Wheel lug nut torque

[Jeremy Parrett]

Just installed new front tires here in San Diego.CA.  The dealer did not know the correct torque settings so we looked in the Magnum chassis manual. It says 450 ft/lbs.
Does anyone know what the corresponding psi setting on a 1 inch CP  797  impact wrench  should be??  The max is 90 psi.  Thanks, jeremy

[Gerald Farris]

Jeremy,
There is no way to adjust the air pressure on an impact wrench to get a specific lug nut torque. Three different impact wrenches will give you three torque readings at the same air pressure. The torque delivered by an impact wrench will vary with the cubic feet per minute of air at the wrench (controlled by hose and fitting diameters, and hose length), condition of wrench, condition of socket, length of extension, and how long the wrench is allowed to hammer on the nut.

If you want a specific torque on your lug nuts, you need to use a torque wrench.

Gerald

[Jeremy Parrett]

Thanks Gerald,
  I guess we have to relax and go with this, as it seems everyone in the industry including Lazydays in Tampa, commercial trucking service outfits, etc. are all using these impact wrenches !!! No where we have been, actually 'torques' the lug nuts !!!        Jeremy

[Joel Ashley]

When we had problems with the balance of our front tires/wheels, the Portland Goodyear service center, Wingfoot Commercial Tire, rebalanced them.  They had state of the art equipment and were definitely not your everyday tire dealer. They said to recheck the nut torque after 150 miles.  The torque on our rig is supposed to be 500 ft lbs.  Gerald is correct;  in fact dealers are supposed to regularly calibrate their air wrenches for the proper torque output, but who knows if yours did.  I'd find a resource, such as a tire mfr.'s authorized regional service center or a friend with a torque wrench capable of 500+ ft lbs., and check it by hand.  Air psi is no indicator.

-Joel

[Edward Buker]

Given the difficulty of finding hand torque wrenches that are capable of 500Ft Lbs of torque and then finding someone able to apply the necessary forces to attain the proper torque, maybe it would be best to go to an alternate truck tire shop and have them bump each bolt with a second air source and suitable impact wrench. The chances of both dealers being on the light side would be pretty low. If you can observe and see that the lugs do not move you can be pretty sure that you were O.K. torque wise and the second impact helps confirm that.

 You can also mark each lug cover and wheel with an "index point" mark with a Sharpie to see if over time there is any rotation movement of any of the lug nuts.

Not quite as good as a 500lb calibrated hand torque but much better than wondering if the lug nuts are tight enough. There is also something to be said for the impact component of air driven wrenches to get the lugs tight....

Later Ed

[Jeremy Parrett]

Hi Ed, Joel and Gerald,
  We go back to the tire shop Tuesday to have the new steering tires filled with Nitrogen.  He had run out.
The air wrench he used is a CP 797 and probably the most common truck/bus service centre tool.  He did ask me to find out if there was a way to tell how many foot pounds 90 PSI was equal to. The answer is 1400 foot pounds if you let the wrench keep going till it stops.  The mechanics I have talked with tell me they can judge pretty closely when a lug nut reaches the right torque.  The can set this tool at 4 different lower settings for PSI,but it will still need 'feel' to get it right...say on a small car lug nut that might need only 45 ft/lbs.
I have marked the lug nuts with an indelible marker until I can find the yellow covers that you see on many trucks. If I can find a torque wrench we will use it to check the ft/lbs presently applied and use this as a guide . This still remains a rather vague field . Even my bus company in Toronto use the same impact wrench and no torque wrench.    Thanks for all the help and suggestions.  Jeremy and Jane

[Richard And Babs Ames]

This is why newer wheels are Hub Pioleted instead of Stud Piloted. If a stud pilot wheel is over torqued it can crack the wheel.

[Gerald Farris]

I was at a rally 2 weeks ago in California and a Beaver coach there found a cracked wheel at a lug nut hole when changing tires. The crack was probably caused by an over torque condition.

Most automotive repair and tire shops have started using torque wrenches to tighten all wheels because of the problems that arise with disc brakes from improperly torqued wheels. However improperly torqued wheels on trucks, buses, and motor coaches has not been enough of a problem to force the change yet. Any large truck shop will have a torque wrench that will read 500 ft. lbs. because it is necessary in large diesel engine repairs.

I carry a 3/4 inch drive ratchet with a three foot handle that I hand torque my lug nuts with, but it is not a torque wrench, so I tighten them by feel which may be no better than an impact wrench.  

Gerald

[Jeremy Parrett]

Gerald, I am going to buy a torque wrench.  I might become popular at the sites we visit!!   jeremy

[Joel Ashley]

Ed's right, though, Jeremy.  You probably won't find anything capable of over 250 ft/lbs at your local handy-dandy Sears store.  I know of a reliable source for torque wrenches capable of 600 ft/lbs, but they ain't cheap - $250 and up.  Let me know if you want their info.

-Joel

[George Harwell]

When I bought my coach I took it to my tire dealer and had them loosen the lug nuts and then I tightened them with my 350 lb. gun. That lets me remove the wheels at home during maintenance. I bought the coach in July 04 and have 80,000 on it without a single lugnut becoming loose. My personal opinion is anything over 450 on these motorhomes is overkill. Huge 90,000 trucks need the high torque due to the rugged duty they encounter. Fortunately we get to do most of our travels on smooth service interstates. I do have torque wrenches and use them as required in other areas on the coach.

[Bob McCORMACK]

You can also buy a torque multiplier which will allow a regular torque wrench to supply the higher figure at the wheel.  We have used many over the years on the race cars with center nuts.   Good quality high torque air guns are expensive.  The teams that use them for pit stops spend a lot of time making sure they are calibrated correctly and of course they run off of nitrogen bottles at high pressures.

Racer Bob

[Roy Mueller]

Proper wheel torque is the only way to go. Too loose, you will egg out the wheel; too tight you may crack the wheel . Over torque can stretch the studs to their breaking point. On the AK, trip one coach broke lugs leaving the camp ground.   When I checked the rest, 3 more fell off.  Trying to get the wheel off to get the broken studs out, the lug nuts were will over 1200  hundred FT/LBS. All the studs had to be changed. I use a 1/2 inch air wrench to snug up the lug nuts to 300 ft/lbs.  Then I use a 12 to1 torque multiplier with a 1/2 inch torque wrench set at 50 ft/lbs.  I bought a 1/2  inch torque wrench for $100.00, and a 12 : 1 torque multiplier for $ 600.00.
If you have coach with left hand threads on the left side of the coach, you must buy a torque wrench that will torque in both directions. Use 600 ft/lbs. as a good number.  It will vary between steel wheels, steel and alum, and all alum.

Roy Mueller

[Gil_Johnson]

I'm amazed at how many truck tire centers solely rely on their air impact tools.  I went to two that both said the same thing, "500 lbs is right about where the air impact tools stop".  A torgue multiplier and torgue wrench is the right way to go.  Although I have seen torgue multipliers on line, I've never sen one in person.

Gil

[Jeremy Parrett]

Hi Joel,
Way down here in Guerro Negro, Baja Sur, I am going Whale watching tomorrow !!!  Please give me the info on the torque wrenches.  The $250 seems a heck of a good price!!   It will have to wait till I get back to San Diego, at the end of March though. So, no hurry!!!