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Old 12-15-2015, 02:06 PM   #1
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Setting Torque on Berkshire Freightliner wheels

I notice that the Freightliner manual recommends annual re-torquing of the wheels and re-torquing within a few miles of any service that removed the wheels.

So, for safety, I became interested in torque multipliers and I am reporting the results of my research (and purchases) here.

I originally wrote this as a reply to a slightly older thread
Nut size on Berk Wheels

Someone on that thread recommended a compact torque multiplier that is seen all over the web, such as at Torque Multiplier Truck Trailer RV Lug Nut Wrench Labor Saving Wrench with Case by ALTOCRAFT USA: Amazon.ca: Tools & Home Improvement

I believe that there are two problems with using that kind of torque multiplier for setting torque (as opposed to removing nuts):

1. This kind of torque multiplier has a very high multiplication ratio (typically 58:1), which means you need a torque wrench setting like 10 ft lbs. I've found torque wrenches to be very unreliable at such low settings (more on this below). Moreover, they don't cite the friction loss. The online videos describe a "half-back" system for setting torque but are very careful to qualify the importance of going to a tire shop to have the torque checked afterward. So it doesn't solve my problem of checking the torque after I've driven it home from the shop. Also, lug nuts need a wide variety of torque settings, and the half-back system will either break studs or wheels on stud-aligned hubs (that can only handle lower torque) or they will under-torque the hub-aligned wheels like on a Berk. It is just a little too casual for safety.

2. Torque multipliers need a reaction bar, or in the case of the multiplier cited above, a reaction foot. Using my high-school Newtonian mechanics, if you have a 58:1 multiplier, you provide one part of force (say 10 foot lbs) and the reaction foot delivers the other 57 parts (say 570 foot lbs), assuming (only for simplicity) that you need 580 ft lbs on the nut. Now, the reaction foot on the multiplier cited above is about 6" from the centre of the nut, so to get 580 ft lbs, you need over 1000 lbs of sideways force from the foot. They recommend placing the foot alongside another one of your lug nuts. But, if that nut isn't tight, it will be sliding all over the place with 1000 lbs of lateral force on it. I can't imagine that the result is reliable or safe.

So, I settled on a more professional torque multiplier, the X4, which is used in the oil industry to tighten flanges, for example. I got the LM 750 model shown at
3/4" Torque Multipliers

I bought it used on Ebay for $180 and it arrived in good working order
X 4 Torque Multiplier LW 750 | eBay

The X4 is a 4:1 multiplier and in my tests, I found a friction loss of about 10%, so it works like a 3.6:1 multiplier. So, for the Freightliner wheels, I'll be using 135 ft lbs on my input wrench to get 486 ft lbs (inside their 450-500 ft lb range).

The X4 needs a longer reaction bar and I'm using a 1" black pipe that is 36" long. I plan to have the reaction bar hit the ground, rather than press on any part of the wheel or wheel studs. This will require a 12" extension bar for the 3/4" output from the X4. The reaction bar presses the ground in the direction opposite to the pressure from the input breaker bar. This has the advantage that I won't tend to push the centre of the torque wrench downward and off the nut with the downward force exerted on the end of the 12" extension bar – the reaction bar is pushing up to offset me.

I've still got my Berk parked for the winter, so I haven't tested this on my system, but I've done a lot of testing on my torque systems, etc. I'm confident it will work well.

For my testing, I bought a torque calibration tool from Princess Auto 1/2 in. dr Digital Torque Adapter | Princess Auto

If you aren't in Canada, and are looking for this, the item is patented as a Taken ETorque torsion tool and the instruction manual calls it a Titan, which is distributed by Star-Asia USA. I did a lot of testing of this tool, comparing it to a Craftsman beam torsion tool (rated at +/-2% accuracy), luggage weigh scales on a 2 or 4 ft breaker bar (and the weigh scales match the airport scales), and finally with a Torsion Click Wrench. These were all providing the same figures except the click wrench, which understated torque by 5 ft lbs at the 80 ft lbs that Honda recommends for my car. The click wrench also doesn't work on left-hand threads (and Freightliner says the left side of my Berk has left-hand threads).

So, I plan to do my wheel nut checking with the X4 torque multiplier, driven by a breaker bar with the Taken ETorque tool in between.
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Old 12-15-2015, 02:25 PM   #2
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I'm thinking the above post will be converted to a document in my RV maintenance folder - thanks Gordon!
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Old 12-15-2015, 03:58 PM   #3
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Quote:
Originally Posted by BamaBob View Post
I'm thinking the above post will be converted to a document in my RV maintenance folder - thanks Gordon!
You're welcome Bob. I'm actually writing up a bunch of the notes I make to myself on RV maintenance and operations issues. Eventually, it will become a PDF and I'll post it for others as an augmentation to the Forest River manuals.
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Old 08-02-2016, 11:12 PM   #4
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Update on Torque Multiplier

I finally found time to use my Torque Multiplier to check my wheel nut torque. I did it over a trip in July and only now have gotten back to send in the results:

I used the system to check the wheel nut torque on our Berkshire 34QS. This is after a year of use.
• Removed the hub caps to verify the presence of the aligning tangs, which means that the wheels really are hub aligned.
• I bought a 1 5/16" deep 3/4" socket, which is slightly smaller than a 33mm socket. But the socket is still a comfortably loose fit on the wheel nuts.
• All the wheel nuts are right hand thread. The left hand threads mentioned in the Freightliner manual are for the large decorative nuts on the rear hub caps.
• Set the digital torque gauge to 140 ft lbs. With the 4x multiplier and friction loss of 10% to 20%, this gives a torque between 450 and 500 ft lbs as recommended.
• All of the wheel nuts started to feed back resistance at about 120 ft lbs and gave approximately 1/2 to 3/4 turn on the breaker bar before getting to 140 foot lbs. This is consistent with 45° to 70° of rotation of the wheel nut, assuming that no slack is taken up in the gearing. It suggests that the nuts were slightly under-torqued, unless there is no friction loss in the multiplier.
• When advancing the wheel nuts, the wrench doesn’t spring back, so the nuts are tightening rather than just bending elastically.
• The reaction bar was the 1" threaded black pipe. The force on the reaction bar cause the ends to deform slightly and split. Without the threads, it might have been sufficiently strong to not deform. Or, I could have threaded a couple outside the nuts and cut it to be even with the end of the threaded pipe. This would give an extra support around the threads.

–Gordon
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