Balancing brake drums (who does it, or DIY ?)

[MoPar~Man]

I've had front and rear drums turned. I have no shudder during braking (because the new front drums needed turning) but I think the front pulls to the left so I will swap the front drums left to right and see if that changes anything. I've had all 4 wheels balanced, but only the rears were road-force balanced. The fronts were regular balanced.

But something is shaking at pretty close to 60 mph, in the front.

When you search the web for brake drum balancing, you don't find much. You'll find a ton of stuff for drum servicing in general.

There's a video of a guy that made a jig out of aluminum U-channel. Another channel comes up at a right angle, the drum center hole rides against it. The idea is to balance the drum on slightly off-set knife edge, place a scale so the free edge of the drum rests on the scale. Mark the drum at 90 degree locations, then lift and reposition the drum 4 times, take a weight measurement each time. You can figure out where the heaviest point is, and remove material (or maybe weld new material) as needed. He makes the observation that rust takes a toll on the balance of these drums.

There are others that say that you can balance a drum on a standard wheel balancer. I don't see why not, but after billions of videos posted to utube there doesn't seem to be one for that.

What I found interesting is this thread:

Projects - Balancing Brake Drums

Posts 14 and 15. The (seemingly high-end ?) Boling Brothers drums are not measured for balance! And they needed balancing!

"I did confirm with Boling Brother that they do not balance their drums. So I sent the drums out the the engine shop to have them balanced and they found that each drum was 20 grams out of balance. Because the drums were machined so well on the outside they were able to add the weights to the outside, rather than drill the drums."

I'm starting to think that any drum that does not come with machining marks, drill holes, or welded weights will almost certainly not be balanced and should be balanced. What this means for aftermarket drums vs factory OEM, I don't know.

(later, as I do more searching...)

Well lookie here:

https://www.chevelles.com/threads/who-balances-brake-drums.647705/

Post #17: "Quick lesson: look for the balancing weights."

The question does pop up in the old car / old vehicle forums -> "Who balances brake drums". There is no consistent, universal, or actionable answer. Always in these threads they will say back in the olde daze you balanced the wheels while on the car (not sure how they did that on the rear wheels). That took operator skill I suppose, but all I can think about is the interaction with the suspension and steering during that has got to be influencing the results.

 

[CBODY67]

If there was no balance-related shaking/vibration before the drums were turned, there should be none after the drums were turned.

The reason the new drums needed to be turned was that they were warehoused vertically in the box. Which will put a slight flat spot where the drum touched the bottom of the box. NOT uncommon.

Why were the front tires not road-force balanced? Front rotating assy balance is more critical as there is no heavy rear axle to dampen any vibration tendencies.

The BEST way to get the drums balanced is by getting each wheel spin-balanced on the car. That used to be the "high end" level of wheel balancing. It was not computerized and required a tech that knew how to do it. After that, the lug nut stud that was pointed to by the wheel valve stem was marked so the wheel could be replaced in the same wheel/tire/drum relationship if it should need to be taken off. That would also mean that all 4 wheels would need to be re-balanced when the tires were rotated.

Brake drum balancing is how they come from their builder. In theory, if the casting is done correctly, the finished drum would be "in balance". IF it was not, metal would be ground off the outside edge of the casting. So, when it was put in the box at the factory, it was within balance specs. What happened after that was in the domain of the warehousing operatives.

On new drums, for the best and most durable situation, new drums should not be cut, but the dryms should be run a while to better-cure their metal so that cuts after that will be of cured metal and not "green" metal. Not unlike the best cyl blocks to use are used blocks rather than new/green/uncured blocks . . . so the machining remains "as cut" rather than "moving around" as the metal casting cures from hot/cold cycles. As stated in the Grump Jenkins racing book of the 1980s.

It should be possible to use a normal wheel balancer (bubble or otherwise) to balance brake drums. ONLY thing is that metal weight will be removed rather than added. Once removed, pretty hard to put it back on if too much was removed.

CBODY67

 

[volksworld]

keep in mind that just cause a tire is dynamically balanced doesn't necessarily mean that it's actually round... sometimes you can spot an up and down hop or a side to side twist on the balance machine but many new ones cover the tire in the interest of safety so you cant see what's going on...they can also wear the tread funny if they've spent any time on bad suspension components...you'll replace the bad ball joints, bushings or tie rod ends, get the thing aligned and balanced and the damn thing will still shake till you throw out the tires that look perfectly fine...rears are less prone to wearing funny so try swapping front to rear and see if the shake goes away or moves from the steering wheel to the seat of your pants

 

[MoPar~Man]

Tommorrow I'm planning to bring 2 of my tires (mounted on 14" Magnum rims) to a shop that has a Hunter road-force balancer. I had these tires mounted/balanced early this year at a different shop that has a standard balancer (not road-force). At the time I didn't know that road-force balancing existed. Around here, the vast majority of small / independent shops don't have road-force balancers but most or all car dealers have them. The tires are brand new 215-75-14 Hankook kinergy, they now have 1k miles on them.

I had these tires on the front of my Monaco, and I think that they were fine at highway speeds *before* I had my (new) front drums turned. There is now a shake at around 60 mph, I don't know if it's the tires or the drums. I can't be sure if that shake was or wasn't there before, but I think not.

The rear 2 tires I had mounted and road-force balanced at a shop that does have the Hunter machine, and told them to use crimp-on lead weights (not the stick-on type).

Today I talked to a Hunter service tech by phone, asked him if Hunter machines can check brake drums for balance, he says yes as long as the shop has the "fingers" and cone for it, which we agreed they should have if they stud-mounted the previous pair of Mag rims.

He explained the difference between static and dynamic balancing (which again I didn't know, I just thought that balancing was balancing and if the tire was spinning on the machine then that's all that was needed).

It seems that most rims today, which are aluminum, are static balanced, because they use stick-on weights, not rim-crimped weights, and especially not rim-crimped weights that could be on the front or back side or maybe some of each. If I understand this correctly, if you've got a rim that has a weight crimped on the front side, and one on the back, then that's a 100% indication of dynamic balance. If only crimped on the back, it might be dynamic, but if you have stick-on weights then for sure it's only static balanced.

The Hunter guy said that dynamic balancing was sort-of invented by John Force. It gave him an extra 10'th of a second on his drag runs.

He also said to tell the tire shop to turn off the "Smart weight" option on the machine. Looking on-line, Hunter really doesn't say what "smart weight" option mode is, beyond saying it minimizes weights used and maximizes throughput.

 

[Just Carbs]

I've had good success by removing all the heavy grease "and grease seal" from the front disc/drum and putting the disc/drum back onto the front spindle to find the heavy spot on said out of balance disc/drum. Then use method of choice to remove metal to balance disc/drum. I grind tiny amounts at a time. Haven't tried drilling, probably won't.

Now that the fronts are done.
Time for the rear drums.

Now put the rear drum on the just balanced front disc/drum as you would mount a tire (but mounted inside out/backwards) with all lug nuts snug (a little impact action) for checking the balance of the rear drum. Then balance the rear drum that's now mounted (inside out/backwards) on the front disc/drum as needed in the same way the front disc/drum was balanced.

It can make a BIG difference in how the car feels at 70. Even on a car you think feels good before you balance all the rotating brake parts.
If your wheels and tires are round and balanced and the rotating brake parts are balanced the car can feel silky smooth. All the tiny little unnoticed vibrations that add up to not good may now be gone. That's assuming the tires have good innards.

Unfortunately, it don't fix that annoying the wind noise. That takes $$$$$$......

 

[volksworld]

this has nothing to do with your issue but just to clarify , most alloy wheels, especially FWD have so much offset that they can be dynamically balanced with stick on weights...a set close to the inner edge and another as far outboard as possible...many rims have machined areas in these spots for the weights...but I don't think most balancers have settings to figure this out so they just give up and static balance them...I just set my machine's rim width as the distance between where you can put the weights and it works fine

 

[CBODY67]

Not just fwd vehicles, but ANY vehicle that uses front hub assys rather than front wheel bearings per se. Which includes the model year break point when Ford Crown Vics went to front hubs from wheel bearings.

Since about 1978, at least in Chevrolet vehicles and their first model year of factory alloy wheels on Camaros, there have been aluminum wheel-specific wheel weights. Plastic-coated, usually light gray in color, with a clip that matched the contours of the outer edge lip of the wheel. As steel wheels (even chrome-plated ones) still had the normal lip configuration on them. Didn't take the aftermarket vendors long to match them. As the normal method of balancing a "mag" aluminum wheel was to use stick-on weights and then cover them in duct tape on the inside of the rim, out of sight.

Enjoy!
CBODY67

 

[MoPar~Man]

Well I did bring in my 2 front tires and drums. The first tire was put on the balancer and in road-force mode it came up with a crazy low value of 2 lbs of force. The guy had never seen such a low value before. It had a string of maybe 6 of the stick-on weights on the inside face of the rim, he took those off and redid the balance, then crimped a weight of similar value to the inside rim, the laser shows where to put it. So that rim and tire were just about perfect. The second wheel was put on, he ran it, took it off and repositioned it and secured it again, ran it, and called me over. He showed me how when it rotates is had a wobble. Very slight. The balancer detected it, but it still balanced with no weight needed (in static mode). He switched to dynamic, then removed a few of those tabs that were on the rim, and it was a very good balance. Road force of 6 lbs. No weights at all on the rim.

So then I asked him to try balancing the drums. This was uncharted territory for him / them. Another tech thought the laser wouldn't focus on the drum. Well sure enough it did. It thought that the inner surface (the brake surface) was the inside of the wheel, and when it was done it painted it with the laser line to show where to add the weights. Those grey tick-tak weights that come out of a box like tape, you tear off how-ever many you need. Each one is 1/4 oz. Well, this drum needed 2.25 oz, or 9 weights. Instead of taping them to the inside, they were put on the outside rim, where they stuck pretty good since it was a new drum and still very clean. Spinning it up as a test, it wanted to take 1 weight off. This makes sense, because the weights were put on the outside, a little further away from the center of rotation. The other drum only needed 3 weights. When I got them home, I marked where they were, and scraped them off, and welded a strip of 3/16 steel to the same spot, with the same weight. I'll know more tomorrow how this works at highway speed.

But there ya go. Drum balance can be checked on a tire machine!

 

[Sixpactogo]

I have never thought about balancing a drum.......I thought the manufacturer did that when they were cast.
Here is a pic of the drums that were on my 68 Charger when I swapped them out for discs. Pretty good sized weight on one of them.