Rear rotors longevity

[Gohawks63]

I just had my first brake job on my 2004 the other day. The rig has 53K miles and the dealer told me I had 5% left on the fronts and 10% on the back.

Not really a surprise since I expected to have the brakes replaced and I was still on the original pads.

What surprised me was that the SM told me I needed new rear rotors! I expressed disbelief and asked if they were scored. Couldn't of been since there was still pad left and the brake wear indicator hadn't begun to make noise yet.

He confirmed that they weren't scored, but said that the rotors will wear due to the semi-metallic pads. I could see this, but not to the point of needing new rotors.

He said he would go back and check with the tech, and lo and behold, they said that they were able to do a light cut. Now I know that for liability reasons they wouldn't cut past the tolerances so I'm wondering if the dealer was full of crap and trying to pad the bill.

Have any of you needed to replace rotors after the first brake job (assuming they weren't scored)?

 

[SINCITY100]

https://forum.ih8mud.com/showthread.php?t=121302 ;p

 

[Steph23]

I had rear pads put on my '03 at 55k. Everyone I talked to (dealers and repair shops), was trying to get me to turn or replace the rotors. I did neither and at 66k, I haven't heard a squeak or had a single problem. Smooth braking (with no fade) every time. IMO, they were probably trying to pad the bill.

 

[Gohawks63]

I saw that, but it still doesn't answer my question.

 

[NMuzj100]

so I'm wondering if the dealer was full of crap and trying to pad the bill.

I'd say yes. My rears still were at 18mm at 100k and wouldn't have needed anything except I let one pad go metal-to-metal. 18mm is the same thickness as a new rotor! The minimum is 16mm and after machining my right still had 17mm. Rotors can actually get thicker with use as pad material binds to the surface.

I doubt you have much wear. The FSM procure would not be to replace or turn unless the runout was out of spec or there was scoring or roughness on the disc. Even with excessive runout you check bearing play, axle hub runout and attempt to adjust runout by repositioning the disc before turning or replacement. Have they tried all these things?

 

[Gohawks63]

I doubt you have much wear. The FSM procure would not be to replace or turn unless the runout was out of spec or there was scoring or roughness on the disc. Even with excessive runout you check bearing play, axle hub runout and attempt to adjust runout by repositioning the disc before turning or replacement. Have they tried all these things?

I'd say no. I think they were just trying to get me to purchase new rotors. Once I balked they backed off. I had a CPO '98 LC before that I bought with 46K miles on the clock. I had the rear pads replaced at around 65K and never had the rotor issue come up.

I just found it hard to believe that as overengineered and heavy duty the LC is, that it would have such paper thin rotors that would require replacing on the first brake job.

 

[NMuzj100]

Dealers are unbelievable!

 

[LXPearl]

Sounds like the dealer was either playing it safe (good) or trying to pad the bill (not so good). Most tend to have a policy that their standard practice is to do the "full" brake job, so unless you tell them not to turn the rotors, they will do so.

For most customers, this makes sense. After the brake job, the brakes will be smooth and work well. The dealer minimizes return jobs because the brakes are pulling, rough, etc.

If you maintain your vehicle well and know its quirks, you will know when it really needs the rotor turned or not. If you look at the rotor and it is not scored and does not have a glaze on it, then likely the new oem pads will work without a hitch. If there is a glaze, I have used a little emory paper on it and the new pad had worked well (when the rotor is smooth).

 

[Jim_Chow]

I took a look at my '03's rear rotors at 56K mi..wear was barely detectable (i.e., virtually new thickness). At this rate, they'll easily last 100k mi. Front's measured to about the new thickness, too. My rear pads are at maybe 35-40%, will slap new OEM pads on when I do the 60K service. My plan is to just clean and apply disc brake grease to the anti-squeal shims, no rotor turning. I imagine the pads will just wear to the shape of the rotors.

 

[Dandon]

(...)
I imagine the pads will just wear to the shape of the rotors.

Yes, you hit the nail on the head there. I don't understand why a normally worn, or even a scratched rotor (due to an overused pad) has to be an issue. Pads are by definition softer than the disc, so a new pad on an used rotor will just wear faster at the beginning (smaller contact surface and therefore higher pressure), until it adapts to the shape. Only a (really) warped rotor, or one worn beyond minimum spec'd thickness needs to be replaced.
I'd rather spend my money adding gadgets

 

[Tinkerer]

Yes, you hit the nail on the head there. I don't understand why a normally worn, or even a scratched rotor (due to an overused pad) has to be an issue. Pads are by definition softer than the disc, so a new pad on an used rotor will just wear faster at the beginning (smaller contact surface and therefore higher pressure), until it adapts to the shape. Only a (really) warped rotor, or one worn beyond minimum spec'd thickness needs to be replaced.
I'd rather spend my money adding gadgets

I used to reuse rotors too. Or turn rotors. Back when I owned vehicles that were junk and I could not afford new rotors. Did it on a lot of others' vehicles too, back when I used to spin a wrench on others' vehicles for $. So I'll tell you my own experience:

Sometimes you can do this without problems.

But frequently it leads to problems and early failure of the brakes in question.

Interesting things happen to the rotor over time, in service. You may think it is OK, with no significant warpage etc., but it may be degraded nonetheless.

The issues are not just dimensional, or whether the new pads will wear to fit the surface of the rotor.

The rotor surface (and substrate) hardness is affected by use as a brake rotor, over time, due to heat and work hardening effects. This can lead to hardness variation around the rotor pad contact surface, which can cause brake pedal pulsation.

And if you turn the rotor - see my earlier comments about this gamble. Yes, it can work OK sometimes - but many times it will fail. Whether the machining is done by El Cheapo Auto Parts Chain store or the specialist machine shop you trust.

If I am redoing brakes on an old junk car, I may try to reuse or turn rotors, because such a car is not worth investing a dollar into anyway, and I don't care whether its brakes are smooth or not.

But a vehicle like a 100 series in good condition deserves excellent brakes, like they were when new. And I don't have time and $ to spend redoing brake jobs that fail due to reusing or turning rotors. The only way to ensure a 100% successful brake job is to replace pads and rotors with all new OEM parts (or better-than-OEM new parts if you abuse your brakes on a regular basis).

But good luck with your rotor reuse or turning - you MAY get lucky with it.

 

[jamisobe]

My rear brakes have worn slowly just as I have experienced on all of my other vehicles, that I can remember, in the past.

However, the front pads on my 80 were wearing out at about 10-15k miles with my rotors mainting a like new finish. I never turned them and the OEM rotors lasted to 140K. Not bad.

I decided that I was going to try another route at 140K as the rotors measured too thin and I was starting to experience the shakes on hard stops. I went with Powerstops and Hawk HD ferro/carbon pads after doing some research(I ended up using crossdrilled even though early research suggested crossdrilled rotors may not hold up- deeper research suggested that results would likely depend on brand of crossdrilled rotor). I wanted longer pad life foremost and was interested in not having to turn my rotors if it all possible.

This set up has performed beautifully and 40k miles later I have 50-60% pad left with rotor surfaces that are as smooth as a baby's butt. I also have felt as if I am experiencing better braking.

I drive hard, was going through pads left and right, and was willing to experiment. The chamferred holes work well with the semi-metallic compound allowing gases to escape, helping pad material to be removed uniformly, and apparently helping to maintain a smooth rotor. I am very glad that I switched.