Since I bought the Focus (1.8 Zetec petrol engine with IB5 gearbox) it has had an issue which I haven't been too bothered about, and couldn't find an answer by searching Google so put it on the "back burner".

The issue is that there is an intermittent high-pitched whining noise when the clutch is depressed.  When the pedal is released it is completely silent and never makes a noise when driving, even during heavy acceleration.  By intermittent, I mean it is there 75% of the time and the other 25% it just vanishes.

Am I correct in saying it sounds like the throw out bearing, and if so how long should I expect it to last, and if/when it "goes", how exactly would it fail? 

At the moment the noise level is audible over the engine, but not obscene to the point where it sounds like the gearbox is going to explode!! 

Either way, the car cost £190 so I am hesitant to do anything until it is absolutely necessary, so if it will last another few years, or can even be left until it does fail (provided the car isn't driven far away from home), then I'd rather do that than fix it straight away.

A whining thrust bearing isn't the end of the world. Eventually it will give up but as to how long it will last, how longs a piece of string comes to mind.
Once the thrust bearing gives up changing gear will be impossible. The thrust bearing pushes on to the fingers of the pressure plate which in engages and disengages the friction plate to/from the flywheel. But if the thrust bearing is whining then you question if it has a replacement clutch or not in its life and there is always the possibility the clutch may need doing soon. Once it goes though the whole clutch is worth doing while the box is off regardless of condition of the clutch. It's a MK1 so it may be an old style thrust bearing or it may be a concentric slave cylinder, they do the same job but are marginally different as in one is moved by a fork lever actuated by a cable assembly and the other is operated by hydraulic fluid.

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The mk1 uses a concentric slave cylinder. As above though, personally I'd leave it alone for now. 

I would live with it. I recall having one which changed note depending on how far you pushed the clutch pedal down so you could kind of play a tune on it.

20 hours ago, stef123 said:

The mk1 uses a concentric slave cylinder. As above though, personally I'd leave it alone for now. 

Sounds good to me!

11 hours ago, isetta said:

I would live with it. I recall having one which changed note depending on how far you pushed the clutch pedal down so you could kind of play a tune on it.

Well, that'll keep me amused in traffic jams if there is nothing good on the radio!!

1 minute ago, jmurray01 said:

Sounds good to me!

on a car that has cost you £190 you want to leave the gearbox in place haha. 

Just now, stef123 said:

on a car that has cost you £190 you want to leave the gearbox in place haha. 

Indeed I do!!  It only has 70,000 miles and is on the original clutch (plenty of life left) so I think it would be wise to follow the old saying "if it ain't broke don't fix it".

....

Wb the dual clutches we believe ours is starting to get a lot louder especially when it's cold in the morning

....... 7 years later a reply to a thread started in January 2017

I have a rattle noise when i press the clutch pedal half way down, no gears selected. Is that possible to come from throw out bearing ?? is there any emergency to replace it?

I drive a Ford Focus mk4, 1.5 diesel Ecoblue, 2019, manual transmission

Thanks for any advice. Paul