What is the most useful size for working on a 308? 1/4 in 1/2in in or 3/8 drive? Digital? Good brand/accurate brand? Thanks, Steve
What are you using it for? You will probably need two. For lug bolts, 1/2". I have had excellent performance out of my Utica Tools/Cooper Tools torque wrench. Over 20 years of use, and always tested within spec (until I stupidly broke it recently and had it repaired). It is the "clicker" type, simple and effective. If you are using it for low torque stuff, you want a 3/8" rated in inch/lbs. Don't try and use the 1/2" for that, they are not as accurate at the extremes of their range, and usually won't fit anyway, since they are so long. I've used the fancy digital ones from SnapOn, they are nice too. Regardless of what you use, make sure to have it checked every couple years to ensure it's accuracy. Always dial it down and never drop it. After I got mine back from repair, it came with a testing analysis, certifiying the accuracy in each direction and all the specific numbers. I have had a friend buy two brand new Sears Craftsman wrenchs (one in 1/2" and one in 3/8") and both failed an accuracy test and needed to be calibrated.
If only picking one.....a 3/8 digital. As long as the range permitted (and should with a good one), it can torque most things on the car that you want to torque on a semi-regular basis, like wheels, steering/suspension, and brakes parts. However, if on a budget and not planning on rebuilding any engines, I would get an inexpensive "click type" 1/2 for wheels, and a decent digital 3/8 and 1/4 for doing more precision work like intake/exhaust manifolds, vc gaskets, etc. This is of course assuming this is for recreational use at home. HTH
Understand that simply having a digital display does not denote the inherent accuracy of the tool. Quality construction and calibration are the key to accuracy. Utica "clicker" type torque sensing wrenches are not inexpensive, running $300 to $400 each. I know when I got mine repaired it came back with a certificate of accuracy of +-4% from stated setting, and included a data sheet for my specific wrench identified by serial number. http://www.cooperpowertools.com/brands/torque/index.cfm You can download their catalog and read more about how torque wrenches are used, how theirs are constructed, they even make and sell the calibration devices.
I'd recommend a 3/8 drive Snap On click type like this: http://buy1.snapon.com/catalog/item.asp?P65=&tool=hand&item_ID=55257&group_ID=954&store=snapon-store&dir=catalog The most accurate and reliable torque wrench is the beam type but they are difficult to use compared to the clickers. A good clicker, like a Snap On, is an excellent tool and, as has been mentioned, it needs to stay in its box and not be abused. It is certainly not to be used for any other purpose. OLD craftsman wrenches from 30+ years ago were quite good but that was then and this is now... As noted, you should have a 1/2 drive torque wrench for the 70Lb and up type stuff - the same type of Snap On would serve you well. Note that were talking about 500+ bucks worth of torque wrenches. Buy the 3/8 first if you don't want to buy both at the same time. BUt note that there is a lot more to torquing fittings than setting the wrench and hauling 'till it clicks. Are the threads clean? Are they supposed to be torqued dry or lubed? If lubed, with what? You need to know that before you tighten a bolt. If you lube a bolt that was supposed to be torqued dry, there is a fair chance you could strip the threads, especially in Aluminum.
I'm a fan of Stahlwille but they're not inexpensive either. http://www.stahlwille.de/EN/drehmom_schl.php?kbz=prod&subkbz=prod_drehmo&lang=EN They have simpler, less expensive models than the one shown in this link. The one I have is purely mechanical. I like it because it can be adjusted VERY quickly/easily.
Under these circumstances I think 3/8" would definitely be the best compromise but it really is a question of the wrench in question having the high and low range you need for the different applications. Also, accuracy typically drops as you get near the low or high end of a torque wrench.
+1. I use a Utical Tools wrench. http://www.cooperpowertools.com/brands/torque/index.cfm You can download their catalog which has a lot of good information. Their wrenches come with a testing certificate. They are accurate to +-4% but only on the upper 80% of the given range. The lower 20% is where all wrenches become less accurate....usually applying too much force.
Although 3/8" likely would be the "most used" torque wrench, the cam bearing caps and valve cover torque values are in the 6.5 lb-ft. range. For these critical fasteners, a 1/4" torque wrench is a necessity, as accuracy will be the highest. Your typical 3/8" torque wrench cannot accurately secure a fasteners at less than 16-18 lb-ft.
If you are serious with torque, you need 3 wrenches: 5-25 ftlbs 15-75 ftlbs 25-150 or 250 ftlbs You likely will find them in 3/8 and 1/2 inch size. An accurate 1/4 size tw is hard to find. Some people don't like Sears but i found the 3/8 inch sears ones to be very accurate and quite adequate for home use. I do have the older ones. The inch-lb one is at least 15 years old and still calibrates to 3-4%. I don't like the newer 5-25lbs sears version today because of the handle-adjuster design. As far as torquing values, +/- 5% is all you can expect to get. If you set a torque wrench to 40 lbs and torque away until it clicks, and you actually get to within 38-42 lbs, then you are a very good mechanic.
The most versatile is a 3/8 100lb-ft wrench. That will cover most of the things you need to do. If you're filling out a torque wrench toolkit you'll need three more - a 3/8 25lb-ft and a 1/2 250lb-ft, as well as a good beam-type so you can check the condition of the clickers.
