Rear brake problem

[Fster]

I changed tires the other week and while the bike was on the center stand and up on the lift I started it and put it in gear. With the rear wheel spinning under idle power I applied the front brake lever and nothing, the rear wheel keep spinning with no signs of slowing at all. Any suggestion on where to start looking?

 

[okmurdog]

Applying the front brake alone without any forward movement of the bike (or the front tire spinning under force) will not apply any braking power to the rear brakes. The Secondary Master Cylinder (SMC) mounted to the front left caliper is actuated by two things - one being the caliper grasping the rotor, and the other is the forward movement of the rotor (thereby compressing the SMC and applying braking power to the rear caliper).

To check the action, place the bike on the center stand and have a buddy spin the rear wheel by hand while you manually push the SMC forward - you should then see the rear brake actuate and stop the rear tire.

 

[Tom Mac 04a]

Well, remember you were working against the engine ( even tho at Idle )... and the front brake only works ONE of the rear pads.

DID you pump the brakes after installing the tire? Many time when you remove the tire you push in the piston... there are no brakes till they are pumped back out!
Did you actually sit on the bike and roll it and try the front brake? Are the pads in good shape? Did you try the rear pedal?

As a guess with the info given, I think there is prob nothing wrong that pumping won't cure.


edit;
forgot about SMC... tks dog

 

[Mellow]

Applying the front brake alone without any forward movement of the bike (or the front tire spinning under force) will not apply any braking power to the rear brakes. The Secondary Master Cylinder (SMC) mounted to the front left caliper is actuated by two things - one being the caliper grasping the rotor, and the other is the forward movement of the rotor (thereby compressing the SMC and applying braking power to the rear caliper).

To check the action, place the bike on the center stand and have a buddy spin the rear wheel by hand while you manually push the SMC forward - you should then see the rear brake actuate and stop the rear tire.

 

[Al Gully]

I have had my bike since 2009 and I just learned about the secondary master cylinder (AKA the "SMC") that is located on the front left side caliper.
Wife did the turning of the rear tire and I pushed on the SMC. Holy crow it worked, it locked up the rear tire.
Sneaky way of doing things Honda.

 

[Fster]

Thats it guys, you are exactly right. I took a harder look at things and figured that with out forward motion and friction on the front disc it will not activate the rear caliper. Thanks guys.

 

[Blrfl]

Sneaky way of doing things Honda.

This'll bake your noodle even further: If you step on the rear brake, the linkage to the front will actuate the fronts, causing the SMC to compress and sending pressure to the outer pistons on the rear.

Picture: CLICKY

--Mark

 

[Shadowfax-ST]

...the pistons being different diameters.

Now, is this because of the mechanical / hydrolic force being different for each diameter, or so you don't get the pistons mixed up during overhaul?

I've always wondered. This seems a good time to ask. I hope it's not just, 'because they are'

 

[st1300r]

If they were the same you couldn't mix them up LOL.

And yes it's for a reason the force is the pressure*piston area.

 

[sennister]

I have disc brakes on my mountain bike and they use different size pistons so that as you squeeze the brake lever the smaller piston moves out first to apply light braking action. As you squeeze harder the second larger piston joins in the party and really clamps down on the pads. The reason for all of this is to give better control to modulate the brakes. Basically does a better job of lots or little braking power. Smaller pistons are not as strong but are quicker for the light work.

This may be part of the reason.

 

[Shadowfax-ST]

Cheers, Guys. If you never ask you never know