Transmission (synchros?) "hollow" rattling noise?

[radian]

Hi all,

Hopefully someone can put my fears to ease. Anyone else with an RS (or perhaps any manual Sonic for that matter) notice a "hollow" rattling noise when shifting gears? I find it most apparent when coasting at say 20kph with the clutch held in and slowly shifting between gears (clutch still held in). Does not make the noise while shifting when stopped.

If I had to guess, I'd say it sounds like the synchros connecting, or maybe something loose that may be rattling. 99% sure it's transmission related. I didn't notice this noise on a manual Cruze, but then again, the Sonic RS is not as refined (a good thing!).

Thoughts?

 

[River_Rat]

driving at low speed next to a building or concrete wall with the windows down and music off, i can hear some noise as i'm shifting, which i consider to be more-or-less normal. don't know about this hollow sound you're describing.

 

[radian]

Yeah it's pretty hard to describe. Once it clears up outside I'll take a video and see if I can capture the sound!

 

[RS Turbo]

Sounds like your just shifting to slow. Yes I have heard it before but its only when I am lazy slow shifting. Try normal driving and do not use the clutch, just shift and keep pressure on the next gear you shift into... you will then get an Idea of the time it takes to shift at closer rpm points. I rarely use my clutch except for first gear.

 

[radian]

So it sounds like it’s the synchros meshing together that I hear?

Considering the case when coasting at 20kph, with the clutch pressed in, in neutral, both the input and output shafts would be presumably at 0 RPM (disengaged from engine and wheels). Then when shifting into gear (still with clutch in), the input shaft should still be 0 RPM and the output shaft should then be quite a bit greater than 0 (eh, let’s skip the math), so the synchros will have a lot of ground to clear to match the input shaft to the output shaft speed. I guess the more matching required, the noisier the meshing.

Does this make sense?

This is my first manual car, so slowly learning the subtleties and noises.

In any case, thanks for assurance folks!

 

[Preloader]

It's normal.

And just to help with the mechanical relationships involved..... The output shaft rev is directly related to the wheel speed. So when you are going 20kph, the output shaft is spinning at a direct ratio to that speed. Even in neutral with the clutch pressed.

I'll even go a step further to say that even in neutral, the input shaft is spinning at the same rpm as the engine (foot off the clutch), it's just not coupling those revs to the output shaft.

 

[Dragcamaro]

my rs is pretty noisy shifting. especially when cold, its kinda crunchy. Im going to try switching to mt90 to see if it helps.

another thing ive noticed is that double clutching seems to help a little. I try to do it not when Im cruising, since I skip gears anyway

Ive thought about taking it to a dealer but I feel like it will get blamed on my tune

also I notice if im pulling around my neighborhood in 3rd, 20 or so mph, with some turns and elevation changes, I hear a whining noise, it sounds like a rear end getting worn out, or a fwd Toyota 5 speed when being driven in reverse, but not that loud