rear brake sticking

jzanutto said:

I had already ordered an SMC overhaul kit, and since I cant ride the bike I figured I'd take the left caliper off and open up the SMC. Snap ring, rubber boot and plunger came right off.

It's completely packed full of rust powder. and the SMC piston wont come out. I've got some cleanup to do prior to the SMC kit arriving. Hope this is the cause

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Just wondering if you keep your bike garaged while not riding? Or is it exposed to the elements all the time? Can't imagine that much deterioration of the SMC.

I just bought the bike from a Fresno State professor. Its an 04 with only 39xxx miles on it and it looks brand new; in fact those who are not ST savvy think its a new 2015 bike. It never sits outside.

The corrosion is inside the rubber seal, under and around the plunger and I'm sure it's worked it's way into the SMC passages

there is not a cleaner 2004 st1300

I'm new to this bike (less than 1,000 miles) but I've looked at the SMC issue and I expect I'll need to fix mine someday. When that day comes, I expect I'll buy a replacement unit rather than a rebuild kit because the whole SMC assembly is pretty reasonably priced around 120 bucks.

With a new unit, I won't risk discovering problems (like cylinder pitting, for example) after paying for a rebuild kit and while I've got my bike out of commission.

I have mine apart and I didnt find any of that. The cylinder bore is nice and clean. The fluid inside was like a white gel with some rust bits floating around. Interesting how brake fluid attracts and holds moisture.

I pulled apart the compensator valve and cleaned it up too. Actually the seals are fine, and it wasnt leaking. I could probably just put it all back together but since those seals are 11 years old and its apart I'll wait for the kit to come

Bobert said:

Just went to my local Honda dealer to buy some Molly paste for a gift, went to the counter and asked for a tube of Molly Paste. His reply was " molly what" I said "Molly paste" His reply was that they did not carry it. I asked, "what do you use?" He called to the back, and asked a tech if they had any, No, he thought they used Molly grease! I left and ordered it on line. Does make one wonder.

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One of the first things I check for when entering a new Honda dealer... No Moly? No sale.

I'm late to the game here but gonna offer a suggestion. This worked on my 2001 ST-1100A so it might work on a 13 as well. When I first bought this bike (54,000 miles), the rear brake was dragging badly. Primary reason I was able to get it cheaply as the dealer used by the previous owner couldn't fix it and potential buyers were put off. It sat for over 2 years.

Anyway, after checking, reading, learning, and leaning on other members here, no success. Finally, Deba suggested, "It's ABS, right? Maybe it's never been used."

So, with heart in mouth, I took it out and Exercised the ABS, both rear (not too hard), and front (Yikes!) A few applications, and all was good and has been for ~150,000 miles. Talked to Norm in Canada (ABS guru) and he agreed, a little crud might accumulate in a modulator valve, and the rear brake valve resides below the front brake valve in the unit. So, just a thought.

Try it, can't hurt and might help. Well it could hurt if the ABS doesn't work when ya grab the front brake. Be careful and wear all yur gear.

jzanutto said:

there is not a cleaner 2004 st1300

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In the USA 2004 models are blue. 2003 is silver.

Not so clean on the inside though.

Glad you found at least one of the problems with the rear brake and at least now you know the hydraulic service probably wasn't done on time....maybe since the bike was new. This bike can be intolerant of brake system short cuts or neglect. The SMC is oriented downward and moisture and air can collect in the upper end of the bore. It's important to remove and tilt the LF caliper at the proper time when flushing and bleeding the system.

dduelin said:

A defective rear master cylinder or a bit of trash blocking the fluid return orifice on it could lock up the rear caliper then allow a slow release of fluid pressure. If it did the PCV and the SMC could both be blamed and yet be good.

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Absolutely.


My thinking was that if the rear master cylinder was the culprit, then the problem would manifest in all rear master cylinder hydraulic circuits.

When Mr. Jzanutto reported that the center bleed screw did not release the locked-up brake caliper, that information indicated to me that the brake components involved in the center piston, rear brake caliper hydraulic circuit were operating properly.

As the rear master cylinder is one of the components in that specific hydraulic bake circuit, it appeared unlikely that the rear master cylinder was a contributing factor to the locked-up rear brake issue.


With the rear master cylinder, and the center piston of the rear brake caliper ruled out, what's left?

In Mr. Jzanutto's original post he stated that operating the front brakes, did not induce any rear brake lock-up. This information indicated to me that either the SMC hydraulic circuit was operating correctly, or the SMC was not operating at all.

When Mr. Jzanutto reported that the rearward bleed screw did release the locked-up brake caliper, this information pretty well narrowed the fault to either the SMC, or the proportional valve. This would have been the time to attempt to manually operate the SMC, to determine if the SMC is functioning. Perhaps I missed seeing this report, however as the ST1300 SMC has a well documented history of failures due to water ingress, it seemed very likely that he SMC was at fault, probably with a seized piston (most likely due to water intrusion at the push-rod end) blocking the flow of returning brake fluid to the rear master cylinder.

As we know from experience bleeding ST1300 brakes, the rear master cylinder 'pushes' brake fluid through the SMC, and on to the two outside pistons of the rear brake caliper (via the proportional valve), to the rearward bleed screw.

This knowledge along with Mr. Jzanutto's observations, allowed me to imagine a probable sequence of events that could lead to a locked-up rear brake caliper. I imagine the most likely scenario is this:

1. When the rear brake pedal is applied, brake fluid passes through the SMC, through the proportional valve, and on to the outside two pistons in the rear brake caliper, where the brake pads are applied to the brake rotor.
2. When the rear brake pedal is released, brake fluid is prevented from returning (to the rear master cylinder) from the rear brake caliper via the SMC, due to the SMC's seized piston blocking (or partially blocking) the compensating port. Thus the brake pads remain applied to the brake rotor.

I would add that you should pack the SMC boot with brake grease. The new manual I bought has that as a maintenance item along with bleeding the brakes. It will help keep water out of the SMC. Good luck fixing you brakes.

yes as you suggest, I was thinking of packing the rubber with grease to prevent corrosion.

George said:

So, with heart in mouth, I took it out and Exercised the ABS, both rear (not too hard), and front (Yikes!) A few applications, and all was good and has been for ~150,000 miles. Talked to Norm in Canada (ABS guru) and he agreed, a little crud might accumulate in a modulator valve, and the rear brake valve resides below the front brake valve in the unit.

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Honda must have known that was a problem because the modulators on the 13 get exercised every time ABS computer starts up.

--Mark

Reginald said:

I would add that you should pack the SMC boot with brake grease.

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That's sounds like an excellent idea. Just make sure that you use a brake compatible grease, as rubber brake components do not get along with petroleum products, which most greases (is that a real word?) are.

jzanutto said:

I just bought the bike from a Fresno State professor. Its an 04 with only 39xxx miles on it and it looks brand new; in fact those who are not ST savvy think its a new 2015 bike. It never sits outside.

The corrosion is inside the rubber seal, under and around the plunger and I'm sure it's worked it's way into the SMC passages

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It's probably real clean because it was washed a lot and water got in the SMC. When I wash mine I wrap the area with electrical tape around it. I replaced mine at 50k just for preventative measure and it was still fine. I did pack silicone grease under the boot.

Anna'sDad said:

That's sounds like an excellent idea. Just make sure that you use a brake compatible grease, as rubber brake components do not get along with petroleum products, which most greases (is that a real word?) are.

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Just an FYI, Plumbers Grease (available at yur local hardware store) is non-petroleum as ABS and PVC plastic don't like petro either. Car and bike places charge a premium for such as "specialty" product.

Thanks for the tip on the 1300 modulator, Mark.

George said:

Just an FYI, Plumbers Grease (available at yur local hardware store) is non-petroleum as ABS and PVC plastic don't like petro either. Car and bike places charge a premium for such as "specialty" product.

Thanks for the tip on the 1300 modulator, Mark.

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That would be silicone grease. I had some that I used on a Moen faucet left over.

My opinion that this "keep out the water" is a hit or miss idea. I ride year round, ride in rain when it's raining which is fairly often and wash my bike 1 to 4 times a month (maybe 250 wash jobs?) yet after 9 years 153,xxx mile my SMC still works fine. Once in a while I pull the boot back to check for corrosion but none so far. At 100k I bought the parts to rebuild it but it's never needed it yet.

I do flush the system at least every 12,000 miles and do every step in the flush with no short cuts. Keeping the fluid clean and the SMC flushed is important with the linked brake design. The boot won't keep moisture out of the SMC bore if it's not serviced regularly.

I think I fixed it. I have gone on a short ride and it should have hung up by now.

This issue can be fixed without buying any parts. The brake piston rubbers were just fine, no problems in the bore. The issue was the gooey gelled brake fluid in the SMC and most importantly, up in the compensating chamber of the SMC.

Dont overlook this- the compensating chamber is removed by removing the 2 bolts holding the retainer plate and then pulling out the compensator valve body. It is a white plastic valve body that has a spring loaded one way check valve. This had the goo in it, and I think the function of this valve was compromised.

Just a good cleanup and purging out of the crap was really all that was needed. But I ordered the new SMC piston anyway.

Then I went through the bleed procedure twice. There was a TON of air when I got up to the proportioning valve.

this picture makes it look like its part of the casting, but its a removable assembly

Great news on getting it fixed.