Technical Rattling noise in certain gears

[unfacedman]

Hello world!

All of a sudden, a strange rattling noise started to appear when the third gear is engaged. But only when I release the acceleration pedal. At the slighted touch of it - the noise stops. Also when I disengage the clutch - no noise.
That was easy to diagnose. A bad synchronizer, isn't it?

Well, not so fast.

One day after the noise has begun, it spread itself further.
Now, the noise appears at the third, 4-th and 5-th gears, and even when I press the clutch pedal!
Also, if I put the transmission on neutral - after one of these gears, the noise still appears, and again, even with pressed on clutch pedal.
Disappears only when I press the accelerator.
First and second gear - no noise.

 

[koalar]

Sounds like a bearing inside the gearbox

My guess would be the input bearing

I had a couple fail but the symptoms only partly match

I can't see any option except dropping the gearbox and examination


@rmjbn1
@irc

Looking for oil inside the bell housing would be my first step

There's an inspection hole at the top

 

[unfacedman]

Thank you for your reply!
Wouldn't the input bearing rattle at all speeds?
Also, shouldn't it stop when pressing the clutch?

 

[koalar]

Thank you for your reply!
Wouldn't the input bearing rattle at all speeds?
Also, shouldn't it stop when pressing the clutch?

The plastic cage can break up

They normally rattle more when the gearbox is not under load, they get worse and more noisy as time goes on

They definitely rattle in neutral

 

[irc]

As above, worse under light load, rattles in neutral.
I did have one which had no detectable oil leak into the bellhousing, but when removed the shaft could be moved a couple of millimetres left and right. But usually there will be an oil leak and clutch will be "grabby".

 

[rmjbn1]

My failed input shaft bearing was definitely rattling in neutral.

But the noise stopped with clutch depressed as the input shaft stops turning.

Is it still rattling when stationary with the clutch down?

Unless your clutch is also dragging? Any difficulty selecting a gear?

I couldn't really hear the rattle once on the move, too much other noise going on.

But the car was much quieter with a new bearing.

Mine also resulted in a failed input shaft seal and a coating of gear oil inside the bell housing - as koalar says easy to identify with a finger through the inspection hole.

 

[unfacedman]

The research continues...
(rmjbn1 - no, no noise at all when stationary. Strange, innit?)

I found an empty, long road downhills, and turn the engine off. Started to slide down with no engine revs/clutch spinning at all.
When I put the trans into the third, surprise! The noise emerged again, and was keeping even when I pressed the clutch pedal to disconnect the trasmission from the turned off engine. Even when I put it back to neutral.
I would have suspected the noise have something to do with the driveshaft/wheel bearing, it doesn't make any sense why, in that case, would it appear only in certain gears engaged!

Another funny thing - upon smooth, even terrain like parking lot floor - almost no noise, if any.