brake issue

Sometime ago, my back brake sensor is broken. The mechanic said it's normal to have brake warning light on because of it. After there are plenty of brake pad left at the rear, I didn't replace it for some time.
Then come this month and I realize the front brake doesn't sound right. Checked without unmounting the tire, there seems low pad but not too little. Dragged for 2 more weeks and finally replaced it DIY today. To my surprise, the inner side of pads are totally worn out. On the passenger side, the inner pad even make rotor circle cuts. I have to replace the pads today. But I know I need to replace rotor immediately as well. But the back brake pads seems not much touched. So my questions are:
1. how come the braking won't affect the back brakes? Is there any more issue?
2. when I replace rotor, should I replace both together given one passenger side inner surface is bad?
3. is there a problem to let the new pads run for a week until I get the new rotors then reuse these pads on the new rotor?
4. I heard resurface rotor cost $10 each if you take out rotor by yourself. Should I resurface or replace? resurface both rotors?
5. should I buy micrometer to measure the thickness of rotor?
6. autozone has front rotor Price: $38.99/each. Is there any better after market parts sites?
7. Bought a 4 Allen bit set for the brake pad replacement project and 36mm socket for oil filter. Is there any wrench set with good price/value ratio I can buy? It seems I need 16mm, 17mm & associated wrench (3/8, 1/2, etc) for rotor and oil change.

Thanks.

Originally Posted by yxd0018

Sometime ago, my back brake sensor is broken. The mechanic said it's normal to have brake warning light on because of it. After there are plenty of brake pad left at the rear, I didn't replace it for some time.
Then come this month and I realize the front brake doesn't sound right. Checked without unmounting the tire, there seems low pad but not too little. Dragged for 2 more weeks and finally replaced it DIY today. To my surprise, the inner side of pads are totally worn out. On the passenger side, the inner pad even make rotor circle cuts. I have to replace the pads today. But I know I need to replace rotor immediately as well. But the back brake pads seems not much touched. So my questions are:
1. how come the braking won't affect the back brakes? Is there any more issue?

I'm not sure what you mean by this.

2. when I replace rotor, should I replace both together given one passenger side inner surface is bad?

Yes, always replace brake components symmetrically on each axle.

3. is there a problem to let the new pads run for a week until I get the new rotors then reuse these pads on the new rotor?

You'll run the risk of damaging the new pads depending how bad the rotors are.

4. I heard resurface rotor cost $10 each if you take out rotor by yourself. Should I resurface or replace? resurface both rotors?

Replace, they're not that pricey.

5. should I buy micrometer to measure the thickness of rotor?

Not an issue if they're being replaced. And if they're badly grooved they need replaceing anyways.

6. autozone has front rotor Price: $38.99/each. Is there any better after market parts sites?

http://www.fcpgroton.com, www.pelicanparts.com

Get Brembo or Zimmerman blank rotors (no cross drillings or slots)

7. Bought a 4 Allen bit set for the brake pad replacement project and 36mm socket for oil filter. Is there any wrench set with good price/value ratio I can buy? It seems I need 16mm, 17mm & associated wrench (3/8, 1/2, etc) for rotor and oil change.

Thanks.

For tools, I always get the best I can afford, saves me a lot of trouble in the long run. I try to get good quality tools when they're on sale, opposed to when I 'need' them for jobs.



Ed.

Thanks for quick answer.
#1, what I meant is I always think when you press brake, it applies braking force on all 4 brakes, 2 front, 2 back. But because my back brake pad seems not touched much, does that mean all braking force is applied only to the front pads? Is it normal?
#3 I don't have a choice but to use the new pads. I cannot use good pad on one side and bad one on the other side. Later if I find the surface of pad is smooth, does it mean it's not damaged?
#6 On fcpeuro site, the following are of the same price before discount. But after discount, Meyle is 1/2 of price of brembo. I might buy 2 Myele of the price of one brembo if there is not too big difference.
Brembo 34111160674, after $60
Meyle 40406129, after $30
On pelicanparts site, Zimmermann Coat Z cost $48/each.
#7 what are you using for DIY auto maintenance?

Thanks a lot.

#8 on the side, is there really any difference between front brake sensor and rear brake sensor. As I use rear one for the front at this moment.

Don't know, but realoem.com is a great source to check little questions like that.

addional to #1 I see my rear rotor only has 1 disc comparing with front 2-disc rotor. Is it normal? I see some site has both 1-disc and 2-disc rear rotor listed.

on the side, from oemparts, I couldn't find this spring pipe out of filter cartridge. Anyone know the name in the graph?

Edit: Called part dept of dealer, this part is called rubber boot. Online cost $20 and dealer charge $60

Originally Posted by yxd0018

addional to #1 I see my rear rotor only has 1 disc comparing with front 2-disc rotor. Is it normal? I see some site has both 1-disc and 2-disc rear rotor listed.

Yes, it is perfectly normal.

They are both considered single disc. The front one is ventilated (the ribbed slot in the middle, but it's all one piece), the rear one isn't. Since the front brakes do about 80% of the braking, they heat up a lot more than the rear and need the ventilation slots to cool them down. That's also why you have brake ducts from below the bumper directing air onto the front brake discs but none on the rear.

Thanks for the clarification. Don't understand why they don't put braking on all wheels evenly. Is it just BMW or almost all the cars?
Just ordered BMW Brake Disc Front Meyle 40406129, $30/each. Hope my new pad won't get destroyed in this week.

Weight transfer.

When you hit the brakes, more weight is loaded onto the front tires, which in turn gives them more grip.

If your brakes were exactly 50/50 front/rear, your back brakes would want to lock up every time you stopped quickly or braked in a turn.

Sent from my LG Revolution 4G using BimmerApp

Originally Posted by yxd0018

#8 on the side, is there really any difference between front brake sensor and rear brake sensor. As I use rear one for the front at this moment.

IIRC, the only difference between the front and rear sensors is the length of the wire.

....and now to *really* confuse the #@!^%## out of everybody....

most vehicles use a splt brake design of some sort to keep the brake pressure equal to all 4 wheels, but will also 'default' if one of the wheels loses pressure from a seal loss.

throw in abs and this whole thing becomes even more confusing for the lay-person. however, bottom line, don't worry about how the brakes work. it's all done by majic, k??

and chad, i believe that you mean 'load transfer', not weight. (technicalities, i know....buuuut....)



df

Don't bother Chad. He's out hunting peasants.

Technicality. You see them used interchangeably all the time.

Sent from my LG Revolution 4G using BimmerApp

Originally Posted by yxd0018

To my surprise, the inner side of pads are totally worn out. On the passenger side, the inner pad even make rotor circle cuts.

Is there any wrench set with good price/value ratio I can buy? It seems I need 16mm, 17mm & associated wrench (3/8, 1/2, etc) for rotor and oil change.

Thanks.

The calipers are supposed to "float" on the guide bolts that hold the calipers to the caliper mounting bracket. This allows the calipers to center so that the pads wear evenly. For this to happen reliably the guide bolts need to be smooth and properly lubricated. If not the caliper doesn't center and you get uneven pad wear on the inner or outer pad. I suspect your have been run dry for a long time and have steps worn into them that the calipers are hanging up on and not centering.

For the home DIY'er Harbor Freight tools are adequate and cheap if you haven't got much to invest. They have a combo wrench set for $25 that includes about every size you need including the 32mm required for the water pump nut.

"1. how come the braking won't affect the back brakes? Is there any more issue?"

Front and rear brake pads often wear at different rates, but it is possible that your rear brakes are not working normally. E36s are 13-20 years old now, and depending on whether the brake fluid has been routinely flushed, you could have rear caliper(s) freezing up from internal corrosion. A very rough check is, after you have driven it a while using the brakes, (carefully) feel how hot the brake rotors are at all four corners. If one is significantly colder than the others, you have a frozen caliper at that wheel.

Thanks dc_wright.
From the diagram http://realoem.com/bmw/showparts.do?...69&hg=34&fg=05 can you indicate where is guide bolt? Is it the sliding channel on the caliper where the brake pads sits? I might need to check when I replace the rotor. I can use brake grease to lubricate it, right?
Since this incident, I cannot just look at outer brake pads for thinkness any more. But with the tire mounted, how do you check inner brake pads regularly? Of course, brake sensor helps but I need to verify it with eyes.

Thanks JKRIT, I will check tonight. For frozen caliper, if I take out rear brake caliper and clean it and put some brake grease on it, will it be enough?
I haven't flush brake fluid ever. When I changed brake pads, I see brake fluid is clear and sufficient. Is there any sign for me to flush brake fluid? Can the flush be done DIY?

In that diagram the part labelled GUIDING BOLT (#6) is the guide bolt.

Thanks. It's a little bit hard to put these guiding blot into the hole with heavy caliper. I didn't put grease on it. Should I use grease to lubricate it? How can I make sure the bolt is inserted properly so that the caliper is centered?

Originally Posted by yxd0018

Thanks. It's a little bit hard to put these guiding blot into the hole with heavy caliper. I didn't put grease on it. Should I use grease to lubricate it? How can I make sure the bolt is inserted properly so that the caliper is centered?

Yes, use a product like these.

do not *ever* use chassis grease on a brake system. the stuff like ed linked is fine, as it is designed for brake systems, but remember, more is not better.

make sure the parts are clean and free of dirt and debris first, then apply just enough lube to keep the slideds moving freely.

far, far to often i have taken apart too many brake systems that were improperly lubed which led to premature failure/contamination of the brakes.





df

I use the packaged brake grease bought from autozone, not chassis grease. I know the graphite-based grease is heat resistant. I think 1 package is enough for both pairs of pads.

...hoping you really didn't put brake grease on the pads...

Originally Posted by yxd0018

Thanks. It's a little bit hard to put these guiding blot into the hole with heavy caliper. I didn't put grease on it. Should I use grease to lubricate it? How can I make sure the bolt is inserted properly so that the caliper is centered?

They are a precision fit so it just takes some care in lining things up. Just make certain that a smooth and properly lubricated guide bolt is inserted and tightened to the correct torque value. This should ensure the caliper is able to travel laterally and center itself properly. If done correctly the caliper will find its way to a centered position on its own as you drive and use the brakes.