Front Hub Tightening

[Chase, Jim]

Viv and Dai have both commented about the need to adequately tighten the front hub nut against the spacer, although there appears to be considerable difference in the tightening torque recommended from different sources. The TABC list technical page suggests 40 - 70 ft.lb Viv Recommends 60 to 80 ft.lb Dai Recommends 150 ft.lb The higher the tightening torque the better as far as protecting the stub axle against fatigue failure. However I have some reservations about the 150 ft.lb torque recommended by Dai. This may be OK for repaired stub axles with axle pins made from high strength steel bar with a yield strength of around 70,000 to 90,000 psi. I have no idea what yield strength would be for the original axle pins, which are forged integrally with the steering knuckle. I suspect more likely 50,000 to 60,000 psi. If any one has a broken original axle pin it would be interesting to do a tensile test. From memory the thread on the end of the stub axle is 5/8inch. I am not sure what thread but this would have a core diameter of about 0.5inch for a BSW thread or 0.5334inch for a BSF thread. I would estimate the tensile load in the stub axle to be about 14,400 lb for a torque of 150 ft.lb. using the engineers rule of thumb. T=PD/5 where T is the applied Torque, P is the tensile load and D is the nominal bolt diameter, all in consistent units. This correlates reasonably well with tables of bolt load v tightening torque for coarse thread bolts. Higher load for fine thread. This gives a tensile stress in the threaded end of the stub axle of about 73,000 psi for a tightening torque of 150ft.lb, which is probably far too high for the original material unless anyone has any better data. A maximum of 80ft.lb would seem to be safer for original stub axles. Worn hub inner surfaces can be a problem and as Viv James wrote it is best to replace the hubs, however there is an alternative that I have used successfully. That is to have the hubs electro-less nickel coated. The thickness can be controlled accurately by the time in the plating tank. If you do this make sure that the location surface for the brake drums is masked or else the brake drums won't fit. I didn't have the splines masked which are now a much better fit in the wheel hubs. Mike Sherell suggests that the reason for inner hub surfaces wearing is the bearing thrust washer being put on the wrong way round at some time in the cars past. The correct way is with the concave side outwards so that it doesn't bear on the outer race of the bearing. Regards Jim Chase

[Ray McCrary]

Hi guys, So I would extrapolate that 70 lb./ft. would be the target if using an accurate torque wrench......assuming you have good, cracked checked original stub axles on your car. By the by, who makes the best new stub axle assemblies as far as strength/fit? Best, Ray McCrary "Speed is Life; of course Luck and Altitude are helpful, too."

----- Original Message ----- From: "Chase, Jim" Jim.Chase@fuelsubsea.com> To: mg-tabc@yahoogroups.com> Sent: Tuesday, May 22, 2001 12:21 PM Subject: [mg-tabc] Front Hub Tightening > Viv and Dai have both commented about the need to adequately tighten the > front hub nut against the spacer, although there appears to be considerable > difference in the tightening torque recommended from different sources. > > The TABC list technical page suggests 40 - 70 ft.lb. > Viv Recommends 60 to 80 ft.lb > Dai Recommends 150 ft.lb > > The higher the tightening torque the better as far as protecting the stub > axle against fatigue failure. > However I have some reservations about the 150 ft.lb torque recommended by > Dai. > This may be OK for repaired stub axles with axle pins made from high > strength steel bar with a yield strength of around 70,000 to 90,000 psi. > I have no idea what yield strength would be for the original axle pins, > which are forged integrally with the steering knuckle. I suspect more likely > 50,000 to 60,000 psi. If any one has a broken original axle pin it would be > interesting to do a tensile test. > From memory the thread on the end of the stub axle is 5/8inch. I am not sure > what thread but this would have a core diameter of about 0.5inch for a BSW > thread or 0.5334inch for a BSF thread. > > I would estimate the tensile load in the stub axle to be about 14,400 lb for > a torque of 150 ft.lb. using the engineers rule of thumb. T=PD/5 where T is > the applied Torque, P is the tensile load and D is the nominal bolt > diameter, all in consistent units. This correlates reasonably well with > tables of bolt load v tightening torque for coarse thread bolts. Higher load > for fine thread. > > This gives a tensile stress in the threaded end of the stub axle of about > 73,000 psi for a tightening torque of 150ft.lb, which is probably far too > high for the original material unless anyone has any better data. A maximum > of 80ft.lb would seem to be safer for original stub axles. > > Worn hub inner surfaces can be a problem and as Viv James wrote it is best > to replace the hubs, however there is an alternative that I have used > successfully. That is to have the hubs electro-less nickel coated. The > thickness can be controlled accurately by the time in the plating tank. If > you do this make sure that the location surface for the brake drums is > masked or else the brake drums won't fit. I didn't have the splines masked > which are now a much better fit in the wheel hubs. > > Mike Sherell suggests that the reason for inner hub surfaces wearing is the > bearing thrust washer being put on the wrong way round at some time in the > cars past. The correct way is with the concave side outwards so that it > doesn't bear on the outer race of the bearing. > > Regards > > Jim Chase > > > > > Your use of Yahoo! Groups is subject to http://docs.yahoo.com/info/terms/ > >