84 FJ1100 bleed front brakes?

[Sparky84]

With regards to "scientific research" will we get the full unedited version of the tying back and release of the lever video?
Will you leave a light on the lever overnight so we can watch and wait patiently for the outcome         


Cheers Alan

[jdvorchak]

got the rear brake cleaned and bled. I had one little snag that had me stumped for a while. The piston in the rear MC was frozen solid. I tried hitting with a punch but decided that it was in all the way and not budging. So I got the idea of using my bench front MC, that I have bolted to a piece of handle bar and clamped in my vise, to push the piston out. I just hooked the output of my bench MC to the output of the rear MC and pumped it. Easy as can be the piston started moving and finally popped out. I also must mention that I had plugged the reservoir hose with a bolt and hose clamp. That was to force all of the fluid and pressure to work against the stuck piston and not go spraying all over the shop. Since I had already put my Mighty-Vac away I did the old school pump pump hold routine. Within a couple of minutes I had the rear brake bled and working perfectly with a rock hard brake pedal.

I don't know if you guys normally just remove the rear MC from the frame or not. I decided to remove the whole frame assembly and I'm glad I did. I was then able to clean all of the moving parts, confirm the brake light switch worked and clean the connectors. But most importantly I was able to pull the brake lever pivot out, clean, re-lube, and install. If you do it this way be sure and have a foot pound torque wrench as that swing arm nut has to be torqued to 65 foot pounds. Also that cotter pin on the linkage would have been an absolute nightmare to get out and put back in with the side frame still attached. Actually I'm not sure there is enough room to remove that clevis pin with the assembly still attached to the bike.

[CutterBill]

How master cylinders work...
https://www.youtube.com/watch?v=SFbt46mN2k8

Pay close attention to the piston, the primary seal and the compensating port.  You can see that when the piston is depressed, there is NO connection between the reservoir and the fluid ahead of the piston. There is no way for air in the line to escape to the reservoir.

Just as a single data point, last month I disassembled and rebuilt the clutch, front and rear brake systems on my '93.  I did this to fix the stuck caliper pistons and because I was switching over the DOT 5 fluid and wanted to clean the parts. So I was starting with completely dry systems. Now, I don't know what people are doing when they say that they have so much trouble bleeding their clutch or brakes, but it took me about 30 minutes, start to finish, to do all three systems. Working alone. Didn't have any trouble.

But then, I've been doing this a while...
Bill

[racerrad8]

How master cylinders work...
https://www.youtube.com/watch?v=SFbt46mN2k8

Here's a couple about tying the lever back.

https://youtu.be/ex-evh2g1O0?t=5m28s
https://youtu.be/MQtT3XpB_B0
https://youtu.be/m4wlSQDsEHw?t=5m34s

LIke I said before...

For reasons I have not been able to determine, understand or figure out yet...

I am not sure why it works, but it does.

But then, I've been doing this a while too...

Randy - RPM

[FJmonkey]

Just some thoughts on what happens when holding the lever back to bleed the brakes/clutch. More so on the brake than clutch but the compression will only affect air trapped in the system. The air bubble is compressed into a smaller bubble. This reduces its over all size, Also reducing its surface area. This reduced surface area makes it easier to break free, float up, where it can escape into the port back into the master reservoir. i don't have a dog in this fight, my last experience with the clutch was bled with a few strokes of the lever.

[Pat Conlon]

Markus, I think you're on to something.

I've often wondered about that...If brake fluid under pressure affects the gravity movement of air bubbles.

I didn't think of compression affecting the actual size of the bubbles.
Makes sense to me:  Compression = Smaller bubble size = less surface area of the bubble to adhere, easier for the smaller bubbles to move up to closed bleed port.
We all agree that with the lever squeezed the bleed port is closed, correct? No bubbles can enter the reservoir...that was Bill's point.

However, relaxing the lever opens the bleed port allows the accumulated bubbles into the reservoir.

[Yamahahammer1300]

One of Murphy's Laws of Combat is:  If it's stupid, but it works, it ain't stupid.  Old school, Mity-vac, reverse syringe, they all work.  Tying the lever back certainly doesn't hurt, so why not try it?
Hell, I even used a palm sander, minus paper, to vibrate the bubbles up and out of the system.

[FJ_Hooligan]

Just some thoughts on what happens when holding the lever back to bleed the brakes/clutch. More so on the brake than clutch but the compression will only affect air trapped in the system. The air bubble is compressed into a smaller bubble. This reduces its over all size, Also reducing its surface area. This reduced surface area makes it easier to break free, float up, where it can escape into the port back into the master reservoir. i don't have a dog in this fight, my last experience with the clutch was bled with a few strokes of the lever.

I'll buy into that!

DavidR.

[racerrad8]

This was covered way back too. I recall this post and thought to myself it would not work back then.

It should be bleeding obvious

But, once I tried it I use it almost every time.

Randy - RPM

[jdvorchak]

There is a lot I don't know. But I've been buying old non-running bikes for a few years, fixing them up and flipping them. I have one major rule. I won't sell it until it runs well enough and is safe enough to put one of my sons on it for a cross country ride.

The compressed bubbles theory is what I've always thought as to why it works. It shouldn't work but it does. Kinda like engineers and scientists absolutely proved that a bumble bee can't fly. But for some reason they can fly.

I also try not to over think things. If it works, I don't really care why. For the past 11 years I've been tying the lever back, or weighting the brake lever down overnight. If the brakes aren't rock hard in the morning I know I missed something.

My new to me FJ1100 had a bone dry clutch system when I brought it home. I was in a hurry and mad as can be that the PO broke one of the slave mounting bolts. So after I bled the system a bit I decided to quit and finish up the next day. I got a largish rubber band and tied the clutch lever back. The next morning I had full clutch action and no more bleeding necessary.

Long story short. It can't work. It shouldn't work. There is no way it works. But it does.

[ribbert]

The compressed bubbles theory is what I've always thought as to why it works.

A few lines from an old post on this subject (in this case, specifically about the clutch):

"It is a basic fact of fluid dynamics that with any bubble in any liquid, the smaller the bubble the more slowly it rises."

"While smaller (compressed) bubbles have less surface area and less friction, the fluid density remains constant and the smaller ones have less buoyancy."

"In the case of the FJ clutch, the route from the slave to the M/C is all uphill and the air will naturally want to rise to the top anyway, but slowly. IMO all the tied lever overnight does is inadvertently allow time for this process to occur naturally. "

Noel