- Joined
- Mar 18, 2006
- Messages
- 2,833
- Age
- 70
- Location
- Ilkley, W Yorkshire, UK
- Bike
- 2013 ST1300 A9
- 2024 Miles
- 000679
- STOC #
- 2570
Going back to things you have said that may mean something.
i) Corrosion under the rubber boot.
The rubber boot is there to keep water out. If you have corrosion there, then you also have corrosion behind the circlip and washer and spreading into the bore where the secondary seal moves.
ii) The rear outer pistons and the rearmost bleed valve on the rear caliper.
While it is true that the rear outer pistons are operated by the SMC, when working on the bike in the garage, you will note that the brake pedal also results in the operation of the rear outer pistons. The fluid flows from the rear reservoir to the front centre pistons, SMC and on to the rear outer pistons via the Proportional Control Valve. It is able to flow past the primary seal which actually seals only in one direction (like all primary seals in master cylinders).
I mention this in case that you draw the wrong conclusions when you open the rear most bleed valve on the rear caliper.
iii)Regarding the Rear Master Cylinder
You ask whether or not it could be the rear master cyclinder ? The same master cylinder has two lined connected to the Banjo bolt. One goes direct to the front left centre piston before continuing to the SMC. (It also goes to the front right, but it is subjected to a pressure delay by the delay valve). The other goes to the rear centre piston. If the centre pistons release after applying the brake pedal repeatedly, then it isn't the rear master cylinder that is causing the problem. You can also try pushing in the rear centre piston or the front left centre piston to see if fluid returns to the rear reservoir. (The rear centre is the better one to choose, as the fluid can go only in one direction. From the front left, the fluid could go in two directions).
But check out the documents - Going on an Airhunt and Avoiding the pitfalls will give a pretty good idea of how the brakes work and where the fluid goes from where.
Of course, your rear brake problems could always be due to a badly fitted front wheel.
What ? How?
Badly fitted front wheel = caliper offset in relation to the brake disk rotor = one pad of the left caliper catching on the rotor (especially if new) = SMC is applied = dragging back brake.
So see how the front wheel should be fitted. Here is one source.
www.st-owners.com
Do the research, go through the brakes systematically, don't dismiss anything. See what you find.
i) Corrosion under the rubber boot.
The rubber boot is there to keep water out. If you have corrosion there, then you also have corrosion behind the circlip and washer and spreading into the bore where the secondary seal moves.
ii) The rear outer pistons and the rearmost bleed valve on the rear caliper.
While it is true that the rear outer pistons are operated by the SMC, when working on the bike in the garage, you will note that the brake pedal also results in the operation of the rear outer pistons. The fluid flows from the rear reservoir to the front centre pistons, SMC and on to the rear outer pistons via the Proportional Control Valve. It is able to flow past the primary seal which actually seals only in one direction (like all primary seals in master cylinders).
I mention this in case that you draw the wrong conclusions when you open the rear most bleed valve on the rear caliper.
iii)Regarding the Rear Master Cylinder
You ask whether or not it could be the rear master cyclinder ? The same master cylinder has two lined connected to the Banjo bolt. One goes direct to the front left centre piston before continuing to the SMC. (It also goes to the front right, but it is subjected to a pressure delay by the delay valve). The other goes to the rear centre piston. If the centre pistons release after applying the brake pedal repeatedly, then it isn't the rear master cylinder that is causing the problem. You can also try pushing in the rear centre piston or the front left centre piston to see if fluid returns to the rear reservoir. (The rear centre is the better one to choose, as the fluid can go only in one direction. From the front left, the fluid could go in two directions).
But check out the documents - Going on an Airhunt and Avoiding the pitfalls will give a pretty good idea of how the brakes work and where the fluid goes from where.
Of course, your rear brake problems could always be due to a badly fitted front wheel.
What ? How?
Badly fitted front wheel = caliper offset in relation to the brake disk rotor = one pad of the left caliper catching on the rotor (especially if new) = SMC is applied = dragging back brake.
So see how the front wheel should be fitted. Here is one source.
Article [13] - ST1300 - Maintenance - Front & Rear Wheel Install and Front Axle Animation | ST1300 Articles
Animated sequence to show the correct procedure when installing the front wheel into the forks of a Honda ST1300. The right hand side of the bike is the side with the brake lever. Left is the clutch lever side. This is the convention used in the Honda manuals. The video and the photo below...
Do the research, go through the brakes systematically, don't dismiss anything. See what you find.
I would start from the beginning....