/7 brake woes -- frozen front brake

took the master cylinder apart and checked everything thoroughly, put it back together again. this time, it does pump fluid through...so....who knows what went wrong the first time? I didn't do anything differently...
Now to get it back on the bike and test that rebuilt caliper...

Time to start ... heavily.

Got the rebuilt caliper and master cylinder onto the bike.
Pumped 1/2 a bottle of DOT 3 through her.
Keep getting air bubbles coming out of the bleeder valve at the caliper end, and air bubbles coming up through the reservoir on the master cylinder end.
The lever feels as sloppy after the bleeding as it did before.

I can't see fluid leaking out from the master cylinder. I can't see fluid leaking out of the lines. I can't see fluid leaking out of the caliper.

So if no fluid is leaking out, how is air getting in? Is it the way I am bleeding? I tried several different methods:

1) open valve, pull lever, close valve, release lever.
2) start slowly pulling lever, open valve, keep pulling lever, close valve, release lever.
3) pump lever several times, pull lever, open valve, close valve, release lever.

Needless to say I am pretty frustrated.
Either I am bleeding wrong, or air is getting into the system somewhere...or both.

Any suggestions? Tips on how to track down an air leak? If air can get in, can't fluid get out from the same place?

nhlkats said:

So if no fluid is leaking out, how is air getting in? Is it the way I am bleeding? I tried several different methods:

1) open valve, pull lever, close valve, release lever.
2) start slowly pulling lever, open valve, keep pulling lever, close valve, release lever.
3) pump lever several times, pull lever, open valve, close valve, release lever.

Any suggestions? Tips on how to track down an air leak? If air can get in, can't fluid get out from the same place?

Click to expand...

Have you replaced the brake line?

Bill Burke said:

Have you replaced the brake line?

Click to expand...

Replaced it with a stainless steel line.

Sounds like air in the master cylinder. I recently had the same problem. If you look the MC is angled in such a way as to let air collect at the front. You need to loosen the stop light switch bolt at the front of the cylinder and gently pull in the lever until some fluid seeps out, then tighten before releasing pressure on the brake lever. Easier as a two person job, but can be done by one. You need to be very careful to prevent spraying brake fluid, also known as fast acting paint remover, everywhere.

Alternatively, if you have a steep driveway, try pointing it down hill and pumping the brake lever.

Ccolwell's advice is good imo. Do you have a MityVac bleeder? Available at Sears for about $25. Worth it's weight in gold for this job. Potential sources of air: the pocket, as described by ccolwell, the connection of the Speigler at the m/c, the threads on the bleeder screw itself. I recently had a new Galfer SS line turn out bad because of the design of the fitting at the m/c end of the line. The hex head bottomed out on the m/c before a tight seal was obtained: air (and fluid seep under lever pressure). Replaced the line with a fitting made by Earls. In addition, I used a new bleeder screw. Be sure your Speigler is torqued tight in the m/c and lather heavy grease around the bleeder screw. With a totally empty system, like you have had at the start of this project, it can be a challenge to get at all the potential air. Once you get a decent (but not necessarily good) lever pressure, wrap a bungie around the lever and let it sit overnite. This can dissolve further bubbles out of the fluid solution.

The last couple of posts have hinted at "bleeding the master cylinder". The standard way to do this is get a short piece of brake tubing with a fitting and screw it into the m/c outlet. Then bend the rest around to make a loop into the m/c reservoir. Submerge the end of the tubing in the m/c fluid and pump away until you get the air out.

Question 1] In regards to bleeding the M.C. using the Clymer's method of thumb over the brake line outlet, pump the lever until pressure builds, release (letting fluid and air escape), rinse repeat, then "quickly reinstall the brake line": How is that not letting air in? In other words, whats the point, if you expose the system to open air again? The brake light switch method mentioned by ccolwel probably exposes the system to less air than the Clymer method...

Question 2] Brake line adjustment at the M.C. end. German instructions that came with the rebuild kit say 1.2mm clearance of the M.C. piston (achieved by tweaking the brake line). Clymer manual says 0.25mm clearance. It makes a whole world of difference between the two. The Clymer clearance of 0.25mm feels better, but I would go even less, to about 0.1mm, or 0.05mm clearance of the piston. That way, the handle bar lever feels "right", but the piston is barely protruding beyond the M.C. housing. Am I at higher risk of snapping my brake line like this? Is this an improper way to achieve the lever feel I want? The piston seems to still have an "almost" full range of motion, in my desired feel setting. Comments and suggestions especially welcome on this topic...

BTW, thanks for all the help folks

nhlkats said:

Question 1] In regards to bleeding the M.C. using the Clymer's method of thumb over the brake line outlet, pump the lever until pressure builds, release (letting fluid and air escape), rinse repeat, then "quickly reinstall the brake line": How is that not letting air in? In other words, whats the point, if you expose the system to open air again? The brake light switch method mentioned by ccolwel probably exposes the system to less air than the Clymer method.

Click to expand...

If you are careful and maintain light pressure on the lever while loosening and tightening, you won't allow any air in. You first break it loose, 'untorque' it, as it were, so that it is finger tight. No air will get in, or brake fluid out, at this point.