Re: Strange noise from Scion tC

Spark knock ?

My dad's Ford truck broke a gear. It was a sharp knock.

I'd like to think that you could not break gears in your tC, but any noise that comes from only one gear means you have to consider a broken transmission.

I could give you my standard "noises, vibration, and harshness are difficult to diagnose without experiencing them first hand" sermon...

Jeff is kind of thinking along the correct path to diagnosis except that broken gear teeth with no other problems in a constant mesh transmission are as rare as hen's teeth. I have looked at a lot of broken transmissions, including abused transmissions, and have never seen a broken gear tooth that wasn't caused by something else in the transmission breaking and getting caught in the gears.

If you have a manual transmission and the noise is actually coming from the transmission and not elsewhere in the drivetrain, then I'd start by checking the transmission fluid level. Try altering the pressure on the shift lever to see if the noise changes. Do you drive with your arm resting on the shift lever? Bicycle card sounds can be caused by the teeth on the synchro ring touching something, most often caused by the driver leaning on the shifter all the time, which wears the shift forks, which create a little slop in shifting. The problem usually shows up in the gear that is used most.

I try not to rest my hand on the lever, I have heard of this condition before. I'll have to check to make sure. About the only time I leave my hand on the lever is if I think I will either be downshifiting to 3rd or upshifting to 5th SOON.

The sound happens in 4th gear, ~2200-2500 RPM, and then goes away when ~40MPH is reached and I let off the accelerator, or above 2500RPM or so.

I was thinking lugging, but the damn thing is geared so low you can be at

That doesn't sound like a transmission noise. I'm thinking that something is touching at just the right torque. How many miles on the engine?