If you are not up to removing the wheel, then you are probably not up to doing what else is necessary. I see that you have taken the banjo bolts off.
You don't need to take the rear axle out - but you do need to slide it out part way to allow the caliper bracket to be removed from the axle. The axle can then be slid back in to support the wheel.
But. You have to remove the stopper bolt. at the front end of the caliper bracket. To do that you have to swing the left exhaust down slightly. And In order to slide the axle bolt out, you have to swing the right exhaust down slightly.
The exhaust is held by three bolts. 1) The obvious one above the silencer. Leave that 'til last. 2) There is a small nut and bolt that supports the silencer at the front end. Use a ring spanner on the inside of the silencer (to catch the nut). 3) The clamp band that pinches the silencer to the main exaust. Slacken it off. You may need some penetrating oil - You may also need a replacements - I use stainless steel clamps - the originals tend to rust and snap.
With the clamp band slackened, support that part of the exhaust with one hand and twist the silencer so that the silencer exhaust tube rotates within the female part of the exhaust.
Ok remove the large stopper bolt that is bolted to the swing arm.
Slide the axle out - catch the spacer and catch the caliper bracket with the caliper atatched.
Actually - you may have difficulty getting the caliper bracket off the brake disc.
I see that the pads are tilted at an angle, and that the pad pin has got a spring on it. Who the hell ........ never mind. That is an indication that someone had problems before and they have used a spring to try to get the pads to release. The problem is probably elsewhere.
So before you do any of that little lot, try to get the pad pin out and remove the pads. Make sure that you catch that spring. Find a suitable container to put it in. A rubbish bin is ideal.
DO NOT remove those slider pins. There are two. The one that you circled and there is another fitted to the caliper bracket.
The caliper bracket should slide away from the caliper on those two pins. You should feel a smooth glide. If you don't then that is another part of the problem. That caliper needs to be able to move easily and smoothly.
I know form the photo that it probably won't move that easily. The reason that I say that, is that the rubber boot that seals against the slide pin is not properly in place. That may mean that the pin is all rusted up.
With the caliper off, the pads out, and the caliper and bracket separated, there is some inspection and cleaning up to do.
0. Let all of the fluid drain out of the caliper
1. Check in the roof of the caliper. There should be a pad spring. Take a good look at the sahpe of it. Like a capital letter H (ish). One side of the H has a wider upright than the other side.A bit like this
I-I - Not which side that wider part is - It should be closer to the pistons. I wouldn't be surprised if it wasn't
2. Clean up both slider pins.
Refit that misplaced rubber boot. If it is too big to fit then that is because someone has used ordinary grease on the slider pins. It makes the rubber swell. If that has happened, or if it is torn, it will need a new one. If it wont fit, remove it for now and slide the two caliper and the bracket onto their respective slider pins.
The caliper should move easily back and forth without binding on any metal. If it doesn't then there is a serious issue -
possibly one of the slider pins is cockeyed
If that is the case, then there is a good chance that you may need a new caliper.
That slider pin that bolts into the caliper is incorrectly labelled in one of the service manual diagrams with the torque setting of the Stopper bolt.
The slider pin has a torque setting of 27Nm. The Stopper bolt has a torque setting of 69Nm!!!
You should never have to remove the slide pins. But if someone has, it is so very easy to cross thread it - and then (incorrect) 69Nm of turning force to a bolt that clearly isn't up to taking that load - the threads inside the caliper will have stripped.
That cannot be fixed - and you need to know that before spending time and money taking out seals and pistons. Hence the need to check that the caliper and bracket slide towards and away from each other easily. If the pin has been cross threaded, it will not be parallel to the other pin and the movement will tighten up at one end of its travel.
3. Check the elongated hole in the caliper bracket. Are there any spiral grease marks or spiral scratches ? Check the smooth shaft end of the caliper bracket stopper bolt. Are there any scuff marks ?
4. Check the fit of the chrome clip that is located on the caliper bracket. It is where the forward end of the brake pads seat. That clip should be a snug fit in the recess. IT will probable have a worn lower part, which means the clip is a very sloppy fit.
5. Check how easy it is to move the pistons in by hand. That will give you some indications as to whether or not the psitons were the reason for the brake drag. But also check the state of the seals. If there is evidence of hardened rubber then that is a sign that the brakes have got really hot and have melted the seals.
Let us know what you find.
While you are pondering about this, take a read of this for some additional information.
A close hands-on look at the Honda ST1300 braking system. These are personal observations about the things that can go wrong, why they go wrong and what can be done to keep things working sweetly. Updated April 2020 and to address more recent observations, to include information about the SMC...
www.st-owners.com
It is a pity that you have no fluid in the system One issue could be to do with brakes on the front forks causing the rear to drag. Someone at sometime has recognised that the rear brake is not releasing and attempted to fix it by putting that spring on the pad retaining pin. The often quoted cause of this is the SMC not operating properly and blocking the return of fluid from the rear caliper.
But it could also be due to the front wheel not being installed properly - the front brakes will then catch on the brake disc and drag slightly - but that will be enough to apply the rear brakes - constantly. "Often Quoted does not mean "this is the correct diagnosis". I've just given one of many examples where there could be another, seemingly unrelated, cause. The point is that you do not know until you investigate. But without fluid in the system it will be difficult to tell whether or not the SMC is behaving properly.
Is this the bike that you bought in 2019 - the silver 02 - or was it 03 ? And is this the first time that you know of that anything has been done with the brakes ?
There's a fair chance that there is a lot of sludge and grunge lurking behind pistons and seals. It is also probable that there is some gunge inside the SMC. You will be able to feel whether the plunger is operating smoothly - now that the fluid is out - but you won't know whether the compensation port is being 'opened' when the plunger / piston returns to its resting position. You need fluid in the system for that OR you need to take the SMC apart (not for the feint hearted). Is it is suspect, a new SMC is the best answer.
SMC - the front left brake brakcet is mounted on a needle roller bering pivot. When the front brake is applied, the pads grab the front disk, and the caliper tries to rotate forward around with the brake disk. It doesn't get very far, but that movement operates a plunger on the top of the brakcket . That plunger is a master cyclinder - like the one on your clutch or brake lever. It is called a secondary master cylinder - and it operates the rear brakes outer pistons. An important part of all master cylinders is a tiny pressure relief port, so that when the brake lever (or the SMC) is released, the tiny hole (compensation port, or recuperation port) is opened up and any excess pressure in the fluid can escape and fluid returns back to the reservoir and allow the pads to release.
So your project is probably a lot more complicated than you were thinking. But it all needs solving otherwise you will have the same issue again.
If you're not up to doing it yourself, you need a dealer that is familar with the ST1300 setup - or with the goldwing, or the VFR. The answer may be to just replace the seals, but you won't know until you cover all of the bases. I'd be expecting a load of work and a hefty parts bill - that way if I'm wrong I'll be quite pleased.
