t2d2

iTrader: (8)

I just received my new Centric 121.44107 (LS400) front rotors and noticed right away that one felt heavier than the other when unboxing them. Sure enough, they weighed in at 19 lb 14 oz & 21 lb 9 oz, respectively, with a listed weight of 23.0 lb. Furthermore, the heavier one is 1mm thicker on each face (10mm vs 9mm) but 2mm less vain thickness (8mm vs 10mm), so the same overall (28mm).

Is it normal to see that much of a discrepancy? I'm happy to have them be quite a bit less than the rated weight, as long as there aren't any durability issues that go along with such loose tolerances. I went with Centric because they were recommended as being a toss-up with OEMs for quality.

t2d2

iTrader: (8)

Also, they have markings on the side of face and the lighter one begins with 121-44107, while the heavier one begins with QA3116. They both go on to specify the 26mm minimum thickness, plus a few other numbers of no significance to me. Searching for QA3116 yields nothing, so I'm not sure what it indicates. They're both in Centric boxes with the correct part number, but I can't help but think the heavier one is a repackaged off-brand. (Edit: Actually, more likely is it was spec'd and branded by Centric for someone else, seeing as they're a big OEM provider supposedly, and brought back under their label for whatever reason.)

FWIW, the stock SC400 front rotor is supposedly 20.8 lb, although I haven't pulled mine off yet to weigh them. At 20.7 lb avg for these Centrics, that bumps the weight loss potential of the LS400 brake upgrade up to 17 lbs, with no rotor weight penalty to offset the lighter aluminum calipers. If one could somehow guarantee getting two of the lighter Centrics, that would be closer to 19 lbs total.

t2d2

iTrader: (8)

I sent an inquiry about it to Centric and am waiting to hear back... While going through the info on their site, I discovered that 121.44107 isn't a newer version of 120.44107, as I had assumed from cross-listings. 121.44107 is "standard" while 120.44107 is the "premium" electro coated version. Hopefully, standard isn't their term for economy, as that would probably mean less than the OEM equivalent quality I was assuming.

Rather than start a new thread for it, here's a loosely related question about the LS400 calipers. My rebuilt set arrived today. I noticed there's a millimeter or two discrepancy in how far the various pistons are pushed in. Is it necessary to have all 4 pistons be pushed in the same distance, or do they only have to be pushed in far enough to insert the pads (which I'm still waiting on) and then they'll equalize themselves under hydraulic pressure?

I figure there's no harm in trying to compress them further with a c-clamp and block of wood while there's no brake fluid to bleed, but I've read that all four need to be compressed simultaneously. Maybe that could be done with a c-clamp on each side and some ambidextrous tightening of both clamps... (Edit: I cut a block of wood to about the size of the brake pads, plus a thin strip of wood for the outside of the caliper to avoid marring the surface, and a big c-clamp made quick work of evening out the piston depth. Whether or not it was important to do so, at least I've got a good blank slate now!)

Blkexcoupe

iTrader: (8)

They'll equalize once pressurized, so there is no real issue there. As long as the pads fit once mounted that is all that matters.

t2d2

iTrader: (8)

What do you mean by "equalize once pressurized"? They're the exact same thickness, so they'll wear down evenly and always be ~2 lbs apart. Which also relates to the last point about fitting the pads being key!

Edit: My bad, you were responding to the part about the caliper pistons, not the rotors. It's been a taxing day!

I heard back from Centric earlier today but didn't have a chance to check in at the time. A very helpful fellow emailed me back and then followed up with a phone call before I even had a chance to reply. He hit me with a ton of info, including details about fine grain casting and vane taper construction, that I couldn't fully digest that quickly... The important points are:

- the different part numbers are due to different batches.

- 10% weight difference is within spec for Centric and Toyota, which is basically my 2 lb difference.

- 121.44107 is their "standard" line which is equivalent to standard/premium offerings from Duralast and the like; Centric doesn't have an economy line, but their "standard" is a bit shy of OEM. They hit the price point via less expensive casting methods that limit cooling effectiveness ever so slightly, but not enough to be noticed in street driving. If I were to do it again, I'd probably go with 120.44107 or OEM/Brembo, but these will probably be fine.

- 23.0 lbs is the rating for max shipped weight, so my SC rotors will probably be lighter than the rated 20.8 lbs shipping spec, as well.

t2d2

iTrader: (8)

This being my first caliper and rotor change, the "doh!" moments are all starting to lead toward a clearer picture of how the whole system fits together. I was looking over the calipers and trying to figure out what retracts the pads when pressure is released from the pistons. Nothing! Now I understand the comments about how pads normally drag slightly on the rotors. (Side note: Why did no one design a spring-loaded pad system to prolong pad and rotor life?) That's the back story explanation to Blkexcoupe's response about the pistons equalizing once pressure is applied. They only retract a fraction of an inch to release pressure on the pad against the rotor, and don't retract fully unless manually done so for pad changes.

oldManTan

yep, calipers are pretty dumb

t2d2

iTrader: (8)

Just gotta be smarter than the caliper.

alltrac

The spring would lose tension after being heat cycled a million times and probably break. Even when they aren't being abused, brakes are still hot. A little bit of drag is a good thing. The immediate feel in the brake pedal is because the pad is on the disk. If the pad is not touching at all, that difference has to be made up somewhere, usually in 2-3 full pedal strokes. You will see when you put the calipers and new pads on and hit the brake the first time.

Brake pad change is easy, just remove one bolt from the caliper that holds it to the bracket, and the caliper will hinge open making the change literally a 1 bolt job. OK, 1 bolt of 5 nuts if you count taking the wheel off. A pair of large C- Clamp vise grips make pushing the pistons back in easy too.

oldManTan

that's what gives us the right to call them dumb

t2d2

iTrader: (8)

Fair point. Use a titanium spring then. Or how about a magnet between the pad (either semi-metallic pad or metallic shim) and piston? There's got to be some way of easily retracting the pad that naturally wants to be free and clear of a moving object (the rotor).

I disagree with your reasoning there. The multiple pedal strokes are only necessary because the pistons have been retracted fully after a pad change, but they don't retract that far in actual use. The immediate response is because the piston is very close to the rotor, not because the pad is already dragging. So, that doesn't make pad drag a good thing. It's just an acceptable thing, out of laziness as far as I can tell.

I wonder if part of the thinking is to not have heat being transferred from the pad to the piston to the brake fluid constantly when you let off the brakes? I've seen the track numbers on how rapidly heat dissipates (500+ degrees) within half an inch of the rotor, so a few mm of air space between the pad and piston could perhaps make a big difference.

True for the stock brakes, but keep in mind the original topic of this thread stems from switching to LS400 brakes with the fixed caliper. Now that I have a much clearer picture of how they work, they're actually quite a bit easier to change the pads on. Just unclip the pins and slide them out!