Lug nut Torq?

[67 GTO]

I would venture a guess that the manual provided with my 2LT is the same for a SS.

My manual covers both, same wheel nut torque.

[redman]

Since torque specifications are based upon bolt diameter and attendant stretch on tightening the 100 ft/lb value technically seems correct. It would be a mistake in my opinion to base torque specification on anything other than bolt stretch (ie GVW) as suggested above.

[Nine Ball]

Agreed with redman. As an engineer myself, I've had to spec bolts and torque values numerous times in my career. Torque has always been based on the bolt material and size/thread specs, as well as coating type. The bolts can only handle what they can handle, that is based on properties of the bolt itself. The bolt sizes are chosen based on loads.

Weird that a 3.6L 304hp V6 Camaro with less weight shows 140 ft-lbs in the manual, but the heavier CTS 3.6L 304hp Cadillac shows 100 ft-lbs. Seems like GM fails at internal communication, but we already knew that.

[67 GTO]

Originally Posted by Nine Ball

Agreed with redman. As an engineer myself, I've had to spec bolts and torque values numerous times in my career. Torque has always been based on the bolt material and size/thread specs, as well as coating type. The bolts can only handle what they can handle, that is based on properties of the bolt itself. The bolt sizes are chosen based on loads.

Weird that a 3.6L 304hp V6 Camaro with less weight shows 140 ft-lbs in the manual, but the heavier CTS 3.6L 304hp Cadillac shows 100 ft-lbs. Seems like GM fails at internal communication, but we already knew that.

This may be the answer, so any harm to the studs after taking to 140 ft lb and then backing off to say 100?

Thanks.

[scythezo6]

Make everyone happy and go to 120 ft/lbs =P

[97one]

Originally Posted by redman

Since torque specifications are based upon bolt diameter and attendant stretch on tightening the 100 ft/lb value technically seems correct. It would be a mistake in my opinion to base torque specification on anything other than bolt stretch (ie GVW) as suggested above.

I myself have owned since 2001 Three new GM vehicles & one FORD with the SAME size Stud & ALL 4 Manuals said to Torque to 140lbs.
I am sure ALL 4 Manuals were NOT misprinted.

Hey I have a small trailer with small 15" alum.wheels & that manual says to torque to 120lbs.

[Nine Ball]

I've owned more than four GM vehicles since 2001. I also have never used the owners manuals as a source of engineering specs, nor have any of the dealer techs or performance shop techs I know. The information within Factory Service Manuals always precedes a lowly owners manual.

Again, we just want the correct answer here. I'd lean towards what service manuals say over owners manuals. It seems nobody has the actual correct answer so far in this thread.

[Nine Ball]

Originally Posted by 67 GTO

[/COLOR]

This may be the answer, so any harm to the studs after taking to 140 ft lb and then backing off to say 100?

Thanks.

Shouldn't be a problem. 140 ft-lbs isn't enough to stretch the bolt to failure. If you do decide to do that, just make sure you don't simply back them off. Loosen them first and re-torque properly.

[redman]

Torque specifications are determined by the diameter and grade of the bolt. The 100 ft/lb mentioned ASSUMES the Camaro studs are grade 8.8 which in my experience is most common for the application. However they may be specified to a higher grade. Best way to know for certain is to look at the head of the stud (the flat head behind the hub face opposite the stud end). There usually is a grade marking here. If it's 8.8 the spec is 100 ft/lb if it's 10.9 the 140 ft/lb would be correct.
If anyone can look at the studs please post the grade. It's too cold here (Michigan) for me to work in the garage.

[67 GTO]

Originally Posted by Nine Ball

Shouldn't be a problem. 140 ft-lbs isn't enough to stretch the bolt to failure. If you do decide to do that, just make sure you don't simply back them off. Loosen them first and re-torque properly.

Thanks. I have a summer/winter wheel & tire set up and change in my garage. So although 100-140 ft lb may not be a big deal,
knowing what is safe is a plus.

[Nine Ball]

Based on experience, I'd say anything 100-140 should work just fine. Some guys over on the Cadillac forums were saying to torque their CTS-V lugs to 158 ft-lbs. Noooo thanks! Me personally, I'm going to continue using 100 ft-lbs on my lug studs. I don't enjoy stripping threads or busting studs. Never had a wheel loosen on me before, and I've gone over 200 mph in personal vehicles with that torque spec.

The goal is to have the wheel sit flush against the hub. It doesn't require a lot of torque to do this. Check them periodically and if none of them are loose you are good to go.

[Russell James]

There is a misprint somewhere. I'll have to retract my earlier statement that 140 is correct. Now I don't know. I just looked in the Service Manual, it say 140 Metric 100 English.

Then I checked my car. I have a new SS in my garage untouched off the truck with still under 100 miles. I know nobody touched it, I prepped it. I checked all the lugnuts, the best I can tell they are all in the 100 to about 110 lb/ft range. Definately none over 120. With my wrench on 120, I could get the nuts to turn tighter just a bit before a click. Moving to an untouched wheel and trying loosening torque, anything under 100 my wrench clicked before the nut loosened. At a hair over 100, I could loosen most without a click, the ones that did click before budging I could go to about 110 and then they loosened without a click. So my guess at factory torque is around 100 to 110ish. Definately not 140.

I'm thinking owner's manual misprint. I have a friend that is a Service Manager with some engineering connections. I'll ask him to see if he can get the straight scoop.

I retorqued all mine to 110 after feeling what the assembly plant had them set at. I'll bet anything in that 100 to 120ish range would be just fine.
I'll post back in a few days if my friend can find out which is correct the owner's manual or the service manual.

[Nine Ball]

Nice. Even the robot fixtures that install the lug nuts got a different memo with 110 ft-lbs

[two_wheel_mayhem]

They will take 140 without breaking, so thats all that matters.

The studs wont strip, they are too hard. The lug nuts are another story.

If 140 scares you, then dont torque them to 140. You can go 80 and they still won't come loose.

It's more important to drive 50 miles and recheck them after the aluminum wheels go through a heat cycle.