Re: BRAKE SERVO : HAVE TO PUSH HARD THEN SUDDENLY WORKS
Posted: Sat Nov 12, 2022 5:02 pm
Hi.
It does sound like an air leak to me. I reason that when driving i.e. throttle open part way, there's not much vacuum in the manifold to pull a vacuum on the servo, so that if you have an air leak in the servo when you brake there's no or little servo action - in this situation the air leak rate is greater than the manifold vacuum pulling rate. But, while you are braking, there's a good vacuum in the manifold, so the manifold vacuum pulling rate is greater than the leak rate, i.e. the servo is being sucked on quite hard. It may take a little while for the servo to 'kick in', so to speak, while a vacuum is pulled on the servo diaphram. When you start braking there's extra air coming into the manifold from the servo diaphram, so you hear a slight change in not of the engine due to the additional air.
So I reckon it's an air leak, not the non return valve.
A test would be to try braking hard with your foot still on the accelerator - heel toe I think it's called as used for double de-clutch - try this carefully of course haha - you should find that the servo doesn't kick in as the vacuum in the manifold will still be weak.
I hope that helps.
Regards.
Sean.
It does sound like an air leak to me. I reason that when driving i.e. throttle open part way, there's not much vacuum in the manifold to pull a vacuum on the servo, so that if you have an air leak in the servo when you brake there's no or little servo action - in this situation the air leak rate is greater than the manifold vacuum pulling rate. But, while you are braking, there's a good vacuum in the manifold, so the manifold vacuum pulling rate is greater than the leak rate, i.e. the servo is being sucked on quite hard. It may take a little while for the servo to 'kick in', so to speak, while a vacuum is pulled on the servo diaphram. When you start braking there's extra air coming into the manifold from the servo diaphram, so you hear a slight change in not of the engine due to the additional air.
So I reckon it's an air leak, not the non return valve.
A test would be to try braking hard with your foot still on the accelerator - heel toe I think it's called as used for double de-clutch - try this carefully of course haha - you should find that the servo doesn't kick in as the vacuum in the manifold will still be weak.
I hope that helps.
Regards.
Sean.