The dreaded SMC and rear dragging brake question

[macclan5]

My apologies up front..asking the question out of frustration rather than pure ignorance. Despite speaking live with Larry "the ST whisperer" , watching many you tube videos, following John Heath's Pulitzer worthy instructions on the brake bleeding, ordering a slew of new parts including the SMC, and multiple bleeding..the rear continues to drag. My best guess the issue is the new SMC..and thought best to see what other think--which is why the post. With the SMC assembly off the bike, tilted down 15 degrees and an old Gold Wing disk inserted so that the pads/pistons cannot over extend, i physically pump the SMC to bleed out air from both the proportional valve and outer bleed valve on the rear brake. The amount of brake fluid coming out both the proportional valve and rear caliper is much less when compared to pumping the rear brake. To prevent air entering the system, a motion pro brake bleeder is used.

Should the same amount of brake fluid be discharged whether the SMC or rear brake pedal is pumped? If yes, then what? Ready to hang a for sale sign on the bike. Any guidance truly welcomed.

 

[SMSW]

The SMC activates one piston, the rear brake a couple of them. I'd expect more brake fluid from the pedal than the SMC.

More info, please. While you were replacing the SMC, the brake lines were open. Did you give the rear wheel a spin to see if it dragged then? Before you began work, when you did the famous lie-on-the-floor-alongside-the-bike-give-the-rear-wheel-a-spin-with-your-foot-and-activate-the-SMC-with-your-hands test, did the rear wheel drag before the test? Did you release the rear nipple to bleed pressure from the SMC activated piston? What I am driving at, is were you able to get the rear wheel to spin freely on the center stand and no SMC involvement?

I think a rear wheel/caliper removal is in store and a complete cleaning and inspection of the caliper, pistons, guide rods, and bracket stopper bolt hole is warranted.

 

[Sidekick]

My apologies up front..asking the question out of frustration rather than pure ignorance. Despite speaking live with Larry "the ST whisperer" , watching many you tube videos, following John Heath's Pulitzer worthy instructions on the brake bleeding, ordering a slew of new parts including the SMC, and multiple bleeding..the rear continues to drag. My best guess the issue is the new SMC..and thought best to see what other think--which is why the post. With the SMC assembly off the bike, tilted down 15 degrees and an old Gold Wing disk inserted so that the pads/pistons cannot over extend, i physically pump the SMC to bleed out air from both the proportional valve and outer bleed valve on the rear brake. The amount of brake fluid coming out both the proportional valve and rear caliper is much less when compared to pumping the rear brake. To prevent air entering the system, a motion pro brake bleeder is used.

Should the same amount of brake fluid be discharged whether the SMC or rear brake pedal is pumped? If yes, then what? Ready to hang a for sale sign on the bike. Any guidance truly welcomed.

I had exactly the same issues after replacing the SMC 3 years ago and like you I was ready to put a sign on my driveway, do not give up!
You must still have some air trapped behind the SMC caliper pistons or somewhere in the line near them.
As much as I understand your situation, I believe that you would have better success if you could keep the piston fully retracted, not half way.
Immobilize them with anything thick enough to keep them fully retracted and bleed again.
When the pistons are not fully "in" or retracted, it's much harder to vacuum any residual air pockets behind them.

 

[Sadlsor]

Can we clarify that you're using OEM pads on the rear brake? I'm confident that speaking with Larry, he would have been adamant about that. Many aftermarket pads are a bit too thick to work well.
As mentioned by @Sidekick above, minimizing the extension of the pistons will work in your favor, and I use an automotive-style screw clamp to push them all the way into the caliper after I've cleaned them.
Everything is figureoutable.
If you are getting frustrated, take a break.

 

[macclan5]

Wow...great questions. Sorry for late reply. Decided to take a break and get frustrated rebuilding the fork seals on my 78 Gold Wing. Amazes me the level of detail associated with this system. So..all NEW OEM parts. Pads. Pins. Caliper pad spring. Rear brake was off the bike. Slide pins all lubed up. Rear brake pistons removed, cleaned and new seals. Actually had Larry on the phone, spun the rear wheel and got about 1--1/2 revolutions. Then ordered the parts he said and bled and bled. When replacing the SMC, yes the line were open. The only time the rear wheel has spun freely is when moving the rear caliper side to side and compress all three pistons.

 

[MidLife]

The SMC activates one piston, the rear brake a couple of them. I'd expect more brake fluid from the pedal than the SMC.

SMC: Two rear pistons
Rear Pedal: One

 

[SMSW]

SMC: Two rear pistons
Rear Pedal: One

Thanks, I keep screwing this up. Must be because I no longer own an ST and don't have to play with their brakes.

 

[MidLife]

..... I no longer own an ST and don't have to play with their brakes.

Lucky you!

The front will give you the two outers all over, 2/3rd of the total available breaking power, plenty in most cases (for me!). Need a bit more, the foot will engage the middles all over, accessing the remaining 1/3rd.

 

[jfheath]

SMC: Two rear pistons
Rear Pedal: One

That is probably true when riding, but in the garage when the SMC is not operated it is

SMC : Two rear pistons
Rear Pedal : Three rear pistons.

If you don't believe me, open up the rear bleed valve on the rear outer caliper and press the brake pedal.

This is because the primary seal in all of the master cylinders is cup shaped / flared. It acts in a similar way to the seal in a bicycle pump, applying pressure on the down stroke, but yielding to the fluid behind on the upstroke, to allow fresh fluid to fill the bore. In all of the master cylinders this is how you are able to pump fresh fluid through the system with the lever/pedal. It also explains why you never have to adjust your brakes as the pads wear down, like you do with brake cables.​

​

So when you press the rear pedal in the garage, the fluid which flows to the front left centre piston, also feeds the inlet port of the SMC - and it flows straight past the primary seal and on to the rear caliper outer pistons via the proportional control valve.​

If that channel doesn't produce much flow then check out these in sequence

1. Lower Bleed valve front left caliper. (centre piston) Press the brake pedal
2. PCV bleed valve, brake pedal
3. Rear bleed valve rear caliper (outer piston), press brake pedal.

If the flow from any of these is sluggish, then you may have a blockage. I am going to guess that it is at the PCV valve. If so, weight the brake pedal, remove the bleed valve. Protect the bike from leaking fluid, clean out the valve. Then having protected the bike and you from the brake fluid that will be ejaculated, give the pedal a few hard pumps to eject any solid matter. If there is a blockage it is likely near the hole and will be shot out like an air gun pellet. On the last pump, keep the pedal pressed and carefully replace the bleed valve, taking care not to cross thread it.

The SMC is a little more difficult to operate as when it is pumping fluid towards the rear, it is also having to suck fluid from the rear pedal reservoir through the lengthy pipe work to the front left caliper.

 

[MidLife]

That is probably true when riding, but in the garage when the SMC is not operated it is

SMC : Two rear pistons
Rear Pedal : Three rear pistons.

If you don't believe me, .......

There ain't no not believing you on that....you wrote the book on it!

And that's a fact, the lines to the three rear pistons are fed from the one rear reservoir.

 

[SMSW]

Lucky you!
The front will give you the two outers all over, 2/3rd of the total available breaking power, plenty in most cases (for me!). Need a bit more, the foot will engage the middles all over, accessing the remaining 1/3rd.

I question said luck when I'm on my VStrom. Yes, it's a very good bike, but I really miss a lot of the features of the ST. What I miss: the sureness and planted feeling I got from the ST in turns, the way it absorbed bumps (after RaceTech), the big tank and range, weather protection, all around handling. The VS is a better bike than I am a rider, but it is still no ST.

I remember that using both front grip brake and rear pedal on my ST had a much better braking 'feel' to me than using only one of them. It was not a matter of needing more, it was the way the bike handled braking, and I remember using both most of the time. The VS does not have linked brakes, so on gravel I tend to use the rear to slow for curves and both when coming to a stop. Otherwise, I try to use both to settle the suspension.

 

[Larry Fine]

I remember that using both front grip brake and rear pedal on my ST had a much better braking 'feel' to me than using only one of them. It was not a matter of needing more, it was the way the bike handled braking, and I remember using both most of the time.

Both of my 1100s are non-ABS/non-linked. I also use both brakes. I apply mostly the front first, and modulate the braking by adding the rear.

 

[macclan5]

thank you John...will confirm the 3 locations listed using the brake pedal later today and report back.

 

[Buckeyechris]

Hello @macclan5!

I understanding your frustrations. If you haven't already, you may find the article I wrote about my efforts to purge all the air in my ST13's system (link).

Perhaps I misunderstood your question, but I'm not sure why you were trying to expel brake fluid solely by activating the SMC. That's not part of the bleed sequence. Lesson no. 7 in the article describes how @Igofar helped me rid that circuit of air. Massaging the plunger in the SMC in between bleeding that circuit by pushing down the rear brake pedal will help push trapped air into the rear caliper. Nevertheless, the amount of fluid expelled from each bleeder should be relatively the same. I can personally attest that the suggestion made by @Sidekick is extremely helpful.

That said, sometimes water and sediment can build up in the calipers and lines. @jfheath's suggestion will help you clear any blockage. However, I recommend that you try bleeding the system with the caliper piston fully pushed in before disassembling the PCV from the brake lines. If you can't get that circuit to flow freely, then chances are you may have either a blockage or faulty PCV.

Wishing you the best of luck!

 

[Sidekick]

Then having protected the bike and you from the brake fluid that will be ejaculated

LOL

 

[oude geit]

Did away with my SMC and it only goes about 1.5 revs per spin. Lot of stuff moving back there to the secondary output shaft. Mine been good for about 100000 miles.

 

[macclan5]

Hello @macclan5!

I understanding your frustrations. If you haven't already, you may find the article I wrote about my efforts to purge all the air in my ST13's system (link).

Perhaps I misunderstood your question, but I'm not sure why you were trying to expel brake fluid solely by activating the SMC. That's not part of the bleed sequence. Lesson no. 7 in the article describes how @Igofar helped me rid that circuit of air. Massaging the plunger in the SMC in between bleeding that circuit by pushing down the rear brake pedal will help push trapped air into the rear caliper. Nevertheless, the amount of fluid expelled from each bleeder should be relatively the same. I can personally attest that the suggestion made by @Sidekick is extremely helpful.

That said, sometimes water and sediment can build up in the calipers and lines. @jfheath's suggestion will help you clear any blockage. However, I recommend that you try bleeding the system with the caliper piston fully pushed in before disassembling the PCV from the brake lines. If you can't get that circuit to flow freely, then chances are you may have either a blockage or faulty PCV.

Wishing you the best of luck!

Very helpful..thank you. My sense is lesson #7 may be what is needed. At this point, having looked at so many posts--not recalling where these steps are explained- possible to point me where the step to do are located. Being Labor day tomorrow..this sounds like a perfect project to spend time on.

 

[Buckeyechris]

Very helpful..thank you. My sense is lesson #7 may be what is needed. At this point, having looked at so many posts--not recalling where these steps are explained- possible to point me where the step to do are located. Being Labor day tomorrow..this sounds like a perfect project to spend time on.

@macclan5 , click on the following link (here) to my article and just scroll down to Lesson No. 7.

 

[macclan5]

thank you...repeating back for understanding...after purging air from MC on handle bar, proceed to SMC and PCV. press/pump SMC and bleed PCV. goal is to have SMC firm/barely moving when pressing it. them move to rear pedal and PCV and repeat. goal is firm brake on first pump/push. remember to open bleed valve 1/4 open, use motion pro, check reservoir fluid levels, close bleed valve during pump/push..not when at end, and be tapping lines/cylinders with wood block to free up air bubbles. that catch the intent?

 

[Buckeyechris]

You're description is close to the process. I recommend the following sequence/steps.

Remove the the SMC/Caliper and tilt it at least 15 degrees. If you have a car jack stand, the bottom of the SMC brackets will fit on the stand between eyelets.

1. Pound on the rear brake pedal a few times, then hold it down.
2. Next open the PCV bleed nipple and fluid will start to come out. Be sure to close the bleed screw before the pedal bottoms out and before you release it.
3. At this point, start tapping on the SMC and surrounding lines (I used the handle of a small hammer).
4. Then, push the plunger in on the SMC all the way. The first time you do this, you're unlikely to encounter much resistance.
5. Next, repeat steps 1 and 2, followed by step number 4. The second time you will likely feel some resistance.
6. Again, repeat steps 1 and 2, followed by step 4. The third time, you will experience a good deal of resistance.
7. Continue to repeat steps 1 and 2 until you no longer get any air bubbles.

As you noted, keep an eye on the fluid level in the rear reservoir. Then you complete the rest of the bleed sequence. If you don't reinstall the SMC/Caliper to the fork, be sure to place a shim the same thickness of your rotor between the pads. If you are not certain of the remaining bleed sequence (there are four more steps), please let me known.

At this stage, recommend that the you weight down the brake pedal and tie the brake lever as close to your grip as possible. Leave it overnight. In the morning, release the lever and pedal. Test both, and if you feel any sponginess, follow the bleed sequence from start to finish again. NOTE: overnight, any remaining air will migrate to the calipers just behind the pistons. Doing a final bleed, following the sequence, should rid your brake circuits of the remaining air.

If you're thinking this is a lot of work to get the air out of your brake lines, you're right. It's just one of eccentricities exhibited by the ST13. It also requires you to devote at least double the amount of time you think it will take to complete the bleed sequence. Others recommend to allot a full two days for the entire process. If it takes less time, you are doing extremely well.