How much rear brake drag is normal?

[Tommo]

Hi Guys.

I've owned a coupe of non ABS ST1100's and a familiar with a tool kit. Swapping brake pistons / calipers / hoses a fluids not an issue on that bike.

I recently purchased a 2002 Non ABS ST1300 with 31,000 miles on it. A few days later a realised when the bike on centre stand the rear wheel wouldn't freely rotate, I could turn it by hand but there was no rotation without me physically pushing it.

So, I did my ST1100 thing. Removed the rear calliper, pushed out the brake pistons, cleaned and lubricated them, then pushed them back in, using a G clamp and wood combination. This improved the situation a little, as the wheel does rotate a bit.

Since then I have removed the front callipers, cleaned up and lubricated the pistons. The right ( when sat on it ) hand calliper had seized on the sliders, but that was also sorted, and now slides easily.

I then performed a brake fluid flush, following GTs Garage technique : - Bleeding Linked-Brakes (ST1300a) Step by Step - YouTube

So, how much brake drag is normal ?? I've tried to attach a video but it won't accept MP4 formats. " https://youtube.com/shorts/h82GJu64A7s?feature=share "


Or does this indicate a problem with the SMC or proportional control valve ?

Thanks in advance

 

[Kevcules]

Your rear wheel is definitely dragging more than normal. You could remove the rear caliper and try spinning the wheel to determine whether it's brake related. Most likely it is. 1.5 to 2 rotations is normal.
Definitely check your SMC function and again, more than likely it's failed. Common problem. Lots of how to's in the article section.

 

[dduelin]

With the rear pads in place in the normal position ready to brake a good healthy shove with your foot should give 1.75 to 2.5 rotations.

 

[Cincykz]

I get about two spins out of a good kick on the center stand. I've heard that three is better, but I'm not sure if I get three full rotations (hard to tell)

 

[Jjonahjamison]

I have found that rear wheel free rotation is improved by firmly engaging the rear brake pedal while you are torquing the rear axle (when reassembling after wheel removal). It just seems to ensure that the rear brake assembly is better aligned on the brake rotor as everything gets tightened.

I have had a second person hold the rear brake pedal down during the process, and have also used a ratchet stap connected to my lift (both work).

 

[ToddC]

Check your SMC.........!

T

 

[sky.high]

A much better way of detecting brake drag is to ride the bike from cold brakes a few miles on a straight road, slow down to a stop without using the brakes, front and rear rotors should be about the same temp as before the run.

 

[Igofar]

I would suggest you NOT ride your bike at all in that condition or you will cause a lot of damage to your rotor, bearings, rear caliper bracket, rubber brake lines etc.
Or…. Your bike could toss you off without warning!
Before you start throwing money at things that MIGHT fix something, search the articles for John heaths avoiding the pitfalls, and research SMC failures etc.
Your SMC is probably locked up, causing your rear wheel to drag etc.

 

[Tommo]

Thanks for your comments.

I have been looking through the various articles including those by @jfheath. Am I correct in thinking, if I'm satisfied that the 3 rear brake pistons are mechanically free to move. Then the issue is hydraulically transferred from elsewhere in the braking system.

So if I cant push back by hand the rear centre piston ( bleed nipple closed off ), the problem is on the rear master cylinder line, and if the outer two won't move back, its on the SMC line?

 

[Igofar]

No
Don’t get caught up and confused with theory, cut to the chase and inspect your SMC before you start looking elsewhere.
Does your SMC have any free play in it?
Can you shake it back and forth and make any noise (not good) if you can, could mean your piston is stuck inside the bore, and the return port is obstructed.
Gently lift the rubber boot and look beneath it,
I’m betting your gonna find rust.

 

[Igofar]

Probably find something like this.

 

[oude geit]

SMC sucketh. Ive never got 3 spins out of my wheel, even with the caliper off. I do get about 1 to 1.5 turns everything assembled. Dont ride it that way, the smc, linked break failure mode is ridiculously dangerous.

 

[Sheriff41]

Heed what @Igofar has to tell you on this. The @jfheath articles on brake maintenance are invaluable.

 

[jfheath]

You can get useful information from moving the pistons (or not), which you cannot get after the fluid has been drained. So it's handy to be able to find out what is moving properly and what isn't so that you can address all of the known problems before filling it up again.

But the SMC is so exposed to the elements; is apparently so frequently badly maintained; has the potential for such sudden and drastic consequences - that if there is even a suggestion that it might be faulty (like being 20 years old and having relatively low mileage), you'd just fit a brand new SMC before they stop producing them and know that it is OK.

Fowlers are major importers of Honda parts and have rapid delivery. There's not much advantage in shopping around for genuine Honda spares in the UK - Everyone sells the parts for the same price. Some quote VAT, some not. Delivery may be the deciding factor. Or if you have a local dealer that you have used, they may give you a discount, they are always getting spares in and will probably not charge you delivery.

I've had my ST1300s from new. I service the brakes thoroughly every winter and came across a behaviour that I had a bit of doubt about. I didn't think that it was the SMC that was at fault, but I bought a new SMC because there was a slim chance that it was part of the problem. I was wrong. It was something else, but - it means I have a used spare SMC which is perfectly OK - except for the circlip, so I'd probably put a new service kit in it if I ever needed to use it again.

Just looked to see where you are. You're only 50 miles away if you need help.

 

[Tommo]

Probably find something like this.

To be fair to the PO, this bike looks as he stated. Had it from new, regularly serviced and well maintained, and the miles on it appear to have been dry days, and summer tours of Europe. ( He had other play bikes ), underneath the plastics, it's in really, really good condition. When I changed the brake fluid, it was clean and new looking, with no colour difference to what I was replacing it with.

This is the SMC outer piston, with boot removed, and to me it doesn't look bad.

I read somewhere that non OEM brake pads can also cause problems, the final picture is of the rear ones, looking at the parts fiche, it appears the original have 4 friction areas per pad while these have 2, could this be anything to consider?

 

[Tommo]

SMC sucketh. Ive never got 3 spins out of my wheel, even with the caliper off. I do get about 1 to 1.5 turns everything assembled. Dont ride it that way, the smc, linked break failure mode is ridiculously dangerous.

Yeah, I've tried it with the rear pads out, and I'm getting about 1.5 to 1.75 turns out of it. I will abide by your good advice ( and that of others ) and I won't be riding it, until its all sorted.

 

[mjc506]

If the pads are removed, there's no way the SMC is getting involved. Any drag is in the bearings and drivetrain (which 'loosens up' a lot once it's been run and is warm)

If you get significant additional drag with the pads in and brakes cycled, that does indicate a problem somewhere, anywhere between the pads getting hooked on a notch worn in the pin (or the spring in the 'roof' of the caliper), to a failing hose acting as a partial one-way valve, to the SMC not operating properly, or even the front left caliper dragging (and operating the SMC, applying the rear brake)

 

[Tommo]

Symptoms change.

Had the rear pads out and very slightly pushed the pistons back, then put the pads back in and the wheel rotated ok.

Had the boot of the SMC piston, greased it up with silicon grease, and put the boot back in with the help of a 40 year old draper small sized plug socket ( pulled the rubber out it first ) it was like it was designed to get that boot back in !!

Lay down pushing the rear wheel with my foot and activated the SMC by squeezing it towards the forks. The Back wheel locked up, and released to an acceptable rotation. did this a few times, and the rear wheel rotated ok. Then I pressed the back brake pedal, stops the wheel but it didn't release as much, reducing the rotation.

I'm tending to think there is something wrong with the rear centre piston, or rear master cylinder.

 

[Igofar]

A couple other things that can cause that….
You have non OEM EBC pads in there. These often have fitment issues on these bikes.
The rear caliper guide dowel is probable dry and dirty not allowing the caliper to float side to side.
The rear caliper mounting bracket may be damaged (loose clip tilts binding wheel)
Look inside the stopper plug hole, if you see what appears to be flutes, or spirals, the bracket is damaged.
The rear wheel may have been assembled in the wrong sequence, the stopper plug needs to be tightened BEFORE the axle nut.
The front pads being non OEM can cause your rear wheel to drag as well for several of these reasons.
As well as damaged rear driven flange bearings, a damaged inner o-ring behind the spline hub etc.
You will need to examine alit of stuff before you start spending money trying to fix the problems.
Do NOT take the rear caliper APART, to clean things, or you risk damaging it.

 

[Igofar]

Notice the wear marks on the stopper plug, in the middle on one side, and at the end on the other. This is a sign the rear caliper is crooked etc.
Check the rear caliper bracket clip, is it worn or loose as in this picture?
Are your guide dowel grommets pinched as in this picture?
Upper clip bent or damaged?
Is your caliper clean or is dirt jamming the pistons up?
Even if the pistons move manually if the are dirty they won’t release etc.