How much should I expect to pay for a half decent micrometer? Just one good enough the mic brake rotors.

 

For the purpose of runout? 50+ bucks for complete kit... it has been a while since I bought one.

 

I used to sell them, what I have is a vernial caliper...reads both inside and outside. Mine has a dial guage which is accurate to .0005". I was selling them for $35, but retail will cost you about $80 for a good one.

 

i had one from snap-on that i paid 200 for digital and worked great till my brother drove over it with his car..they wouldnt warrantee it can you believe it! :D

 

A micrometer will measure thickness of the rotor but not runout which is a bigger problem. For that you will need a dial indicator.

 

I just bought a set from Harbor Freight. You get what you pay for. DUH.

My buddy is a master welder. He has a set of micrometers that ran close to $500. They are incredible. And accurate as hell. Mine are toys by way of comparison. But I'm a shmoe working on his hobby, in his garage. This guy is a professional. So I guess it all depends on what you're looking for.

Do yourself a favor, don't buy the cheapest. You'll regret it. Go midgrade at least.

 

Brake rotor micrometers and standard machinists micrometers are not the same tool.

The first has pointed tips (anvil) to get into the grooves worn in a rotors surface for an accurate minimum thickness measurement, and the latter has polished flat surfaces which cannot give you a very accurate reading if a rotor has wear grooves.

Having said that... I ball-park rotors using standard machinists micrometers... depending on the application: 0-1" and 1-2".

FYI

.... and what he said... a dial indicator is necessary for measuring runout. Micrometers are for thickness only.

 

Thanks for all the info people. So what exactly is it that makes runout so important? I dont feel any pedal pulsing or shaking when braking. Since a good mic and dial indicator will cost me probably more than im willing to pay for such an infrequently used tool, ill probably have the the streetrod builder do the measurements for me. He has all the high tech snap on stuff. I definatly plan to at least have my current rotors turned so long as theyre thick enough. That should correct any possible runout condition, correct?

 

An excess of runout causes the brake pads to push apart. When this happens a they will suck in a small amount of air. So as you brake and release the brakes are getting progressively less effective.
If you don't have any problems with weak brakes the I wouldn't worry about it, unless your replacing stuff back there anyway.

 

"So what exactly is it that makes runout so important? "

GM designed the C2/C3 system components to operate with very little runout compared to other designs.
As posted, runout causes the pads (and thus, pistons) to pulse in & out. Because of the GM internal seal design, this causes air to enter the calipers around the seals, which produces a spongy brake pedal.
The o-ring design pistons do eliminate the air pumping, but do not correct for warped rotors. Eventually, a combination of o-ring pistons and severely warped rotors causes enough damage to sleeved calipers to render them non-repairable.

"I dont feel any pedal pulsing or shaking when braking. "

You won't feel the pulsing until it gets extremely bad. Other designs will allow you to feel the pulsating a lot sooner than the C2/C3 system does. You cannot compare the operation of a standard system to the Corvette system.

"I definatly plan to at least have my current rotors turned so long as theyre thick enough.
That should correct any possible runout condition, correct?"

Not necessarily...
Brake lathe operators are usually trained by other operators who were never trained how to use the equipment correctly.
Plus, many brake lathes are in serious dis-repair, having been tipped over by heavy bus, dump truck, or firetruck drums.
The internal shaft gets bent from such maneuvers. This type of equipment requires regular maintenance, and usually gets none.

Most shops still have equipment that cannot provide a "non-directional" final finish surface as specified by GM.

And finally.... if any rotor is too thin to dissipate braking heat (not enough metal for heat sinking), the rotor will re-warp and you will be back at square one. This can happen even if a rotor is within its specified minimum thickness.

I did a brake job on an Olds Cutlass (70's vintage) and it came back 3 times... the owner refused to buy new rotors because his were still within spec... each time I turned them, they re-warped, even though they were within the specified minimum thickness.

Turning the rotors works sometimes.... not always.

GM turns each rear spindle & rotor combo assembled together. This compensates for runout on the spindles as well.
Replacement or turned rotors that are perfectly straight cannot correct the runout of the spindles themselves.
-0- runout becomes a running target during a service operation as opposed to GM's original process.

As a side note, when comparing rotors by price, you also need to consider the thickness of the inner & outer plates individually, not just the over-all thickness of the rotor. Cheap rotors will very often have the same over-all thickness as more expensive rotors, but the separate plates are thinner.... leading to pre-mature warping (poor heat dissipation) and precluding turning as an option during future servicing.

 

Try
http://www.mscdirect.com/browse.process

They are one of the biggest tool-suppliers in the US. Generally, if you can't find the tool here, it may not exist!

 

A lot of the cheap chinese mic's will be able to measure to .0001, perhaps .0005 accurately, which is more accuracy than anything you will need to do. There is no need to spend $120 on a Starrett when a $20 Chinese will do. If you were a machinist who used the mic every day and often did need accurate measurements then it's a different story. But avoid the absolute cheap (like $20 for a set of mic/caliper) because the extreme cheap ones are junk.

A good place to check is Enco (www.use-enco.com), also Harbor Freight (www.harborfreight.com) and Grizzly (www.grizzly.com) have low cost but reasonable quality items. LMS (www.littlemachineshop.com) has a nice set of 3 mics (0-3") for $39.95, I have these same micrometers that I bought a few years ago, and they are very nice for the money.

For general measuring you may want to consider a caliper instead, they are accurate to at least .001 which is good enough for automotive work, and they measure 0-6" or even more with just one tool (mics are generally in 1" increments). Vernier calipers are cheap and accurate but a pain to read, a cheap (but not too cheap) dial caliper ($25+) or even a Chinese digital caliper (like on ebay, $30-50) are excellent.

LMS also has a chinese dial indicator with base for $20, it's fine for doing automotive work like checking runout. The point set is probably useless for anything you'll do.

Rob

 

Thanks again and extra gratitude to you tom454 for spending the time being specific and thurough on my questions.

These brakes have never been 100% since ive owned the car. I hear when they are, the really work good. They work ok but i believe ive neglected them long enough. With power to go, it sure would be nice to have optimum power to stop. So where do I get new quality rotors that are finished in non-directional and just ready to put on and go? Think im gonna get 4 new rotors and all new pads as well.

I got a "new" master from Autozone on the car already. Found that it may be leaking out the back seal already. They told me it was "new". Think I paid like $60or$70 for it. I cleaned it up good cause it may have been residue from the old master. I gotta new booster too that is still holding vacuum good after shut down. Gonna give the "new" master a few days to sit and be used then go back in for another inspection. Guess I should be lookin for my reciept. Its around here somewhere. My luck I wont be able to find it.

 

Thanks robzr, i should have bought an entire kit along time ago. Surely would have paid for itself by now. With plans changing towards new rotors, the mics and dials may not be so nessisary at this point. but there I go again, putting it off longer. Oh well.

 

[QUOTEill probably have the the streetrod builder do the measurements for me. He has all the high tech snap on stuff. I definatly plan to at least have my current rotors turned so long as theyre thick enough. That should correct any possible runout condition, correct? [/QUOTE]

The streetrod builder will probably do what us other shop mechanics do...we just pull the rotors and send them out to the brake/clutch specialty shops and have them use their equipment which includes a machine that inspects it, machines it, refinishes the surface all without touching it with human hands...you don't want to get any oil (including skin oil) on them. It's way cheaper to do it that way, many shops charge just $20 a rotor, while a shop mechanic would spend about 20 minutes setting up the guage and measuring it...thus costing about $20 any way, and with the specialty shop you get the rotor back surfaced and ready to go.

 

Heads Up on the "real world"...

The current going rate for turning a rotor is $10. Some places may still do it for $7.

Most shops do not have expensive CNC type machines that measure, cut & finish rotors automatically... it' not cost effective when you can get them done to suit most purposes for $10. However, this would be a directional final finish.

The "hand oil" idea is a non-issue... it's impossible to do a brake job without touching the rotors or getting oil/grease on them, and if you look around, you'll see that most guys still do not wear latex gloves while they work. A simple degreasing after final assembly with Brakleen is the norm to combat grease/oil. Although I do occasionally use latex gloves, most of my work is done with bare hands. The gloves can't stand up to the abuse that I dish out..... I'd be putting on 15 new pairs a day. Also.... the Red can Brakleen works... the Green can Brakleen does not.

Even if you use a CNC machine, and everyone that handles the rotors wears latex gloves, (the machine operator, the cashier, the delivery guy, the mechanic, the owner etc.), a final degreasing using a product such as Brakleen is still necessary, and makes sanitary handling up to that point unnecessary, impractical and cost prohibitive. Current, practicing mechanics will agree.

Thickness measurement takes about 30 seconds. If your shop charges you for measuring rotor thickness, or it takes them more than 30 seconds, go elsewhere. Virtually no shop with a standard AMMCO type drum/rotor machine will take the time to set up a dial gage to measure runout... they just mount, cut and bill. If the rotor is straight, the bit will barely cut the plates. Otherwise, the runout will be obvious to the operator, and everyone else within hearing distance.

Maybe they handle live-in Pinto brakes differently than Vette brakes? :)

I've been doing these (as a real professional mechanic) for over 35 years, owned & operated my own machine shop and 7 bay facility.
Although I've sold off most of my heavy equipment (except for the SIOUX valve facing & head re-conditioning equipment) I still do brake work quite frequently, and that includes work on several Corvette Forum members cars.

It would be nice if rotor turning was done in a clean room, by a CNC machine.... but most places are still using the old standard equipment, and greasy hands prevail.

Now... notice I am referring to *most* shops. Not the shop R & R is referring to.

 

Tom,

Thanks for that quick lesson in disc brakes!!!! That was one of the most informative posts I've read in quite some time . . . time for a cup of coffee. Sure wish you lived in TX. :cheers:

 

You're welcome... my posts are not always appreciated here because they are based in experience rather than philosophy and book knowledge. Practical experience vary often collides with theory & book reading... particularly when it comes to hydraulics & brake work. I try to keep my mouth shut about topics where I have no real experience. You'll never hear me telling someone how to select a high performance cam.... there are others here who are way better at that than me. I've read the books, but do not have enough experience in cam selection to be a "guru".... so I just listen & learn.

A man's gotta know his limits.

BTW... I have life-long friends (and former customers) in both Ft Worth & Austin... I like the Lake Travis area. Last time I was at the lake, a guy rolled up in a 67 435 TriPower convertible with sidepipes. Gotta love it.

Back to the brake questions...

ALL replacement master cylinders should be dis-assembled and checked for flaws before installation.
New master cylinders may sit on the shelf for a long time before they are sold. They can be rusty on the inside even though they are new and have a rust inhibitor in them.

I recently did a C3 brake job and went through two off-the-shelf rebuilts (customer supplied) which were defective... rust & pits.
One was honed & shiny, but was severely pitted... it should have been sleeved or trashed... not rebuilt.
The other was both rusty & pitted, and even had a used piston assembly in it with obvious wear damage.
It had been honed, but was still junk.

Finally ordered a new M/C and it checked out okay when I dis-assembled it prior to installation. Not all of them do.

Also.... vernier calipers cannot read rotors properly. You need to find the current minimum thickness.... which will be a "single point of contact" as opposed to the surface area sampled by a vernier caliper. Based on experience, a used rotor will be non-uniform in wear and measurement requires a different tool than can be used on a new, un-worn rotor. The rim rust alone (if not removed) will prevent a vernier caliper from being used effectively.

Measuring thickness does not have to be that exact... accuracy to .001 is sufficient, but you do need to know the actual current minimum thickness to judge if the rotor is even serviceable. That's why an actual rotor thickness gage has points at the anvils... to get into the lowest spots. Runout is another story... your dial gage should be fairly accurate. Mine reads to .0005.

FYI - Rotors have a minimum thickness allowed AFTER resurfacing.... it's either stamped on the rotor, or is looked up in a table. If a rotor is below the spec, it should not be used. If a machinist cuts a rotor to less than the spec, he can also be sued for negligience in the event of an accident. In some states, it is illegal for a shop to turn rotors to less than spec.


[Modified by Tom454, 10:30 AM 5/28/2002]