Rear brake pad question


#1

Hi all,

So, I got some new tires today (Pirelli Cinturato P7’s) on my 2012 Subaru Legacy 2.5i Premium. While doing the tires, the tech told me that the front brakes looked great, but the rear pads were getting pretty thin. Is this normal? I always thought front brakes wore out much faster than rears? He said that my calipers were sticking, and my e-brake (electronic) seemed ok.

Just curious why this is? I do have 45k miles on the car with stock pads.


#2

The rear pads are generally thinner than the front ones even when brand new. It would be unusual for calipers to stick (either pistons or slides) on a 2012 model Subaru unless you live in an area that uses a lot of road salt or you’re out on wet/muddy roads a lot.

It’s possible the sticky caliper diagnosis was a wild guess based on pad thickness only.

The park brake uses separate park brake shoes on the rear along with rear pads.

Whether or not your car needs pads I do not know. That depends upon the actual thickness of the pads and if they are needed calipers can be checked for sticking when they are removed for pad replacement.
Offhand, I tend to think the calipers are fine.


#3

@Jman136

Nowadays, rear brakes do far more work than in the past. It’s all about handling and tire contact.

The days of the front brakes doing 80% of the work are long over. By having the rear brakes do more of their share of the work, the front doesn’t nose dive when you apply the brakes. And that means all 4 of the tires maintain good grip on the road, which results in better handling and decent stopping distances

stability control is also part of the reason, but I’m not going to get into that right now

More than likely your rear calipers are just fine. The guy that said your calipers were bad is using old logic. He’s clearly not an expert on modern brakes


#4

“By having the rear brakes do more of their share of the work,”

Curious, how is that done? electronically?


#5

Rear brake pads are usually much smaller than front brake pads and this also leads to faster wear. I live in the snow belt of New York State and the constant spray of snow and salt from the front wheels onto the rear ones also helps eat rear brakes. Up here rear drum brakes last 200,000 miles or more but rear disc brakes typically go 30,000 to 50,000 miles. Rotors in the snow belt, front and rear, also take a beating due to winter conditions and road salt.


#6

Yes, the salt doesn’t help. My last front brake job was required because the rotor had rusted out (you could see holes in it) before the pads were gone.

That could be solved with the proper materials for the rotors??


#7

I can tell the OP that, when I had my 2011 Outback serviced recently, I asked for a brake inspection in view of the 56k miles on the odometer. The mechanic reported that the front pads had 6mm of material remaining on them, and the rear pads had 5mm of material remaining.

It isn’t unusual on modern cars for the rear pads to need replacement before the front pads. That was what a friend of mine experienced last year with his Rav-4, and it appears that I may wind up replacing the rears before the front pads on my Outback are replaced.

However, I do have to add that some cars with drum brakes also exhibited this same trait years ago. When my brother had his '64 VW bug, the rear brake shoes had to be replaced much more often than the front brake shoes.


#8

Curious, how is that done? electronically?

The short answer is Yes, @Bill Russell. The longer answer is the brake system is biased to apply more brake at the rear than would be allowed by the Federal standard. The front is supposed to lock first at all times so the car will remain stable. Rear lock causes a spin. In the old days, that meant the rear brakes did very little work.

If you let the ABS prevent rear lock, you can use the rear brakes more so you get all the advantages @db4690 stated in his post. The ABS includes a fail-safe that biases braking to the front if the ABS has an error or is completely failed.

You also help even out the brake wear in heavy traffic places like LA or Boston and prevent overheating of the front brakes in hilly regions.


#9

Driving conservatively, how many miles could you go with 5mm pad left in the rear and 6mm in the front? I know there are a lot of variables, but was just looking for a rough guess.


#10

^
With my largely rural and highway driving pattern, I think that 8k miles–or maybe 10k miles-- would be possible. If I drove largely in an urban environment, maybe only 5k miles.


#11

Don’t rear brakes just tend to be smaller overall than fronts, rotors and all?


#12

I’ve never owned a 4-disc brake vehicle that had different size rotors in the rear then the front.

Rear brakes can be smaller…most of the braking is done with the front brakes…simple physics…as you brake the center of gravity moves forward.


#13

My wife’s car - 2007 Ford 500 - came with softer brake pads on the rear than on the front. They threw off a lot of dust and wore rapidly. I replaced them with ceramic pads and the dust problem went away.


#14

the tech told me that the front brakes looked great, but the rear pads were getting pretty thin. Is this normal?

Perhaps for a tire shop but I normally wouldn’t recommend replacing brake pads @ 5 mm thickness.

Your front/rear brake wear (6 mm front, 5 mm rear ) is quite even. New brake pad thickness is usually 12 mm for front pads and 10 mm for the rear pads so your brake pads are worn to half of the original thickness but less than half of the usable material remains. The minimum pad thickness is usually 1 mm but replacement is often recommended @ 3 mm to avoid an unscheduled service visit. If your wear sensors begin to rub 500 miles before your next service visit (oil change) your reaction might be to stop at the nearest brake shop instead of your usual shop.

If you have your vehicles maintenance performed at a full service shop they will normally inspect your brake pads and tell you when the pads measure 3 mm or less. You might get 20,000 more miles from your front and rear brake pads.


#15

how many miles could you go with 5mm pad left in the rear and 6mm in the front?

Too many variables affect pad wear. On the rear, given you’ve gotten 45K miles out of the pads, brand new pads have about 8.5mm of lining and you have 5mm left. You used 3.5mm in 46K miles, so you’ve got a good 30K left if driven the same.

On the front, new linings are about 11.5mm thick and you’ve got 6mm so you used 5.5mm of pad in 46K. I’d say you have 25K left.


#16

According to my math, linear pad usage results in pad failure in roughly 65,700 (rear) and 50,200 (front). Did you throw in a “fudge” factor?