This is just a generic mechanic question. I see many instructional videos telling you to use torque wrenches to tighten the nuts. Is this really important? Also, I have a 3/8 wrench from walmart. Would I be able to replace the rear wheel bearings (eg. take off the wheel assembly) using the 3/8" wrench? I'm just worried it might break or something.

 

There's a couple schools of thought on that. The first is the "by-the-book" people who use a torque wrench religiously. The second is the guys who use an impact wrench for everything(time is money). And the third group usually only use it when putting an engine together. A lot of guys with some experience behind them can come dam close to spec without a torque wrench. Start by always using a torque wrench and go from there.
----------------------


Undercarriage bolts are usually a PITA as they're usually rusted to whatever they're holding. Go get a 1/2 inch breaker bar for those undercarriage bolts. Cheapest one I've found is $20 @ Harbor Freight.

Notes:
-Apply a good penetrating oil (not WD-40) and let it sit overnight before beginning work
-If the breaker bar doesn't work you can beat the bolt with a hammer
-If that doesn't work, apply heat
-If that doesn't work, cut the bolt(s) off and replace

 

I agree with this advice. Also for what it is worth:

1.
The actual stretching of the bolt and hence how it clamps one part to another is what is key.

2.
For the same amount of torque applied with a calibrated torque wrench, clamping achieved may vary a lot for any given bolt. The variation may be due to ambient temperature, bolt mating surface condition, use of a lubricant and other factors.

3.
In general do not use lubricants unless the OEM manual says to. Do I subscribe to this? Um sometimes. Exhaust system bolts can be so difficult that I find resisting using high temp anti-seize when re-assembling difficult.

4.
For any given bolt application, a range of clamping exists that will be fine. Torque specifications are precise, but given all the uncertainties, do not expect precision in the final clamping achieved.

5.
I think overtightening, shearing and stripping of bolts is far more common than undertightening. It seems the natural, unconscious line of thought is "tighter is better." Not so if said overtorqued bolt fails spontaneously while driving. Lugnuts for one are famous for being overtorqued and causing brake problems.

6.
Like Lazlong suggests, my low range inch-pound torque wrench is from Harbor Freight. I have been using it for over a decade. All on my Civics has worked fine.

 

I agree to all of the above but a beginner should use one just to get a feel of things in my opinion