SMC Failure observations

[sirbike]

At least as I have observed it, there is a failure mode of the smc that is the opposite of locking up the rear wheel.

I realized at some point that a quick easy road test to know if the smc is working is to find that after coming to a firm stop with and maintaining pressure on the front lever alone, that the bike settles on its suspension as the lever is released. Seems the rear releases first so the feeling is that the back settles down.
During the sale test ride my latest bike there was little to no settling regardless of how hard I stopped.
The smc required a lot of force to apply rear brake when testing on the center stand.
Otherwise the bike was in great condition.
I rode 370 miles directly home with minimum braking, practically no use of brakes in the turns. The next week I rode to the state inspection. On the way back the smc started working fully.
Either way, smc working correctly or not, the rear brake showed no signs of drag when tested on the center stand.
The other day I was riding the 2003A. All was well, then I came to that next stop and it wasn’t. The bike barely settled when I released the brake.
It may be hard to entirely describe or get what I am saying, but when riding one bike that is fully working then immediately riding one that is not, the difference is clear.
I flush the brakes annually but don’t know the history previous to my ownership.
The 03A’s new smc will arrive next week.
The 09A’s will be ordered soon.
I have successfully rebuilt one but all new is more thorough and easy.
I’ll flush the system first then install then bleed.

 

[core-aggie]

One would have to be VERY familiar with the ST13 and its idiosyncrasies to understand what you wrote.

Some may not even sense those subtle characteristics.


However, that's a great observation and worthy feedback to the community!!

 

[dduelin]

Part of what one feels when the bike settles on the suspension after braking is attributable to shaft jacking. Because the Honda swing arm isn't fully floating on the STs when we stop under medium to hard braking the weight transfer "drops" or lowers the swing arm and slightly shortens the wheelbase. If you stop with rear brake applied, the rear of the bike cannot drop down and level the swing arm until the brake pressure is released. Release the rear caliper pressure and the rear wheel rotates backwards ever so slightly as the bike settles to at-rest sag position. If the SMC won't release pressure to the rear caliper the bike won't drop when the brakes are released or it drops gradually without notice instead of the easily noticed drop with correctly functioning brakes. Other contemporary sport touring bikes by BMW, Kawasaki, Moto-Guzzi, etc., have the swing arm, frame, final drive and another component form a trapeziod that passes jacking forces into the frame and away from the suspension. I was always nicely surprised the only noticeable jacking issue with my ST1300 was this one under braking and never under acceleration/deceleration where rapid suspension ride height changes can be quite dramatic.