Prev: Car registration sequence that really shouldn't have been issued
Next: Sticky wheel?
From: T i m on 30 Jun 2010 05:53
On Tue, 29 Jun 2010 23:32:15 +0100, "Mrcheerful"
<nbkm57(a)hotmail.co.uk> wrote:

>
>"Bob Dodds" <13013dodds(a)gmail.com> wrote in message
>news:b7600c8a-6ef6-470d-8433-5e6dd1b0fca6(a)e5g2000yqn.googlegroups.com...

>
>OK I give in to people with more experience, it just seems strange to
>me that a virtually sealed system can be affected at its remote ends 2
>to 3 meters down a micro bore system by the tiny breather hole at the
>reservoir which is sealed with a "rubber" relief valve.
>
>Bob
>
>the fluid at the 'bottom' end seems to draw in dampness past the seals in
>the cylinder or caliper, this is easily seen by the discolouration of the
>fluid, when you change it the fluid almost immediately changes colour, long
>before the fresh fluid could get there. at the top moisture pulls past the
>breather cap and seems to accumulate at the bottom of the master cylinder
>bore. happily the dampness rarely seems to effect abs units which are the
>furthest from moisture entry points.
>

Most of our motorbikes have completely sealed systems in that there is
a rubber concertina diaphragm at the master cylinder between the fluid
and atmosphere that expands and contracts to follow the fluid volume
changes (pad / shoe, wear / replacement etc).

However, I've also had to de-rust, de-corrode / replace quite a few
calipers and drum pistons over the years.

T i m
From: Chris Whelan on 30 Jun 2010 06:25
On Wed, 30 Jun 2010 10:53:52 +0100, T i m wrote:

> On Tue, 29 Jun 2010 23:32:15 +0100, "Mrcheerful" <nbkm57(a)hotmail.co.uk>
> wrote:
>
>
>>"Bob Dodds" <13013dodds(a)gmail.com> wrote in message
>>news:b7600c8a-6ef6-470d-8433-5e6dd1b0fca6(a)e5g2000yqn.googlegroups.com...
>
>
>>OK I give in to people with more experience, it just seems strange to me
>>that a virtually sealed system can be affected at its remote ends 2 to 3
>>meters down a micro bore system by the tiny breather hole at the
>>reservoir which is sealed with a "rubber" relief valve.
>>
>>Bob
>>
>>the fluid at the 'bottom' end seems to draw in dampness past the seals
>>in the cylinder or caliper, this is easily seen by the discolouration of
>>the fluid, when you change it the fluid almost immediately changes
>>colour, long before the fresh fluid could get there. at the top
>>moisture pulls past the breather cap and seems to accumulate at the
>>bottom of the master cylinder bore. happily the dampness rarely seems
>>to effect abs units which are the furthest from moisture entry points.
>>
>>
> Most of our motorbikes have completely sealed systems in that there is a
> rubber concertina diaphragm at the master cylinder between the fluid and
> atmosphere that expands and contracts to follow the fluid volume changes
> (pad / shoe, wear / replacement etc).

Indeed, but the volume changes will be much smaller on a motorcycle.

I'm guessing that the reason for them using a semi-sealed system is due
to the likelihood of them spending some of their life in a non-vertical
orientation. That's certainly the case with my Son's Gas-Gas trials
bike...

> However, I've also had to de-rust, de-corrode / replace quite a few
> calipers and drum pistons over the years.
>
> T i m

Do you mean on cars, or motorcycles? I've never seen hydraulic drum
brakes on a bike.

Chris

--
Remove prejudice to reply.
From: T i m on 30 Jun 2010 06:36
On Wed, 30 Jun 2010 10:25:02 GMT, Chris Whelan
<cawhelan(a)prejudicentlworld.com> wrote:


>> Most of our motorbikes have completely sealed systems in that there is a
>> rubber concertina diaphragm at the master cylinder between the fluid and
>> atmosphere that expands and contracts to follow the fluid volume changes
>> (pad / shoe, wear / replacement etc).
>
>Indeed, but the volume changes will be much smaller on a motorcycle.

True, but the volume of the reservoir is that much smaller as well.
>
>I'm guessing that the reason for them using a semi-sealed system is due
>to the likelihood of them spending some of their life in a non-vertical
>orientation. That's certainly the case with my Son's Gas-Gas trials
>bike...

Yup, that and difficult to be vented as they are often out in the
weather.
>
>> However, I've also had to de-rust, de-corrode / replace quite a few
>> calipers and drum pistons over the years.
>>
>
>Do you mean on cars, or motorcycles? I've never seen hydraulic drum
>brakes on a bike.

Ah, yes sorry, a bit of blurring of machines in my head. The last bike
I worked on was my old GPZ550 with a rear hydraulic disk and the
master cylinder was the most corroded I thing I've ever seen in my
life (other than a car battery terminal probably).

It all seemed a shame as well as the entire hydraulic system
(reservoir, master cylinder and caliper) is about 50cm long. ;-(

Cheers, T i m




From: DavidR on 2 Jul 2010 17:38
"Bob Dodds" <13013dodds(a)gmail.com> wrote

> I've heard and read about hydraulic fluid absorbing moisture from the
> air many times but the bit that always puzzles me is the hydraulics
> are a sealed system so how does the oil come into contact with the air/
> moisture.

http://en.wikipedia.org/wiki/Brake_fluid
//
Once installed, moisture diffuses into the fluid through brake hoses and
rubber seals and, eventually, the fluid will have to be replaced when the
water content becomes too high.
//


First  |  Prev  | 
Pages: 1 2 3 4 5
Prev: Car registration sequence that really shouldn't have been issued
Next: Sticky wheel?