Sticking Brakes

[jagarra]

The dust seals can be a PIA. They have a tendency to want to not finish seating as you work the seal into the groove. They really want to go in evenly without any cocking as that makes it not want to seat. I ended up using a ring, (old wheel bearing race) approximate same diameter as the outer edge and tapping that with a hammer to work it in.

[jimmyg]

I have everything installed and I'm bleeding the brakes. All is good, all bubbles gone, but I notice the lever has a lot of travel before engagement.

The master cylinder piston is adjusted per the 'gapping forked tool' in the stock toolkit.

This bike does not have a cable adjuster on the hand lever (1975 R90s), so the only adjustment is on the M/C.

Is there another way to achieve the 2-4mm desired free play at the handlebar lever?

Thanks,

jimmyg

[Ken in Oklahoma]

I have everything installed and I'm bleeding the brakes. All is good, all bubbles gone, but I notice the lever has a lot of travel before engagement.

The master cylinder piston is adjusted per the 'gapping forked tool' in the stock toolkit.

This bike does not have a cable adjuster on the hand lever (1975 R90s), so the only adjustment is on the M/C.

Is there another way to achieve the 2-4mm desired free play at the handlebar lever?

There is more to having the 'bubbles gone'. I didn't buy this when I first heard about it (here on Boxerworks).

When bleeding the brakes on the swinging ATE caliper setup I was never quite satisfied with the amount of play left on the lever, even after I was pretty sure I had bled the brakes as well as they could be bled.

What I now do after bleeding the brakes is to put several 'inner tube rubber bands' (cut from an old innertube) around the brake lever and the hand grip, using as many bands as you think you could possibly need. Then you do nothing and let the bike set over night. A few people had posted that this would 'finish' the bleeding process.

I was almost disgruntled when it seemed to work. How could this be? This is the theory I developed (probably not original). By 'squeezing' the lever hard you are pressurizing the master cylinder and thus the fluid in the calipers, lines, and the chamber of the master cylinder where the piston strokes. My thought is that by putting that pressure on and keeping it there, the bubbles, being air, are compressed to a smaller diameter. The smaller diameter bubbles can then more readily find their way to the master cylinder and escape into the brake fluid reservoir.

It still seems to me like that shouldn't work very well, but the few times I've tried it the results seemed good.

It is possible, I suppose, that eventually the bubbles will dissipate on their own and the brake lever will firm up. But whatever the mechanism, I am convinced that the rubber bands around the brake lever thing--works.

By the way, I never pay any attention to the forked tool. If squeezing the lever pressurizes the brake lines, and the pressure goes away when I release the lever, I'm content with that result.

Ken

[jagarra]

You will need that cable adjuster to properly adjust the lever. Good news, they are available from the dealer.

12 CABLE ADJUSTER 1 32721230876 $17.64

I would double check that number as the controls changed between the 74 and 75 model year, not sure which one I grabbed.

gg

[barryh]

I was almost disgruntled when it seemed to work. How could this be?

I had a similar feeling, again because I couldn't see the mechanism by which it should work. But it does work for me every time I try it.

As to how it works, I feel that somehow it takes the localised trapped air that's causing the soft brake lever and redistributes it throughout the entire system so that it can find it's way to the reservoir. I'm not convinced it could do that by making the bubbles smaller because given no physical obstruction smaller bubbles rise more slowly than larger ones.

I'm not totally convinced this is the mechanism of redistribution but brake fluid will allow some small amount of air to be dissolved into it. With the system under pressure it must dissolve more air just like fizzy soda does. When the pressure is released the dissolved air will come out of solution again but now it's not just trapped in a localised spot so it can rise up to the reservoir.

The part that doesn't totally convince me is when you remove the rubber bands the lever is immediately firm and air can't have risen that fast. Does air come out of solution in brake fluid as fast as it does in soda ? I don't know the answer to that but it would have to come out a lot slower for this explanation of the mechanism to be correct.

Next time I change the brake fluid and tie the lever back overnight I will remove the reservoir cover to observe what happens when the lever is released. Will I see a bubble rise ?

[Ken in Oklahoma]

I kinda like your air-bubbles-going-into-solution idea.

Ken

[lskbike]

Just saw the problem was a stuck caliper piston... so what I wrote below doesn't apply.... I used compressed air but wrapped the caliper well with a lot of rags to prevent the piston from flying across the room or damaging part of the caliper.

I have a recommendation, if all else presented doesn't alleviate the problem...do the following. But first, a little simplified technical info may help SO...The way hydraulic front disk brakes works is... the rider pulls the front brake lever toward the handlebar thus increasing the pressure of the non-compressable brake fluid inside the master cylinder, which in turn pushes the brake fluid out of the master cylinder, down the brake line into the caliper, which then presses the caliper's brake cups outward against the brake pads, which in turn presses the brake pads against the disks. This is a lot of fluid pressure pressing against these components all the way down to the disk. In order to release the front brakes there must be a way to allow the brake fluid inside the system to return to atmosphere (Zero pressure) inside the master cylinder. What typically one sees that does this, is that there is a bleed off hole drilled somewhere within the brake master cylinder body that allows the pressurized brake fluid to bleed off back into the master cylinder once the brake lever is released and the hole is open to the main "tank" of the master cylinder. My bet is that the brake fluid bleed off hole in your bike's master cylinder is plugged up with crud, which prevents the brakes to release. To correct this problem, you must open your front Master Cylinder and unplug this "hole". AT THIS POINT I MUST CAUTION YOU...Do not get brake fluid on any part of your bike as it can quickly damage both painted and metal surfaces, so cover everything well before you start work. Completely drain the brake fluid from the entire system. Once you open your front master cylinder, clean it out, locate this pressure bleed off hole and clean it out. You should also inspect the master cylinder's internal operating mechanisms as I have seen some of the rubber parts degrade, which allows bits and pieces to fall off, migrate to, then block the bleed off hole as well. If you are this far into it, I suggest you go ahead and replace these parts with new stuff anyway... Back to the discussion about cleaning out this vent hole; Remember this hole is very small and maybe hard to find. Also you must be careful when you clean it out as you do not want to damage any of the body of the master cylinder or enlarge the hole. Try a very small wire, or a sewing needle and then use compressed air to get it open. Once this hole is open, and you have replaced the working parts inside the master cylinder, if needed, and the master cylinder in reinstalled on the bike, you will need to get fresh brake fluid back in the system and get it pressurized. This can be a "bitch". The only way I have been able to do this with a totally "dry" brake system is to use a brake fluid pump that attaches to the bleeder valve at the caliper and sucks the fluid down through the system and eliminates all the air. Accomplishing this work should solve this problem for a very long time, especially if you replace the brake fluid every other year.

[Chuey]

I use a bicycle toe strap to hold pressure on the brake lever. It has worked for me. I'm not even going to try to figure out why it works. If Ken in Oklahoma is still only guessing, I will probably never know.............but it has worked for me, as well.

Chuey

[jimmyg]

You will need that cable adjuster to properly adjust the lever. Good news, they are available from the dealer.

12 CABLE ADJUSTER 1 32721230876 $17.64

I would double check that number as the controls changed between the 74 and 75 model year, not sure which one I grabbed.

gg

Thank you sir, I think I know which one I need.

jimmyg

[jimmyg]

A little more info.

I do need to get the hand lever cable adjuster as mentioned previously. But another observation when working on it again over the weekend, is that the right side caliper was moving as I applied the brakes. I deduced that the inside pad wasn't quite perfect and therefore, when pressure was applied, the caliper was shifting to attempt to align the inner pad, as the outside pad was forcing it to do so.

So I spent another 1/2 hour or so aligning the inner pad and at least the caliper isn't shifting around anymore when applying pressure.

Another thing I tried was to try and pull the bubbles out from the M/C. To do this, I went to the local hardware and got a 1 1/2" rubber stopper that would fit inside the M/C opening. Then I drilled a small hole in the center and with my Mity-Vac hardware kit, inserted one of the long tapered fittings. This fitting would then hook up to the Mity-Vac pump where I could create vacuum at the M/C, in hopes of pulling the air from the caliper all the way up to the reservoir.

I'll see how this works tonight as I created about 15" of vacuum and will let it sit over-nite.

thanks everyone. The saga continues............................

jimmyg