Lug Nut Torque, 66

[John L.]

The manual states to torque lug nuts between 55 to 65 ft lbs, have read number of posts recommending 75 ft lbs, what is the consensus? Also, should this be done with full weight of car on wheels? And do you recommend using ant-seize? thanks

[Bill M.]

Re: Lug Nut Torque, 66

I always go 60 lbs. final check with car on ground. I re torgue after 100 miles. I spray WD 40 on the studs. I may be wrong but I believe that anti seize is to abrasive for fine threads.

[Edward J.]

Re: Lug Nut Torque, 66

I tend to go on the tighter side of the torque, the reason is torque wrench calibration accuracy. also older wheels (steel wheels)that that have been off a zillon times.

[Leif A.]

Re: Lug Nut Torque, 66

The '66-'76 Corvette Shop Manual calls for 80 lb ft on the wheel stud nuts. I've always used 75 lb ft and have never had any issues.

[Michael G.]

Re: Lug Nut Torque, 66

Tighten to the mean of the specification. Your car didn't have oil or anti-seize on the wheel fasteners when it left St. Louis, so don't oil the threads, unless you want to take a chance of breaking a stud. Anti-seize isn't necessary, assuming your studs are clean and dry when installed and are re-torqued occasionally.

[Joe L.]

Re: Lug Nut Torque, 66

The manual states to torque lug nuts between 55 to 65 ft lbs, have read number of posts recommending 75 ft lbs, what is the consensus? Also, should this be done with full weight of car on wheels? And do you recommend using ant-seize? thanks

John------


AIM says 55-75 lb/ft.

[Joe L.]

Re: Lug Nut Torque, 66

Tighten to the mean of the specification. Your car didn't have oil or anti-seize on the wheel fasteners when it left St. Louis, so don't oil the threads, unless you want to take a chance of breaking a stud. Anti-seize isn't necessary, assuming your studs are clean and dry when installed and are re-torqued occasionally.

Michael------


I agree. However, I do recommend the use of a small amount of anti-seize compound on the tapered surface of the lug nut. The interface of the nut and wheel galls resulting in damage to the nut and, worse, the tapered nut seats of the wheel. The nuts can be easily and inexpensively replaced, of course, but the wheels are another matter. Over time, the nut seats become so badly worn that the only solution is to use "bulge" lug nuts.

[Frank D.]

Re: Lug Nut Torque, 66

John------


AIM says 55-75 lb/ft.

Yes - this also avoid the tapered nuts from eventually digging into and enlarging the lipped hole in the wheel where they reside eventually causing problems...

[John F.]

Re: Lug Nut Torque, 66

Discount Tire torque chart says 53-82, use 80 ft lbs. Above that 100 ft lbs.

[Edward B.]

Re: Lug Nut Torque, 66

Don't you just pull the trigger on the impact wrench until it stops?

[John F.]

Re: Lug Nut Torque, 66

They use a torque wrench here.

[David S.]

Re: Lug Nut Torque, 66

Don't you just pull the trigger on the impact wrench until it stops?

I was going to make a similar comment although admittedly, always check the torques with a wrench anyway.

Most impact guns will torque above factory spec.

Best,
Dave

[Frank D.]

Re: Lug Nut Torque, 66

I've never used anti-seize but replaced all my lug nuts not long ago...
I have a battery impact wrench and snug them up with that but I do a final check with a 4-way lug wrench and I always get about a 1/4 turn on them with that. Never had any come loose and never a problem getting them off...

[Michael G.]

Re: Lug Nut Torque, 66

GM specifies torque specifications as a range, say 70-80 ft-lbs. What they really mean is “tighten it to 75 ft-lbs, period”.

They specify the published plus or minus range (ie: 75 +/- 5) for several reasons, but the most important one is that tightening tools and installers cannot consistently hit 75 ft-lbs, so they are given a range of “acceptable", but not ideal, values. Those values are tested to insure that the high end of the range does not result in a load that permanently yields the fastener and that the low end does not fail in the validation of performance. They set it somewhere in between those limits so that you have target torque. You should therefore not tighten to anything but that target, the mean of the torque specification. This is not my opinion, it is not debatable, it’s the way the engineers at GM really did, and still do, it.

If you are dealing with an old car, you must realize that the conditions that GM expected when developing the torque specification do not exist anymore. The most critical aspects of tightening are affected by those changed conditions; those two aspects being: 1) the frictions that exists between the fastener threads and 2) the friction between the bearing face of the tightened component in its mating surface. In an old (or restored) car, unless you have replaced components with original new components, both of those frictional relationships have been significantly altered.

Corrosion, galling, reproduction finishes, different component paints, and many other variables in restoration all change the friction, and therefore all change the relationship between the torque you tighten to, and the clamp-load created in the fastened joint. What that means is that the torque specs GM developed are nice guidelines, but when utilized on restored vehicles, they probably don’t stretch the fastener to the design specs, therefore, vehicle validation goes out the window.

If you maintain or attempt to duplicate the original components and finishes on and old car, those specs will probably work well, but the minute you start adding oil, or anti-seize, or buffing, or scraping, or anything, say goodbye to the production intent.

Regarding wheel attachments in particular: when tightening wheel nuts, the original friction was very high. What this meant was that variation in tightening had minimal effect on clamp load - a good thing. If you lube up the threads or bearing surface or increase the torque to the upper end of the range, you get more clamp load, but you may break the fastener, damage the wheel, or make it more susceptible to loosening. My recommendation, therefore, with wheel attachments is: restore it to as close to original surfaces as possible, tighten it to the mean, and check it frequently.

Regarding use of anti-seize: Thread and surface galling is a direct result of too much friction. Overtightening and corrosion are the chief culprits in that. Unless you’re driving in the north, in the winter, a car driven as sparingly as our Corvettes shouldn’t need anti-seize, assuming that the nuts are torqued to the design spec, and are checked regularly. Regarding badly corroded, galled, or collapsed wheel cones: That damage is not caused by repeated application of the the production torque and clamp load. Impact wrenches, (used in most repair shops over the years), apply too much torque and therefore, excess load, and damage the cones. Corrosion on a thusly damaged, split, or galled surface is much more destructive. Everything has a usable life. Some things cannot be restored. If its damaged badly enough to affect the tightening, the wheel and/or nuts are scrap. Put it on for shows only, and don’t drive there.

Just to avoid arguments about the above: I am an ex GM Fastener engineer and engineering supervisor, who personally developed thousands of production specifications. I also sat on GM’s fastener technical and finish committees for many years. I don’t work for, and haven’t worked for, them for many years, so I can’t speak for either the old or new GM, but the above is accurate, IMHO.