10" brake drum turning?

[scott]

the gb says the max is .030 that the drum can oversized and rn tech page says 1/16" (~.060). does the gb mean you can machine off .030 of the surface which would increase the dia to 10.060"?

[rovertek]

the more adjustment you have left the better the braking will be ,i machine until i reach about half of the brake adjustment, if there is no adjustment left (the drums should be replaced) and also the wheel cylinders will be out too far and you will lose brake pedal.....

[Andrew IIA]

Recycling this Thread

So I got to working on the brakes of the SIIA (new wheel cylinders and shoes) and things went pretty well (moderate cursing, moderately bloody knuckles) until I went to put the drum back on... it doesn't want to go back on

I triple checked that everything is installed correctly per the Green Bible but the new shoe setup is ever-so-slightly too big around and the 9-year old drum won't go back on (yes, the adjuster is backed all the way off). Is this something that could be remedied by having the drums 'turned' at my local brake shop ? The metal on the very edge of the drum (which must pass by the shoe for installation but isn't contacted by the shoe in operation) is a bit .. expanded (?) by age/rust; the diameter of the drum in the contact (wear) area is an itsy-bit wider.

Before/After Pic:

[gudjeon]

The trick with worn drums is to find an 'Old school" shop that has a shoe arcing machine. The drum can be measured to whatever it is, and a gauge can translate this to the arcing machine that will sand the linings on the shoe to match the diameter perfectly. I have done this many times in a former life when I worked for a brake remanufacturing machine shop.

No wear in needed and lining has full drum contact right off the bat. This can also solve the oversize problem at the same time.

[Sputnicker]

You could try carefully filing, grinding or sanding that ridge of material off on the edge of the drum. Since the shoes don't ride there it won't hurt anything. If you have all the right parts; they're assembled correctly and adjusters are backed off all the way, it should fit (without arcing the shoes). Any chance the wheel cylinder pistons aren't fully retracted? If you are only having trouble with only one wheel, try swapping drums. If you are having trouble with more than one, something is wrong. You could take the shoes off and place them in the drum to check the fit. If the radius is too big, they will be hitting at the front and rear of each shoe, rather than in the middle. Good luck.

[4flattires]

Hmmm...before grinding anything...

Since the system still needs to be bled, it may have residual pressure from the air introduced in the hydraulic system. Crack a bleeder screw at the cylinder. Force those shoes back into a retracted position.

Ensure the shoes are square to the backing place and not cocked to one side, making the O.D. larger than it should be and creating interference.

Finally, if this still does not work, measure the shoe O.D. and the drum I.D. and post your results. Lets see the interference we are dealing with.

Jeff

[Andrew IIA]

Hmmm...before grinding anything...

Since the system still needs to be bled, it may have residual pressure from the air introduced in the hydraulic system. Crack a bleeder screw at the cylinder. Force those shoes back into a retracted position.

Ensure the shoes are square to the backing place and not cocked to one side, making the O.D. larger than it should be and creating interference.

Ok, will check this today (rain permitting) and re-evaluate

andrew

[Andrew IIA]

Followup:

I checked everything on the new brake parts again, twice ! (Correct assembly, complete wheel cylinder compression, correct part numbers, correction for Coriolis effect, moon phase.... everything!).

So, I took the drums to my local old-school brake shop and explained that the old rusty drums were a short-hair too tight to fit over my new thick-ass brake shoes. The boss (Bill) felt the drum with his middle finger and said “that’s a weird size drum, I’ll have to see,” and he took it from me, “heavy!,” he says on the way into his shop. A couple of minutes later he returns and says “ok, I can do it,” … ‘great,’ I say and I leave him with both front brake drums (there was no mention of point-zero some-number-point-somethingn-over-some-tolerance, no mention of cost, no nothing).

A few hours later I went back to the brake shop. All done, $20 bucks. The drums looked happy and shiny.

Back at home, I go try out one of the newly skimmed drums over the fat-ass new brake shoes……..

A perfect fit !! …

I’m so happy….. ...

[gudjeon]

I remember turning Rover drums on a large regular machine shop lathe. The inside hole (for the hub) is quite a bit larger than what is normally seen. The usual attachments on a brake drum lathe usually won't fit.

The drum are made from a harder, more durable cast than what is commonly found on North American made things. The philosophy was to replace brake shoes as the wearing component. Today's idea is to have hard friction materials and softer drums/rotors. Brake jobs now, the drum/rotor is a consumable item in a brake job. Also, most don't keep a new car long enough to find out when to change.

[4flattires]

Clearly the new lining was a short hair larger than OEM.

Glad you're up and running.....and happy!

Jeff

[JackIIA]

Today's idea is to have hard friction materials and softer drums/rotors. Brake jobs now, the drum/rotor is a consumable item in a brake job. Also, most don't keep a new car long enough to find out when to change.

Ain't that the truth! I remember watching my grandfather turning many a rotor or drum, as a kid (and don't even think we thought about brake pad asbestos!). I wish I had that machine now though.

Last time I needed a brake job in my other car and asked for the rotors to be turned, I got this same answer, and it blew me away.