A few complaints have been received of truck disc wheels (AA-1015-C) cracking when operated over heavy roads having deep ruts.
Investigation of these complaints dearly proved that the trouble was not with the wheels but in the manner in which the wheels had been installed.
For example, instances were found where drivers had failed to tighten the wheel nuts. Others showed that owners had mounted wheels with an accumulation of mud and dirt between the face of the disc and the hub flange. Under these conditions the wheel instead of being drawn securely in place worked back and forth on the hub. Figs. 912 to 914 show what happens under such conditions.
Both owners and mechanics must clearly understand the correct method of mounting wheels. This applies particularly to truck drivers whose wheel changes are usually made at the roadside and often under unfavorable conditions.
The following instructions should be carefully read and brought to the attention of truck owners.
(1) RIGHT- AND LEFT-HAND THREADS are used on all assemblies to insure wheel nuts staying tight. In mounting hubs, or in replacing studs or nuts, right- hand studs must be used on right side of chassis and left-hand on left side. RIGHT and LEFT sides are seen by the driver facing forward. (See Fig. 915.) All studs and nuts are plainly marked “R” and “L” and must be so used.
(2) WHEELS MUST BE CLEAN. Always examine wheels before mounting on hub to be sure that (a) countersunk holes, where ball face of wheel nut seats, are free from dirt, and (b) face of disc and hub flange, where they bear together, must be clean and free from dirt or grease. The same applies to the surfaces of both rear duals where the two come together. Presence of foreign matter will prevent proper bearing and create high spots which are likely to cause loose fits, play and wear. Watch this point, particularly in mounting spare wheels, which may have picked up road dirt. The countersunk holes should be carefully cleaned.
(3) DUAL WHEELS are of the double cap nut type. The inner dual wheel is individually held by the sleeve-shaped inner wheel nut to insure positive drive and tire alignment. The inner wheel must be mounted and tightened before the outer wheel is put on. The outer wheel slips over the inner wheel nuts and is independently held by the outer nuts (see Fig. 916). The front, or single wheel, is held by a single set of nuts.
(4) TIGHTENING NUTS should be done with the truck jacked up. Outer wheel nuts must be backed off at least two full turns to tighten inner nuts. THESE NUTS MUST NOT BE NEGLECTED. In mounting wheels or tightening nuts, proceed in a criss-cross fashion and not around the circle.
(5) DO NOT USE AN EXTENSION ON THE REGULAR WRENCH HANDLE AS SUPPLIED. Ordinary pressure as exerted in tightening cap nuts with the handle is sufficient to drive wheel nuts home, without use of an extension.
(6) TIGHTEN ALL WHEEL NUTS AT THE END OF THE FIRST FIFTY TO ONE HUNDRED MILES ON A NEW TRUCK. Thereafter, only an occasional check of nuts for tightness is necessary, but this should especially be done soon after a · spare tire and wheel change. Nuts properly installed and given the subsequent tightening will remain tight indefinitely.
(7) CLEARANCE OF STUD HOLES in wheels with the ball-faced nuts filling the opening permits of easy mounting and eliminates wear. WHEELS DO NOT PILOT ON HUB AT CENTER, the entire load being carried through the cap nuts and studs.