how important is it to torque the nuts to spec?

[rh71]

Do the guns the mechanics use allow for a specific torque amount? I doubt they look up each recommended spec for your vehicle. Is it worth it to spend $50 on a wrench of your own just to get it to the exact amount?

 

[Ferzerp]

Depends on the application. Certain torques are so that you don't pop the bolt. Certain torques are so you don't break weak components (plastic intakes for example). Certain torques are given to make sure you seal things. Well, you get the picture.

 

[rh71]

any chance of improper torque causing vibration only at highway speeds?

 

[Ferzerp]

I'm not enough of a car guy to know. What nuts?

 

[Arcanedeath]

If they use an Air gun to torq on your lugnuts too hard it can warp your break rotors that can sometimes cause vibration, but usually it would just be when you are breaking and not just at highway speeds.

 

[woodie1]

any chance of improper torque causing vibration only at highway speeds?

If you are talking about lug nuts the answer is yes.

 

[TakeNoPrisoners]

If you are talking about bolts that keep the transmission from coming loose from the engine block it is extremely important.

 

[Bignate603]

Depends on the application, on some it's extremely important. For example, the head bolts are very sensitive. It's counter intuitive but if the torque is too low it can cause the bolts to fracture under the cyclic loading. On the other hand the torque on something like the mounting bolts on your radiator is much less sensitive.

 

[Pacfanweb]

any chance of improper torque causing vibration only at highway speeds?

Not unless the bolts are tightened VERY unevenly. Enough to warp the center of the wheel a bit.

With today's floating rotors, you really aren't going to warp the rotor by over torquing lug nuts. The hub (center section where the stud holes are) of the rotor sits flat against the hub on the car, and the back of the wheel fits flat against that.

Warping rotors by over tightening really applied more to older style rotors, that had the wheel bearings and studs made into them. When you over tightened them, you were pulling on the rotor itself.

Not to say it can't be done with the new stuff, just that it's not real likely.


And I'll give you a dirty little secret about mechanical shops, with few exceptions: Almost nobody uses a torque wrench to tighten lug nuts. They just don't.

A good mechanic who does this stuff all day long can get the torque on each nut pretty close just by feel.....certainly close enough.
Also, they have torque sticks....you put them on the impact gun, and the end of it has whatever size your lug nut is, and they flex and won't let the gun apply too much torque.
So you just run it down until it quits turning and you're good.

As far as other parts of the car go: Nobody, and I mean nobody, uses a torque wrench for transmission bolts. Just run 'em down until they're tight.
Head gaskets? Yep, that's a pretty critical tolerance on most engine.....then again, I knew a dealership engine guy years ago who did those with a 3/8" impact and he did it day after day with no comebacks.
I wouldn't try that one at home, though.

Intake bolts...some do, some don't. Water pump...almost nobody does. Honestly, unless you're an engine BUILDER, there simply isn't as much use of torque wrenches as everyone thinks there is or should be. There are some things mechanics consider 'critical' to use a torque wrench for, but not as many as you might think.

 

[5150MyU]

Pacfanweb gave some very worthwhile info.
Older MOPAR 2.2 and 2.5 I would over torque the front center head bolt -did no damage and didn't leak.

Before they came out with the revised head gasket for the NEON I was over torqueing the rear head bolts (did it help-I think so) after I had done 3 or so I realized Chrsyler had a problem-too bad peppy littile enegine.

 

[5150MyU]

@ Pacfanweb I also did a few(at least 40) of 4cyl pistons on cavaliers and S-10s.
The only thing that got torqued(to spec) was the cylinder head and the connecting rods.

But you have to note that you also have to have a feel for torque-doesn't take much to break/snap a valve cover bolt.