Easy way to measure brake rotor thickness accurately?

This site may earn a commission from merchant affiliate
links, including eBay, Amazon, Skimlinks, and others.

e9999

e9999

Gotta get out there...
Moderator
10 Year 15 Year 20 Year
Joined
Sep 20, 2003
Threads
1,087
Messages
19,239
Location
US
I did another tire rotation tonight and took advantage of that to check all the brake nuts, pads, disks etc under there. Unfortunately, in the rush I didn't see a good easy way to measure the rotor thickness accurately without taking things apart. There is no easy way to use calipers directly cuz my rotors have an unworn lip on the edge so I'd have to use spacers in a tight spot which is a pain, or guess what the lip thickness is on the inner side, which is what I'm doing now but is hardly satisfactory. My micrometer is only 1" so it does not fit the front and there is no room to put in the back IIRC.

I'm tired and my DIY lobe has shut down for the day, so I gotta ask: any good easy way that doesn't require removing the rotor or caliper or cutting into the metal guard or an expensive new tool? I'd want to measure to much better than 1mm accuracy to be able to tell how close to replacement I am.
 
Tape a quarter to both sides of the caliper jaws, then subtract the amount of the two quarters stuck together? You just need to offset the jaws a bit, right?
 
Or use the butt end of the caliper against the outside of the rotor and let the little stick measure to the back side.
 
math said:
Tape a quarter to both sides of the caliper jaws, then subtract the amount of the two quarters stuck together? You just need to offset the jaws a bit, right?
Click to expand...

thanks, but quarters would be too big to fit readily on the inner side. There is only a sliver of space between the dustguards and the calipers, just enough for skinny calipers. I did think about adding some foil pads wrapped around the caliper fingers and it could be done but it's a bit of hack work and a bit awkward.

jeffro109 said:
Or use the butt end of the caliper against the outside of the rotor and let the little stick measure to the back side.
Click to expand...

thanks but that would be worse than what I do know (straight calipers across the lips and then measurement of the outer lip thickness + guessing the inner lip thickness) because you'd have to approximate where the probe should be ending at.



This dustguard doesn't come off with just a couple of bolts, does it? (Yes, so do the calipers, but I'd rather not futz around with those bolts too much.)
 
This sounds very complicated just to measure a rotor thickness but :cheers: to you none the less.

Maybe you could measure between the brake pads using the internal side of the caliper arms. Or use a thin straightedge behind the rotor to use the little stick idea.


Just make sure you take enough samples to be statistically significant :bang:.


Edit to add--the dust shield is held on by several bolts and you have to take the hub off to get there. But you could easily measure the rotor once it was sitting on the floor.
 
Take the Rotors off and grind the lip off in one spot with a flapper wheel.
Then call O'Reileys and ask if they turn at your thickness.
Or Power Stops for $100 set on Rock Auto.
 
jeffro109 said:
snip

Maybe you could measure between the brake pads using the internal side of the caliper arms. Or use a thin straightedge behind the rotor to use the little stick idea.


snip
Click to expand...



can't do the inside measurement cuz of the lip that's covering the pads



Hornd said:
Take the Rotors off and grind the lip off in one spot with a flapper wheel.
Then call O'Reileys and ask if they turn at your thickness.
Or Power Stops for $100 set on Rock Auto.
Click to expand...

yes, I did think about grinding off the lip, that could probably be done in-situ actually. Extra time of course and a (tiny) bit of unbalance. But then you either have to grind a new spot each time you make the measurement or you have to lift both wheels up -which I'd rather not- to rotate the disk to the right spot, a pain. So not a great solution either.




Maybe the easiest thing to do is to enlarge the dustguard opening next to the calipers so there is room to work but that thing is there for a reason...



Am I the only person who's trying to measure the damn things?
 
e9999 said:
...
Am I the only person who's trying to measure the damn things?
Click to expand...

On the rig, likely. Most would only care to measure when they are off, to decide if they can be turned or need to be replaced.
 
For the record what is the minimum thick for both front and rear?

Thanks
 
30mm and 16 per FSM IIANM
 
Tools R Us said:
On the rig, likely. Most would only care to measure when they are off, to decide if they can be turned or need to be replaced.
Click to expand...

interesting point. But in a way it's like saying you'd have to remove fully the brake pads to find out how thin the linings are in order to know if you have to replace them. Me, I'd rather know *before* removing them so I can plan, order new etc.
 
Basically, if your rotors are warped, replaced them.
If they have the sides missing, replace them.
Otherwise, throw in another set of pads and go wheelin'......

I have seen rotors that were actually missing one of the smooth sides for braking and they still stopped the truck. The woman claimed "they didn't make any noise", even though the pad (including the actual steel part of the pad) was missing, so just the caliper piston itself was being used to stop the truck as it ground away with each stop. An example is shown below.

So, drive it until they feel warped, grind, make noise, or weld themselves to the caliper....THEN replace them.
bad-brake-rotor.webp
 
e9999 said:
interesting point. But in a way it's like saying you'd have to remove fully the brake pads to find out how thin the linings are in order to know if you have to replace them. Me, I'd rather know *before* removing them so I can plan, order new etc.
Click to expand...

So,,, pull the caliper and measure, it's like two bolts?:idea:
 
izzyandsue said:
Actually this what I use:

http://www.amazon.com/Anytime-Tools-Caliper-Electronic-Micrometer/dp/B006Y1OWKS/?tag=ihco-20

snip
Click to expand...

that's right. that's exactly the sort of thing needed, if a bit too thick probably for in-situ measurement on my 80. Which gave me an (obvious) idea: instead of adding spacers to the caliper fingers, which is iffy, I can just take an old cheap pair, and grind recesses for the rotor lips. Should work just fine. Be accurate enough. And would put one of my unused cheapo calipers to good use for once. Should take all of 10 mins to do and be useful for other jobs. Excellent! Thanks!
 
You must log in or register to reply here.

Share this page

Back
Top Bottom