gearbox issue

[and32]

hello, i have a 199 v plate audi a3 1.8 turbo agu engine. The problem i have is there is a noise like an intermittant rattle comeing from the gearbox when the engine is ticking over, especially when cold. When the engine warms up if i wind the window down, when i change gear i can hear the rattle when i lift my foot off of the clutch, the rattle always stops when i press the clutch.

[caledonianewan]

might be your clutch release bearing

[charlescampion]

Am not very familiar with VAG engineering practices yet since all my previous cars have been Fords but in my limited experience most modern gear box shafts have a needle roller bearing where the input shaft locates inside the end of the crank shaft. When the needle rollers start to break up they often make a rattling noise. The part is not expensive but the job is a pain to do.

The reason for the symptoms you describe is that when the clutch is depressed with the engine running the crank turns at the engine idle speed (obviously) but the input shaft is stationary thus the needle bearing is rotating around the end of the input shaft. However, when the car is out of gear & stationary (or in gear & moving) then the crank shaft & input shaft rotate at the same speed & so the needle bearing is effectively stationary.

The danger in this situation is that say you are in the fast lane of a motorway & disengage the clutch whilst braking heavily this worn &/or damaged needle bearing goes almost instantly from rest to rotating very quickly & seizes which leaves you stationary in the fast lane without being able to select a gear. Not very desirable...

[charlescampion]

Am not very familiar with VAG engineering practices yet since all my previous cars have been Fords but in my limited experience most modern gear box shafts have a needle roller bearing where the input shaft locates inside the end of the crank shaft. When the needle rollers start to break up they often make a rattling noise. The part is not expensive but the job is a pain to do.

The reason for the symptoms you describe is that when the clutch is depressed with the engine running the crank turns at the engine idle speed (obviously) but the input shaft is stationary thus the needle bearing is rotating around the end of the input shaft. However, when the car is out of gear & stationary (or in gear & moving) then the crank shaft & input shaft rotate at the same speed & so the needle bearing is effectively stationary.

The danger in this situation is that say you are in the fast lane of a motorway & disengage the clutch whilst braking heavily this worn &/or damaged needle bearing goes almost instantly from rest to rotating very quickly & seizes which leaves you stationary in the fast lane without being able to select a gear. Not very desirable...