Packard Forum Index » Post-War (1946-54)

Regarding the disagreement about the tapered shaft vs. the key providing the transmission of torque: You're both right. How's that for settling an "argument"?

The very high tension on the drum against the tapered shaft provides substantial friction. Also, the key must shear before rotation occurs and it's function is to act as a "fuse". If rotational forces exceed a design limit determined by the frictional and shear sum, the key will shear, preventing broken axles or other major parts.

Two problems arise. I've once had the threaded portion of an axle snap off while driving. At that point there is little to prevent the wheel and drum from parting company with the vehicle. Without a drum there is total loss of both hydraulic and parking brakes on all wheels. Fortunately I was traveling slow at the time, heard a scraping noise and came to a stop with the drum almost off the axle, but not quite.

Another problem with tapered shafts is galling. Over time metal transfers from one surface to another practically welding them together. Good luck getting them separated. A simple old-time preventive is to coat the clean shaft with Milk of Magnesia (MoM). Plain or flavored is your choice, but I prefer plain. This prevents galling but does not impede the frictional properties.

Scott

Thanks Scott. What I like about this site is the information that is shared. I can feel confident that eventually the correct information will be posted. I enjoy reading the discussions and like to contribute when I can. Sometimes I am mistaken, but then someone will come along and post the correction. Sometimes I notice an incorrect posting, or one I think is incorrect, and will try to correct it. Some here are extremely helpful and we owe them a big thank you for their time and efforts to get the correct information to us.

(o{}o)

I still don't think the extra "tightness" to "press" the taper is warranted nor necessary. Especially if done "dry". If you torque to dry specs wet(inadvertently), you're way over. I'd bet this procedure was done frequently back in the day without the benefit of a torque wrench and maybe even a cheater or large monkey wrench was used. The nut is pinned, so it's not going to come off. Each application of that kind of torque stretches/deforms the threads. If hub nut has been on tight enough to fatigue crack the axle threads to the point of causing break off or stick the hub ad infinitum, it's simply too "tight"... (another problem of "outboards" the external threads rust.) The brake linings can also still be holding, also, on some of these that have set for long periods and the cylinder froze/rusted. So checking / detaching that should be done before attempting removal.
There's little to no rotational "friction" on the taper if the key is acting because there's little relative movement. The joint can only move if it's too loose(sloppy) which means it wasn't installed properly. Without studying the dynamics / harmonics, it's difficult to predict, if there's any other detrimental movements. I do not think that was well known at the time of this design.
A smear of antisieze lube will fill the taper voids and prevent the sticking. I would not recommend to use a water based product like milk of magnesia.
The wheel loads transferred to the axle and vice versa are applied over the entire hub contact area, so taper helps with stress distribution and the smooth diameter transition prevents stress concentration which can lead to fatigue cracks. A taper is easy to machine, centers the wheel, destresses, and that's why it's commonly used.
I'm not going to reuse this style rear end, so I won't have to worry about this again.

The initial torque on the nut tensions the drum against the tapered shaft but this torque relaxes as the drum heats and cools. The drum expands and is pushed onto the shaft. It cools and tightens it's grip on the shaft. Friction is very high after a good heat cycle. The drum does not separate easily from the shaft even with a puller after this occurs.

MoM works just fine. It prevents galling and with the tight fitment the joint doesn't rust. No oxygen. A very light film of anti-seize grease could be used as well.

Scott

no matter how many opinions say it is something else

1. Galling-This only happens if the shaft and the hub move relative to each other, if movement is occurring then the joint is in failure mode due to improper or loose) installation..There should be absolutely no movement between shaft and hub Wheel bearings either tapered or roller that gall have either no lube or are adjusted too tight.

2. Tapered shafts/hubs are designed to be installed DRY. No service manual whether Chrysler, Jeep , Packard or other recommends anythng be used. The problem encountered is that they are difficult to remove, Loctite or similar will create a film which will keep the axle/hub from being in 100% contact thus disturbing full contact. Anything that makes it easier to remove will decrease the integrity of the joint. It is the taper acting as a wedge combined by high torque on the nut that allows the coupling to transmit power, see an engineering manual

3. Lubricant of any kind on the shaft or nut will give a false torque reading.

4. Rust is not what is holding the joint together, the mating parts are finely machined to mate perfectly, the only place of water entry is beneath the nut and beneath that is a keyed leather washer.



5. If you install a drum, torque it and remove it, then the removal is painless. If installed for 40 years there is a bit of "creep" due to the taper and high torque and heating/cooling and the drum moves up the taper ever so slightly. The ever so slightly is what makes it impossible.

6. There was a day when virtually all automobile used taperred shafts, but they didn't sit for 50 years without being removed.

6. The secret is pesistence with a heavy duty puller and a moderate amount of swearing.

I have to agree with j@kanter on this one. Jim? is it? think I saw on another thread.Dry on the taper and nut tightened to spec or you are setting up for a potential failure. You seem to be talking about the driving force and the keyway and forgetting about the downward force of the weight of the vehicle acting on a different part of the mating surface as the axle rotates. the machined male and female taper need to mate and be tightened to become one. any looseness or allowed play here will cause hub movement on the shaft with each revolution and WILL cause wear,chafe,heat,fatigue and failure. Same as ball joint or tie rod taper design. I have seen under torqued tie rod taper nuts elongate holes and eventually fail. be carefull here. multiple manufacturers R+D over years of testing and parts examinating should not be rethunk here! A good puller, slow application of force with heavy hammer blows on the tool between tool tightening and slight heat will do the job.

1. Movement does occur when the drum expands due to the high heat from the brakes. The drum will creep onto the tapered shaft. This high pressure movement can result in some galling. It doesn't take much to form a bond.

2. MoM is a dry and very thin film like a powder. It's not a lubricant but inhibits metal transfer and is tolerant of high heat. The problem with commercial antisieze is that it is heavy bodied -- basically a light grease with metal powder. Use MoM and the drums won't be so hard to remove when the next brake job comes around. I've not used commercial antisieze on brake drums but did try it for a short while on small engine flywheels that can also be very difficult to remove down the road when assembled clean. That resulted in flywheels shearing the key during use so I abandoned that product and went back to the MoM. No more problems.

3. Lubricant on the shaft or nut will not give what I would call a false torque reading. General torque tables publish two torque values, dry and lubricated, which are slightly different. They are equally valid. As for the specific application under discussion, the torque value is not precise but is a pretty wide range. It's a castellated nut that must be aligned for the cotter key. Assuming undamaged threads the difference between dry and lubed is less than the published range. BTW, who said anything about lubricating the threads? I must have missed that.

4. Did someone say rust holds the joint together? I stated it didn't. Someone suggested that MoM, if not dried first, could contribute to rust. I stated it's not an issue.

5. It doesn't take 40 years for creep to occur. A few heating/cooling cycles under pressure will bond them quite well. After that, on a clean joint absent a barrier, bonding on the molecular scale will continue slowly over time. So even if the car sits and does not undergo additional heating cycles the parts will continue to increase their bond.

6. I have a very heavy duty drum puller that has a handle designed to accept the blows of a sledgehammer (and it has received many). I've removed lots of drums from cars that have not been serviced for many years and they can be a bear. Rosebud acetyl/O2 heating torch and hammer blows and patience will eventually get them to part company but in these difficult cases I find the surfaces are no longer smooth but are roughened due to some metal transfer. As an aside, in one strange case a pea-sized lump of metal came off the shaft with the drum about a half inch from the end of the taper. That's the only time I've seen two parts weld together so strongly in one spot.

I removed the rear drums from my '48 during the winter. One of them was quite easy to remove but the other was really tight. The weren't torqued very evenly.

When I was putting them back together I noticed what might have caused the problem. In the shaft there was only one hole for the securing pin. The nut had six grooves and its pitch was quite thick. So if I want to tighten the nut so that it remains in contact with facing surface the "tightening intervals" are between ~60 degrees.

How is this supposed to work? Should the nuts have more grooves than mine have? I don't like the idea of reversing the nut to the last groove as this might leave possibility of rust issues in the possibly opening gap.