Brake shoe to drum clearance?

[Jolly_John]

Hi. I'm using one of those large calipers for measuring brake drum diameter and brake shoe diameter for the first time.

Using this caliper, what is a good clearance to wind up with between the shoes and the brake drum? The car has self-adjusting brakes, but I want to get close before putting the drums back on. Thanks. John

[ply33]

What are the specifications for the car you are working on? That would be a good place to start.

If you don't know that, maybe if you state the year, make and model of the car someone can post the specifications.

[CarlLaFong]

Why bother. Put the drum on, adjust until the shoes drag slightly, pump the pedal a few times to center everything, adjust again until they drag again, then back off a bit until the drums turn freely

[poci1957]

1950s Pontiacs actually had slots in the brake drum so the brakes could be adjusted with a feeler gauge, the gap was to be .015. That would probably be a good number to use, good luck, Todd C

[A by the sea]

A more important question.

Are the shoes arched to the same diameter of the drums?

This is more important as you will not get 100% shoe to drum contact if the radius of the shoes is different then the drum radius. Ya, they can wear in, but on the antique car driven little this may take years.

[keiser31]

Why bother. Put the drum on, adjust until the shoes drag slightly, pump the pedal a few times to center everything, adjust again until they drag again, then back off a bit until the drums turn freely

As a brake mechanic, I use this process except I do not adjust them to turn freely....just enough to hear the shoes rub the drum slightly.

[Dave@Moon]

Why bother. Put the drum on, adjust until the shoes drag slightly, pump the pedal a few times to center everything, adjust again until they drag again, then back off a bit until the drums turn freely

As a brake mechanic, I use this process except I do not adjust them to turn freely....just enough to hear the shoes rub the drum slightly.

Keiser31's advice is the same advice anyone has ever given me for a drum brake job. In fact if you take healthy drum brakes from another car and spin the wheels off the ground you should hear (but not likely feel) a slight resistance from the shoes on the drum.

As for clearance when putting the drum back on, that's immaterial so long as the shoes are adjusted in enough for the drum to fit. The shoes get adjusted outward after the drum is on.

Calipers are used mainly to determine if the drum has been turned too many times and is out of spec, which could result in the shoes being automatically adjusted beyond the capacity of the wheel cylinder to operate properly. That could be catastrophic.

[Rusty_OToole]

Chrysler products before the sixties are a lot more critical about shoe alignment. Follow the procedure in the repair manual.

[ply33]

Keiser31's advice is the same advice anyone has ever given me for a drum brake job. In fact if you take healthy drum brakes from another car and spin the wheels off the ground you should hear (but not likely feel) a slight resistance from the shoes on the drum.

As for clearance when putting the drum back on, that's immaterial so long as the shoes are adjusted in enough for the drum to fit. The shoes get adjusted outward after the drum is on.

Calipers are used mainly to determine if the drum has been turned too many times and is out of spec, which could result in the shoes being automatically adjusted beyond the capacity of the wheel cylinder to operate properly. That could be catastrophic.

This is decidedly not true for vehicles, like the 1920s through at least early 1950s Chrysler products, that use Lockheed brakes. For Lockheed brakes, the shoes are supposed to be ground to match the diameter of the drum. If you follow the factory service manual, they are installed and adjusted with some special tools to have the correct heal and toe clearance prior to the drum being installed.

Thus my original response on this thread asking the year, make and model. It might actually make a difference.

[Jolly_John]

Thanks for all of the good input, guys. As Ply33 noted....knowing the car being worked on does make a difference. I'm doing the brake work on a '55 Chrysler, and the shop manual does specify using one of the double brake caliper tools to do the set-up.

I think have have enough info to proceed now. Again, I appreciate everyone taking the time to help. John

[c49er]

I always Arc- fit the shoes to each drum for full contact. As with the double anchor Lockheeds ( used on early MoPars) this is even more important. Don't even bother with the 1750 Ammco tool or the factory Miller tool till the shoes are arced!

Edited December 25, 2013 by c49er (see edit history)

[Guest]

I always Arc- fit the shoes to each drum for full contact. As with the double anchor Lockheeds ( used on early MoPars) this is even more important. Don't even bother with the 1750 Ammco tool or the factory Miller tool till the shoes are arched!

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Your a lucky fellow, arching has been banned in my state at least 25 years and the state doesn't care if the shoes are asbestos free.

A note on Todds comment; some manufacturers kept the slot on the backing plate long after self adjusters were in use because many people converted back to the manual adjusters. Seems after a predetermined ( 4 times for my 59 & 62 Pontiac's) number of times of adjusting the owner knew it was time to look/replace the shoes. With self adjusters the pedal always felt good and brakes were often neglected until the metal to metal sound. One good thing about early VW and Porsche drum brakes is they had their adjusting holes big enough so you could not only adjust, but look at the condition of the wheel cylinder and the thickness of the shoes without taking the wheel off.

Don

[c49er]

A little late reading this... Ha Ha. With all my MoPar lockheed hobby cars I will arc shoes all day long with my ammco machine to make me and my friends brakes safe! I would just hate to rear end a state ecology person because of fading brakes!!!

I like a rock hard and high brake pedal after a brake job.

Some times safe sense is better than dusty rules.

Edited December 25, 2013 by c49er (see edit history)

[Rusty_OToole]

Could you arc your shoes with a belt sander or sanding block? Checking them against the drum frequently?

[GLong]

Some of my '20s cars that have anchored shoes use .006" as the spec. Which seems really difficult to imagine unless the shoes were perfectly arced to match the drums.

On my '41 Plymouth PT125 pickup, the heel anchor moves the shoe both in and out against the drum, but depending on which way you rotate the anchor, it can move the shoe up and down some as well.

The mid-shoe adjuster at 3 and 9 o'clock can only move the shoe out against the drum..

A comment about the 'slight drag' of a properly adjusted brake shoe..

I was helping a guy over the phone and via email to adjust the rear EXTERNAL contracting brakes on a teens Studebaker.. I told him to NOT have any drag when he was done.. he didn't pay enough attention.

The car was driven only a few hundred feet after his adjustment, then went into a trailer..

I was the guy to drive the car next.. I didn't notice anything until about 2-3 miles down the road, the car started to pull to the right.. I pulled to the shoulder, thinking it had a flat tire, but smoke was pouring from the right rear wheel..

And, my luck, the shoulder was narrow, not much room for a car, and the weeds and field next to the shoulder were tinder-dry.. a field fire for sure.. So I drove a few hundred more feet to a side road apron... Thankfully no fire, just a very hot brake drum and band.

The external contracting brakes must be left a bit loose to allow the brake drum to expand and not drag against the band.

With internal brake shoes, a very small amount of drag won't cause any problem, but if the shoes perfectly match the drum, they can be adjusted to have no drag.

I have 'arced' shoed on a belt sander with a table, and on a big disc sander with a table. the critical item is that any friction material is removed perfectly evenly across the shoe, or it will get odd side loads and can chatter and do other weird things.. It's best to go drive the car and remove the drum again and inspect the wear on the friction material to make sure it's flat and even.

Using a sander would be a last-resort for shoes and drums that have a really significant mis-match of radius.. Some re-arcing should reduce the amount of spongy pedal.

Greg L.

Edited December 25, 2013 by GLong (see edit history)

[Guest]

Could you arc your shoes with a belt sander or sanding block? Checking them against the drum frequently?

You could ...do anything, but a arcing is done with a precision tool. As drums wear and are cut on a lathe the diameter becomes larger. Shoes are standard in size and therefore arcing is done to fit the shoe to the larger diameter and that means the center or middle of the shoe lining is cut/grinded thinner and the outsides are the original or near original thickness lining. But as said before, arcing shoes is illegal in many if not all states today.

The alternative:

Before 1984, it was common to re-arc brake shoes to match the arc within brake drums. This practice, however, was controversial, as it removed friction material from the brakes and reduced the life of the shoes as well as created hazardous asbestos dust. Current design theory is to use shoes for the proper diameter drum, and to simply replace the brake drum when necessary, rather than re-arcing shoes.

And just a FYI, Having retired from a career in the automotive field of over forty years I have known just a few mechanics in my time out there that succumbed to lung cancer. So have at it guys, and don't forget to blow all those brake parts off with compressed air while your at it. It's not just the guy doing the job, but everyone around him too.

Edited December 25, 2013 by helfen (see edit history)

[GLong]

Brake drums, new or useable used might not be available for many early cars.. and as long as proper procedures are followed, there is nothing unsafe or dangerous about re-arcing shoes..

The trucking industry still uses drum brakes and re-arcing is standard practice where needed.

Obviously only a slight amount of grinding/sanding is safe, you don't want to remove so much lining that the center of the shoe friction material is thin.

Just a few thousandths of miss matched shoe and drum radius' will make for a very spongy pedal,, and that IS unsafe.. A properly arced shoe will fit the drum, and you will have a solid pedal and maximum shoe/drum contact.

Modern friction material has no asbestos.. if you are cleaning old brake shoes, mechanisms, backing plates.. I doubt very much if anyone doing a brake job on an early collector car would be in a big hurry like the flat-rate mechanics making a living doing brake jobs.. THOSE are the guys who used compressed air to blow off the brake dust.. I'm sure a collector car's brakes would be carefully washed or vacuumed then washed.

Common sense and mechanical skill is always required.. or join the list of 'Darwin Award' incidents.

Greg L

[edinmass]

Here is how I do my brakes on pre war cars. I reline the brakes with a thicker liner, than machine them to the drum with the machine showen in the link. Works perfect and you get 95 percent contact from the start. It also will allow for an oversize drum. Check out the link.

http://forums.aaca.org/f124/barrett-brake-dokter-sale-328832.html

[c49er]

All the above is right on!

[Rusty_OToole]

Some old brake drums can be machined oversize up to .25" (yes 1/4") and still be within factory specs. I am thinking of early 50s Oldsmobile specifically. All the others could be machined but not quite as much. The brake drums were very expensive to replace but were made to last the life of the car.

Cheap throw away brake drums came along in the eighties. So if you are working on an older car arcing the shoes is usually necessary.

[Guest]

[h=2]Asbestos-Related automotive Parts[/h]

• Hoodliners - Over the past few decades, millions of vehicles have been manufactured with automotive hoodliners constructed from asbestos fibers. While asbestos is remarkably fire-resistant, it is also the leading cause of mesothelioma, an extremely deadly form of cancer.
  
• Brakes - During normal automobile use, asbestos brake linings wear down through friction, releasing asbestos dust just as sanding wood creates sawdust. Much of this asbestos dust is trapped in the brake housing. When the brake housing is opened, that dust is released into the air where workers can inhale it or ingest it.
  
• Clutches - Some clutch parts in use today both in new and older cars contain asbestos. During normal wear, the asbestos is ground down and may collect around the parts and in lutch compartments. When the disk, clutch cover, drum or wheel is removed, that dust may be released into the air where it can be inhaled or swallowed.
  
• Gasket Material, Heat Seals, Valve Rings and Packing - For decades, asbestos-containing gaskets, heat seal material, valve rings, and packing were used in virtually every system that involved the transport of fluids or gases. Prior to the mid-1970s, some automobile exhaust systems contained asbestos gaskets either at flanges along the exhaust pipes or at the exhaust manifolds of the engine.
  

[h=2]Hazardous Cleaning Techniques[/h]

The Occupational Safety and Health Administration (OSHA) advisory instructs mechanics to assume that all brakes contain asbestos because a mere visual inspection does not indicate which brakes include asbestos and which do not.

[h=4]The following brake cleaning techniques can result in the release of asbestos into the air and consequently may lead to employee exposure:[/h]

• Using a shop vacuum cleaner - a shop vacuum filter is not fine enough to collect asbestos fibers
  
• Using a compressed air hose to clean drum breaks
  
• Wiping with a dry rag or brushing dust from the assembly
  
• Wiping with a wet rag or brush - a wet rag will still scatter asbestos fibers (furthermore, once it dries, the fibers can still spread around the work area)
  
• Using liquid squirt bottles or solvent sprays
  
• Using a water hose
  

[h=2]Asbestos Exposure Among Car Enthusiasts and Home Mechanics[/h]

Nonprofessional and home auto mechanics that repair or replace their own brakes or clutches are also in danger of exposure to asbestos and asbestos related illnesses. Rarely do people working on cars at their home take the proper precautions to prevent fibers from entering the home, which also poses a great risk to their families and pets. Many experts believe that exposure at home can be even more severe, as many auto enthusiasts are not in possession of tools used by most shops to make the jobs quicker and easier. This can lead to actions that further disturb asbestos, including repetitive strikes with a hammer to release the older product.

[h=2]Deaths Expected to Rise[/h]It is estimated that more than six million mechanics have been exposed to asbestos in brakes since 1940, and those exposures are now resulting in about 580 excess asbestos-related cancerdeaths a year. Many analysts also believe that over the next 10 years, the expected rate of mesothelioma deaths as a result of exposure to break dust will reach 200 a year, acknowledging that for every mesothelioma case diagnosed there may be dozens of cases of asbestosis. Deaths caused by exposure to asbestos brake products had been previously expected to peak around the year 2012, however, because asbestos is still in some brakes being sold today, it could mean the deaths would continue to climb.

[h=2]Safety Measures[/h]

The Environmental Protection Agency (EPA) has issued a detailed brochure that offers information regarding OSHA's regulations for commercial automotive shops concerning asbestos. The recommendations are separated into commercial automotive shops that perform more than five brake or clutch jobs per week, and those that perform less than five.

[h=4]OSHA regulations require shops performing more than five brake or clutch jobs a week to use one of the following practices:[/h]

• Negative-Pressure Enclosure/HEPA Vacuum System Method: This kind of enclosure and vacuum system features a special box with clear plastic walls (or windows), which fits tightly around a brake or clutch assembly in order to prevent asbestos exposure.
  
• Low Pressure/Wet Cleaning Method: This specially designed low-pressure spray equipment wets the brake assembly and catches the asbestos-contaminated runoff in a special basin to reduce or prevent airborne brake dust from spreading.
  

[h=4]For shops performing less than five brake or clutch jobs a week, the following method should be used:[/h]

• Wet Wipe Method: This method uses a spray bottle (or other device that can deliver a fine mist of water), or amended water (water with a detergent), at low pressure to wet all brake and clutch parts. These parts can then be wiped with a cloth.
  

For those who repair or replace their own brakes or clutches at home and have no way of knowing if the materials contain asbestos (as is the case in most instances), the EPA recommends having the job done at a commercial shop to avoid exposure. If this is not an option, the agency then recommends using the preventative measures required of commercial shops performing more than five brake or clutch jobs a week. If an individual lacks the professional equipment required, then the wet wipe method is recommended.

[Guest]

Brake drums, new or useable used might not be available for many early cars.. and as long as proper procedures are followed, there is nothing unsafe or dangerous about re-arcing shoes..

The trucking industry still uses drum brakes and re-arcing is standard practice where needed.

Obviously only a slight amount of grinding/sanding is safe, you don't want to remove so much lining that the center of the shoe friction material is thin.

Just a few thousandths of miss matched shoe and drum radius' will make for a very spongy pedal,, and that IS unsafe.. A properly arced shoe will fit the drum, and you will have a solid pedal and maximum shoe/drum contact.

Modern friction material has no asbestos.. if you are cleaning old brake shoes, mechanisms, backing plates.. I doubt very much if anyone doing a brake job on an early collector car would be in a big hurry like the flat-rate mechanics making a living doing brake jobs.. THOSE are the guys who used compressed air to blow off the brake dust.. I'm sure a collector car's brakes would be carefully washed or vacuumed then washed.

Common sense and mechanical skill is always required.. or join the list of 'Darwin Award' incidents.

Greg L

Just a final note. My shop didn't throw away it's arcing equipment on it's own, and I can't remember whether or not it was the bureau of automotive repair or OSHA who came in and said we had to get rid of it. I do remember trashing the equipment on orders of the powers that be.

[c49er]

Lets start talking about our older homes and asbestos. Lets go jogging and breathe in real deep and hard hard along the roads for an hour. Umm good!

Lets not. Lets learn how to have safe stopping brakes on old antique cars.

Edited December 25, 2013 by c49er (see edit history)

[Guest]

Lets start talking about our older homes and asbestos. Lets go jogging and breathe in real deep and hard hard along the roads for an hour. Umm good!

Lets not. Lets learn how to have safe stopping brakes on old antique cars.

The machine I had to throw away was just like the one you have. Was very tempting to take home.

[c49er]

They seem to sell for good money these days.

[GLong]

Well, I'm certainly not going to get rid of all my old cars for fear of asbestos, or pay someone else to do my brake jobs and clutch replacements. I've used some of the OSHA approved and overpriced washing machines. It's pretty simple to use a pump sprayer with a water/soap solution, spray down the brakes/hardware and backing plate over a trashcan with a trash bag liner, do all four wheels, tie up the trashbag liner, and discard.

I won't run in fear, screaming the sky is falling.. we all are exposed to carcinogens everywhere, every day for most of our lives..

Margarine, artificial sweeteners, GMO corn and other foods, most solvents etc etc etc..

Nobody gets out of this deal alive.. while I don't want to speed up the process, I certainly don't want to live in fear of every potentially dangerous action, procedure or chemical.

What I fear: fire, be prepared with Halon fire extinguishers in your car, at the door to the house, kitchen, workshop and car hauler trailer.

What I fear: Loss of control, inspect ball joints, tierod ends, shocks Loss of brakes,, keep 'em in good shape, don't overload, Buy the best tires available.

What I fear: poor quality work, or poor quality parts.. I do 99% of my own work, and either know who does the other work, and I know what the parts are that go in my cars and trucks and home.. or i make them myself if possible.

What I fear; more agencies like OSHA, Bureau of Automotive repair, and others who respond to political pressure and greed, and don't really help anyone but the agency or politicians..

I'm not a fool, I won't take a sniff of all the brake dust and clutch dust I find in my old cars. But it's less dangerous than a gasoline leak, rusty brake line or a boiling battery, or a bad staircase.

Sorry about the rant, but some fears are blown way out of proportion to the risk.

Greg L

[Guest Bob Call]

"I'm from the government and I'm here to help."

Before the industrial revolution all of the things that people seem to fear and rant against, fossil fuel, pesticides, hormones, antibiotics, etc., the average life expectancy was 40 years its now about 70 and even higher for the fair sex. Give me gasoline and asbestos in moderation.

Edited December 26, 2013 by Bob Call (see edit history)

[benjamin j]

Well, I'm certainly not going to get rid of all my old cars for fear of asbestos, or pay someone else to do my brake jobs and clutch replacements. I've used some of the OSHA approved and overpriced washing machines. It's pretty simple to use a pump sprayer with a water/soap solution, spray down the brakes/hardware and backing plate over a trashcan with a trash bag liner, do all four wheels, tie up the trashbag liner, and discard.

I won't run in fear, screaming the sky is falling.. we all are exposed to carcinogens everywhere, every day for most of our lives..

Margarine, artificial sweeteners, GMO corn and other foods, most solvents etc etc etc..

Nobody gets out of this deal alive.. while I don't want to speed up the process, I certainly don't want to live in fear of every potentially dangerous action, procedure or chemical.

What I fear: fire, be prepared with Halon fire extinguishers in your car, at the door to the house, kitchen, workshop and car hauler trailer.

What I fear: Loss of control, inspect ball joints, tierod ends, shocks Loss of brakes,, keep 'em in good shape, don't overload, Buy the best tires available.

What I fear: poor quality work, or poor quality parts.. I do 99% of my own work, and either know who does the other work, and I know what the parts are that go in my cars and trucks and home.. or i make them myself if possible.

What I fear; more agencies like OSHA, Bureau of Automotive repair, and others who respond to political pressure and greed, and don't really help anyone but the agency or politicians..

I'm not a fool, I won't take a sniff of all the brake dust and clutch dust I find in my old cars. But it's less dangerous than a gasoline leak, rusty brake line or a boiling battery, or a bad staircase.

Sorry about the rant, but some fears are blown way out of proportion to the risk.

Greg L

Hey don’t forget CFCs that are burning a hole in the ozone layer HAHAHA. There was no way to prove what was causing a hole or if there was a hole but by god freon companies made out on that story.

[GLong]

Yeah, and now it's believed that methane is a huge contributor to 'ozone layer damage'.. do you know the main sources of methane??

Swamps, decomposing vegetation and Cows, Cattle. yes.. COW FLATULENCE is a huge source of methane in the atmosphere.

Is the government going to legislate that our cattle are fed 'Bean-O', that is supposed to reduce gas ?? LOL..

BACK TO BRAKES; I almost bought a brake shoe grinder at Hershey this fall, but a friend bought it instead. So i might have access to it

if I need it.. a neat tool.. That I probably won't need..

I think I'd hand fit the new shoes to the inside of the drum and see if the shoe 'rocks' or fits tight against the drum. make your decision from what you find.

Greg L.

[Barry Wolk]

I knew it wouldn't take long for this discussion to devolve into government bashing.

Edited December 29, 2013 by Barry Wolk (see edit history)

[GLong]

Well Barry, when irrational overblown fears lead to government regulation and oversight that results in this example not having the correct tools [brake shoe arcing machine] to do a SAFE brake job.

Like I said in an above post, common sense and mechanical skill is needed for most repairs.

I don't think it's inappropriate to bash the government when it's overzealous use of regulation and enforcement CREATES an unsafe situation.

A mechanic who knows what he's doing and needs to arc a set of brake shoes to the drums on an early car that new, standard size drums are not available for, is stuck with doing something, somehow, to make the shoes fit the drums, and have good contact. without good contact, the brakes are unsafe until the shoe wears to fit the drum.

i worked for decades in the auto repair business, and the Bureau of Automotive Repair did NOT care about the real problems with a car, or the legitimacy of a customer complaint, or how exemplary a business is or how well the car was repaired.. it only wanted to enforce silly regulations.. and because of that, many very good shops shut down because of a few 't's not crossed and 'i's' not dotted.. truly a sad situation.

Greg L.