'92 Q rotors: how thin before can't be resurfaced.

[kdkrone]

I am now living in a small town (45k population) without an Infiniti mechanic. There is a brake shop with a good reputation and I have OEM brake pads and rotors with me. I have no idea yet what the rotors look like, but at what thickness should they be replaced as opposed to turned?

ThanksKen K

[maxnix]

Can't remember what Q45tech posted, but I bet it is in the FSM. The problem is that the thinner they get when you turn them, the sooner they are out of specification in service. Turniing cuts should be as minimal as posssible.

A nationally franchised brake shop scares the bejeezus out of me. Better an ASE certified technician in an independent shop where work quality is controlled rather than a coporate franchise where production goals are met first and foremost.

[qship96]

If you already have new rotors in hand,install those and keep old rotors which you can then look up spec later and carry in hand to a shop to measure/cut if warranted and use at a later date

[kdkrone]

No, no, no, Maxnix. This is not a national franchise. It is a local shop owned by an ASE certified tech, just not an Infiniti tech. Why is it I frequently forget to look in the manual???

qship96, good suggestion.

Thanks both of you,Ken

[goody90q45]

Why is it I frequently forget to look in the manual???

Here you go Ken, I'll save you the trouble:

From the 94 FSM, pages BR16-19. Same brake pads and rotors, should be the same specs for the 90-93:

Rotor Repair LimitFront.....26.0mm (1.024")Rear........8.0mm (0.315")

Runout(Measured in at least eight places)Front.......0.07mm (0.0028")Rear........0.07mm (0.0028")

Any shop that turns rotors will have a guide that should give them the same numbers and they'll usually check them on the spot and tell you if there's enough meat left to turn them again. This is a good excuse to buy a set of calipers so you can check them yourself. I need to do the same.

If you put new rotors on at the last brake job and they're not grinding or wobbling then there will be enough meat to turn them to get through the next set of pads.

[Q45tech]

The main safety reason is that thinner than mimimum rotors with worn out pads allow the caliper pistons to become over extented, wearing the piston seals leading to a sudden and dramatic loss of brake fluid.

You can cheat on rotor thickness [at your own risk] if you install new pads and and replace pads WAY before you reach minimums.

Not the correct thing to do but in emergenicies as long as you UNDERSTAND the consequences.

For safety reasons we recommend that the brake calipers get rebuilt [new seals, new slider pins, new shims, and cleaned internally] at least every 7 years or 120k.

[ericthered]

I had always thought that thin rotors also meant lower heat capacity, and thus higher temps and longer stopping distances under hard braking....

yes?

[goody90q45]

I had always thought that thin rotors also meant lower heat capacity, and thus higher temps and longer stopping distances under hard braking.... yes?

Yes. There's nothing better than brand new but hopefully the Infiniti engineers took all this into consideration (braking distance, heat retention, warping) when they set the minimum rotor thickness. Assuming that your rotors are above minimum thickness, the real limiter is caliper piston travel. If the rotors are too thin, the caliper pistons overextend and your brake pedal goes to the floor.

To add to Tech's statements- Any mechanic in a shop repairing brakes is a fool if he surfaces a rotor to less than the mimimum thickness. If any mechanic ever offers to surface a couple thousand's below min to get you through a brake job and save a few bucks don't do it. In fact, if he's willing to do that he doesn't care about your safety and I'd be suspicious of all his other work, take my car somewhere else and never come back. If the owner of the vehicle were to get in an accident because of the brakes not only could the shop be sued but the mechanic could be facing up to involuntary manslaughter charges depending on the severity of the driver's injuries.

[elwesso]

With Q rotors you may get 2 good resurfaces out of a nice set of OEM rotors. however, when I got my rotors resurfaced it turns out they were just glazed to all hell so they just had to remove a bunch of caked on brake pad junk and didnt have to remove much metal.