Hi, my R53 has developed a weird hissing noise from the brake pedal. It went loopy one day and it sounded like Darth Vadar was in the car. Went to a mates garage and by the time we got there it had stopped. We drove in silence for a couple of weeks and now, it hisses at us when pressing the brakes. I am guessing a faulty servo unit, but has anyone else had this to prove it is the servo? We have traced the servo hose for leaks, but is silent under the bonnet, just noisy in the car. Brakes work fine, not getting heavy,as if it was a failing servo. Car runs good ( apart from the steering pump which has just failed and the sump gasket which was just replaced !!) Anyone shed any light on this please?
Does it hiss if you press the brake pedal with the engine off?
A servo will hiss as the vacuum is removed and air enters for several presses without the engine running, this will prove its the servo and nothing else?
The servo does hiss after the engine is off and is depressed, which baffles us as well, as if the diaphragm is split, it would go straight away. The noise increases as you press the brake pedal when running.
When you press the brake pedal the air replaces the vacuum and this is what gives the braking force via the diaphragm.
When you press the brake pedal the pushrod cracks a valve open that allow air back into the servo, so normal atmostphere coming in at the pedal end pushes the piston with the diaphragm forwards as its lower pressure on the other side due to the vacuum and this gives you the extra force for braking.
The air enters around the pedal pushrod end, so maybe you have a slight leak on the valve that allows air in even though you arent pressing the pedal??
It wont cause brake failure but it would mean your servo isnt holding its vacuum as effectively as it should hence the hiss.
You will probably have to remove the servo to check it properly, might just be a case for it sticking or need a blow out or something, before you go buying a new one.
I doubt these days its a component you can strip and buy a repair kit for.
Hang on while maybe someone else here might have some tips/suggestions.
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