DU Mechanics, what does a bad pinion gear in the transmission mean?

[NickB79]

That's my brother's diagnosis on my old car, but I have no clue what this means. He didn't even try to explain it to me, and just suggested I sell it as soon as possible because otherwise I'd have to replace the transmission?

[billyskank]

1. When two cogs mesh with one another, the pinion gear is the smaller one

A broken cog means you need a new gearbox, which means several hundred bucks. I don't know what "bad" means but it surely means that a broken cog is going to happen sooner or later.

[sendero]

2. Never heard of there being a pinion gear..

.. in the transmission (not saying there isn't) - there is one in the rear end (differential).

Any time you have a failed gear, it is bad news. Not only is it bad because you need all of your gears to be intact, it's bad because if it goes bad it leaves metal chunks in the transmission/rearend fluid, which then will damage the rest of the gears and bearings.

I assume the thing is making noise, like whining or something, because that's usually the only way you know you've got that kind of problem, other than the car refusing to move any more :)