Machining brake drums

[pooch]

Who in Australia machines rear brake drums?

I have contacted several chains, and they say the hole in the taper is too small for their brake lathes.

Modern drums are easily removable from the studs and the large centre hole fits the lathe cones.

I pressed out a front drum and it is a very precise fit on centre alone without studs (lugs).

Les Andrews book says to true drums after they are swedged on.

Easy enough with the fronts, but not the rears.

How critical would it be if I was to put a rear drum on a front hub, have it just centralized on the large hole and 5 hex bolts tight , machine it, then swedge it back on to rear hub?

I have a spare axle, so another alternative is to bolt the axle in the hub and hang the whole shebang in a centre lathe.

When I showed just the drum , to a local garage with a normal brake lathe, they said, just to cone it up and turn it, it will fit centrally back on hub.

I am not so sure with the early steel AR drum being so thin and possible flexing. while turning

But bolted to a front hub will make it more rigid when turning.

Are the aftermarket new cast iron drums just not precisely machined for instant use ?

What views do others have?

 

[Grapejuice]

I had my fronts turned on a conventional lathe, but the rear drums were indeed too small for the lathe arbor to slip through. Seeing as how they're old stamped drums, I intend to upgrade to cast drums and have new friction surfaces on the shoes arched to fit them. I may use Brattons for the entire operation, but I haven't decided.

 

[pooch]

So, what are your plans on truing up the rears when you get the cast ?

 

[Brentwood Bob]

On a set of replacement cast iron rear drums I had to have the emergency brake surface cleaned up so the new lining would fit. I think some run the old emergency linings to avoid this problem. My understanding is that any time you swedge hub to drum you need to true up the drum. Bob

 

[Jim Parker Toronto]

Its all about location, too bad you are 1/2 way around the other side of the world, or you could bring them to me! You know that the Service Bulletins say NOT to turn the steel drums, but sometimes they just need to be cleaned up. The drums with the hubs attached will fit on my Brak Docter lathe just fine. Given your situation, I would try the bolting to the front hub, but use the wheel studs and cut some flat washers so they fit flat and use Grade 8 nuts and tighten them down good. The shoulder on the stud should hold them in place. Then have them turned, remove them from the front hubs and swedge them on the rears.
All of the drums that have come to me needed to be turned. The cheaper ones 0.020 to 0.030". The good ones, Brattons or Snyders, only need 5 to 10 thousandths.
You will not have any problems with the E-brake lining, because you don't have any, right?

 

[kenparker]

I take my drums - steel and cast iron- to a local automotive machine shop. His modern Brake Lathe has a Volkswagon Brake Drum adaptor. I machined a "cone" that converted his Volkswagon adaptor to fit the diameter of the Rear Model A Brake Drums. Ask your local Brake Drum machine person if he can turn Volkswagon drums. ken

 

[Kevin in NJ]

After sweging the drums will be distorted and must be trued.

The hub face must be checked for true. You can seriously warp the face by incorrectly taking out the studs. You also want to run a flat file around to take off any burrs.

The tool we used is a good old Barrett Drum Doktor. It has a small shaft and the proper adapters to fit the bearings. The rear uses a plug with a snug fit in the rear bearing. Do not just assume the drum doktor is good. Check for a bent shaft and then check for repeatable mounting of the drum. My brothers Drum Doktor adapters for the front were used to beat something and needed to be put in a lathe and trued up. When done we had 1/2 thousands out. Final cuts in the drums had less then .002" out of round. Mounting a wheel with uneven paint on the mounting surface will cause your drum to deform, one wheel I had would deform a drum by .012". This deformation went away once I sanded the mating surface of the wheel to metal.

Hmm, maybe too much information...

Anyway..

Look for an old shop and ask if they have a drum doktor. You will need to make sure they know how to operate and check it performance.

BTW, I included a pictures of a brake doktor in action. It cuts the shoes to size and makes them centered on the wheel. The little extras that make for great brakes.

 

[Brentwood Bob]

thanks kevin, just learned from you how to check the drum for out of round. I would imagine once you mated the rim to the hub that then becomes the exact orientation on the vehicle. How do you mark the rim, and drum? Drill, or metal punch marks? Bob

 

[Kurt in NJ]

When I have mated a wheel to a particuler orientation I would take a file and make an X on the end of a stud nearest the valve stem location.

 

[Kevin in NJ]

I did not mate wheels to the drums.

The wheels are all interchangeable to the hubs.

I only put the wheels on the one hub and checked that when torqued down by my carefully calibrated hand there was no distortion introduced into the drum.

All of my wheels caused distortion until I took some sandpaper and took the center wheel to hub contact points (two circles) down to metal. This would happen in use eventually anyway. Once the wheels were sanded down only a small amount of distortion was introduced. By small amount I am talking in the .001 and under range. As compared with as much as .013" before I sanded the wheels down.

What is not shown in the pictures was my first checking the out of round on both front drums. The rears are harder to check and I rely on the machine being carefully calibrated and checked before cuts were made. Based on the repeatability and the results on the two front hubs I am likely to have less than .002" distortion on the rear. The front hubs were like .0014 and .0007.

The picture just happened to be taken while I was doing the wheel checks.

Ford was very careful about repeatability. The wheels should be such that any good wheel will not cause any meaningful distortion of the hub/ drum.

If you look at original drums you will find some were installed on the hub and machined at the 3 places where the wheel touches the drum. I have seen others that were not machined and they might have been later drums?

When restoring mechanical parts it is important to understand that most machined parts were built and assembled to thousands or sub thousands accuracy. You really need to own dial calipers and micrometers. Everything needs to be checked for original specs. The A was not just thrown together like some would lead you to believe.

One of Fords difficulties in switching over to the A was setting up high accuracy production equipment.

 

[pooch]

Why did Ford swedge the drum on ?

Modern drums locate by the central hole and lugs and are clamped between wheel and hub.

Why cannot a model A be mounted the same?

ie, push fit over lugs.

 

[Mike V. Florida]

Did the old Beetles not have a small opening in the drum? If so could check there clubs to see if they can help.

 

[dave in australia]

Pooch, have you tried an engineering job shop as opposed to an auto shop. For a lot of similar things in the area I live, I go to an engineering shop. Although the area I live in is the centre for the local oil/gas platforms and finding oddball solutions is what they do well.