When do I change the Rotors?

Some people say when you change the brake pads, you should 'turn' thr rotors (on a lathe), but with the prices for rotors these days (I've paid as little as $6 each) it's better and cheaper just to replace them.

Unless, of course, you have Genuine OEM Toyota rotors. Then, use this: There should be a number somewhere on the rotor, either near the hub or along the edge. This is the tolerance. You can measure the rotor with a measuring tool like calipers or a micrometer, etc, but the easy was is with a wrench. So, for example, the rotors on my Supra say 14. This is

14mm. At 14mm, they should be changed. Now, if they were OEM Toyota rotors, I would measure them. Let's say they came up 17mm. If they had a lot of gouges from bad pads, or a 'lip' around the outside, I would have them turned as long as they stayed above 15mm. This gives me a couple years; however, semi-metallic pads will wear them down rapidly.

If you have a 12 on the side (Most tolerances are 8, 10 or 12mm) and you measure 12, then replace them. You *can* let them go a little longer, but replaement is better. Under 12, replace them for sure.

NOTE: I have a Mazda that says 15. The rotors were RIGHT AT 15mm. They looked good, so I left them. But, after I pressed in the puck with a clamp, ALL THE WAY TO THE BOTTOM, and put in the new pads, I had one HELL of a fight to get the loaded caliper back on the car! I really doubt there is enough play for the caliper to lock!

Provided they aren't scored badly or warped, you dont need to change them. Mine are original on a '96 with 185,000ks roughly 110,000 miles and they are fine. Unless you've had pads which went down to the metal,..or you have wobbling steering when braking,..no worries.

Jason

$6 each for a rotor? Where?????????

Michael

Not a Camry. CarQuest for an '83 Tercel AWD wagon. Drums were a whopping $18.

YOU HAVE GOT TO BE KIDDING. Disc rotors have a minimum thickness which is i guess what you are refering to. Yes it does need to be measured ,bur certainly NOT with a spanner and preforably not with verneer callipers.This due to rotor lip is usually highly inacurate.A rotor micrometer (or even a standard micrometer)is the correct way of measuring rotors. 3 readings are needed one inner one middle and one outer , usually on the last section of wear surface.You then take an average and calculate your taper if any,this will tell you if the rotor is servicable or requires machining or replacement. Rotors should be machined at least every third set of pads, in my workshop we will usually do them every pad change.This is due to pad material causing rotor glaze and this the results in squeel , shudder and VERY premature pad wear. Bi metalic pads DO NOT wear disc rotors un usually.ANY pad will wear a rotor, bi metalic pads have the advantage of superior stopping via less heat generation due to transfer and compound structure. Cheap pads are not worth buying and disc rotors at $6 each.......good potplant stands.Usually these cheap rotors have no machining tolerance or if they do its half of what it should be. BRAKES ARE SERIOUS REPAIRS, NOT SOMTHING TO BE GUESSED . dave

YOU HAVE GOT TO BE KIDDING. Disc rotors have a minimum thickness which is i guess what you are refering to. Yes it does need to be measured ,bur certainly NOT with a spanner and preforably not with verneer callipers.This due to rotor lip is usually highly inacurate.A rotor micrometer (or even a standard micrometer)is the correct way of measuring rotors. 3 readings are needed one inner one middle and one outer , usually on the last section of wear surface.You then take an average and calculate your taper if any,this will tell you if the rotor is servicable or requires machining or replacement. Rotors should be machined at least every third set of pads, in my workshop we will usually do them every pad change.This is due to pad material causing rotor glaze and this the results in squeel , shudder and VERY premature pad wear. Bi metalic pads DO NOT wear disc rotors un usually.ANY pad will wear a rotor, bi metalic pads have the advantage of superior stopping via less heat generation due to transfer and compound structure. Cheap pads are not worth buying and disc rotors at $6 each.......good potplant stands.Usually these cheap rotors have no machining tolerance or if they do its half of what it should be. BRAKES ARE SERIOUS REPAIRS, NOT SOMTHING TO BE GUESSED . dave

Dave, I respect the fact you workin the industry, but expensive "metal-king: pads" will cause significant wear of Ford cast-iron rotors. In fact they wore the light-scoring to smooth in the 351 Falcon (Australian) I have and that was with sedate driving :-).

Jason.

Why would you need to calculate the average, surely if your three readings are different the rotor needs machining (at least) so you would just compare your lowest reading to the minimum spec and if it's close or lower just replace.

Plus if the surface is level and the brakes are good then there is no need to machine. If your 'rotor glaze' is such a problem the I would think that it should be done at every service.

And finally - if you could buy rotors at $6 each you wouldn't worry about machining them you would simply change them with the pads.

1)You calculate the average to determine taper.Why, well ok say you had a rotor with lets say 3mm taper, would you not then be looking for a reason??like a worn / sticky slide or fault in retaining hardware ,possiply a hydraulic fault.Not to say that everyone does it , but its the CORRECT way to do it. 2)As I said we maching on almost every pad replacement ,rotor glaze is just that , a glazing of the rotor surface and results in as I said several problems.Sure , if you dont want to machine rotors and just want to throw pads at it,fine,AGAIN Im talking abuot the CORRECT way to do it. 3)If I could buy rotors for $6 each I would strongly suspect they would be chinese copys or similar,the ones that I have seen have been made of inferior materials(eisily tested with rockford hardness tester or similar) and have problems with heat dissapation, this causing run out (warping) heat stress cracking etc.Again go for it , but like any parts that you fit to a vehicle ,you get what you pay for.

Wow!

Well, I live by the rule, "When in doubt, change it out."

And I use the same quality parts as any person who walks into Meineke or Midas and says, "Give me the cheapest parts possible." It just costs me $325 less.

But thanks for the tip on the spanner (wrench? You UK types REALLY need to learn to speak the language! ;) yeah I can see that. An old mechanic showed me that trick at.. Meineke...

But on that Mazda, there was NO WAY I was going to get the caliper on with a thicker rotor!

(it was a free car with a $25 paint job, only run in the winter and even at that, 2.5 years and 12,000 miles...)

1) How does an average tell you taper? Wouldn't you just take the difference between your outer and inner reading. Pad wear will also help you detect problems. 2) Does your glazing only ocur when the pads are at their minimum thickness? Surely if glazing is going to cause a problem then that is the reason you would be doing the work anyway (an you should have found it during one of the routine services you do). 3) These are better reasons than lack of machining tolerance.

iM OUT , WONT EVEN BOTHER TO GO THROUGH THIS AGAIN.. BEST OF LUCK.

No im back again , HOW will an average NOT tell you taper?? if you are going to post please do it with SOME KNOWLEDGE. If you wish to question my work ethic or that of my staff , please come and spend a day working as a mechanic not a backyard expert.

Not questioning your ethic, just what you claim is CORRECT. So the average can tell you taper - prove it.

My maths Take three readings Inner 2 Middle 2 Outer 2 Average 2

Another three readings Inner 3 Middle 2 Outer 1 Average 2

Which Average tells me I have a taper?

Well I stongly suggest you do a fitting and machining course.

I just hope you're not the teacher. How hard would it have been to just answer the question.

I was able to find the details behind your ?average reading? claim in less than 30 seconds talking to mechanics at work and it requires more than three readings.

From all this I came out with the following.

1. Cheap rotors are possibly inferior quality
2. Use the correct tools to measure rotor thickness (you need to get past any ridge at the outer edge)
3. Imagine three circles around your rotor and take the average of several readings around these. The difference between these averages will give an indication of the wear pattern.
4. Rotors should be machined at each pad change if the surface is not true (i.e. flat and parallel), unless once machined they would be below the minimum thickness.
5. Strange wear patterns of the rotor or pads could indicate other problems to investigate.
6. Check for leaks, sticky slides, loose or faulty components while in the area.

How could an average reading possibly require more than 3 readings?

You're the one that claims to be the expert so I shouldn't have to explain to you. This was the way it was explained to me (and I suppose 'several' could be three)

So why would I even bother ,taper is a basic principle ,as a point of FACT I do teach.and in MY feild yes im am conidered an expert, but I gues you know more than me so Ill leave it for now.Just hope you NEVER do a brake O/H for anyone.A little knowkedge is a DANGEROUS thing.