Motorcycle Repair: 82 Yamaha XJ650J front brake, ring pliers, hydraulic clutch

Question
Hi Chris,
I've had trouble with the front brake in the past - put new pads on a few hundred miles ago, but they never really 'grabbed' well. Now there is nothing - the lever just pulls in with little resistance (and no braking) and then barely returns. I don't see any leaks, so suspect some part of the cylinder. Is there a good way to diagnose it? From online exploded views, it looks like the only active parts are in a 'master cylinder kit'. Are these easy to replace?
Thanks,
Robb

Answer
Hi Robb.
 Have you bled the brakes?  What you are describing sounds more like the line has air in it.  Now if you have the type of master cylinder that I recall for that model, then there is an additional proceedure to follow (One that the mechanics and the manual never tell you about):

1) Bleed the brake line like normal.

2) Put a wrench on the banjo fitting at the master cylinder and squeeze the lever.


3) (NOTE: Use a box end wrench for this) While holding the clutch/brake lever in, crack loose the fitting and reclose it quickly. Have a rag over the fitting connection that you are working on because it will spit at you as pressure expells the air and a little fluid.
IMPORTANT NOTE: Do not release pressure on the lever till the fitting is tightened back up or you will suck air back into the line.

4) Test the brake again.  If done correctly, you will have pressure near the beginning of the lever movement rather than at the end.

5) repeat as needed, but should not need more than 2-3 times.

This also works on any bike with a hydraulic clutch where the master cylinder is of a design which would allow a reverse trap in the line.

Now, if this doesn't work for you, then rebuilding the master cylinder is in order.  It is not difficult to do, but you will need a set of ring pliers to do it.

Good luck.
FALCON