Any banjo bolt that you remove or slacken needs to have new crush washers fitted. These are either aluminium (or an aluminium alloy) or copper - a soft metal. During the tightening process, they are squashed / deformed so that the metal faces seal perfectly against any tiny imperfections in the surface of the banjo union or the casting of the caliper, master cylinder or banjo bolt. Once crushed with the correct torque, they cannot be re-used - they are no longer soft and will not seal properly. I use copper bought in bags of 100 from goodridge, but your dealer/service centre will probably sell you some cheaper than buying them individually.
When reassembling, I tend to tighten these to about 20 Nm so that they seal ‘enough’ for bleeding and checking purposes, but the washers are not yet crushed. The actual torque required is much higher than this - but this allows me to slacken the bolt to burp any air at the union.
Front brake outer pistons on both sides are not affected by work on the rear master cylinder, but you will have to bleed at the centre pistons (ie the lower bleed valve) on both front brake calipers.
It is worth exercising the SMC while bleeding at the rearmost bleed valve on the rear caliper. The SMC operates only on the two outer rear pistons.
From the rear master cylinder there are two brake lines. The shortest and easiest to bleed is to the rear centre pistons- the one in the middle top of the rear caliper. Then bleed the centre pistons on the front calipers (lower bleed valve) - right side first. Then the rearmost bleed valve on the rear caliper. Repeat.
Air bubbles get trapped at the top of ‘n’ bends in the hoses and at the bottom of u bends. Also at any joint. Flex and tap as you are bleeding to dislodge them.
Take a look at this link.
https://www.st-owners.com/forums/th...g-all-the-air-out-of-the-brake-system.156754/
Now before you say - ‘mine is an ST1100’. I know. I have owned an ST1100 with ABS II and linked brakes. The plumbing is almost identical to the 1300 so much of what I say applies equally to the 1100….
… except for two things that are mentioned in that article:.
1. The SMC on the 1300 is integral to the caliper bracket and it is not upright - it therefore needs to be tilted. The SMC on your front left caliper is positioned vertically like the rear master cylinder and doesn’t need to be tilted. But it is worth checking that the bracket linkage moves freely while you have no fluid in the system. It can seize up with time and neglect and may cause the same rear brake locking issues that are often seen with time and neglect on the 1300 SMC I’ll post a link to that info for the 1100, below.
2. The 1300 has a bleed valve at the highest point - roughly near your right knee when sitting on the bike. It is referred to as the PCV bleed valve - as it is near to the proportional control valve. Don’t go looking for it on your bike, because the ST1100A does not have that bleed valve. Any air in the system after the SMC has to be pumped out through the rearmost valve on the rear caliper.
Apart from that, the logic in that article link applies to your ST1100.
Also watch the video of bubbles trapped in plastic tubing at n bends, u bends and joints.
Final tip. When you get to the point when you have got rid of most of the air, but your pedal is still softer than you want, pump the brake pedal a few times and hold it down. Tie it down tight. Also suspend a heavy weight from it. Leave it overnight. The weight will take up any drop in pressure due to release of trapped air and contraction as temperature drops. Then bleed at the two front calipers centre pistons, right first, then left. And at both valves at the rear caliper, rearmost valve first. You can expect a stream of cloudy fluid, and fluid with lots of bubbles.
Don’t forget to torque up your banjo bolts . Check the exact value - I believe that it will be around 34-35 Nm. But check for yourself.
St1100. SMC linkage : post #14 -
https://www.st-owners.com/forums/threads/linked-brakes.191361/
