Brakes again

[Hal88]

My brake light came on again , time for rear brakes now.....I'm tired of changing brakes on this thing.

[FSETH]

How often are you doing it? I bought my X5 with 56k. It now has 133k and I changed pads and rotors once.

[Hal88]

I think maybe 25k mls ago? It seems not too long ago.....and the rears should last longer

[FSETH]

Yeah, that is way too often. Are you hard on them? Do you tow?

[Hal88]

Not hard at all, i drive like a grandma.....and no, I don't tow.
Good thing I know how to replace them myself (thanks to this site) otherwise I'd be in the poorhouse.

[jdd]

You’ll find the brake bias on cars with ABS favours the rear wheels a lot more than cars without ABS. This causes the rear pads to wear much quicker, proportionally to the front compared to older cars without ABS.
The style and type of driving also affects brake pad wear; while you may drive like a grandma, if it’s in a lot of stop start traffic this might account for the high wear.
Also, the type of pads used is probably the biggest influencing factor to pad wear.
With a 50/50 mix of city and highway driving using OEM pads in an auto (driving sensibly), you should be able to get at least 70K miles from a set of pads (front and rear).
BTW, make sure you grease the calliper slide pins with the correct grease when changing pads as not doing this can cause excessive pad wear.

[JCL]

Originally Posted by jdd

You’ll find the brake bias on cars with ABS favours the rear wheels a lot more than cars without ABS. This causes the rear pads to wear much quicker, proportionally to the front compared to older cars without ABS.
The style and type of driving also affects brake pad wear; while you may drive like a grandma, if it’s in a lot of stop start traffic this might account for the high wear.
Also, the type of pads used is probably the biggest influencing factor to pad wear.
With a 50/50 mix of city and highway driving using OEM pads in an auto (driving sensibly), you should be able to get at least 70K miles from a set of pads (front and rear).
BTW, make sure you grease the calliper slide pins with the correct grease when changing pads as not doing this can cause excessive pad wear.

Point 1: You can't change physics. The front brakes do most of the stopping, due to weight transfer. ABS doesn't change that. If it did, stopping distances would be much longer with ABS. ABS shouldn't be intervening much anyway. The only way the rears would wear faster from stopping is if you drove in reverse more than forwards, or put a much softer pad on the rears. What can wear the rear brakes is the traction control, as it will intervene on the rears more than the fronts.

Point 2: Never grease the slide pins. BMW service manuals specifically instruct that the pins are always to be dry, due to the design of the sleeves. Clean them, and ensure the dust caps are in good condition, but don't grease them. Only apply high temperature grease to the ears of the pads where they touch the calipers.

[Hal88]

Yea, that's what I thought, you are not supposed to grease the caliper pins, I read that somewhere.......
Now that I remember the last time they were changed by an indy shop....who knows what pads they put in there.....I'm sure not the best quality.

[JCL]

While the pad composition certainly matters in terms of life, so does the surface finish of the rotor. It is the rotor that wears the pad.

[jdd]

Originally Posted by JCL

Point 1: You can't change physics. The front brakes do most of the stopping, due to weight transfer. ABS doesn't change that. If it did, stopping distances would be much longer with ABS. ABS shouldn't be intervening much anyway. The only way the rears would wear faster from stopping is if you drove in reverse more than forwards, or put a much softer pad on the rears. What can wear the rear brakes is the traction control, as it will intervene on the rears more than the fronts.

Point 2: Never grease the slide pins. BMW service manuals specifically instruct that the pins are always to be dry, due to the design of the sleeves. Clean them, and ensure the dust caps are in good condition, but don't grease them. Only apply high temperature grease to the ears of the pads where they touch the calipers.

Re: Point 2; thanks, it’s handy to know this as every other car I’ve worked on has required the slide pins to be greased. I’m yet to do a set of pads on my X5 but I will remember this when the time comes.

Re: Point 1; I understand what you are saying however; every ABS equipped car I’ve come across has had a higher proportion of rear bias than an equivalent car without ABS. A number of years of circuit racing various cars have provided this experience.
I believe the reasoning behind this is because it is undesirable to have the rear wheels lockup before the front so quite a bit of safety margin is built in so that this can’t happen on non-ABS cars.
With ABS equipped cars, this safety margin is removed and more rear bias applied as it doesn’t matter if the rear wheels reach maximum braking point slightly before the front under heavy braking as the ABS will take care of it.
I know some of the older cars I’ve worked on over the years can do 3 or even 4 sets of front pads to one set of rear pads.
Many newer cars wear front and rear pads at a similar rate and some even wear the rear pads faster than the front. I’m aware some of this is due to pad surface area and in some cases material difference between front and rear, but some of would also be due to the additional rear bias.