[breaking shd be braking, of course. subconscious slip = am i breaking gear teeth?]

You're putting it into first from neutral. How the car is rolling doesn't have much to do with the transmission, so I don't know why it would be grinding anything. Usually grinding gear teeth makes awful sounds.

I'm going to put my guess into Nothing Wrong With It, but mostly because I do this a lot.

Right. It's not as if first gear is spinning backwards (unless it's an odd car and first/reverse are the same gear.)

Stupid question!

There's just more resistance on the engine since it has to overcome momentum in the opposite direction.

I would say you were putting more wear on the clutch if anything. Kind of like using the clutch to hold yourself from rolling backwards on a hill rather than the brake.

eekacat has it. You have to let the clutch out slowly to prevent a jerk forward, and letting out the clutch slowly increases wear on it, so you'll have to get it replaced sooner, if this becomes a habit.

General rule of thumb is don't use parts of the car for purposes other than they were designed. The brakes are there for slowing and stopping, the clutch not so much.

Yeah, you're killing the clutch.

I was taught to use the clutch nearly as much as the brakes but then my mechanic pointed out how much cheaper it was to replace brakes than clutches, so I've mostly stopped.

It's no worse on the clutch that jumping from 1st to 3rd, just t he plates spinning faster relative to each other than normal.

It's not as if first gear is spinning backwards

But if the wheels are going backwards then something in the gearbox needs to be spinning backwards when you engage first. Depends on the exact design whether this does any damage.

But if the wheels are going backwards then something in the gearbox needs to be spinning backwards when you engage first.

Yeah, I guess that was what my mind was grasping at when I asked the question...

The accelerated clutch wear sounds possible, but then again I've never ever had to replace a clutch. Then again I'm super easy on the clutch at all other times.

What you're describing is just the same as doing a sloppy handbrake start on a decent hill... it's what the clutch is for. Whether you're killing the clutch depends on the degree to which you're doing it.

Taken to extreme: face your car uphill, near the top of a huge hill. Roll backwards, while in first, and slow yourself down using the clutch. Wasteful and dumb, clutch-wear-wise, but I wouldn't have thought fatal for a while.

(and I'm with small_ruminant's mechanic on this one. I can change brake pads myself vs last year when my clutch died for $650, plus towing)

I was taught to use the clutch nearly as much as the brakes but then my mechanic pointed out how much cheaper it was to replace brakes than clutches.

Many of us were taught to do the same--it's a relic from the old days when even race cars didn't have reliable brakes. I figure my dad learned to drive in the 50s, from someone who learned to drive in the 20s, when it was, indeed, better to rely on the clutch. Sort of like pumping your brakes in a skid--used to be true, now, with automatic anti-lock brakes, isn't.

Already been said, but brakes are much cheaper to replace than a clutch and the clutch is wearing out faster when you use it to stop the car as you are. Just to drive the point home, I recently had to replace the clutch in my car and the original cost for a genuine part was $3,600 (including labour). Even with an aftermarket (non-genuine) clutch kit, it still cost me $2,000. I could replace the whole braking system on the car for that much.

Brakes used to be a lot less effective, but modern brakes are absolutely fine for any stopping you are likely to have to do outside a race track. Use the clutch for starting off and changing gear and the brakes for stopping and you car will thank you.