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I want to change my brake calipers so will not to remove wheels and caliper bolt.
When reassembling, do I need to use a torque wrench to get to the recommended tightness or can I just use a normal rachet and go as far as it can go?
If I must use a wrench, will something cheap like this suffice for wheel and caliper bolt?
Using a torque wrench for both of these is good standard practice. Do you absolutely need to use it for these? No. But the outcome may not be what you desired.
It's important to use a torque wrench when putting the wheel on, because without it, you run the risk of warping your rim. It's the same reason you want to put the lugs on in an alternating pattern, so you don't have load in any give direction, but rather an equal amount of load around the wheel to hub interface. You'll often see tire shops employ torque wrenches when putting a wheel back onto a vehicle. This is outstanding ... in theory. I've seen way too many times where the operator of the torque wrench doesn't know what they are doing. They'll roll the car and bounce the torque wrench during tightening, which easily causes them to over-torque any given lug (if not all of them). For this reason, I invariably loosen and retorque them when I get home.
As for the caliper, it's also good technique to use a torque wrench. The main reason is so you don't over-tighten then, which might strip out the housing the bolt goes into, or ruin the mounting bolt in the first place. Doing either of these will cause long term issues with repair and/or safety concerns, especially if you don't realize you've stripped the threads. Stripping threads can make it so your caliper may come loose during operation, killing your ability to brake the vehicle safely, and ending up hurting most likely your vehicle, but also you, your passengers, and whomever may get in your way.
As far as torque wrenches go, you can get one for very cheap from Harbor Freight (or the like). Just because these are cheap (under $20 US), doesn't mean they are of poor quality. One will work perfectly for non-critical fasteners like these (NOTE: "Critical" in this sense meaning, if they aren't torqued near to spec, you won't cause your vehicle serious, if any, damage ... a head bolt is a much more critical item in this sense.)
About lug nuts only: having and using a torque wrench is not enough. You have to also use it properly. I once wanted to torque my wheels to 120 or 130 Nm (the correct torque is 110 Nm, I remembered it incorrectly). I also looked at the incorrect scale in the torque wrench, torquing them to 120 or 130 lb ft. That's a helluva lot of torque! No damage was done. It did feel a bit strange to torque them to such high torques due to my good muscle memory, but I blindly trusted the incorrect scale on the torque wrench and torqued them tight anyway!
There's a huge safety margin in wheel lug nuts. If you have any kind of muscle memory, just use the same lug nut wrench and torque to approximately the same torque they originally had. That will do in most cases. If it's overtorqued by 20% or undertorqued by 20%, it won't fail.
This year, when changing the winter wheels to summer wheels, I first torqued with a lug nut wrench, then checked the torques with a torque wrench. They were very accurately torqued due to my good muscle memory. I assume the accuracy was about 15% or so.
Note, my answer is only for wheel lug nuts. Other fasteners may not have such a good safety margin in automotive applications. So, if you need to remove the caliper bolts, I would go ahead and purchase the torque wrench. And if you are going to purchase the torque wrench, why not check your lug nut torque with it anyway?
And oh, if at all possible, avoid the clicker-type torque wrenches that should be periodically calibrated and select a beam-type torque wrench that won't go out of calibration (apart from perhaps needing to be zeroed properly by bending it, if heavily damaged). It's slightly less convenient (you need to look at the scale from a particular direction orthogonally). However, the beam-type wrench is actually the mechanism that is used to calibrate the clicker-type wrenches! Not only that, but also the beam-type wrenches are cheaper.
Of course, in tight spaces the clicker type wrench may be better, so you may want to purchase both. Brake jobs are not tight space jobs.
Good responses above. Few things I have learned along my journey:
If you are very experienced, you can use muscle memory to pretty much hit the same torque over and over. I am definitely not though, definitely more the weekend warrior than anything, so I got a couple of cheap torque wrenches, different torque ranges. It's peace of mind really.
