Not happy with my brakes

Joined
Oct 9, 2014
Messages
32
Location
Isle of Man
Bike
ST1300
Just done a big service on my ST1300 (2002, no ABS), and bled the brakes with fresh fluid.
When I was done, with the bike on the centre stand and rotating the back wheel by hand, it locked up well when the rear pedal was depressed - as expected.
However, the brake seemed slow to release. I could rotate it (just) by hand but it was dragging. After I'd turned the wheel two or three times it began to free up, another few turns and it was fully released. This doesn't seem right to me, surely the wheel should be free once the pedal is released.
I thought the calliper seals might be the culprit, so got a replacement set and overhauled the calliper completely. The pistons and bores were in pretty good condition and no major faults were found. I've rebuilt the calliper and its back on the bike.
After bleeding through the sequence, it would seem I've still got the same problem, back brake slow to release after depressing the pedal.
I've also noticed another issue, that when I push the SMC by hand, it does not feel as firm as I remember it used to be, a bit squishy.
I'm beginning to think I've not successfully got all the air out of my lines, but after spending a WHOLE DAY and bleeding 3 litres (about 5 pints) of fluid I'm getting short of patience. Aaaarrrgghhhh!!
I've got a Haynes manual which I've followed, and have also read the extensive instructions from other riders on this site, just don't seem to be getting the thing right.
Anyone got any wisdom for me?
 

wjbertrand

Ventura Highway
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The SMC should not come into play when the bike is stationary on the centerstand, it requires front wheel rotation to engage. If it were stuck you would not have had to apply the rear brake pedal to cause the observation. I would look at a possible partial occlusion of the relief port in the rear master cylinder. This is a very small passage that allows applied rear brake pressure to bleed off back to the master cylinder after the piston as returned to it's resting position.
 

Mellow

Joe
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The PCV is also tough to bleed, not sure what the Haynes manual says about it.
 
OP
OP
Double oh nine
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The bike had a new SMC just two years ago, only done about 10k miles mostly in good weather. I'm not convinced the SMC is at fault, but I'm not sure of anything at the moment. WJ Bertrand's comment is interesting, I was thinking along those lines...
 
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British Columbia
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Just done a big service on my ST1300 (2002, no ABS), and bled the brakes with fresh fluid.
Did you replace the brake pads? Some drag is quite normal with disc brakes and new pads can make this more obvious, since they aren't yet worn into the wear pattern on the rotor.
 

Reginald

cyclepoke
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Georgetown, Tx
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8898
Having experienced a failed SMC, your symptoms are very similar to mine. My SMC would slowly release over a period of hours freeing up the rear brakes and allowing the rear wheel to spin. Really sounds like your SMC failed. Buy the whole assembly, not the rebuild kit. Other riders have experience mixed results with the rebuild, there's a little valve in the SMC you can't get during the rebuild. The manual says to drain all the brake fluid, but I didn't do that. I just release pressure from the PCV, rear brake bleed nipples, and removed the rear reservoir cap. Then took the old SMC assembly off and installed the new one with new crush washers (be sure to have a pan to catch what little fluid drips out). Made flushing easier, not as much air to push out. When you remove the SMC assembly is a great time to clean up the calipers and re-grease the slides. Lastly, be sure to smear some brake grease/silicone grease under the boot and on top of the washer there (best performed when the SMC assembly is off the bike). It'll protect the SMC from water and should be performed annually to extend the life of the SMC.
 

SteveST1300

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I would look at a possible partial occlusion of the relief port in the rear master cylinder. This is a very small passage that allows applied rear brake pressure to bleed off back to the master cylinder after the piston as returned to it's resting position.
I had not heard of this before but if your SMC is new I would look at this next and then the Proportion Control Valve (PCV)
 

dduelin

Tune my heart to sing Thy grace
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I'm with Jeff in post #4. If you only press the rear brake pedal with the bike stationary on the center stand then the SMC is not part of the circuit applying pressure to stop the rear wheel.
 
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Aug 11, 2013
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kankakee
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with the bike on the center stand , have someone hold the brake and open the bleeder while trying turn the wheel. If it frees up quicker then it is a hydraulic problem ad not the caliper.
 
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Why don't you just ride the thing and see how it works? Disk brake pads don't retract, They just get knocked out of the way. It's probably fine.
Ever had a real tank slapper on a disk braked bike? Better pump the lever before you actually need to stop. The pads get knocked all the way in, and you get nothing at all. This happened to me recently. NOT on the ST.
 

Reginald

cyclepoke
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8898
As I understand it - All brake circuits rely on the same principle that the fluid can return through a relief port, once the plunger (of the primary seal) has returned to its normal position. The SMC is no different, except that the SMC can, over time and inadequate servicing, acquire crud inside the SMC body and behind the secondary seal (the one nearest the circlip). This can stop the SMC from returning fully, and keep the relief port closed.
This is exactly what happened to me. I could ride around using the front brakes then get home put the bike on the center stand and press the rear brake pedal and oops the rear brake locked up. There is a ball valve (relief port) in the SMC that can corrode, clog, and keep pressure on the rear caliper when the rear brake is operated. ANNA's DAD posted a diagram of the SMC that displays the valve; although I can't find it right now. The SMC appeared to be working for me but it wasn't! IGOFAR (Larry) was kind enough to insist it was the SMC though I demurred at the time and he was right. I replaced the SMC and all was well in brake-ville.
 
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Also check steel brake lines make sure it did not get dented or smashed, that could slow down the fluid return. never overlook the basics.
 
OP
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Double oh nine
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Isle of Man
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Thanks everyone for your thoughts. I can't get back to work on the bike till next week, busy weekend. I'll try to work out which piston is sticking, thanks fjheath post no 13. I'll also hang a weight from the pedal overnight and re-bleed to see if I can tease any more air out. I wrapped PTFE tape around all nipple threads when the system was drained, been intending to do that for a while I think it helps with the vacuum bleeder. I did not install new pads on this service, just cleaned the last ones and calipers as there's plenty left on em. If I'm still stuck i suppose I'll have to drain down again and look at the rear master cylinder and SMC
 
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Jan 28, 2017
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Air in the system will cause spongy brakes, it wont cause the rear to drag, why would it, less pressure wont make anything grip harder.
With the bike stationary on its mainstand pressing the rear pedal will fully push out the smc piston if it is sticking in a little, as has been suggested, and therefore open it beyond the 'compensating port' thus releasing any pressure, If the rear is still sticking its something binding in the rear caliper.
Nearly all Hondas I have worked on have white fluffy stuff built up on the inside of the dust seal which is the outer seal in the caliper, this build up caused the seal to sit high and this tightens the piston. You should be able to press the caliper pistons back in by hand.
PS, when you are finished with the vacuum bleeder, re do it all the conventional method, that will probably solve your problem.
 
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