Easy way to measure brake rotor thickness accurately?

[Howard705]

The only time to worry about it is when replacing brakes. It isnt just about the thickness. Sometines more than the min thickness needs to be turned off so its less. Sometimes one rotor surface is too thin even though the other sude is like new. Sometimes is the rust bels the inner fin area rusts the surfaces from the backside out or even the fins rust su badly that the rotor collapses from the pressure of the caliper. Mostly the thickness is used to sell you rotors.

 

[e9999]

The only time to worry about it is when replacing brakes. It isnt just about the thickness. Sometines more than the min thickness needs to be turned off so its less. Sometimes one rotor surface is too thin even though the other sude is like new. Sometimes is the rust bels the inner fin area rusts the surfaces from the backside out or even the fins rust su badly that the rotor collapses from the pressure of the caliper. Mostly the thickness is used to sell you rotors.

much of that is true. But I'd like to be able to measure the rotor thickness in 30 secs when I have the wheel off and without removing anything else. So I know what it is, and how close I am to necessary replacement, thickness-wise. A routine, quick measurement. With the modified calipers I'll be able to do that.

 

[serenity]

Meh, use a ruler, if it's 30mm or less get new rotors. It's not rocket science.

Now let's get back to discussing cupholders...

 

[NLXTACY]

Doesn't running 100 series pads get rid of the lip on the rotor? I just did brakes on @Dr Gil 's truck and he was running 80 pads and I took off the caliper and measured. Within spec but had the small lip. I haven't done my pads in so long I don't really remember if the lip is there or not.

 

[e9999]

I am not running 100 pads so I don't know. If the 100 pads extend outward of the rotor, that could make for some interesting braking the first few times you try to brake with them. Either the pad will have a nice groove dug in and the lip will stay there, or the pad will grind down the lip with reduced braking at first. Don't know what will happen. Those lips are nasty rusty rough affairs.

I do remember the lip on one end -the rear I think- was quite pronounced, a good chunk of a mm probably so would make the measurement completely wrong if not accounted for, and those are the rotors that are closer to minimum so I need to keep an eye on them. From memory, the standard thickness is 18mm and the min 16mm so if I'm correct on that you really have only 1mm of wear allowed on each side. I suppose one way to look at that is that if the lip is 1mm on the outside (easy to measure) and IF it's the same on the inside (hard to measure), they're done.

 

[NLXTACY]

My last set of pads had a lip actually on the pad (100 series). But I don't remember the rotor.

 

[e9999]

Not aimed at you NL, but another way to say this is -to restate the obvious--: If there is a lip to the rotor because the main face of the rotor is being recessed due to wearing down but not to the edge, and you measure the thickness of the rotor with standard Vernier calipers without taking the lip into into account, you will *always* measure the as-new rotor thickness, as if your rotor is not wearing down at all, hardly a great way to assess the rotor thickness, I would think... (assuming no other metal loss due to rust etc).

 

[NLXTACY]

Agreed but I use Mitutoyo calipers which have a recess on both sides of the jaws. The lip on the rotor fits inside the recess without affecting the measurement.

 

[jtwopark]

brakes are the only thing i get done at the dealership

i have had instances where i did the brakes with some cheap auto zone rotors and not, NOT a good experience!@

Took it to the dealer had it done, redone under warranty. later found out i had a bad and sticking caliper that was causing the rotors to fade.

from my experience, every third brake job being done should call for some new rotors. Aprox. 30k

 

[e9999]

Agreed but I use Mitutoyo calipers which have a recess on both sides of the jaws. The lip on the rotor fits inside the recess without affecting the measurement.

true enough if you can get the lip to fit in there. It didn't seem like i could do it without removing the brake caliper but I may have just missed it.

 

[jeffro109]

Agreed but I use Mitutoyo calipers which have a recess on both sides of the jaws. The lip on the rotor fits inside the recess without affecting the measurement.

This is how mine are too with the little recess.


and yes @e9999 you can't get to the actual pad to measure, but I meant the backing plates though you'd have to measure the pad thickness then too....

 

[george_tlc]

e9999 in perfe

brakes are the only thing i get done at the dealership

i have had instances where i did the brakes with some cheap auto zone rotors and not, NOT a good experience!@

Took it to the dealer had it done, redone under warranty. later found out i had a bad and sticking caliper that was causing the rotors to fade.

from my experience, every third brake job being done should call for some new rotors. Aprox. 30k

Are you saying new rotors every 30k??? or each brake job is done at 30k and so you replace the rotors every 90k??

I've got about 130k on my rotors and still within spec, stops nice and straight... Yes, these heavy automatic petrol powered whales use up brake pads pretty quickly (versus a manual diesel), but I don't see replacing rotors unless needed... A lot depends on how you drive and anticipate red lights etc. I've yet to allow a dealer to touch anything on our 80 since it went out of warranty in the last century.

cheers,
george.

 

[NLXTACY]

Yeah brakes are one of those things that are deceptively easy on the 80s. I can't see ever going to the dealer, or a mechanic, to do them.

 

[e9999]

Mine has 97K. I drive very conservatively acceleration- and braking-wise.
The front rotor has plenty of meat left from my very rough measurement/guess. The rear not so much. (But it's harder to estimate correctly on an absolute scale in-situ as amply discussed above.) It is highly likely -but I do not know for a fact- that both are the originals. I think I may have readjusted the proportioning valve after the lift, but I don't recall the specifics. Maybe I messed that up.

 

[ppc]

With all the time spent reading and writing these posts you could have removed the calipers and measured both rotors. I agree with George. If it ain't broke it don't need fixin.

 

[jeffro109]

@e9999 The rear rotors come off very easily, just take the caliper off and it slides off, not like the fronts where you have to take the hub off.

 

[mechanist]

Make your own gauge using old plywood from reclaimed kitchen cupboards. Sort of like piece of wood in the FSM used in the caliper rebuild. Sand it down to the minimum viable thickness and then place it against the rotor to see if it's in the ball park. Would that work?

Or you could sand down a piece of scrap aluminum from an old pot picked up at a thrift store.

 

[NLXTACY]

I could have driven to e's place, taken off his tires, taken off his calipers, measured. Given the thumbs up or thumbs down, put it all back together, driven back home, and I'd still be back soon enough to reply to this exact posting at this exact time.

 

[ppc]

Yes but then you would create another 27 pages of posts talking about it.

 

[e9999]

Yes but then you would create another 27 pages of posts talking about it.

maybe, but he seems to be one of the few who understand what's going on here and what I'm trying to do. Even better, he seems to have invented a time machine as evidenced in post 38, which would be damned handy for my mechanical misadventures... So I'll gladly take the 27 pages!