Thread: New hubs

My new hub assemblies finally arrived late Friday. Got both of them in by 12 today.Truck rides so much better now.Like gliding on butter!One of them had developed a dull noise so I decided if I was gonna change 1 I might as well do both.Found great info from the net on what to expect.Here are a few pics and some interesting info on torquing bolts. I managed to break the end out of a 1/2" breaker bar and the nib out of my torque wrench. The torque wrench had a lifetime on it so I got a new one. The breaker bar, I'm taking back tomorrow to see if they will replace it! I bought a 3/4" drive bar and a cheater pipe and the axle nut finally gave up!I ended up using PB Blaster on all the bolts and used anti-seize grease during reassembly.Here's the info on torque I was talking about. Torque specifications given in service manuals are for "clean, dry" threads unless otherwise specified.

That "clean, dry" value is to be modified for the following lubricants -

100% of total for threadlocker compounds.
95% of total for Room Temperature Vulcanising (RTV) "silicone" sealants.
90% of total for PTFE-based thread sealers (preferred to use paste, vice tape.)
67% of total for clean engine oil or chassis grease.
50% of total for anti-seize compounds.

This is done to reflect the lubrication afforded by the various compounds. While you're using a torque wrench to stop at a specific applied torque (turning force,) what you are actually setting is the "preload tension" of the fastened joint - or the clamping force provided by the screw.

You start with the "clean, dry" specification - anything that changes the friction of the threads against each other changes the final preload - dirty or corroded threads will require more torque applied to get to the desired preload, while lubricated threads will require less torque applied to get to the same preload value.

Think of a screw thread as an inclined plane ("ramp" in common terms.) You're pushing, say, a 200# load up a ramp. It's going to take a fair amount of force to move, right? Make the bottom of the load rough, or make the ramp surface rough, and it's going to take more force.

Alternatively, coat the ramp with oil (assume you will have the same traction under your feet.) The load will suddenly be easier to move up the ramp, no?

Same principle applies here. Due to the extreme lubricity of the never-seez, you are reducing the torque by half - in this case, since you have to apply so much preload, you run the risk of overloading the bearings and either brinnelling the races (due to the extra added pressure - particularly when static) or of simply wearing out the rollers (because they're being squeezed between the races too hard. Bearings require a certain amount of preload to work with maximum longevity - too much or too little can lead to premature failure.)

In fact, in cases like this (wheel/spindle bearings,) I've noted an increase in bearing life when lubricating the threads and using a reduced torque value, principally because you are able to preload the bearings more consistently than you would with "clean, dry" threads.

The basic idea here is, if your torque wrench doesn't support measurement of 175 pound-feet of applied torque (most hobbyists won't have one,) you can get the preload value down into the range of your torque wrench by cleaning and lubricating the threads - engine oil or chassis grease brings it down to ~117 pound-feet, and never-seez brings it down to 87-88 pound-feet - both of which should be well within the range of hobbyist's tools. The use of lubricant carries an added advantage - it makes the thing easier to take to bits next time. I also tend to use never-seez on the unit bearing retainer screws - then torque them to 37-38 pound-feet, vice the "clean, dry" spec of 75 pound-feet (so I can take those damned things off later if I need to as well!)

Remember, if the FSM value doesn't list a lubricant as required, it's a "clean, dry" spec. There are two fasteners I can think of offhand that want to be lubricated - the [COLOR=blue !important][COLOR=blue !important]crankshaft[/COLOR][/COLOR] nose screw (1/2"-20, 80 pound-feet lubricated with clean engine oil) and the driver's side front cylinder head screw (1/2"-13, 100 pound-feet with PTFE paste, plumber's pipe dope, or similar thread sealing compound. Not a threadlocker.)

Make sense now? Or have I only succeeded in muddying the waters further? __________________