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Discussion Starter · #1 ·
Am I right in thinking that brake fluid does not circulate around the pipework.
In the same way as water in your central heating for example.
I'm thinking it just moves a tiny bit backwards and forwards as the pedal is depressed and released.
Right or wrong?
 

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Not quite true. As brake fluid is Hygroscopic (it absorbs water) it's density changes. The watery stuff sinks to the low areas. It also heats up and as we know hot fluid will rise in cool fluid (density change). This is why the bottom of a master cylinder rusts ( internally) and why we should replace the fluid regularly.
 

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Fresh brake fluid doesn't which is how it's designed to work, water isn't part of the initial design ;) :tup:
 

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Usually they are sealed systems as the venting is taken care of by a diaphragm which is in effect a seal that collapses down as the need for fluid increases but keeps the outside damp air at bay
 

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Not quite true. As brake fluid is Hygroscopic (it absorbs water) it's density changes. The watery stuff sinks to the low areas. It also heats up and as we know hot fluid will rise in cool fluid (density change). This is why the bottom of a master cylinder rusts ( internally) and why we should replace the fluid regularly.
that may be the case but ive never changed brake fluid in my life on any car(unless working on them),and I recon im not alone.do manufacturers recommend that in services
 

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I've had at least three vehicle that had boiled the fluid due to water content. Worst was the Mk 3 Astras. The stiffeners under the bonnet would direct water to a drain hole directly above the reservoir where it would get in through the vent. Once the fluid becomes saturated the calipers have almost pure water in them. Ford Cargos (pre Iveco) used to have this happen regular if you didn't change the fluid at the recommended interval ( 2 years). There was a time when the Ministry of Transport was bringing this into the Test. Lots of garages bought the test kit and they never brought the rule in. Shame I say! Some cars this is the only check it gets all year.
 

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Discussion Starter · #17 ·
Thanks fellas I was pretty sure I was right.
Reason for the question was I fitted a s/h caliper on a mates car a couple of days ago and bled it through. The fluid that came out ahead of the new stuff was as black as old oil.
Asked him when it was last changed and he said never. The car is 10 years old....
It's only got 30k on it and he's had it 6 years or so.

Anyway the caliper turned out to be as grungy as the one we took off (sticking on) so he booked it in to a local garage for a recon. one to be fitted.
I said to get them to change the fluid while they were at it.

They did the job and told him the fluid didn't need changing as it was ok and they'd used loads anyway???
The caliper is the front offside and I think it has the shortest pipe route from the master cylinder. The clean fluid they saw would've been the stuff I put in the day before.
As for using loads, I reckon I used half a cupful and that includes the stuff in the jamjar.

Think he needs to find a different garage.
 

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that may be the case but ive never changed brake fluid in my life on any car(unless working on them),and I recon im not alone.do manufacturers recommend that in services
When I used to service cars I used to change the fluid every 1 or 2 years depending on the mileage and use.
I've always done a full fluid change on my daily's every 3 years (bit lazy - should do it more!) or so.
 
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