringe before I start.

John in Texas

Click to expand...

If you have a Home Depot and if it's like mine, in the plumbing section they have 1/8" ID tubing. It's sized for small engines and works perfectly on the end of the syringe. The 1" piece supplied is a PITA.

If they don't have it I imagine a small engine shop or lawn mower dealer will.

Take a 1mm drill bit and by hand see if it clears the hole, after taking the piston out first, and do the same with the 3mm hole.
If all is clear put the piston assy back in and see if you can see the seals moving past the hole when fully retracted. That way you'll know it's clearing the vent.
Then move on to bleeding with a vac pump.
Like I said I did mine in about 20 minutes.
Roadscholar's suggestion was a good one.
Or you could just wave some chicken feet over it while talking in tongues.

I've dealt with several hard to bleed new master cylinders through the years. Then, I bought a Mityvac (the MV8000), I realized that doing it the hard old-fashioned pumping method wasted a lot of time. A $30-35 tool that now is a must have.

Just finished up bleeding my stock MK111 rear brake ,( caliper rebuild with SS parts ,a seal kit too) and by using the syringe method it took about 10 minutes. Easy peasy. Took 2 full fills of the syringe. :shock:

Brithit said:

I've dealt with several hard to bleed new master cylinders through the years. Then, I bought a Mityvac (the MV8000), I realized that doing it the hard old-fashioned pumping method wasted a lot of time. A $30-35 tool that now is a must have.

Click to expand...

I have that exact tool and love it. However, it was defeated by the sleeved MC and only syringe worked.

Got back from the Western Slope Norton Riders get together in Dolores Colorado. I hauled my 58 Domi 88 there and had a good time. Got back to work on the brake issue I was having with my 74 Commando.
Did as so many of you advised and got the bike off the lift and onto its side stand. I got a bigger syringe than the one supplied and bled the brake. With it on the side stand it bled and is now functioning. YES!!!
Thank you all for your input and advise.
John in Texas