Rear Brake Service/Function Test

NH478M

NH478M

Joined
May 19, 2010
Messages
27
Location
Rural Aberdeenshire, Scotland
Bike
2010 ST1300
Hi,

Getting on really well so far with the mile muncher. Using a grip-lock for safety on hills/uneven surfaces when parked (for security too I suppose). I've noticed that applying the right lever front brake (even fully on) when stationary seems to not operate the rear caliper. Is this indicative of a CBS system problem or does the rear caliper get its pressure only when the rotors are rotating and so the rear caliper won't operate while stationary unless I use the pedal brake?

Unable yet to determine while riding whether the rear brake is operating through the CBS or vice-versa.

Can anyone advise me please about the system and of any methods of testing the CBS functionality front and rear / lever and pedal without using a 'rolling road'?

Hopeful advanced thanks
Regards
PJ
 
It won't activate the rear brake unless you are moving.
The SMC on the front left caliper assy is activated when the front brake is applied and the wheel rotation moves the caliper against the smc piston.
 
Hi and thanks for such a fast and reassuring reply.

Can I take it then that if I can somehow lift the front left caliper while the machine is stationary I can test the response of the rear caliper?

PJ
 
Never looked at the official procedure but I imagine with the bike on the center stand in neutral get someone to push the rear wheel around and push the left front caliper assy forward they should feel some resistance.

Or the next time you are replacing the rear brake pads pushing the left front caliper assy forward should move the center piston on the rear caliper. Put a wedge in there so you don't push the piston completly out LOL.
 
Yes, if it is working right you should be able to do that. You might need someone to spin the rear tire while you push on the back of the left caliper. The SMC is the rubber boot looking device at the top of the left caliper.

Lately a lot of people have been having problems with the SMC. My 1300 is down waiting on a new one to get here. For me I knew mine was bad because I noticed my left caliper rattling when going over bumps. The piston was stuck in so it didn't have the resistance and the caliper would move around. When I was braking the rattle went away because it was pushed up against the suck piston. I had a feeling this was my problem but and should have ordered the parts before tearing it apart. Now that I know it is on back order I really wish I would have done that. I could put it back together with the suck piston but it will be a pain to bleed the brakes without having it working properly and that could be a safety issue. So I am not going to do it.
 
st1300r said:
Never looked at the official procedure but I imagine with the bike on the center stand in neutral get someone to push the rear wheel around and push the lift front caliper assy forward they should feel some resistance.

Or the next time you are replacing the rear brake pads pushing the left front caliper assy forward should move the center piston on the rear caliper. Put a wedge in there so you don't push the piston completly out LOL.
Click to expand...

Actually I thought it was the center that the SMC operates but from the service manual it looks like it is the two outside pistons.
 
Hi,

Thanks all very much. I'll do a check this weekend when I've stopped pretending to work too. :eek:)

Just had to record another drop of the bike. Got home from a two up ride to Fochabers yesterday just in time to watch England get stuffed by the Germans (again)! As I drove onto the dolly which was properly braked, the rear wedge released as I braked (there's that grippy front brake again). The dolly became mobile on its casters and the rear slipped to the left with the front wedge still holding. This meant the bike went down to the right. No damage just total irritation! Got the dolly out by rocking the bike gently and minimally so the wheels cleared the side of the trough then lifted it upright again.

Tried again but this time with some thin rubber matting between the bottom of the wedges and the smooth concrete (cement) garage floor.

Both wedge brakes worked solidly this time and all safe again with bike now up to the side of the garage so I could get the barbecue out for supper.

Every day is a day at school.

Grateful regards
PJ :)
 
Righty ho....

From the Clymer manual, although for an 1100, as far as I know it's the same;

Rear Brake pedal operation

When the rear brake pedal is operated hydraulic pressure from the master cylinder is applied through two separate circuits.
The line from the rear master cylinder to the rear caliper operates the middle piston on the rear caliper.
The second line applies pressure to the delay valve which activates the middle piston of each front caliper. Just as with front brake lever operation, the braking forces pivot the left front caliper, which moves the pushrod in the SMC.
Hydraulic pressure flows from the SMC through the PCV and activates the two outer pistons in the rear caliper.
The result is that all three pistons in the rear caliper and the middle piston in each front caliper are applied whenever the brake pedal is operated. (WHEN MOVING)


That is how I understand it, but very gentle 'feathering' of the rear brake does not result in any pressure being applied to the front brakes, only when a slightly longer travel is applied to the rear pedal does the delay valve allow pressure to the front, and thence via the SMC and PCV to the rear brake outer pistons.

No pressure is applied to the rear from the front lever when stationary or moving.
Only when moving does pressure result as described above from the SMC.

The front brake lever operates the outer pistons on the front only, then as described above, when the left caliper moves it operates the SMC which operates the two outer pistons on the rear.

HTH.
 
NH478M said:
Hi and thanks for such a fast and reassuring reply.

Can I take it then that if I can somehow lift the front left caliper while the machine is stationary I can test the response of the rear caliper?

PJ
Click to expand...
I was curious about this and just checked mine by myself. I sat down next to the bike where I could turn the rear wheel with my foot while pressing the caliper forward. Pressing the caliper forward like this generated enough braking force that I couldn't turn the rear wheel. Release caliper and wheel turns, press caliper and it stops. Seems to be working - I hope as designed.

Mine has rattled going over bumps since new. The rattle seemingly can be reduced by bleeding but it never goes away totally. We know there is no direct connection between the SMC clevis pushrod and the SMC piston. Mine has maybe 1 mm play between the pushrod and the piston. I can push forward on the caliper and measure the distance from at-rest to when the piston contacts the pushrod with a metallic tap. That is the rattle. The spring on the inside of the bore presses the piston back out after compression. If mine is stuck it is this 1 mm, otherwise the piston would contact the pushrod at all times.
 
dduelin said:
Mine has rattled going over bumps since new. The rattle seemingly can be reduced by bleeding but it never goes away totally. We know there is no direct connection between the SMC clevis pushrod and the SMC piston. Mine has maybe 1 mm play between the pushrod and the piston. I can push forward on the caliper and measure the distance from at-rest to when the piston contacts the pushrod with a metallic tap. That is the rattle. The spring on the inside of the bore presses the piston back out after compression. If mine is stuck it is this 1 mm, otherwise the piston would contact the pushrod at all times.
Click to expand...

Mine had at least 1CM of play causing my rattle. I did read that bleeding can help but I had no braking action when I tried to compress the SMC and after a ride I would have my rear brake dragging a little.
 
Have to say that the frequency of the drops is reducing and being used to it now, it's so good to not panic when it happens! Calm, assess why it happened, learn for next time, sort things out, then set about getting it upright again without damage. Being only human is a pain sometimes! :)

PJ
 
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