Brake Drum Hub Assembly Mystery

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Lenni

Lenni

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Can anyone tell me why the right front lug nut studs are crimped at the drum. I have two vehicles and both right front lugs are that way. The other three wheel lugs are not that way. One Mopar guy told me they did that at the factory on purpose to prevent it from falling off on the assembly line. That does not make sense to me.
Brake Drum 2.jpg
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Brake Drum 1.jpg
 
They are crimped because the drum can get significantly hot in normal use. A pure press fit would eventually work the studs loose.
 
All front drums would be swedged on from the factory.

As to why, as stated, it makes them a unit rather than separate pieces easier to assemble. Might also get balanced as a unit and that keeps it together for the future. Requires you to pull the hub and inspect and hopefully clean and re-lube the front bearings on a brake shoe replacement.

The rears would not. If they were swedged to the axle there would be no way to tighten the axle retaining bolts

The fact that one side is not points to the drum being replaced at some point in the cars life.

Or

If the cars don't have left hand lug studs on the left hand side of the car, ( up to a certain year, 70 something) there is your answer right there, someone changed the studs on the left hand side only to right hand studs.

Also I suspect replacement drums back in the day came with the hub and studs intact. So maybe a combo of the two.

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As mentioned, the drum was swedged onto the hub to create a single assembled unit. Not only does it make it easier to install, but final machining of the drum's inside surface was done after the hub was installed. The pressing process can, and often does, distort the friction surface. If there were any concentricity/runout issues between the hub and friction surface after pressing/swedging, they were eliminated on the brake lathe.

When replacing drums or rotors on a press-together assembly like that, the drums or rotors must be turned after assembly. Years ago, in the days of US and Canadian drum/rotor production, there was always a note to this effect in the box. A friend found this out the hard way recently after installing NOS, US-made Raybestos front drums on a non-Mopar. The note was there saying they had to be turned prior to installation, but wasn't specific about the process. It was common knowledge 40-some years ago when they were made, but now? Well, nobody asked the old guy--me--about this, and the drums got turned before the hubs were pressed. Result? The car shakes during braking. Now they have to come off and be turned again--painful to do on expensive NOS parts made of unobtainium (aftermarket drums don't exist for that particular car).

It's something to keep in mind when replacing rotors on K-H disc-brake cars as well as two-piece drums, though drums are more susceptible to this. Either way, put them on a brake lathe to check before installing.
 
Just got thru replacing the front hubs on a 67 bcuda that'd had the hubs ruined by pounding out the studs without removing the swage.
Yes, Machined drums and arc-ed shoes .

"Swaging is a metalworking process that shapes a metal object by bending or hammering it with a tool called a swage. Learn about the different types of swaging, such as internal, external, combination and dual, and their typical applications in various fields."

Cheers
 
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Do not just press out the studs to remove the drum, if you do your hubs will be trash. You must cut the swedge from around the studs. There used to be a tool to do this, but it is no longer available. The best method I have seen is to use a 5/8 hole saw with no pilot drill to cut away the swedge from around the studs and remove the drum. You may also need to grind away what's left of the swedge after the drum is removed. Failure to do this and just pressing out the studs will result in the holes in the hub being too large for the studs.
 
Dana67Dart said:
All front drums would be swedged on from the factory.

As to why, as stated, it makes them a unit rather than separate pieces easier to assemble. Might also get balanced as a unit and that keeps it together for the future. Requires you to pull the hub and inspect and hopefully clean and re-lube the front bearings on a brake shoe replacement.

The rears would not. If they were swedged to the axle there would be no way to tighten the axle retaining bolts

The fact that one side is not points to the drum being replaced at some point in the cars life.

Or

If the cars don't have left hand lug studs on the left hand side of the car, ( up to a certain year, 70 something) there is your answer right there, someone changed the studs on the left hand side only to right hand studs.

Also I suspect replacement drums back in the day came with the hub and studs intact. So maybe a combo of the two.

.
Click to expand...
Chrysler sold the replacement drums and hubs assembled as a service part.
 
Rear brake drums slide right off as long as there is no axle hub nut like on pre 1965 B or C bodies.

Rear axle studs are pressed into the flange with no swedge.
 
new rear drums were held in place with a push nut (like what hold hood hinges to the body) at the factory so that the whole rear axle assembly could be moved around and installed without the drums falling off. Several years ago I bought a 73 Dart with 27,000 miles on it and there were two pushnuts holding each rear drum. 40 years and the drums had never been off the car...
 
I have a 67 dart that was parked in 1976. It had many oe brake parts. The odometer read 68,000 miles about 7500 miles per year.
 
The swedging could be for a few reasons:
- balancing. Some hubs have holes or a cut out section in the flange, so correct positioning would be important
- so the drum does not come off with the wheel

I am not 100% sure, but I think the drums are bought from brake companies such as Lockheed, Wagner, Bendix, Kelsey-Hayes etc. If so, that would explain why are some are swedged & some are not.
 
I don't know the real reason the factory swaged the studs to lock the drums onto the hubs. But as stated, if you don't cut the swedge before pressing the studs, you will ruin the hub, which is made of unobtanium. I do have the swedge cutting tool in both the "A" body 7/17 size, and the larger car 1/2 size. Years ago I did have the swedge tool, but that disappeared a long time ago.
 
The whole swedging process for these hubs never made sense to me anyway.
I am sure there is an engineering reason for it, but if the studs are pressed into the hub and then the studs are bolted to wheels on the car, the wheel and drum are not going anywhere, even with the added braking heat. If they did your wheels would fall off too, loosing 5 lug nuts and studs in the process.

Many other processes just press on knurled studs and slide the brake drum / rotor over the studs then bolt on the wheel to make a hub flange / drum or rotor / wheel mechanical sandwich.

Maybe it was for hub to Brake drum balance? But if you replaced the brake drum it would be (likely) out of balance again.
 
I say there is no need for swedge. I cannot quote you specific vehicles, but I have "been into" some vehicles, probably mostly 4x4's where the front drums are not swedged.
 
It's also common practice to drill/cut the head off the stud on the inside of the drum, and punch the headless stud thru the front, which I did on this bcuda, replacing with new studs avail from jobber.
No hub damage as the headless stud and swage come out the front.
 
I think that it is not for any functional reason once the car is built. I think, like the rear drum capture it is to save money on the assembly line. I think that they order the whole assembly as a piece. I can remember buying drum and hub assemblies from the dealership in the 1970s. I think that the manufacturer delivered the whole thing complete as this was easiest during the assembly process.
 
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