The faster, the louder

[markintheair]

Hi all,

I’ve got an annoyingly loud noise coming from underneath my car.
Up until ±35 mph I don’t hear it, but as soon as I go over, a whine starts somewhere at the end of the gearbox/halfway down the drive shaft.

At first I thought it might be the gearbox, but that has been fully restored. Also, the whine frequency goes up with speed, and the frequency is the same regardless of which gear I’m in. I’ve tried 3rd, 4th and 5th gear with ±40mph and the frequency is exactly the same, so I think I can rule out the gears.
I only hear it when I’ve engaged the throttle, as soon as I let go of the gas pedal it stops, only to return again as soon as I accelerate (or even just keep the same speed). It’s gotten worse over the years, and it’s so bad now that I can’t even drive with the roof closed as it’s so freaking loud.

I've also got a brand new rear axle/diff so I know that's not it as well. The sound is the same as with my old diff.

Does anyone else know of this issue? Might it be the drive axle itself, maybe the universal joint that’s noisy?

[18Fiatsandcounting]

My first guess is that you've got an issue with the carrier bearing between the shorter front section of the driveshaft and the longer rear section. Could have lost its lubrication and is now slowly frying itself.

U-joints usually start clicking or clunking when they go bad, but whirring sounds are unusual for them.

-Bryan

[markintheair]

Thanks again for your quick reply Bryan, always appreciated!
I'll try to swap the bearing for a new one soon, they're quite cheap to replace.

Does the fact that the whining starts only when the throttle is engaged, correlate with a bad bearing?

[18Fiatsandcounting]

Does the fact that the whining starts only when the throttle is engaged, correlate with a bad bearing?

Yes, usually, because that's when there is a load on the bearing. When coasting, the bearing doesn't have much load on it.

First thing to do would be get under the car and move the driveshaft around with your hands and see if you can feel any looseness either in that center bearing or in the U-joints. Side-to-side, up and down, back and forth, etc.

If you do have to disassemble the driveshaft, make permanent marks in the metal as to how the end of the driveshaft is connected to the differential input flange, and also how the U-joints are oriented from the front section of the driveshaft to the rear section. The driveshaft was balanced at the factory during production, and if you get anything installed 180 degrees out, it can cause vibrations. Not always, but often.

-Bryan

[markintheair]

Hi Bryan,

There is some looseness in the bearing. I've just ordered a new bearing and joints as well since they're really cheap and I'll replace everything once I have some spare time.
Will keep you updated, thanks!

[markintheair]

Well, that was not it unfortunately. I've replaced it all and just went for a drive around the area but it's still there. I've managed to make a video where you can hear the sound.

https://youtu.be/HVxwDeDxNVE?si=z4L7XF4rD-Cki6VT

The whine is only there when the throttle is engaged (as you can hear)

[markintheair]

Well, that was not it unfortunately. I've replaced it all and just went for a drive around the area but it's still there. I've managed to make a video where you can hear the sound.

https://youtu.be/HVxwDeDxNVE?si=z4L7XF4rD-Cki6VT

The whine is only there when the throttle is engaged (as you can hear)