MANY POINTS IN HERE,
:shrug:
Yes many people seem to forget to change the brake fluid. The boiling point, moisture content changes over time affecting its performance and can cause failure, alone, just form the fluid.
Also if the *wrong* brake fluid has been added at some time, the rubber seals can be incompatible and break down. Rubber seals are matched with brake fluid (s).If the wrong sort of fluid is used,the seals can 'blow up' and expand. This can cause a sticking brake pedal with brakes stuck on, or vice versa (no brakes). Amazingly very few people, (apart from Citroen owners (whom have always had different fluids)), are even aware of this.
I have experienced this directly on two cars. Firstly my 1963 2CV van:-When I bought it, the previous owner had (stupidly) put the modern Citroen LHM brakefluid, in it. However when this car was made, Citroen was using the "old fashioned" brake fluid (that nearly everyone else uses today!), and not the LHM brake fluid.
Result was the seals expanded in the master cylinder and wedged it solid. Once the brakes were applied they would not did release. Master cylinder failure.
Second example of the worng sort of fluid causing brake failure, (power steering fluid)was put in a 1999 Ford Fiesta braking circuit. The result was a master cylinder failure, as it could not force the fluid through to the brakes. Weak brake and brake pedal to the floor were symptoms.
Proper servicing and changing of brake fluid is important. I had a 1982 Citroen Visa 652cc. In London, on old brake fluid, the brakes used to overheat, with all the start/stop at traffic lights, the brakes got too hot. The brake pedal used to go to the floor leaving "no brakes". The old fluid vapourised, creating compressible gas in the system.
I think partly the Citroen Visa has brakes which are not up to the job, as they overheated in the Alps once on me too.
"However" with new fresh proper brake fluid.....the problem diminished. You may not think new brake fluid alone can make a difference, but it sometimes can. Make sure you totally flush out the old fluid though, and any rubbish in it.
*Routine* servicing and changing fluid really can make a difference.
One other point. Someone mentioned that to lose both brake circuits at once can only be master cylinder failure.
NOT SO:-....... (I speak from experience)
Most cars have a divided master cylinder reservoir, with a 'dam' halfway up between the two parts. The theory is that should a leak develop in one part of the section, the fluid drains away in *that* isolated section; *but* leaving the other side "intact". The theory is the fluid drops down to the 'dam wall' height between the sections, as it isolates them creating two 'independent' circuits.
HOWEVER, what happens in reality if there is a fault/leakage, is the leaking half drains away; then...
As the car is on the move the bumps/cornering/g forces slosh the brake fluid from the full side across to the faulty side; and that brake fluid then drains away through the faulty side of the circuit......
So you still can get *total* brake failure on Dual circuit system, even with a properly functioning mastercylinder. (
the term dual circuit is misapplied with respect to safety).
All the dual brake circuits (that I have seen) do is to actually delay the time that you get brake failure, and give you more of a buffer zone.. I have never seen a dual circuit braking system, where there are two totally *independent* braking circuits. Say a pipe breaks at the back wheel of a car. The fluid drains away (by gravity and brake application) from that part of the circuit, and that circuit eventually drains away.
As the car is bumping about and with g forces on it, the fluid from the 'good' circuit can slosh over into the breached circuit. The 'good' circuit tops up the leaking circuit, and then that runs out too.
Another point:-
Seizing pistons in the brake calliper can result in binding brakes (to varying degrees) and overheating, then brake fluid boiling and no brakes. I have not owned Fiats long enough to have experienced this. But I have experienced it on Ford Fiestas multiple times; when the cars get to around 12 years old. Ford braking systems are not my favourite (However any 'real' Citroen owner thinks that all brakes on all other cars are substandard and weak).
On Fords the piston in the calliper can rust and seize. Taking it out, copper slipping it and rotating it can keep it going for another 6 months to a year or so without sticking. But you will need a *new* calliper if it is that. So it maybe that too. The sticking calliper causes the brakes to overheat/vapourise, then eventually pedal to the floor with no braking effort at wheels.
Symptoms:-
If it is the sticky calliper the car may go "bang" when pulling off from a roundabout for instance; as they locked on calliper suddenly lets go. It is most pronounced in stop/start city traffic.
I hope all of that makes sense.:bang:
