Brakes: Is it mandatory? Rear brake drum turning

[Hawklover]

The rear drums on my '64 Avanti have never been turned. Soon I plan on new shoes and wheel cylinders. Is it a must that the drums be turned due to the fact of installing new shoes? Thanks in advance for your suggestions.

[Commander Eddie]

I am not a mechanic but have some experience with drum brakes. Since your drums have never been turned they are probably well within legal tolerances. If the surfaces look clean with no pitting or grooves you can probably get away with not turning them. One thing I would recommend, however, is getting your new shoes arc'ed so they contact the drum surface evenly.

[StudeRich]

A good clean, smooth non-glazed drum surface is required for good grip, a "Round" drum helps with smooth Even braking, that is why a Good Brake Job always consists of turning the Drums.

However, you shouldn't have to take .010 or .020 off of a good, never turned drum to achieve that.

At least One thing you could do is, Mic them at 12:00 to 6:00 and 9:00 to 3:00 to see if they are round.
If you are not turning them, De-glazing them with Wet or Dry Sandpaper can't hurt.

[Mike Van Veghten]

YES...

I'd bet that once on the drum turning lathe, you'll see that the drum isn't...as round as you may have thought !!

Mike

[jackb]

as a thought and question.... I once bought 4 NOS drums for a 63' Lark from Newman & Altman. All 4 were out of round. The shop told me the cause was stacking of the drums. How would a drum get out of round in usual driving conditions ? How about sitting, unmoved for a long time.

[DEEPNHOCK]

True enough. Drums are like vinyl records. Storing flat is best.
Max allowable cut by law is (diameter) +.060".
If you have a good shop with a good drum lathe, ask him to take the bare minimum necessary, and just don't hog 'em out with a fast feed rate.

as a thought and question.... I once bought 4 NOS drums for a 63' Lark from Newman & Altman. All 4 were out of round. The shop told me the cause was stacking of the drums. How would a drum get out of round in usual driving conditions ? How about sitting, unmoved for a long time.

[yeroldad]

ALWAYS have the drums turned. And the wheel cylinders should be rebuilt. If the springs and retainers don't look new, replace them. Shoes are all arched these days by the manufacturer or rebuilder. My motto is: "do it right, do it once, then forget about it". Anything less is asking for problems and frustration.

[Hawklover]

ALWAYS have the drums turned. And the wheel cylinders should be rebuilt. If the springs and retainers don't look new, replace them. Shoes are all arched these days by the manufacturer or rebuilder. My motto is: "do it right, do it once, then forget about it". Anything less is asking for problems and frustration.

Putting on brand new wheel cylinders, and will ask the shop to just take 1-2 thousands off, to get a good surface.

[Jeffry Cassel]

The drums do not need to be 'turned' if they do not need it. Oft times people let brakes go til they squeal and by then the rivets or metal backing plate have dug into the drum and it needs to be turned or replaced. Like boring a block; do it if you need to but not just for fun. It is expensive and it wastes metal and money.

[DEEPNHOCK]

True...But...guage
In most service/machine shops that cut drums, their only tool is a drum gauge which only measures the inside diameter.
You would have to mount the drum and rotate it to measure the 'runout' to determine if it is out of round.
Since a drum that has been run a while will have the braking surface 'smoothed and glazed', it should be roughed up at a minimum to run new brake linings on.
Doing a 'touch off' on the brake lathe will tell you how out of round the drum is, it will also tell you the minimum amount of drum material to be removed to bring it back into round condition. That will also provide the best surface for new linings to run in on.
Note: Some 'out of round' condition is tolerable as the brake shoes 'float' on their mounting pins, and are located at the top, or anchor pin. An excessive out-of-round condition will be felt as a pulsing brake pedal, or a rear vibration that changes with road speed.
HTIH (Hope The Info Helps)
Jeff

The drums do not need to be 'turned' if they do not need it. Oft times people let brakes go til they squeal and by then the rivets or metal backing plate have dug into the drum and it needs to be turned or replaced. Like boring a block; do it if you need to but not just for fun. It is expensive and it wastes metal and money.

[TN GT Hawk]

The drums do not need to be 'turned' if they do not need it. Oft times people let brakes go til they squeal and by then the rivets or metal backing plate have dug into the drum and it needs to be turned or replaced. Like boring a block; do it if you need to but not just for fun. It is expensive and it wastes metal and money.

I agree with this view. Recently I bought a '54 Conestoga that had been stored many years that needed new brake lines along with wheel and master cylinders. There was no need to replace the shoes and hardware though, they looked nearly new, and the drums were obviously new or had been turned- no ridge, smooth surface. So I left as is. I guess they could have been out of round, but the car sure stops well.

[jackb]

Keep in mind the availability of these drums and their "real" braking contribution to the PDB system. If you must turn the drums, you probably have experienced some of the knowledgeable symptoms suggested here. Assuming so, spray a light covering of paint on the drum contact surfaces and tell the tech to "just" take off the paint....GL

[Hawk GT SS]

Good idea. I use "Marking blue". Also known as "Prussian blue or Dykem". They are similar but not the same. Antique drums are getting harder to find. Save the ones you have and turn only as needed.

[Hawklover]

Will take all into consideration when the car is on the lift hopefully the beginning of next week. At this moment there is no pulsing when the brake is applied. Lets see what develops when the new shoes are put on.

[Dan Timberlake]

When drum brakes were the norm it was possible to get a very poorly machined drum back from auto machine shops.
Some problems were =
- Eccentric when mounted on the car. I figured that the typical cone centering fixtures could easily cause this if the edge of the drum bore was damaged.
- excessive metal removed . Maybe to remove hard spots. Or maybe because the drum was fixture eccentrically, which should have triggered an investigation by the machinist when the first skim cut only made contact for 45 °.

- I never experienced this one first hand, but believe it - the drum machining had a spiral that caused the shoes to shift axially and smap back repeatedly when the brakes were applied.

[Hawklover]

I have been speaking to many folks about this situation. I have decided to have the drums turned only about 1-2 thousands. The major reason is that from research, I discovered that many brake re-=line companies make the lining a bit thicker, due to the fact they believe most shops will automatically turn the drums. I worry that after the shoes are installed, the drum will be impossible to put back on, its happened more times than one would surmise.
Also would I be correct in assuming that I need a 3/4 inch arbor for the brake lathe?...........just want to make sure the shop actually has one.