Slydynbye
Will ride for Pie
Why confuse the issue? If you do it properly there are less doubts, it's only a couple ounces of brake fluid.
Advice needed on what is causing rear pedal pressure lose.
- Thread starter Langley863
- Start date
Seems not to include the SMC.
Have you looked at the well done braketoy posted above?
Somebody put some serious work into that.
The front lever engages the front outers only. The front lever is hydraulically coupled with the front calipers only, and nothing else.
When the bike is in motion, the SMC is what activates the outer rears, not the front lever, and the SMC is on a different hydraulic loop, no connection with the front loop at all.
Which is a good thing to have. If the rear starts giving you trouble while out in the boondocks, it is good to know you can bleed the rear to get you going, and still rely on the completely separate front brakes loop to limp back to civilization with about 45% of the total braking power of the bike still available.
You may want to re-think your thoughts on being able to bleed the rear system, and limp back on the front system.
It does not quite work like that
OK then, let me try to think about it.
Instead of just bleeding the SMC loop, let's say I remove the SMC, I remove the rear MC, I remove the rear caliper.
Then the front lever will still activate the 4 front outers whenever I pull it, just as it does now when I sit on the bike, no difference moving or not. Enough to limp for a while, no?
Is that like having a front flat tire and just wheelieing the bike all the way home?
I’m gonna have to go with No, and let somebody else try and explain it to you as I’m in the middle of a job right now.
OK. Waiting.
Is that like having a front flat tire and just wheelieing the bike all the way home?
The point I was trying to get to is related to the hydraulics of the ST.
You may know most cars have a divided hydraulic braking system for redundancy; if one side fails, the other offers enough residual braking power to slow the vehicle down.
If you don't, there is more on that here.
That's also how most motorcycles with hydraulic brakes are designed, two distinct hydraulic systems, often just front and rear, if one leaks, the other remains functional and can still help with slowing down. There are no hydraulic connections between the two systems, they are separate.
And Honda of course would not and did not do away with such basic redundancy on the ST.
You can burst or burn all the hydraulic lines between the front lever and the front outers it activates, and your rear pedal will still do its work. The hydraulics linked to the rear pedal won't be affected by a catastrophic failure of the front brake lever system.
And conversely, you can have a massive hydraulic failure of the separate system comprising the rear MC and SMC, lose all its hydraulic fluid, and it still won't affect the capability of the front lever to activate the front outers. If you think it does, please explain.
If you find a path on the schematic below for fluid to migrate from the Front MC system to the Rear MC + SMC system or vice versa, please highlight and post back.
Thank you very much for your time and input.
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The only way I could see fluid being able to migrate from front to rear or vice versa would be through the smc if the seals failed on the piston inside the smc or the piston sticks in a very specific way. Then fluid could in theory I guess travel between the 2 masters.
Just to clarify this is purely a guess from looking at the brake toy posted further up. (Brilliant tool to see how the system fully operates) again this is a guess and I won't make a guess as to if this would still give you brake pressure to stop or not.
Just to clarify this is purely a guess from looking at the brake toy posted further up. (Brilliant tool to see how the system fully operates) again this is a guess and I won't make a guess as to if this would still give you brake pressure to stop or not.
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I had pedal drop at the beginning of my ST1300 owner experience. I bought my 2005 with 1800 miles on it. After the first bleed that I did around 12,000 miles the drop was better but not gone. I went at it again following the Leo 7x24 tutorial. I used a vacuum pump but pumped the brake pedal to help the fluid along in the circuits fed by the rear master cylinder. Using at least two or three full reservoirs I moved a lot of new fluid through each circuit. All but one seemed free of air but the Proportional Control Valve finally gave up several good bubbles. After that bleed the pedal drop was completely gone and never returned. I rode it enough to bleed it once or twice a year, at 12,000 miles, so I never came close to doing it biannually. Like others I feel this service done annually or no more than 12,000 miles will go a long way towards preventing brake system problems. I never again had brake issues and sold the bike at 180,000 miles.
Let's hope to hear from Langley863 that his pedal drop is gone as well!
Was unable to get out and bleed it today bit did yesterday and it definitely improved but still getting the issue. Next decent day I'll go back out and do it again
Progress!
As dduelin suggests, the PCV is an item likely to retain air with its convoluted path. So step 3 is worth spending time on, pumping the brake pedal as dduelin did, moving a lot of fluid there and tapping (or vibrating if you have a way to do it) the PCV while doing it.
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The front lever and the front outer pistons on both calipers are isolated hydraulically. But to ride without the rear system working as it should is potentially dangerous. You do not know why the rear system is misbehaving and I can think of scenarios where this would not be a wise thing to do - and some of those scenarios would be mechanical as issues as a result of applying the front brakes.
You can always feel a very slight dip in the pedal if you release the front brake (and in the lever when you release the pedal) - but that is due to the feel in the lever/pedal as the caliper repsondse to the other piston(s) in the caliper being released.
Air in the system - the rear brake line - is the most probable culprit. And the cheapest to fix. When out riding, I could work where the bubble was located, and was able to flush it out very quickly. But when I try to explain it to myself - or write it down, I cannot make my logic work.
Check out the link to my article and follow the steps in order to go chasing after air bubbles. And watch the video in the first post - it might help you to realise what you are up against.
Article [13] - ST1300 Maintenance - Getting all the air out of the brake system | ST1300 Articles | ST-Owners.com
You can always feel a very slight dip in the pedal if you release the front brake (and in the lever when you release the pedal) - but that is due to the feel in the lever/pedal as the caliper repsondse to the other piston(s) in the caliper being released.
Air in the system - the rear brake line - is the most probable culprit. And the cheapest to fix. When out riding, I could work where the bubble was located, and was able to flush it out very quickly. But when I try to explain it to myself - or write it down, I cannot make my logic work.
Check out the link to my article and follow the steps in order to go chasing after air bubbles. And watch the video in the first post - it might help you to realise what you are up against.
Article [13] - ST1300 Maintenance - Getting all the air out of the brake system | ST1300 Articles | ST-Owners.com
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I just do not see the logic of going through repeated flushing of the front MC system to try to dislodge air in the rear MC+ SMC system.
I doubt jf would bother flushing his front lines to very quickly move air out of the PCV!?
Plus his time and he is going to have to go at it several times, doing something unnecessary. He is not having issues with the front brake. Why mess with something that works?
Good you mention that. So Langley863 doesn't waste his time thinking he can completely eliminate the small drop.
I have just sent a private message to Langley863 in an attempt to assist him with his brake bleeding issues.
I sent it as a private message to keep the confusion to a minimum, so folks would not start arguing and complaining about these instructions, and confuse matters even more for the poor guy.
If it works, he can then cut and paste my instructions on to this thread so everyone can see what worked, and what didn't without all misunderstandings and opinions etc.
Keeping my fingers crossed for Langley863.
I sent it as a private message to keep the confusion to a minimum, so folks would not start arguing and complaining about these instructions, and confuse matters even more for the poor guy.
If it works, he can then cut and paste my instructions on to this thread so everyone can see what worked, and what didn't without all misunderstandings and opinions etc.
Keeping my fingers crossed for Langley863.