Article [13] ST1300 - Brake Bleed Procedure [VIDEO]

HOS

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Nice work! I did have to chuckle a little at the "passenger side/ driver side" references. :)
Thanks for your effort.

-STeve
Perfect, great job. I like passenger vs driver, otherwise left right is meaningless unless you state your viewing perspective and it seems that seldom is the case. Thanks again!
 

jfheath

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Thanks for posting this. Great stuff.

He also mentions pumping the front and rear brake lever and pedal. How do you pump the SMC? Is that not done by operating the Front and/or Rear brake lever/pedal?
With the the PCV bleed valve open, the SMC can be pumped easily - a bit like a handlebar lever - squeezing it with my fingers around the forks and the SMC in the crook between my thumb and forefinger. It's important to do this to ensure that all of the old fluid in the SMC is sluiced out through the lines.

Yes you are correct about the PCV. It divides rear pedal pressure between front and rear calipers with a bias toward the fronts.
I think you may be confusing the Proportioning Control Valve with the delay valve ???

The PCV is a unit that sits in the rear brake line between the SMC and the rear caliper outer pistons. Its purpose is to limit the amount of pressure that can be applied to the rear brake by the SMC. Physically it is mounted just forward of the PCV bleed valve. It contains a spool / small hydraulic piston which (like a caliper piston) is affected by the pressure of the fluid. However, it is held in place by a strong spring. Under normal braking, the pressure that is applied by the SMC rocking forward is applied to the rear outer pistons, and the spring in the PCV is strong enough to keep the spool / piston in place. But there is a danger that under heavy braking at the front, too much pressure is applied by the SMC and that the rear brake will lock up - especially as the rear will get lighter. So what happens instead is that the extra pressure overcomes the strength of the strong spring. The spool/piston yields, creating space in the PCV unit which releases the pressure of the fluid to the rear outer pistons. This system is there whether or not the bike has ABS fitted.

(When the bike is stationery / in the garage, the SMC would not normally operate as the front wheel isn't moving. But the rear pedal has a line to the SMC, and the pressure passes through the SMC from behind the primary seal and on to the rear caliper outer pistons - so in these circumstances the PCV spool may felt to operate as the pedal pressure increases. It would be hard to distinguish it from the action taking place in the delay valve though.)

The Delay Valve:

The rear pedal operates the rear centre piston and the two front centre pistons. The delay valve is a device which controls the amount of pressure that is applied to the front right caliper centre piston. When the rear pedal is first applied, only the front left centre piston and the rear centre piston are activated. The front right centre piston will move only when the pressure on the brake pedal is increased. You will probably be able to feel this additional dip in the pedal if you increase the pedal pressure gradually.

This behaviour is to help prevent the dip in the forks when using the brake pedal to steady the bike in slow manoeuvres.
 
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Dumb question. The video on bleeding the PCV mentions "pumping the secondary master cylinder". He also mentions pumping the front and rear brake lever and pedal. How do you pump the SMC? Is that not done by operating the Front and/or Rear brake lever/pedal?

Scott
Front lever for Steps 1 & 2 only. Foot pedal for all remaining steps.
 

jfheath

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Pumping the SMC can be carried out when the PCV bleed valve is open, or when the rear bleed valve on the rear caliper is open.

i believe that it is important to do this to:
  • exercise the piston through its full range of travel
  • to sluice out the old fluid which lies between the inlet port and the secondary seal
  • to help to purge air that is trapped behind the piston, and in the mouldings on the piston body
  • to feel for any binding or restrictions that may be developing
Bleeding involves removing the SMC and tilting it so that the outlet port is uphill from the inlet port - to encourage bubbles to float up to the outlet port. 0 to 15 degrees tilt.

With one of those bleed valves open, and the bracket unbolted from the fork leg, the SMC can be pumped by pushing and pulling on the plunger.

If the SMC is still bolted to the fork leg, the bracket can be moved by hand. I curl my fingers around the fork leg and squeeze the bracket with the heel of my hand. But simply pushing the bracket is easy enough if one if those bleed valves is open.

With the system properly bled and all bleed valves closed, pumping the SMC is harder. The amount if movement is minimal. A tad more than 1mm. Anything more and either there us air in the system or there are problems developing with the SMC. Or you forgot to reinstall your rear brake pads ! That small movement is enough to lock the rear wheel in the workshop. It should release the rear wheel instantly you release the pressure on the SMC.

Pumping the rear pedal will pump fluid through the SMC. Pumping the SMC helps to make sure all of the old fluid is expelled. I use a vacuum pump on the PCV bleed valve when I pump the SMC, but alternating SMC pumps with brake pedal pumps a couple of times will do the job.

One other trick for testing the release of pressure through the compensation port in the SMC:
With the the rear pistons clean and shiny, and a tube attached to the front left lower bleed valve, push in the rear outer pistons. This should expel fluid through the bleed tube through the compensation port in the SMC. It is easier than pushing fluid up to the rear reservoir, as that involves a much longer length of plumbing, and two tiny compensation ports to negotiate.
 
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Pumping the SMC can be carried out when the PCV bleed valve is open, or when the rear bleed valve on the rear caliper is open.

i believe that it is important to do this to:
  • exercise the piston through its full range of travel
is there anyway you could video this process for us and post up on youtube the next time you do this procedure? :biggrin:
 

jfheath

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I developed a great deal of respect for the people that film their work. I did try it. I had 3 bullet cameras set up to show the calipers, the bleed tubes and the master cylinder and a couple of bright LED lamps as well as normal garage lighting. It wasn't enough. I was amazed at how poor quality the results were.

I need better lighting in the garage and more space. I've got more space, the lighting is awaiting a date. Not for film making, but 'cos I would like it. Brakes won't be touched until Winter now, they've had their service for this year.

So if you can wait.........
 
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So if you can wait.........
I think I have a pretty good idea what you are talking about on this but it would be nice to actually see it.

Yes ---- I can wait-- I appreciate you taking time to do this. I agree with you about the difficulty in filming these instructional video's and the people that do it are pretty good at it and spend some money on camera's lighting.
 
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This brake bleed thing is fresh on my mind. I’m new here, just bought a 2003 with 27k on the clock. Been going through changing all the fluids to kind of establish a baseline just because I don’t know the last time any of it was done. So I’ve now done the coolant, oil, final drive oil, and the brake fluid. But I put a new SMC on after hearing all the stories on here about rear wheel lockup. I have now bled these damn brakes three times(following the right procedure) and they are still spongy. I’m pretty mechanically inclined, but this bike may test my patience at times, it seems lol. Anyway, going to wrap the bleeders in teflon tomorrow and maybe hit them with the vacuum and see if I can get them to stiffen up. Guys, I’m venting, but tell me I will get this damn thing to bleed because I’m feeling a bit irritated right now…lol.
 

jfheath

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If it is still spongey, there are still air bubbles. You know that, but that's all it is, so it helps to have a plan and a map in your head about how the bits and pieces are connected. You can then chase the bubbles around the system to the nearest valve.

Grab a coffee, leave the bike alone for a while and take a look at this.

 
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If it is still spongey, there are still air bubbles. You know that, but that's all it is, so it helps to have a plan and a map in your head about how the bits and pieces are connected. You can then chase the bubbles around the system to the nearest valve.

Grab a coffee, leave the bike alone for a while and take a look at this.

This is one heck of a write up! Thank you! Feeling a lot more confident!
 

Kevcules

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Try lightly clamping the brake levers down overnight. I read that on here and it firmed up my levers when I tried it.
ST Brake bleeding is a real PITA. Since you should do it once a year, you will get better at it. :)
 
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Well got up early and did this procedure again using some of the tricks in the pdf. I tapped this, jiggled that, and this time they firmed up significantly. I don’t know how firm is firm enough but now I can’t get the front brake to touch the bars even when squeezing with four fingers. Might do it one more time for good measure and might clamps the levers overnight like kevcules said. Thanks guys. This website is a godsend. Really appreciate you guys. And yes, PITA is right but I’m already faster at it and can do it from memory so there’s that LMAO.
 
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I don’t know how firm is firm enough but now I can’t get the front brake to touch the bars even when squeezing with four fingers.
One thing that I do before any brake bleed of the ST is to get a feeling for how the brake pull and pedal push is before I start so I know about how it should feel when I am done. It should be about 2.5" from the center of the handle. This picture is pulling back on the front brake lever until I feel firm resistance.
 

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Just want to say thanks again to you guys. It’s a balmy 36 here in northern Michigan so I couldn’t resist a test ride. She stops on a dime. So fast.
You guys rule. Thanks for the help.
 
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One thing that I do before any brake bleed of the ST is to get a feeling for how the brake pull and pedal push is before I start so I know about how it should feel when I am done. It should be about 2.5" from the center of the handle. This picture is pulling back on the front brake lever until I feel firm resistance.
Nice! Great idea
 
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