St1300 rear brake issue

[Arturs]

Hi all
I'm hoping someone can help me. I'm having some issues with my rear brake. I have rebuilt the rear caliper, rebuilt the front secondary master cylinder, bled the brake fluid in the order that the manual advises... When I press the rear brake pedal, the pads are squeezed onto the disk, however the first and third pistons do not release straightaway, they drag the brake pads on the disc and take a while to release. The middle piston works as it should. Any ideas why the first and third pistons are not working as they should??
Thanks

 

[pmatulew]

There goes another one. It's an epidemic lately.

Pistons clean? New seals? Did you clean out the groove the seals live in?

The rear outer pistons are activated by the secondary master cylinder. Igofar will likely be along shortly to give you the dissertation about rebuilding the SMC and why it's often a fools errand.

 

[OkieRider]

I never reuse pistons on a caliper rebuild. Did you reuse? Dental picks used gently are good to clean the seal recesses. Greasing the seals is important. Is the master cylinder working properly?

 

[Igofar]

A few reasons that I am against "rebuilding" the SMC is because its often the bore that is buggered up, and a new piston kit won't help.
Another reason is the filter cartridge that sits behind the SMC often is found clogged up, and the return port plugged (see red circle) this is a guitar string pushing out solid varnish that clogged up the works etc.
You should also pull your rear caliper bracket off and inspect the inner hole area where the stopper bolt sits, if you see flutes as in this picture, your bracket may be damaged beyond repair.
Also inspect the ledge that the forward clip sits in. It should be a very tight fit, and not have any play in it.
The one in the picture shows damage from where the bracket fettered away allowing the clip to tilt, binding the brakes etc.

 

[Arturs]

I never reuse pistons on a caliper rebuild. Did you reuse? Dental picks used gently are good to clean the seal recesses. Greasing the seals is important. Is the master cylinder working properly?

Yes I did that

 

[Arturs]

A few reasons that I am against "rebuilding" the SMC is because its often the bore that is buggered up, and a new piston kit won't help.
Another reason is the filter cartridge that sits behind the SMC often is found clogged up, and the return port plugged (see red circle) this is a guitar string pushing out solid varnish that clogged up the works etc.
You should also pull your rear caliper bracket off and inspect the inner hole area where the stopper bolt sits, if you see flutes as in this picture, your bracket may be damaged beyond repair.
Also inspect the ledge that the forward clip sits in. It should be a very tight fit, and not have any play in it.
The one in the picture shows damage from where the bracket fettered away allowing the clip to tilt, binding the brakes etc.

Thanks for your advice. I inspected the rear caliper and rebuilt it, it seemed fine. I had a look at the SMC and it looked ok inside, but I rebuilt it anyway. But the first and third pistons are still not working as they should. My understanding was that the SMC operates the second (middle) piston, and that the first and third are operated by the rear brake -am I right in thinking that or are all pistons operated by the SMC?

 

[Igofar]

You should spend some time reading John Heaths artical ( ST1300 - Brakes- Avoiding the Pitfalls ).
The SMC operates the two outer pistons on the rear caliper. The center piston is operated by the foot pedal.
Your comment about "looked ok inside, but rebuilt it anyway" makes me think you went no further than wiping out the bore, and inserting a new piston/spring assembly....
Am I correct in assuming this? If so, even though the bore looked clean, and you put in a new part, you probably didn't open the back of the SMC to see if the filter cartridge was clogged up, nor should you, because parts are not available, and the screens and O-ring in there are easily damaged.
If it is clogged up (more than likely) your new piston, in your clean bore, is UNABLE to push the fluid over to the PCV, and then rearward to the rear caliper etc.
Also, if you followed the service manual's instructions for bleeding the system, it may have left air in the system, since you've had the SMC open etc.
You may need to go back and bleed everything a 2nd time.
Lastly, you do know that the circlip in the SMC is directional right? The sharp edge has to face outward, or you risk having it come undone at the worst possible moment.
Let us know what you find.
Good luck.

 

[Arturs]

You should spend some time reading John Heaths artical ( ST1300 - Brakes- Avoiding the Pitfalls ).
The SMC operates the two outer pistons on the rear caliper. The center piston is operated by the foot pedal.
Your comment about "looked ok inside, but rebuilt it anyway" makes me think you went no further than wiping out the bore, and inserting a new piston/spring assembly....
Am I correct in assuming this? If so, even though the bore looked clean, and you put in a new part, you probably didn't open the back of the SMC to see if the filter cartridge was clogged up, nor should you, because parts are not available, and the screens and O-ring in there are easily damaged.
If it is clogged up (more than likely) your new piston, in your clean bore, is UNABLE to push the fluid over to the PCV, and then rearward to the rear caliper etc.
Also, if you followed the service manual's instructions for bleeding the system, it may have left air in the system, since you've had the SMC open etc.
You may need to go back and bleed everything a 2nd time.
Lastly, you do know that the circlip in the SMC is directional right? The sharp edge has to face outward, or you risk having it come undone at the worst possible moment.
Let us know what you find.
Good luck.

There was a bit of corrosion under the rubber boot on the SMC, but the SMC piston was clear and intact. I also pulled out the inspection valve and took it apart. Again there was no grime or corrosion inside. I've been looking on the forum for things to look out for. I'll bleed the system again and see if that helps. I might have to take the SMC apart again and see. I'm wondering could it be RMC?

 

[SMSW]

What was the condition of the old brake fluid? If it had been left in long enough to turn black or look like it had sludge in it, then any small port in the system could be blocked.

A quick test might tell you something. Apply the brakes so that the rear outer pistons squeeze the pads against the rotor. Immediately crack the bleed nipple to release pressure on these pistons. This is often done by guys who have experienced the rear brake lock-up due to a bad SMC. If the rear pistons retract more quickly once you open the nipple, something is preventing the fluid from flowing back in the system. If cracking that nipple does nothing, my guess would be something is wrong inside the caliper.

While you had the bleeding tools and fresh fluid out, you of course, did bleed the clutch as well, right?

 

[OkieRider]

Is the master cylinder working properly?

I'm wondering could it be RMC?

 

[Igofar]

What was the condition of the old brake fluid? If it had been left in long enough to turn black or look like it had sludge in it, then any small port in the system could be blocked.

A quick test might tell you something. Apply the brakes so that the rear outer pistons squeeze the pads against the rotor. Immediately crack the bleed nipple to release pressure on these pistons. This is often done by guys who have experienced the rear brake lock-up due to a bad SMC. If the rear pistons retract more quickly once you open the nipple, something is preventing the fluid from flowing back in the system. If cracking that nipple does nothing, my guess would be something is wrong inside the caliper.

While you had the bleeding tools and fresh fluid out, you of course, did bleed the clutch as well, right?

While cracking the bleed nipple will release pressure on the pistons, it does not necessarily mean that its a fluid/flow issue releasing the pressure would also allow the caliper and/or pistons to shift and possibly correct an alignment issue.
You need to figure out if its a fluid issue, or an alignment issue, such as a damaged rear brake caliper bracket, etc.

 

[pmatulew]

If you don't already have it at your fingertips, you also want this.

 

[Arturs]

While cracking the bleed nipple will release pressure on the pistons, it does not necessarily mean that its a fluid/flow issue releasing the pressure would also allow the caliper and/or pistons to shift and possibly correct an alignment issue.
You need to figure out if its a fluid issue, or an alignment issue, such as a damaged rear brake caliper bracket, etc.

I cracked the rear brake nipple whilst system was under pressure (pedal) and it did release straight away and was spinning freely. At this point I know the alignment and caliper is correct because I took it apart and changed any worn parts. So I guess this is a flow issue..? Any suggestions anyone?
Thanks all.

 

[Igofar]

Are you implying that you were applying pressure by pressing on the foot pedal when you cracked the bleeder?
This does not rule out an alignment issue because releasing pressure anywhere in the system may cause things to move around and re-align themselves etc.
There are many things that need to be checked....
Are you using OEM brake pads? Have you checked all the tabs on the spring clips? Are the alignment pins clean and lightly lubricated? Are either of the front calipers binding, as this will cause the rear caliper to bind as well.
Have you inspected/cleaned the rear brake caliper master cylinder behind the sidestep?
Did you flush the system out completely and correctly?
Did you install the rear wheel in the correct procedure with the stopper bolt being tightened BEFORE the rear axle nut is torqued?
What year is your ST? What mileage is on it?
Did yours fall under the PCV recall? Was it done?
Etc.
Instead of chasing your tail looking at just the rear caliper, I would look/inspect the entire brake system as a whole, from front to rear, and every component in it, to have a better chance at figuring it out.

 

[Arturs]

Are you implying that you were applying pressure by pressing on the foot pedal when you cracked the bleeder?
This does not rule out an alignment issue because releasing pressure anywhere in the system may cause things to move around and re-align themselves etc.
There are many things that need to be checked....
Are you using OEM brake pads? Have you checked all the tabs on the spring clips? Are the alignment pins clean and lightly lubricated? Are either of the front calipers binding, as this will cause the rear caliper to bind as well.
Have you inspected/cleaned the rear brake caliper master cylinder behind the sidestep?
Did you flush the system out completely and correctly?
Did you install the rear wheel in the correct procedure with the stopper bolt being tightened BEFORE the rear axle nut is torqued?
What year is your ST? What mileage is on it?
Did yours fall under the PCV recall? Was it done?
Etc.
Instead of chasing your tail looking at just the rear caliper, I would look/inspect the entire brake system as a whole, from front to rear, and every component in it, to have a better chance at figuring it out.

The rear caliper is aligned correctly as is the assembly as I double checked. My bike doesn't fall under pcv recall as it's a 2003 model (pan European, 38,000 miles). When I was bleeding the brakes I noticed a clicking noise so I've ordered some more parts to reassemble the rear master cylinder and hopefully that's the cause. Feel like I've eliminated everything else so far!

 

[Catmandu2]

Did yours fall under the PCV recall? Was it done?

This is an interesting point. What bikes were recalled for pcv ?? Is there a list of all recalls available somewhere ? This is the first I have heard of any ST1300 recalls (perhaps with the exception of pan-weave),,, cheers,, CAt'

 

[Igofar]

ST1300 - RECALL: Brake Proportioning Control Valve (Bike Years: 2003-2004)
**RECALL WARNING - BRAKES on ST1300 ST1300A

 

[Fawlty]

These may help.

 

[caldercay]

This is an interesting point. What bikes were recalled for pcv ?? Is there a list of all recalls available somewhere ?

BrakePCVRecall < ST13 < STWiki

stwiki.notonthe.net

 

[Catmandu2]

Did yours fall under the PCV recall

Interesting,, and thank you. Here are some some handy links for my fellow Canuck's,,, cheers,, CAt'

Recall Details - Canada.ca

A quick and easy way to search for passenger vehicle and light truck recalls. Just provide the make, model, and year of the vehicle and you’ll get information straight from the Transport Canada Motor Vehicle Safety Recalls Database.

wwwapps.tc.gc.ca

Search Results - Canada.ca

A quick and easy way to search for passenger vehicle and light truck recalls. Just provide the make, model, and year of the vehicle and you’ll get information straight from the Transport Canada Motor Vehicle Safety Recalls Database.

wwwapps.tc.gc.ca