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Twins Technical Talk Technical Talk for Hinckley Triumph Twins: Bonneville, T100, Speedmaster, America, Thruxton, and Scrambler.

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Old 01-01-2013, 01:56 PM   #1 (permalink)
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Brake lever pressure gone?

2010 T100 - usually used every day to commute to work but rode it home on 21st December and not touched until I went to move the bike today - was surprised to find front brake lever goes right back to bars, at which point it is still stopping the wheel turning. No sign of any fluid leaks and everything seems tight so not sure where pressure has gone?
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Old 01-01-2013, 02:30 PM   #2 (permalink)
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It could be the master cylinder seals that have gone, or more likely the fluid level has dropped too low allowing air to enter. Bleed the system and check the rear brake fluid level's ok while you're at it.
Note - The level will gradually fall as the disc pads wear. Check the pad thickness, they could be well down.

Last edited by denbow; 01-01-2013 at 02:55 PM.
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Old 01-01-2013, 03:58 PM   #3 (permalink)
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Quote:
Originally Posted by Grim Rider View Post
2010 T100 - usually used every day to commute to work but rode it home on 21st December and not touched until I went to move the bike today - was surprised to find front brake lever goes right back to bars, at which point it is still stopping the wheel turning. No sign of any fluid leaks and everything seems tight so not sure where pressure has gone?
Brake fluid is hygroscopic - ie. it will absorb moisture. I've known this to happen in the past and never really found an explanation for it, except that there could be worn parts that have allowed the ingress of moist air without there being an actual visible leak in the system (perhaps for example when the brake has been let off and the fluid gets sucked back into the reservoir). It always happens during a period of standing as well, it seems.

It could also be that your brake fluid has got very hot or boiled at one point. Did it begin to work properly if you pumped the lever? If so this could well be the explanation. But both these theories are speculation on my part, but either way a change of fluid and a brake bleed is needed I think.
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Old 01-02-2013, 02:50 AM   #4 (permalink)
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Brakes

Quote:
Originally Posted by Grim Rider View Post
2010 T100 - usually used every day to commute to work but rode it home on 21st December and not touched until I went to move the bike today - was surprised to find front brake lever goes right back to bars, at which point it is still stopping the wheel turning. No sign of any fluid leaks and everything seems tight so not sure where pressure has gone?
Depending on whether you have had any work done on the brakes there can be a number of issue. As your bike is relatively new problem needs to be addressed.

Hopefully you have a manual or at least the handbook. You need to have the bike level and then check the sight glass the minimum mark is middle of the sight. To check the max mark you need to remove the cover there is a raised vertical bar thie ie the max height measure.

Two things cover your tank and anything painted as brake fluid is great paint stripper! Also there is a black rubber gasket make sure this is aligned and pressed out to the sides pre screwing the cap on.

Have a good look @ the caliper to see if there is any wet spots= leak.

As you say the brake still stops the bike, unfortunately with air the fluid will boil quicker and fade. You also will get lock up as you have no real feel. Water will work instead of brake fluid, DONT TRY IT, but not for long.

As the other postee said pad thickness needs to be checked. If you havent done it before and a couple of years old change the fluid.
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Old 01-02-2013, 05:28 PM   #5 (permalink)
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Thanks for your thoughts guys, much appreciated. Had no work done on the bike and only been used back and forth to work so not likely to have overheated at any time. Checked fluid and spot on, no leaks, but took front caliper off to find one of pads very low (bike has only done 7500 miles) - still not sure why brake lever should be coming back so far suddenly but will change pads and bleed brakes as soon as it stops raining here (has poured down virtually every day since before Christmas!).
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Old 01-03-2013, 07:57 AM   #6 (permalink)
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That uneven wear might be an important clue.

If something's stuck and the caliper doesn't float, the disc might deflect and introduce a spring effect into the system. That could account for one of the pads pushing it's pistons back in their bores, resulting in a low "pedal".

Does pumping the lever bring back a normal feel?
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Old 01-03-2013, 10:20 AM   #7 (permalink)
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Pumping lever made no difference. Cleaned caliper and replaced pads - still no difference until I bled brakes and air came out - now seem to be working fine. Going out for cautious test ride...
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Old 01-03-2013, 10:29 AM   #8 (permalink)
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Pull the brake lever back to the bar and hold it there with a bungee or similar and leave it there for a few hours (overnight?). Alternatively just pump it for a few minutes. Both my Trident 900 and Daytona955i tend to suffer with the same problem and both these ideas seem to work. My tame mechanic has had it happen to one of his bikes (can't remember if it was a Suzuki or a Yamaha) and he was at a loss to explain it - and he's got lots of letters of qualifications after his name!!
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Old 01-03-2013, 10:35 AM   #9 (permalink)
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Well done. Don't forget to check the rears, they usually wear out faster then the fronts even when they're not used much.
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Old 01-03-2013, 11:53 AM   #10 (permalink)
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Well done. Don't forget to check the rears, they usually wear out faster then the fronts even when they're not used much.
100% right.

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