linked brake question

new to me '07, rear brake feels weak, but that seems to be normal on "modern" bikes but it's no big deal because I don't use them.

But checking it over in the garage, I find that the front brake lever has no effect on the rear wheel. The rear pedal will prevent me from turning the front wheel by hand, but as I said has litle stopping power on the road.

There must be a blockage in the rear system somewhere. The PO said he had the brakes "service" by the dealer.

Any ideas on where to look?
Thanks

 

As the front wheel is stopped by the front brake it presses against a secondary master cylinder that activates the center piston of the
rear brake. No front wheel movement, no activation of the rear brake.

IMO VFR rear brakes are pretty bad. The best thing to do is replace them with HH brake pads. I did that when I installed stainless
steel lines and the rear brake is now very good.

 

The VFR uses sliding calipers that need to be able to move freely on the sliding pins in order for all the braking force to be generated. At the very least I'd suggest pulling the caliper mount off the swing arm and checking the sliding action is OK. While you are there you can also see if the pistons will move freely, if you have debris caught in the seals this will also rob some brake power.

 

My understanding is the front brake only sends 30% braking power to the rear. The rear brake sends 30% power to the front. Braking power is not evenly divided between the two wheels when using a single lever. When the front brake is applied your front LEVER is NOT sending the fluid to the rear. The fluid is sent to the rear by a plunger that is actuated by the force of the front calipers pushing against a pivot point (only happens if the front wheel is spinning). If you are sure your front has zero effect on the rear I would say you might have a blockage or air bubble in the front line that sends power to the rear. Hope this makes sense.

 

To test whether the front secondary mater cylinder is working, put the bike on the center stand and spin the rear wheel, using your hands, push the secondary mater cylinder on the left fork and see if it stops or slows the rear wheel. You should be able to determine how this works as the caliper pivots at the bottom of the caliper mount. As mentioned, unless the front wheel is spinning the secondary mater cylinder will not be activated. On that vein, it will only activate if the rear center piston if it is working properly.

 

I second the recommendation to change out your front brake lines to SS and go with HH pads in the rear. It makes a world of difference.

Jose

 

Per factory service manual, and I may be interpreting it incorrectly, front brake pushes the 3 pistons on right, and 2 outer on left caliper, braking forces push the anti-dive (manual calls it secondary master cylinder) located at top of left side caliper and it applies pressure on middle of 3 pistons on rear caliper. Rear pedal sends pressure to middle piston of left front caliper and to outer 2 of rear caliper, while at same time the anti-dive cylinder sends pressure to middle rear piston depending on amount of dive front end is taking. So I believe with bike on center stand and applying rear brake the rear wheel should brake. I think your problem may be in one of the proportional valves, rear most likely? Might just be air in it, the bleeding process for a linked brake system per manual is little complicated, fixing to go thru it here with new ss lines, have just replaced rotors, and pads and had trouble bleeding rear proportional valve. Hope this helps.