Norfolkluegojnr
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| posted on 28/10/11 at 03:00 PM |
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tin top brake issue....
Assistance please LCB!
SWMBO has reported a potential brake issue with the tin top (53 plate Focus C-Max).
When approaching a roundabout earlier, she pressed the brake pedal and ‘nothing happened’  and the pedal travelled to the floor, ‘working a bit’.
She then carried on to work, where the car behaved as normal.
She has since driven it around an industrial estate doing some test braking, and all appears fine. Car has now been driven home but I haven’t had a
chance to have a look at it yet.
Am i right in thinking this is possibly the brake master cylinder? if so , why is it now working correctly? Is it possibly to do with the vacuum?
Apparently there is a valve in the vacuum take off which can get stuck open making the system depressurise?
She reports no obvious fluid leaking from anywhere.
Before i get home (and its dark) I could do with a rough idea of what to check first. I have little experience on this car so far so any input is
appreciated. Ta!
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adithorp
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| posted on 28/10/11 at 03:05 PM |
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Sounds like a master cylinder fault and they can be intermittent.Also check all the wheels for bearing play as that can push the caliper pistons back
giving a long pedal next time but would expect it to be less intermitent. If the servo lost vacuum then she'd experience a hard pedal not a soft
long one.
"A witty saying proves nothing" Voltaire
http://jpsc.org.uk/forum/
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Norfolkluegojnr
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| posted on 28/10/11 at 03:09 PM |
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quote:
Originally posted by adithorp
Sounds like a master cylinder fault and they can be intermittent.Also check all the wheels for bearing play as that can push the caliper pistons back
giving a long pedal next time but would expect it to be less intermitent. If the servo lost vacuum then she'd experience a hard pedal not a soft
long one.
great that helps, rules out one 'expert' opinion I has already!
So obvious things to look for on the MC? leaking i presume? anything else?
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AndyGT
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| posted on 28/10/11 at 03:20 PM |
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over-heating brakes due to loose wheel(s) induced by the disc rubbing on pads?
sticking calipers?
All causing brake fluid to boil.
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Norfolkluegojnr
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| posted on 28/10/11 at 03:26 PM |
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quote:
Originally posted by AndyGT
over-heating brakes due to loose wheel(s) induced by the disc rubbing on pads?
sticking calipers?
All causing brake fluid to boil.
Ok, will check wheel nuts for tension and free play of discs too. thanks.
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britishtrident
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| posted on 28/10/11 at 03:41 PM |
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If no fluid loss is apparent most likely cause is failure of one of the recuperating seals on the master cylinder, the fluid leaks past the one way
recuperating valve /seal back into the fluid reservoir
Usual way to test these is with the car stationary and engine running put very gentle constant pressure on the on the pedal. I must stress very
gentle pressure as if you had an egg between your foot and the pedal, if the pedal very gradually sinks then the seal/valve is goosed.
Under hard braking the pressure is high enough the valve/seal is forced into making a good seal so the problem isn't apparent.
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britishtrident
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| posted on 28/10/11 at 03:46 PM |
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quote:
Originally posted by AndyGT
over-heating brakes due to loose wheel(s) induced by the disc rubbing on pads?
sticking calipers?
All causing brake fluid to boil.
ROTF
[I] “ What use our work, Bennet, if we cannot care for those we love? .”
― From BBC TV/Amazon's Ripper Street.
[/I]
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Norfolkluegojnr
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| posted on 28/10/11 at 03:47 PM |
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quote:
Originally posted by britishtrident
If no fluid loss is apparent most likely cause is failure of one of the recuperating seals on the master cylinder, the fluid leaks past the one way
recuperating valve /seal back into the fluid reservoir
Usual way to test these is with the car stationary and engine running put very gentle constant pressure on the on the pedal. I must stress very
gentle pressure as if you had an egg between your foot and the pedal, if the pedal very gradually sinks then the seal/valve is goosed.
Under hard braking the pressure is high enough the valve/seal is forced into making a good seal so the problem isn't apparent.
Great, will give that a go when i get home.
I presume replacement is the obvious solution?
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