Front master cylinder question

I purchased a modified master cylinder from Jim and British Bike Connection and I am having trouble getting it to bleed.
I have followed the instructions to the T. The instructions say to bleed the line from the caliper into the master cylinder using a syringe that is provided.
You open the bleed port and force brake fluid into the caliper and back up into the master cylinder. I have done this and the reservoir is about 1/2 full. When I pull the lever nothing, no pressure. I rebuilt the caliper while waiting for the master cylinder and the line is steel braded. The only thing I can think of it that a piston puck is somehow cocked but that is just a thought.
Any ideas?

John in Texas

N0rt0nelectr@ said:

I have followed the instructions to the T.

Click to expand...

Did that include the following?:
http://www.oldbritts.com/14_061939.html

While holding the master cylinder vertically in one hand, slowly begin to inject brake fluid into the caliper with the other hand. As you inject the fluid, rotate the upper end of the master cylinder in a circle. Holding the master cylinder vertically and rotating the upper end in a circle which injecting the brake fluid into the caliper insures that all air bubble will be forced out of the line and into the reservoir.

Click to expand...

L.A.B. said:

N0rt0nelectr@ said:

I have followed the instructions to the T.

Click to expand...

Did that include the following?:
http://www.oldbritts.com/14_061939.html

While holding the master cylinder vertically in one hand, slowly begin to inject brake fluid into the caliper with the other hand. As you inject the fluid, rotate the upper end of the master cylinder in a circle. Holding the master cylinder vertically and rotating the upper end in a circle which injecting the brake fluid into the caliper insures that all air bubble will be forced out of the line and into the reservoir.

Click to expand...

Click to expand...

No, the instructions didn't say that and to be honest that sounds a bit silly. How on earth do you hold the master cylinder vertical, pump brake fluid into the caliper and rotate the master cylinder while trying to close the bleeder valve?

N0rt0nelectr@ said:

No, the instructions didn't say that and to be honest that sounds a bit silly. How on earth do you hold the master cylinder vertical, pump brake fluid into the caliper and rotate the master cylinder while trying to close the bleeder valve?

Click to expand...

Rotate the master cylinder as you operate the syringe. When the syringe is nearly empty, stop pumping and close the bleed valve (repeat as necessary).

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, set the master cylinder on the rages placed across the handlebars and remove the syringe with the vinyl tube still attached. Reload the syringe and repeat the above operation to insure all bubbles have been displaced.

Click to expand...

Having just re-bled mine I can add that after filling the syringe turn it straight up and tap it fairly hard to get every bubble out of it and then clear it like you were about to give an injection to a person. Attach the syringe to the bleeder whilst expelling a bit of fluid so as not to induce any air into the system. Hold the syringe plunger up so that if there's still any air it will remain in the syringe since you will stop before fully pushing the plunger.

Empty the reservoir, install the cap and do exactly as LAB says while injecting fluid.

I use some 1/8" ID fuel hose to extend my reach. It's sold in Home Depot for lawn mower engines, a good sized roll for six bucks.

This is a common problem... Pull the lever in and Zip tie or tie it in that position and leave it over night.. It will be good in the morning. This is a common thing... I've tried a million ways to get the air out and always have to just tie it closed overnight & all is well...good luck, Glenn T. Suneson

Or get a vacuum brake bleeder. Works every time.

I find that tying the lever back is only a temporary fix. What I think happens is that the air is forced into solution with or entrained in the liquid. Once the pressure is released the air slowly comes out of solution and the spongy feel is back.

Some reading on the subject revealed that bulk fluid is stored with a slight vacuum both to keep moisture and air out.

When servicing airplane wet compasses the entire unit is placed in a vacuum chamber and when you reduce the pressure or apply the vacuum you see bubbles come right out of the fluid. After a short time it stops and you can seal it up. If you don't use the vacuum chamber a small bubble appears in the compass shortly after sealing.

Bleeding as described above really keeps a good feel for quite some time.

Well I am going to go back to square one, drain out all the fluid and give it another go.
I will let you all know how it goes later today.

John in Texas

N0rt0nelectr@ said:

Well I am going to go back to square one, drain out all the fluid and give it another go.
I will let you all know how it goes later today.

John in Texas

Click to expand...

Good luck, we're all counting on you.

I tried my vacuum bleeder, which works well on cars, but had no success. The sleeved MC seems to trap air and the only way to get it out that works for me and apparently others, is the method described above of removing it from the bars and standing it up.

I just sleeved mine yesterday and will be bleeding it today using a vac pump.
I really hope all goes well for both of us. I need to ride.

I don't think it's the MC that traps the air. It's the caliper that has a little place in the path of fluid that air gets trapped in. I've had stock MC's do it, sleeved ones do it and Brembo ones from Colorado Norton Works do it.. I really thought the Brembo would not have this trouble but it did. The common denominator is the stock Norton caliper. Ive never had this trouble bleeding any other brake system on cars or bikes... As JohnNH says, it may not be perfect but it does get pressure to the MC and I've never had it get spongy again.. It's time for me to change my fluids so I'll be trying to get it as perfect as possible this time.

gtsun said:

I don't think it's the MC that traps the air. It's the caliper that has a little place in the path of fluid that air gets trapped in. I've had stock MC's do it, sleeved ones do it and Brembo ones from Colorado Norton Works do it.. I really thought the Brembo would not have this trouble but it did. The common denominator is the stock Norton caliper. Ive never had this trouble bleeding any other brake system on cars or bikes... As JohnNH says, it may not be perfect but it does get pressure to the MC and I've never had it get spongy again.. It's time for me to change my fluids so I'll be trying to get it as perfect as possible this time.

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I've only had trouble with the sleeved MC, never with the unmodified one. The procedure described in Old Brits and referenced above would seem to indicate its the MC. Detaching it from the switch gear and holding it vertical and moving in a circle to get the air bubble backs that up.

Here it is again in it's entirety:

BLEEDING THE NEW BRAKE ASSEMBLY
NOTE: PUMPING” WILL NOT BLEED YOUR NEW BRAKE SYSTEM.

Before attaching the master cylinder to the handlebar, bleed the brake system. Start by draping a few rags across the valley between the handlebars and the headlight. Attach the reservoir cap and gasket to the reservoir. Slip a ¼” 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 unit the syringe is full. Using the syringe, deposit a little brake fluid at the opening of the bleed valve. Depositing the little brake fluid at the bleed valve opening causes a meniscus to form over the bleed valve opening. This meniscus or bubble of brake fluid displaces any air at the opening of the bleed valve. Displacing air at the opening prevents any air bubbles from being injected when the bleed valve is opened. This is especially important if additional bleeding is required. 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. While holding the master cylinder vertically in one hand, slowly begin to inject brake fluid into the caliper with the other hand. As you inject the fluid, rotate the upper end of the master cylinder in a circle. Holding the master cylinder vertically and rotating the upper end in a circle which injecting the brake fluid into the caliper insures that all air bubble will be forced out of the line and into the reservoir. 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, set the master cylinder on the rages placed across the handlebars and 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 12 cubic 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.

BTW, I use a 60CC syringe as there's less chance of injecting any air and it's a one shot deal.

N0rt0nelectr@ said:

Well I am going to go back to square one, drain out all the fluid and give it another go.
I will let you all know how it goes later today.

John in Texas

Click to expand...

Well I drained the whole system. Even removed the caliper as I thought one of the pucks was jammed. Reinstalled everything and now it won't take any brake fluid thru the bleed valve. I even took the steel line from the hose to the caliper off and tried to force brake fluid in to no avail so I am going yet again take the caliper off and check for any blockage but the design is so simple I don't think that there is. I do have a couple of extra calipers that I am going to pull apart and see what condition they are in, can't hurt.

Think I will order a set of SS pucks and a new seal kit. Do I think that will solve my problem, no, but it is a good upgrade.

I do think the solution is something simple just got to work it out.

John in Texas

gtsun said:

This is a common problem... Pull the lever in and Zip tie or tie it in that position and leave it over night.. It will be good in the morning. This is a common thing... I've tried a million ways to get the air out and always have to just tie it closed overnight & all is well...good luck, Glenn T. Suneson

Click to expand...

Too right gtsun, like magic.

Dave

Hi:

I just rebuilt both of my master cylinders and both of my calipers, and I too, had trouble bleeding the calipers. I used the master cylinder to push the fluid in while I opened the bleed valve. What I noticed was that the drilled hole from the bleeder valve to the rear chamber was mighty small. For the air to get out, hydraulic must go in to take it's place and there doesn't seem to be enough room in that small diameter hole for both things to happen at the same time. The next time (if ever) I take my calipers apart, I'm going to open that little hole up some. Also, I believe that the stock Lockheed calipers are all the same, (to reduce production costs) whether they are on a 75 or an earlier model. I sure they were designed for the earlier models, to be mounted behind the right fork leg. On the 75 front and rear they are mounted differently, and the end of that little drilled hole is NOT at the top of the rear chamber. The air can't get out because it doesn't have access to the hole. I removed the calipers and oriented them as if they were on a 74, and was successful in bleeding them.

N0rt0nelectr@ said:

N0rt0nelectr@ said:

Well I am going to go back to square one, drain out all the fluid and give it another go.
I will let you all know how it goes later today.

John in Texas

Click to expand...

Well I drained the whole system. Even removed the caliper as I thought one of the pucks was jammed. Reinstalled everything and now it won't take any brake fluid thru the bleed valve. I even took the steel line from the hose to the caliper off and tried to force brake fluid in to no avail so I am going yet again take the caliper off and check for any blockage but the design is so simple I don't think that there is. I do have a couple of extra calipers that I am going to pull apart and see what condition they are in, can't hurt.

Think I will order a set of SS pucks and a new seal kit. Do I think that will solve my problem, no, but it is a good upgrade.

I do think the solution is something simple just got to work it out.

John in Texas

Click to expand...

Well one of the pucks or pistons was stuck, good thing I have a spare. Now it is taking fluid. Used a bungee cord to hang the master cylinder from the bars.
Put 2 syringes full of brake fluid into the caliper but with the caliper being empty it needs to be 3 1/2 syringes full. But you can't tell with the master cylinder at 90 degrees. I think tall951guy is right about the hole sizes when I operate the lever I see no air bubbles like you do with the original master cylinder. I can feel a little resistance at the lever which is better than I had but not enough.
I have borrowed a vacuum brake bleed tool from a neighbor and will give that a try.
If I wasn't already bald I would be pulling my hair out!
John in Texas

I just did mine using the Madass kit. I used a vac pump and believe it or not, I used one of those back massagers to help push out the air.
Worked like a charm. I had it done in about 20 minutes. What a difference this kit makes.
Use the vacuum tool and maybe a rubber mallet if a vibrator isn't handy.
I went thru about half a small bottle of fluid.

N0rt0nelectr@ said:

Used a bungee cord to hang the master cylinder from the bars.

Click to expand...

Simply "hanging" the master cylinder probably won't do it because air has to be "worked" out in a certain way as detailed in the instructions.

"While holding the master cylinder vertically in one hand, slowly begin to inject brake fluid into the caliper with the other hand. As you inject the fluid, rotate the upper end of the master cylinder in a circle. Holding the master cylinder vertically and rotating the upper end in a circle which injecting the brake fluid into the caliper insures that all air bubble will be forced out of the line and into the reservoir."

N0rt0nelectr@ said:

I think tall951guy is right about the hole sizes when I operate the lever I see no air bubbles like you do with the original master cylinder.

Click to expand...

I believe tall951guy is referring to the drillings in the caliper, however, the reason you probably won't see many (if any) air bubbles rising in the reservoir as you would normally expect when the master cylinder is attached to the handlebar is because the drillings in the sleeve don't always line up with those of the original master cylinder which can leave an air pocket trapped in the cylinder when in the normal operating position and why it's necessary to guide the trapped air out of the sleeve by holding the master cylinder in a vertical (or just off vertical) position and rotating in a circular motion as you inject the fluid.
All this is assuming the master cylinder piston is retracting far enough to uncover the vent drilling in the sleeve.