Brake Changing Tips, Tricks, and Musts
Well, for most of the day at work I was at the garage going through a full brake change (rotors, pads, & calipers) demo on a '93 Buick Regal GS. Some things I knew, others I suspected, and even more I didn't know (needless to say I got my learn on).
This is mainly geared towards the do-it-yourselfers. After reading some of this, the people who take it to shops may consider doing it themselves now.
This is also from a four disc car.
The pads and rotors should be changed at the same time. The rotors really should be replaced with new rotors, but at the very least the rotors should be resurfaced.
Why should the rotors be replaced with new instead of being resurfaced? Two main reasons. First, the very nature of resurfacing means that material is being taken off the rotor. How much material depends on how bad your rotors are "warped". Taking material away from the rotor will reduce the heat capacity of that rotor, meaning your brakes will fade and heat up quicker. The second main reason is because most shops just suck at resurfacing rotors. Most shops don't check to see if the rotor surface is flat and smooth. Flatness can be determined with a $150 tool called a 'run-out' guage. Smoothness can be determined with a finger nail.
If you do decide to just resurface your rotors, here are some helpful hints and tricks. Before you remove the rotor, mark a single stud with a marker as well as the hole on the rotor where that marked stud went through. Now that the rotor is off, take a wire brush, small Dremel tool, or some other small tool and clean off the hub bearing surface (a lot of shops use a big air compressor with a big sander attachment...this makes it impossible to get around the studs and in the other small tight places). Cleaning the hub bearing surface is crucial since this surface mates flat with the rotor hat (center of the rotor). If the hub bearing surface has rust on it, the surface won't be flat and the rotor will wobble back and forth while moving. This will cause vibration in the pedal and/or steering wheel and cause premature pad and rotor wear. Before you put the rotor back on, make sure the inside hat surface on the rotor has also been cleaned. The chance that two flat mating surfaces will be perfectly parallel to each other is impossible. But to decrease wobble you want the closest possible to parallel. This is why you marked the stud and hole. Since the hub bearing and rotor wear together, you want to align the rotor holes with the exact same studs they were in before you removed the rotor. So to do this, just put the marked stud through the marked hole (simple, eh).
Here are some notes on rotor finish. The rotor surface should be flat (no more than 0.003" each way). If the rotor surface has too much variation, the rotor will wobble as the wheel spins, which causes vibration and premature pad and rotor wear. The rotor surface should also be smooth and have a non-directional (cross-hatched) pattern. To check for smoothness, simply take your finger nail and run it along the rotor (from center to edge). If you can feel the grooves, it ain't smooth. A rough directional surface will act like a screw. When you apply the brakes, the pads will be pulled to the outside of the rotor. This causes premature pad and rotor wear, and could lead to more serious issues if the pull is severe enough.
Regardless if you are using resurfaced or new rotors, the following should be noted. Before you are finished, the rotor surfaces need to be cleaned. The best way to do this is to use a brake parts cleaner, spray it on there, and let it air dry. If you are going to use a semi-metallic brake pad, you can clean the rotor surfaces just with the brake parts cleaner. If you are going to be using an organic or ceramic based brake pad you need to wash the rotor with soap and water (dish soap works the best). It's also a good idea to use soap and water if you are going to be using a semi-metallic brake pad. If you are using a semi-metallic pad you can get away with having a directional rotor surface finish (a lathe gives you this pattern and some new rotors are shipped with this pattern). However, if you are using an organic or ceramic based brake pad, the rotor surface must have a non-direction surface finish. Some new rotors are shipped with a non-directional surface finish. If your new rotor didn't or you are using resurfaced rotors, the easiest way to give your rotor a non-directional surface finish is to take some sand paper (about a 120 grit) and lightly rub it on the rotor surface and run it "a little bit this way and a little bit that way". There are fancier ways of doing this.
So how do you know if your brake pads are semi-metallic or organic/ceramic based? The easiest way to do this is to stick a magnent on the friction side of your brake pads (don't be stupid and stick the magnent on the steel shoe side). If the magnent sticks, than it's a semi-metallic brake pad. If the magnent falls off, than it's an organic or ceramic based brake pad.
When putting the new brake pads in the caliper, you will most likely have to push the pistons back into the caliper. When you do this, open the bleeder screw. The reason why your pistons are extended out of the caliper is because as your pads wear, the pistons extended out more and more so the distance between brake pad and rotor surface remains about the same throughout your pads wear life. The lowest point in your brake system is the calipers. All the shit settles to the bottom. Behind the pistons is hydraulic fluid. If you push in the pistons without opening the bleeder screw, you push all that shit back up into the system. With the bleeder screw open, all that shit exits through the bleeder screw. Before you put the pads in, put some grease on the back of the pads and on the ears (if applicable) of the steel shoe. Some shops will use that 3M tacky spray. NO!!! This tacky spray sticks the brake pad to the caliper. After a while, the shim/insulator will be pulled off the brake pad. This will lead to noise (more about noise later).
Which lube to use? The best lube is a Moly lube. You can use silicone lube, but silicone lube tends to wash off quickly. Moly lube will actually impregnant the metal.
Noise. Brakes ALWAYS make noise. The trick is to have them make noise you can't hear. Any vibrating part will make noise. If you have noise, most likely something wasn't lubed correctly or something wasn't installed correctly.
"Warped" rotors. This seems to be a common complaint on this site. As I mentioned above, the hub bearing surface, rotor hat surfaces, and the rotor surface all have to be cleaned and flat. If they aren't, than the rotor will wobble causing vibrations. There are other things that can cause vibrations. Most rotors today use what is called a composite rotor. A composite rotor uses one mateial for the hat (center part) and another material for the rest of the rotor. This makes the rotors lighter. This has also caused problems. Most shops use an impact wrench when putting the lug nuts back on. No, no, no!!!!!! Lug nuts NEED to be torqued to the FACTORY SPECS! If they are torqued too much, the rotor will become "warped". Also, the lug nuts should be tightened in a star pattern.
If you disconnect the brake line from the caliper, after you reconnect the brake line, you need to bleed the system. If you don't, air will be trapped in your brake lines. If you didn't disconnect the brake lines from the caliper, than you don't have to bleed the system. There are about four ways to bleed the system and at least 32 different procedures. Which procedure you should do will mainly depend on your car and to some extent the method you use for bleeding the system. (I'm not 100% sure on the proper procedure to bleed the LH cars).
Some other things to keep in mind. Since our calipers (and most others) are of a floating design, make sure the caliper moves back and forth on it's guide pins. Make sure the rubber boots on the guide pins aren't worn and make sure them and the guide pins are lubbed. You don't want a caliper seizing up on you. This could cause problems in stopping the car or could cause the brake pad or pads to drag on the rotor. If your pads/rotors/calipers come with any hardware (guide pins, sleeves, etc), make sure you replace those. They are included for a reason.
Also, if someone says that these cars (or any car) never needs to have the brake fluid flushed and changed, laugh in thier face and find someone who is competent. Hydraulic fluid is hydroscopic which means it abosorbs moisture. The older the fluid, the more moisture it will have, and the the more moisture the fluid has the lower it's boiling point is. When the brake fluid boils, you will have a very, very hard time stopping.
Well, I know I forgot something. That was a lot of typing! If I find out that I left something out I will add it. If I need to clarify, I will do what I can.
I have a feeling a lot of our "warpage" problems might be contributed to simple things being over looked.