For the second time, when installing new brake drums, I have had to had them turned right out of box. These are the OEM Delco drums for my Silverado., not the Professional or Advantage ACDelco line. Last time I had to redo my whole rear brake job because they vibrated. This time I took them in to get them turned before starting the project. The guy couldn’t believe how warped they were. These were made in the United States. So, next time we’re grousing about import drums, know we can crank out bad ones as well. Is it common practice to turn drums and rotors even when new?
It has never been common for me to do that but I have not had to change a brake drum in over 30 years.
This is a common occurrence if the raw casting is not allowed to site for 2-3 weeks after casting. Cast iron moves around a bit stress relieving itself in that 2-3 weeks. Then you can machine them. If the supplier doesn’t do that, they will warp. I believe Bosch is the brake system supplier but they likely get finished drums from a sub-contractor.
I know it’s common to replace rotors when doing a brake job on disc brakes, but I’ve never seen anyone replace or turn drums when replacing shoes on drum brakes.
Having said that, I don’t think I’ve ever paid someone to do a shoe replacement on my rear drum brakes. I paid to have leaky pistons replaced on drum brakes, but the shoes and drums were fine, so I didn’t have them changed out.
I actually bought the “professional” line when I did the brakes on my truck. I was too cheap for the exact oem, if I recall. But I haven’t had any issues. That single rear “spring” threw me for a loop for a minute on the rear drums! “Special tool” for me consisted of a big screwdriver and a large set of channel locks. 
Well, in my lifetime I’ve machined countless drums and rotors and have yet to see a new anything that needed to be turned right out of the box.
If by vibrate you mean the steering wheel shakes that points to front rotors. Warped rear drums will cause a pulsation in the brake pedal. At least in every case I’ve seen.
In retrospect I just thought of an anomaly I ran across several times in the past but it’s been a while.
Several cars were having severe brake vibration and squealing noises. Repeated attempts at repairs could reveal nothing wrong. One was a new car with 50 miles on it.
I finally determined the wheels were warped. What would happen is that the distorted wheels would warp the drums; either immediately or soon after.
I replaced the rear wheels and the brake issues were gone for good. Just something for consideration anyway.
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Back in the’70s we normally turned the drums on our brake jobs, typically to get rid of the ridge that the shoes created in the edge of the drum. Never remember turning new drums.
Back in the 50s when we did brakes all we had were drums and the front drums were more important than today’s rear drums. We used to check for bellmouth as well as surface condition as well as diameter. If there was enough meat left we turned the drums and if necessary had oversize shoes arc ground to fit the drums.
Yes I know Jaguars had disc brakes in 53 but no one ever brought a Jag to a station I worked at. The 53 Chrysler Imperial had disc brakes but that looked more like a sideways clutch and pressure plate.
For 2013 they actually moved away from the single spring and back to old school
Thats what I mean, pedal pulsation
Well, guy at machine shop told me they were warped as hell. I guess I was right to have it done. That’s disappointing.
As I stated previously, I’ve never run across a new rotor or drum that needed to be turned.
The only suggestion I have at the moment is to check the face of the wheel where it bolts up against the drum for straightness. In rare cases like this one might think the lug bolts would straighten the wheel face out (if it is warped) but actually the drum bends to fit the warped wheel face.
One example I mentioned was a new Subaru that had rear drums. The vibration was horrid and squealing could be heard for a 1/4 mile. The car was a dealer demonstrator with only a few hundred miles on it. Both rear wheels were warped on the face and replacing both wheels finally fixed the problem. That was the first time I ever ran into that quirky issue and I only figured that out after performing a complete brake job under warranty only to have the same issue. Several days of thinking it over led me to the warped wheel conclusion and sure enought that was the cause. Hope that helps and good luck.