308 Rotors - resurfacing question

Yes, once they're off the car, they're just rotors. You can take them to any good place that does brakes.

 

Normaly there is a number stamp or engrave on the rotor indicating the Min. thickness before you can replace it, Im not sure of the exact number of thickness but if you pull one out you should see it somewhere you might have to use a steelbrush to make more visible.

Mike

 

Mine had been turned twice and still fall within spec. Car has 70k on the clock

 

The WSM has the min allowable thickness. It's the same for all the 3x8s. It's also in the 328 tech specs/recalls document, you can download both from Steve Jenken's 'private document colleciton' web site (just do a quick search).

The # of times you can turn a rotor depends a lot on how badly worn it was each time it's turned. On other cars, I've had to replace rotors after they'd been turned once, then with new rotors & softer pads, have gotten 3 turns out of a rotor.

 

Looks like 20 mm minimum for 328 from the Technical specifications. 308 should be the same.

Mine were between 21.6 and 21.3 mm after turning them (308 QV).

 

Read the article on Girodisc Website. They way I understood it the only time you need to turn them is when they are badly badly scored.

 

I used to race bikes, went thru tons of brake pads and never resurfaced a motorcycle disc.

 

That's what i did. More than likely only the "LIP" on your Front Rotors will require Machining. No need to Weaken the entire Disc.

 

In theory, they should slide right off (no requirement to disassemble the spindle), but that looks particularly "dry" (unprotected) and rusted (that first diameter on the flat surface should be a close-fitting cylindrical slip fit). On the (steel) hub-to-brake disc and brake disk-to-wheel surfaces you really need to use a protectant occasionally (I've been using a film of PB Blaster lately, but am open to better suggestions).

 

Anti sieze works well.

 

Unless you are getting a vibration just installing new pads and taking a few miles to bed them to the surface works quite well.

If you are going to turn them 308 rotors can usually stand it a few times if the guy doing it takes the minimum to true them. On the 360's they are soft enough that we just go through 2 sets of pads and toss the rotors.

 

You're probably going to get a bunch of different suggestions (and for the track, i.e., red hot rotors/hubs, maybe a little more initial play would be called for), but, after regreasing the tapered cylindrical roller bearing set-ups for normal street use, I like to:

snug

rotate the hub a few revs both directions

loosen

repeat that sequence a few times, and

finally tighten the nut just enough so that there's no play, but you can still slide the thrust washer under the nut from side-to-side without a lot of force (but it requires more than zero force to do the sliding).

After some real driving, I find that gives a couple~few thousandths of inital play.

Not a very exact suggestion -- it's a "feel" thing

 

When I picked my pads up from Porterfield, they recommended not turning the rotors they said you should just deglaze them with a disc sander and put the pads on. They said rotors are either reusable or if they run-out too much they should be replaced.
As far as turning the rotors, in many cases turning does more harm than good. If the rotor does not fit on the machine exactly as it does on the car and the rotor will likely not run true. The problem is that most rotor lathes do not locate the rotor the exact same way the hub on the car does.
Most of the rotors I have had turned had more run-out after they were turned than before they were turned. I would check the rotor on the car with a dial indicator and if it has less than .002" total run out I would just spin the rotor and hit it with a disc grinder to knock some of the ridges down and deglaze it. To turn the front rotors, a long bolt can be put in the one of the lug holes and the bolt can be used like a crank handle. The rear rotors are easy to spin with the motor running.
For the grinding disc, I would use a cardboard backed 60-80 grit 7" disc--the stone type of grinding discs are too aggressive; the cardboard backed discs will follow what is there and just deglaze.

 

For a 79 308 it's marked on the rotors: Front MIN T.H. 787"=20mm and Rear MIN T.H. 708"=18mm. I would assume this is the same for all 308's with OE brake rotors. HTH.

 

Mine were within spec when we measured them but they "looked" like they were corroding from the inside (vents), they looked very thin, I opted to replace them rather than take a chance. Just a suggestion.

 

I would never turn rotors unless they had major ridges in them or were warped. Minor ridges have no negative effect on the stopping power of the brakes once the new pads are bedded. The pads simply conform to the profile of the rotor. By thinning a rotor you are actually reducing the ability of the rotor to disperse the heat generated by braking.

 

What did you use to replace the originals, where did you get them, and $$?

 

I think you mean, rather, the disc's ability to absorb heat in the style of a heat sink where such heat is created by the friction of the pad on the rotor. It's the ability of the rotor to absorb the heat created by braking that is affected by how much mass (thickness) the rotor has. A slightly thicker or thinner rotor will disperse heat at about the same rate - the difference will not be material.