Greetings,

Sorry if this is confusing, I have a '15 tC with a Manual Transmission and 36k miles. Haven't done a tranny fluid change yet. It's probably almost a year since I've always noticed this sound/feeling.
When at a stop, in first gear, and you're letting out the clutch to engage, and if you give it excessive gas as you take off, I can hear/feel gears/axles clunking for a short moment until you start rolling. It's almost always consistent especially with higher rpm take offs, but if you baby it, it's kinda smooth.
I've first noticed it after getting custom exhaust work done, and ever since then I believed that my clutch was slipping, or some bearing, or something with my axles or even weak motor/tranny mounts? I'll admit to to getting wheel hop moments if this started the issue, or if my custom exhaust work is some how messing with me thinking it's my tranny. It only happens when leaving from a stop usually.
Any ideas or what could I try/look for?

 

Could be exhaust banging on stuff dependsing how it's routed and how close to the chassis it is. How much of the exhaust is custom vs a bolt-in part?

We do have extremely weak front motor mounts (torque damper). Filling its voids with window weld (~50A Durometer) or the DIY urethane motor mount kit (60A) will make a huge difference in smoothness and reduced wheel hop while still being streetable (there aren't any aftermarket mounts still available for this platform). Anything stiffer is unnecessary and you're just asking for unneeded NVH.

 

It's custom after the s pipe, where the 2nd cat started. I remember getting a flex pipe installed and it was real bad that I got it removed and the clamp style installed.
there is a chance it's something with the exhaust, I thought the placement was good. I got some almost crossthreaded spring bolts after the s pipe, but the stock exhaust manifold threads had to get drilled out, and now I'm running an aftermarket. So I don't have much flex at all, but full stock didn't either?
And I always wondered about motor mounts, I haven't really looked at mine because the car still has low miles, unless the 6 years age is it.

 

The front one is the main mount that supports front to back movement of the motor when accelerating. It doesn't support the engine weight - it's only a torque damper - but it's flimsy enough to be able to move with your hands so filling it helps tremendously. Filling any of the other mounts could make the car too loud and vibey and I don't think it's necessary unless you intend for it to only be a track car. The front mount is also the reason the car sucks so much to drive in first gear at low speeds - lets the motor flop around way too much.

I doubt you have many mechanical issues with the mileage being that low. Always a possibility but the motor moves a fair amount stock, if that exhaust is close it could be hitting. Pretty common issue with custom setups. I'd get under there and look around and see if you can shake anything around or replicate the sound.

Here's a link to my post about filling the mount: drizzohs 2014 tC2.5 thread - Page 2 - Scionlife.com Doesn't say much but at least you can see what it looks like to get a better idea.

 

I might try that urethane trick with a new motor mount in the future.

*Edit*
Looked over the exhaust again, I think there is enough overall movement for the exhaust flange at the end of the S-pipe to the catback to hit the subframe I believe? Hopefully making changes or eliminating the flange will get rid of the noise/feel I have

 

I know this is an old thread but I have the same issue. Car is stock. Previous owner said the trans bearing and clutch were just replaced by Toyota. Clunking is getting annoying. I'm thinking it's motor/trans mount related. I'm going to order some window weld and fill the front mount and see if that fixes it. Hope it's that simple.

You ever fix your issue?

EDIT:
Front motor mount was loose. Guessing they forgot to tighten it after the trans work.