pman6

I've seen people talk about replacing brake pads when the material is the same thickness as the backing plate.

Backing plates are usually ~1/4 inch. That's still a lot of pad material left !

Seems like there's still a good amount of life left in them

what's the reason behind this?

mmarshall

From what I understand, when the pads get that low, you start to have heat-dissapation issues....more so than when they are new and thick. Heat build-up can cause glaze on the pads, and glaze results in loss of braking efficiency. That is one reason why all newer vehicles have "Screechers" (wear-indicators) built into the calipers. A small, specially-treated tab sticks out next to the pads. As the pads wear, the tip of the tab gets closer and closer to the spinning rotor. When the pad is down to what the vehicle's designers consider minimum acceptable thickness, the tab will contact the spinning rotor and produce a screeching sound when the brake-pedal is applied. At that point, it's time to get a brake-job or pad-replacement ASAP.....otherwise, you could ruin an expensive rotor.

GSteg

iTrader: (15)

Indeed you're right. Many Toyota/Lexus have minimum pad thickness of 1mm before they get tossed. Go 2-3mm if it makes you feel better, but 1/4" is way too much pad to be wasted.

mmarshall

Even if it goes past the wear-indicators?

GSteg

iTrader: (15)

Of course not, but when was the last time a wear indicator was placed at the 1/4" mark? Considering new pads are a little under 1/2" thick, it would be crazy for the indicator to go off at 50% life and screech for the next 20k miles. On a Porsche, the wear sensors aren't activated until 3mm is left. Most manufacturer spec their pad's life down to 1-2mm. There is enough cushion room built into the indicator/sensor that I've added 2,000 miles without going below the minimum spec.

Toys4RJill

If I recall correctly. Did the original LS400 not have a bulb on the dash when it was time to change the brake pads?

mmarshall

Perhaps. The early versions tended to have undersized brakes (for the vehicle's weight) that wore rather rapidly and sometimes caused heat buildup and rotor warpage. Other than that, though, the LS400 was as bulletproof as a tank.

Toys4RJill

I never asked if it had undersized brakes. And it wouldn't be bulletproof if there was rotor warpage due to heat build up now would it?

peteharvey

I find that at thicknesses below 1/4", the pad sometimes crumbles and shatters [twice in the past 15 years], resulting in the backing plate directly contacting the brake rotor, so it's a good idea to not let the pads go too thin.

mmarshall

It was hard to find a better-built vehicle, especially at the time. The brake issue was the only minor flaw. He's moved off now, but I had a neighbor not long ago with a 1999 LS400 with more than 250K miles on it......still running reasonably reliably, though with obvious signs of wear.

One of the reasons why Mercedes had so much trouble after the 1Gen LS came out is that not only were they caught flat-footed, but they simply, with the high cost of materials and labor in Germany, could not compete with the LS's quality at a similar price.

My0gr81

To answer your question, without the hyperbole and the needless stories. The light would have needed a sensor to detect how far the pads would have worn to trigger it. Most probably an electrical strip at the caliper that gets sheared when I gets too close to the rotor.

mmarshall

A related question, though, would be if the system has both screechers (wear-tabs) and a sensor-light. It would also have to be a somewhat different warning-light than the red "BRAKE" light that typically indicates either loss of hydraulic pressure in the system or when the parking-brake has not been fully-released.

Toys4RJill

So it looks like the LS400 did indeed have one. It appears that the it would work exactly like you said. A small message would appear on the driver information dispaly.
, so there was no bulb (rear taillights had a bulb that would light up if one was out) The LS430 had it as well. I cannot find the information for the LS460.

This a feature that should be on all cars.

Toys4RJill

I have read that too. My assumption would be that after 1/4 left, going to the brake wear indicator is going to be pretty quick depending on your style of driving.

It appears, via some owners comments that brake wear warning lights for Audi vehicles will come on the dash when 25% is left on the pads.

BMW, according to onwers will have a light come on with 3mm left.

I think 1/4 is a safe bet if getting a maintainance service. This way there is no need to return.

Another thing to consider, on some cars (maybe most as I DO NOT KNOW the answer) there is no rear brake warning. So perhaps at 1/4 is a good time to check the rears too.

pman6

I still have the factory brake pads on there, and I hear a light screech already.

It looks like there's 5mm left. Not sure how thick on the other side of the rotor. Maybe it's the inside pads that are screeching.

But anyway, I bought some Akebonos and will be changing them soon.