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Discussion Starter #1
While setting up a rear end for my 69' I noticed something odd. On the brake drums which are original to this BU coded 12-bolt, only one of the 2 drums has a balance weight attached. Both drums have the same part number (3841177) cast in them. I looked VERY CLOSELY with a magnifying glass before and after I sand-blasted them, for any sign that there had ever been a weight attached to the drum. I found NO evidence that there was ever anything welded/bolted/molded to the drum.

Is this a normal thing or should each drum have a weight? Can the drums be that much out-of-balance that GM had to add so much weight to one side and not the other? Is there a right/left drum? Do I use them like they are? Which side gets the weight? Does it even matter? What am I missing here???

Anybody got any clues???......Jb :confused:

p.s.
Before the car was parked I never noticed even a hint of an out-of-balance condition from the rear at 120/plus mph. This rear end was removed (the way it was), and has been stored for 20+ years until last week when I pulled it apart to check / go-thru.
 

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Brake drums are like tires, some are more out of balance than others. If one does not have a weight, it is probably balanced OK and does not need a weight.

If you had a way of hanging the drum open end down from the exact center of the center hole, you could easily see which end is heavy and how much off it was. If you could put it on a bubble balancer at a tire shop, you could do the same thing. Place a sample weight on the high spot where the factory welds theirs and find the weight that balances it.

Drums can also be balanced by putting them on a front hub, friction must be minimized by removing the seal and washing the grease from the bearings, apply oil to the bearings and install on the spindle. With bearings just a tad loose to where there is minimum friction, the heavy spot will turn the drum to the bottom. Brake rotors can be done by the same method.
David
 

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Has amyone tried putting a drum on an electronic wheel balancing machine?

Some yrs back I got my wheels balanced 'on car' was an 'old school guy' who has since passed on.
A motorised wheel was placed against the tyre and spun...this was the best wheel balance I evert had cause it balanced the drums/rotors and wheels all in one.
He would spin up, then repostion the wheel on the studs dor best balance then once that was established then add lead.
Just ment I had to match wheels to each cnr and stud holes to studs...

I have since never found another shop that has this equipment.
 

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They centrifugally cast the liquid cast-iron into a mould that has the 1/8th inch thick steel wheel mount sheetmetal face inserted into it to make them.

Some are fine, other's, a schosh out of balance..

I watched it being done at Motor Wheel, Lansing, MI years ago is how I know this

pdq67
 

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Discussion Starter #5
Thanks guys. I feel better now!

I played in the garage yesterday with the spindle and loose bearing trick. Everything seemed to be OK. I talked to a machinist friend of mine. He has a set-up to balance aircraft props, fans, hubs, etc. He is going to check them and tweek the balance if need, but it is going to cost me. Imported beer ain't cheep!!!

Thanks for the replys....Jb
 

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There is static balance with a bubble gage, then "Dynamic" balance, the old way you mentioned is "Spin Balance" an early form of Dynamic balance which is very good, uses a strobe light to tell the position of the weights and balances the whole assembly. It takes a trained operator and is very good on front tires but on rear wheel drive cars with positraction required the rear wheels to be transferred to the front to balance thtem. Electronic balancers are quicker and tell the operator how much weight to put where, it saves time.

Interesting that most race cars use the old bubble gage balance method and align the cars with bubble gages and string to set toe-in. I think the Indy car guys are now using the electronic balance machines.
David
 

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Imported beer ain't cheep!!!
Spates or Steinlager...nice drop.
Something to watch on imorted beers...they do have expiry dates and over that they can taste like crap...
Hence why Buds are not popular in NZ, they sit on the shelf to long and get a rep of not a good beer..
The dates are usually printed in black ink near the neck oin the glass.
 
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