View Full Version : Brake drum gage. The only way to measure ID of drums??


Nealcrenshaw
08-14-2009, 08:37 AM
Just curious as to how you all measure the ID of your drums. Or do you all posess the lucrative drum gage???

Uncle Buck
08-14-2009, 08:49 AM
I don't measure them myself, unless you have the specific use tool, or a set of dial calipers with a broad enough span (and even then the read would not be accurate) it would be a bit difficult to get a good easy read. Though I am sure some would argue that an ID mic with enough rods applied correctly would get you there, except an ID mic would still not get the accurate reading a drum mic would provide due to the lack of points on the tips of the rods like the drum mic has. I know if it was all you had that would work, but why bother. It is just easier for most guys, not counting someone like OCG to go to the parts house that turns drums and have them measure them for you, I do not find it inconvenient at all.

Yes I am also aware that large inside calipers with pointed ends could also be used, and the measured distance transferred, but it is still just nothing to waste your time with unless you had no choice is it?

rsanter
08-14-2009, 09:18 AM
with calapers or with a brake drum guage

bob

Nealcrenshaw
08-14-2009, 09:22 AM
Good Stuff HH!! I asked because that bad boy will cost ya'. I thought also about the tool (forgot the name of it) that measures the ID of cylinders then you use a mic to measure the diameter,but i'm not sure what size that goes up to,the biggest i seen was 6".

Nealcrenshaw
08-14-2009, 09:24 AM
with calapers or with a brake drum guage

A caliper doesnt have that necessary "point" you need to touch the drum.

SpiderGearsMan
08-14-2009, 09:28 AM
hardly see drum brakes any more , the gauge is a shop tool
but if you think you need em , get new ones

Nealcrenshaw
08-14-2009, 09:38 AM
I like HH's suggestion to have the machine shop measure them,they will before they cut them anyway. Thats frugality @ its finest. Unless i come across @ reasonable price.

krusty the clown
08-14-2009, 09:48 AM
the machine shop will measure them before turning anyway. the only thing you will gain is a new toy.

Kevin54
08-14-2009, 11:14 AM
Good Stuff HH!! I asked because that bad boy will cost ya'. I thought also about the tool (forgot the name of it) that measures the ID of cylinders then you use a mic to measure the diameter,but i'm not sure what size that goes up to,the biggest i seen was 6".

I think you are thinking of a telescoping gage maybe?

speed bump
08-14-2009, 01:45 PM
I just measure them with an inside mic it saves me some time because I can make the determination right there if its worth it or not.

rsanter
08-14-2009, 02:23 PM
A caliper doesnt have that necessary "point" you need to touch the drum.

actually there are brake drum calapers that can be bought and they also make a kit that you ass onto you standard calapers

bob

Nealcrenshaw
08-14-2009, 03:53 PM
[QUOTE=rsanter;557953]actually there are brake drum calapers that can be bought and they also make a kit that you ass onto you standard calapers [QUOTE]

Would you happen to know the whereabouts of such a kit?

A_Pmech
08-14-2009, 04:23 PM
Call me old-fashioned but I use a 16" inside caliper and then transfer the measurement to a 16" vernier caliper for measuring.

Any reading you get is "about right" anyway, as the drum ID never holds cylindricity. Many times it isn't known for sure if a drum is good until after it's been turned. If it cleans up within max ID, all is well. After the initial clean up pass is a good time to pull out the inside mike and sweep a couple readings.

rsanter
08-14-2009, 06:41 PM
[QUOTE=rsanter;557953]actually there are brake drum calapers that can be bought and they also make a kit that you ass onto you standard calapers [QUOTE]

Would you happen to know the whereabouts of such a kit?

enco has them
they work great to measure the ID of a snap ring or Oring groove inside a bore as well

bob

Uncle Buck
08-14-2009, 08:05 PM
[QUOTE=Nealcrenshaw;558005][QUOTE=rsanter;557953]actually there are brake drum calapers that can be bought and they also make a kit that you ass onto you standard calapers

enco has them
they work great to measure the ID of a snap ring or Oring groove inside a bore as well

bob

I forgot about those Bob, yea, yer right a guy could get real near spot on with that little accessory set for calipers. You are speaking of the one that attaches to and changes the tips yes?

Elroy
08-14-2009, 08:13 PM
Elroy wouldn't recommend spending the coin on these unless you do a lot of brake work:

http://www.centraltools.com/brake_force.html

http://www.centraltools.com/all_images/replacement_parts/6469parts.jpg

35mastr
08-14-2009, 08:16 PM
Neal,Its cheaper to just go buy a set of new drums.

caper
08-14-2009, 08:18 PM
Most shops here have drum gauges and disc micrometers since brake measurements are required for provincial safety inspections and if the shop doesn't have the mandated tools they can't do the mandated inspections which can be very lucrative.I,myself,have my own drum gauge good for up to 20" and my own disc brake mic.I hate chasing down shop tools which somebody else usually has mangled half to death.Makes my day go that much faster and fewer headaches.

Here is the disc mic:
http://www.centraltools.com/all_images/products/6459cat.jpg

And if you scroll to the second from bottom,the drum gauge"
http://www.jetequipment.com/products/HT/CAT08-HT_101-108.pdf

Thumper
08-14-2009, 11:21 PM
I've got an AMMCO drum gauge........reads out in thousandths to show oversize.

IDASHO
08-14-2009, 11:46 PM
IN this day and age, I kinda want to respond by....

"whats a brake drum?" :lol_hitti

rsanter
08-14-2009, 11:50 PM
[QUOTE=rsanter;558154][QUOTE=Nealcrenshaw;558005]

I forgot about those Bob, yea, yer right a guy could get real near spot on with that little accessory set for calipers. You are speaking of the one that attaches to and changes the tips yes?

originally when I saw them I thought very little of them. then in a pinch I had to use a set at work and instantly took a liking to them.
I have a coupls sets of my own now and have been wanting to make a set of extended ones that would let me go deeper into a bore

bob

Brad54
08-14-2009, 11:52 PM
I've got a good one, because I play with vintage vehicles.

True, the shops will be able to tell you what the ID is, however, I like to go in there knowing what they're at, about what they'll clean up at, and how big they should be when the Parts Monkey hands them back to me.

If you've got a '54 Buick or '62 Chevy Suburban, brake drums don't grow on trees.

Also helps at the junk yard, so when you DO score one, you know whether it can be used again or not.

-Brad

rsanter
08-14-2009, 11:53 PM
I've got an AMMCO drum gauge........reads out in thousandths to show oversize.

I actually have a spare AMMCO drum guage/mic if anyone is wanting one

bob

J.A.F.E.
08-15-2009, 12:24 AM
I actually have a spare AMMCO drum guage/mic if anyone is wanting one

bob

I would be very interested.

sberry
08-15-2009, 06:52 AM
We live on dirt roads and do a fair amount of brake work, I dont measure them or turn, I put new shoes on and if they are not fit for service toss them. Did one last week where we yanked a wheel and put one new shoe in that we had on hand. Most of our stuff that has drums get the wheels yanked at oil change/tire rotation time and make sure there is no loose hardware and that the adjusters are working correctly.

e-tek
08-15-2009, 11:25 AM
cylindricity

- great word!!!!

A_Pmech
08-15-2009, 12:42 PM
- great word!!!!

Heh, yeah.

In Geometric Dimensioning and Tolerancing, cylindricity is an individual control, isolated from any datum. It is an absolute measurement of how far a feature deviates from a perfect cylinder. Worn brake drums always suffer a cylindricity error but rarely a concentricity error. Neither tolerance can be measured with a two-point brake drum caliper.

:thumbup:

Example:

An old-time machinist's gag trick is the tri-lobed ring. Basically, turn a ring with a wall of about .05", say 1.5" in diameter. Get the ring dead on +-.0002" Polish the OD and ID.

Then, take the ring and gently crush it in a 3-jaw lathe chuck. Not much, maybe .005" or so after springback. Now, hand it to the apprentice and ask him if it's cylindrical.

Measured with a micrometer, it will be 1.5" +- the tolerance any way you measure it. However, measured with a 3-point "Borematic" internal micrometer or on a rotary table with a dial test indicator the lobing will be obvious.

Why? Because any two measurements, the chords of which pass though the centroid of the right triangle, will be equal.

This is one of the reasons why two-point measurements are not always reliable indicators of a feature's true geometry.

Nealcrenshaw
08-15-2009, 01:31 PM
Thats the same example i was going to use.
Thats why i would take at least four measurements,up and down,left ot right.and both diagonals. Look for any taper,the same as an engine cylinder.