I have what I would consider to be excessive travel on the front brake lever on my Triumph Sprint ST 955i. I have adjusted the span adjuster, and yesterday bled both calipers. There isn't a bleed nipple for the master cylinder. The bleeding improved things slightly, but its still not correct. I presume this might be indicative of failed master cylinder seals. The brakes work well, well enough to lock up the front wheel anyway, it's just that the lever comes nearly to the bar when doing so! Any advice appreciated.
Does the travel on the lever increase over time or is the lever travel the same even after bleeding the brakes?
Seals?.......Surely not on that age bike, John? Can you turn the handlebars so the MC is at it's highest point then crack the very top union slightly and see if you can bleed it there? Had to do that with the clutch and the brakes on the SS.....it worked OK.... How's the spigot? Still in place and not leaking I hope..........
Spigot is performing perfectly Al, better than the original! There is no union to 'Crack'. There is a rubber tube connecting the master cylinder reservoir to the master cylinder about 3" long. Chris on here did suggest to me earlier that there could be a bubble of air trapped in the tube, and he suggested a technique of flicking the tube, with the reservoir cap removed, whilst I endeavor to get the master cylinder horizontal. Unfortunately I ain't strong enough to maneuver the bike on my own to attempt this.
I have been riding the bike with the lever coming back nearly to the bars for quite a while now. One of those things that I have just subconsciously adjusted to I think. I crashed the bike last year after locking up the front wheel in an emergency braking situation so I have been conscious of using the front brake judiciously! I don't think that the travel has increased over time though.
That's a good idea of Chris's...........you could also try having the cap off and very gently moving the lever........you can normally see very tiny bubbles coming into the mc as you do it.......... ......but also you could try leaving the bike overnight with the mc as high as possible, then gently easing it in the morning.......that will sometimes bring the collected bubble into the mc.
I will post a photo of the master cylinder assembly later today Al, so as you can see what I'm dealing with. Many thanks for your input.
Ok. My Speed Triple lever used to come back to the bar over time as the seals would creep on the pistons. The newer ones were coated to stop the creep. If it's air in the system, try taking the cap off the reservoir and zip tie the lever back to the bar over night.... That often gets rid of air in the system. Edit : mine is an 05 S3 with Nissin calipers. I changed them to Tokico from a GSXR which was a vast improvement and was the same price as buying the coated pistons from Triumph!
AliT I will have a go at the cable tie on the bar overnight with the mc cap removed. The brakes on my 2001 bike do look brand new. I suspect that the previous owner replaced both calipers ,discs ,and also has fitted those stainless steel braided hoses. When you mention the seal creep on the pistons, are you referring to the the caliper seals?
No it was the rubber ring seals that go in the caliper around the pistons themselves. The pistons effectively didn't go back the same distance when the pressure was released. This meant that the piston would be slightly further out of the caliper on each application of the brake and the lever would get closer to the bar. You could try pushing the pistons back into the caliper (just get a lever between the pads) and seeing if this stops the lever coming back to the bar. You'll need a few pumps on the lever to get pressure back then it should be rock solid near the start of the levers travel (be careful riding as you'll expect it to come back to the bar). If this sorts it temporarily with the lever ending back at the bar after a few rides, it's likely to be the pistons creeping
Thanks for that info' AliT. I have cable tied the lever back to the bars with the cover off and will see if that makes any difference, if it doesn't I will have a go a pursue ding the pistons to move fully back into the cylinder.
Can you remove the hose from the reservoir and raise the end of the hose, then fill the hose completely?......Or can you remove the reservoir from it's mounting and lift it up?....but I'm not sure if it will help, because the reservoir only tops up the system.....
The hose going over the mudguard can keep bubbles in the system too. If the zip tie doesn't work, undo the caliper from the side after the mudguard and hang it from the handle bar with a bungee hook for a night then bleed again. You may find that shifts the bubbles to the caliper rather them staying at the top of the loop (if that makes sense) allowing you to bleed them out of the system. Alistair
As you said Al, the reservoir just tops up the mc, so I don't think there is any air trapped there. I have the lever cabled tied back so I will see what it's like tomorrow. If no progress I will give Alistairs technique a go. Many thanks for your help, much appreciated.
reverse bleed it with a large syringe up through the system,easy peasy. remember to cover tank and all surfaces around top of master as it squirts upards..
If you still get problems John bring over to me and we can try the reverse bleed technique, or it might be where the pistons in the callipers are causing stiction/ vacuum because of brake dust.
Thanks for the offer of help Peter, I haven't had a look at it since I cable tied the brake lever, it will probably have to wait until the weekend before I take a look to see it that has resolved the issue.
Pleased to report that cable tieing the brake lever has worked. Considerably less lever travel now. Wether or not this is a permanent cure remains to be seen. If the problem reoccurs then I shall fit new master cylinder seals
