Author Topic: Rear brake travel after sitting for the winter  (Read 2302 times)

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#10

Offline NiK

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Re: Rear brake travel after sitting for the winter
Reply #10 on: May 17, 2021, 01:32:00 PM
Condensation in the brake fluid will cause said fluid to overheat and boil during intensive use.
This will not however change the pedal travel.

When I found my travel to be a bit excessive (picture the tip of my boot almost touching ground under hard rear braking ;-), I told the dealer.
Diagnostic: rear master cylinder shot dead. This didn't seem to be surprising to him.
Replaced (just) under warranty and off I went.
I'm suspecting (yet another fecking) bad design/manufacturing of the whole part.

#11

Offline Champy72

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Re: Rear brake travel after sitting for the winter
Reply #11 on: May 17, 2021, 02:23:06 PM
Hear what you say Nik, but condensation does make the brake 'spongy' which in turn makes it a longer travel to brake efficiently!

Surprised by your rear master cylinder dying on you... How many years and miles have you got?
If you're not living on the edge, you're taking up too much space.

#12

Offline NiK

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Re: Rear brake travel after sitting for the winter
Reply #12 on: June 08, 2021, 04:00:13 PM
I've had both bubles and a shot master cylinder and I can tell you there is quite a difference!
Bubbles indeed give this spongious feeling under the foot, but the pedal position doesn't change that much.
A shot cylinder however, gives a completely flaccid pedal down to the 3/4 of the travel where it provides minimal braking only.

My bike was less than 2 years old, which for me is around 40,000 km.

#13

Offline Stillwobbling

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Re: Rear brake travel after sitting for the winter
Reply #13 on: June 10, 2021, 07:48:25 AM
My Gen 1 rear MC failed like that and I replaced the seals in it. It cured it but the casting itself was in a very poor condition. Covered in that typical white fur corrosion that alloy gets. It worked fine, but I snagged a used nearly new on on e bay to have as a standby for my Gen 2. Swapping the seals takes dome doing. Easy in theory but getting the little devils on there needs some nimble fingers. The swear box filled up nicely though.

Not entirely sure why fluid would be good inside the bike for two years, but in a closed bottle needs to be discarded after 6 months.  :084:

#14

Offline NiK

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Re: Rear brake travel after sitting for the winter
Reply #14 on: June 10, 2021, 01:46:52 PM
*Originally Posted by Stillwobbling [+]
Not entirely sure why fluid would be good inside the bike for two years, but in a closed bottle needs to be discarded after 6 months.  :084:
Because within the braking system, it is supposed to be airtight.
As soon as you open the bottle, air gets in and the oxygen starts its nefarious work ;-)

#15

Offline Stillwobbling

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Re: Rear brake travel after sitting for the winter
Reply #15 on: June 10, 2021, 01:51:35 PM
And that doesn't happen when you top up the bike? And the bottle isn't as airtight as the MC? The brakes heat up, cool down, get driven through water, shaken to blazes - and the bottle sits in my warm garage.

I'm not buying that.  :164:

But hey, that's the beauty of free thinking.

#16

Offline NiK

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Re: Rear brake travel after sitting for the winter
Reply #16 on: June 17, 2021, 11:37:59 AM
Moisture is the enemy of hydraulic braking systems.
When you brake, the fluid heats up. Easilly to the boiling point of water. And water boiling means bubbles (so gas) within the system.
And a gas is compressible, you get this infamous spongious feeling under hard braking.

So braking fluids must remain as waterless as possible. Inside an MC, there is very few air, as is the case inside a brand new bottle. As you use the liquid from the bottle, it is replaced by air (which contains almost always water), thus contaminating the liquid.

This theory does make sense.
However, I've yet to read scientific articles showcasing solid experimental results to back all this up. In the absence of such research results, we could very well be hostages of popular beliefs under scientific disguise ;-)

#17

Offline pwraight

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Re: Rear brake travel after sitting for the winter
Reply #17 on: June 21, 2021, 01:22:53 PM
Further update… dealer bled the brakes and seemed ok for a while.   Now notice that again there is a fair bit of travel when activations rear break however if I activate front brake first then rear pedal firms up with significant less travel and improved stopping power.  Going to bring to attention of dealer as I am thinking that perhaps having to bleed the system was more of a symptom of another problem vs the problem in itself.

#18

Offline XCaTel

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Re: Rear brake travel after sitting for the winter
Reply #18 on: June 21, 2021, 03:42:49 PM
*Originally Posted by pwraight [+]
Further update… dealer bled the brakes and seemed ok for a while.   Now notice that again there is a fair bit of travel when activations rear break however if I activate front brake first then rear pedal firms up with significant less travel and improved stopping power.  Going to bring to attention of dealer as I am thinking that perhaps having to bleed the system was more of a symptom of another problem vs the problem in itself.


This is because the brakes are linked. Other than for maximum braking (or emergency braking) you needn't use the rear brake pedal, on the open road I never touch my rear pedal at all. Activation of the front brake lever operates both brakes to a ratio Triumph have designed into the system. If you use the rear pedal the link is broken and you are using two independent braking systems. The pads on the front Brembos are HH and the Nissin caliper at the back has regular GG. To me this is a good reason to stick with GG pads in the rear so as not to upset this design ratio. I also know that sticking an HH in the back won't make the bike explode as I am sure many people do it. I stick with GG as I have come to rely heavily on the linked brakes and want to maintain maximum ratio in favour of the front end.

#19

Offline pwraight

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Re: Rear brake travel after sitting for the winter
Reply #19 on: June 23, 2021, 03:50:21 PM
Thanks for the info, much appreciated!

 



nonskid