I'm bored and semi-knowledgable, so here's a small contribution to the site. Feel free to add your .02c and maybe this'll end up in FAQ section.
Braking basics:
The 240sx is equipped with a power assisted 4 wheel disc (vented front, solid rear) braking system using single piston sliding calipers. Some models came with the Antilock Braking System, which allowed for skidding wheels to lose some of their braking force to maintain optimal traction for braking. The standard fluid is DOT 3, pads semi-metallic, and rotors iron, of course.
Breakdown of the brakes:
When you push in the pedal, a rod attached to the end of your pedal is pushed into the brake booster, which, utilizing vacuum created by the engine, helps push pistons into the master cylinder, forcing fluid from the brake fluid reservoir through the lines and into the backs of the brake caliper pistons, forcing them against the backs of the pads (and using that force, also pulling the floating portion of the caliper toward the rotor, forcing the other pad to rub against the caliper). The brake system has 2 proportioning valves, contrary to most popular belief. One is in the master cylinder itself and is non-adjustable. The other is located on the underside of the car near the differential. Adjustment is not necessary, unless you're using a very heavily biased braking system, or your driving needs (mainly on a track) dictate that you do so.
Common problems and their possible (and probable) causes:
Squealing/howling, etc.-
Mostly at slow speeds in reverse, but depending upon problem severity, all the time and/or intermittent.
This is USUALLY caused by low pads. They have a metal wear indicator which, when rubbed against the rotor, makes a nice big squeal! Simple, eh? New pads usually have about 10mm of material before the backing. It can also be caused by items stuck between the baffle plate and the rotor, improperly cut rotors, warped rotors, glazed or heat cracked pads.
Easy fix: resurface or replace rotors and/or replace pads!
Mushy pedal-
Most of the time it's caused by air in the brake lines or excess moisture in the fluid. Air can get into the system by allowing the fluid in the reservoir to get to low, loose brake line connections, or overheating the fluid to it's boiling point. Moisture gets into the fluid via a poorly sealed master cylinder or reservoir. Brake fluid absorbs moisture from the air, so you should never use brake fluid from a non-sealed container.
Easy fix: This can be simply alleviated by bleeding the brake system with new fluid.
As far as differing DOT levels are concerned, I started typing out what I knew, and decided to link you to this page: It explains it in much more detail than I could, better than I could, and it saves me the effort.
http://www.vtr.org/maintain/brake-fluids.html
edit:copied this article into most recent post in this thread for posterity
Pedal requires excessive effort to brake-
Usually it's a vacuum leak, preventing the brake booster from assisting you in forcing the fluid through the lines. Drive a car with no power brakes, and you'll understand better.
Easy fix: check for vacuum leak and functionality of brake booster, and fix it!
Pedal sinks to floor, NO BRAKES!!-
Say goodbye to your master cylinder (specifically the internal seals). No seals = no pressure = no brakes.
Easy fix: replace master cylinder with rebuilt/reman/new one, or rebuild it yourself.. Bench bleed it first (fill reservoir with good fluid, until no air bubbles come out. Make sure the outlets aren't sucking in air each time you pull out the piston.
Vibration and/or shuddering in brake pedal/steering wheel while braking.-
Warped rotors.
Resurface until true or replace.
On resurfacing (aka cutting or turning), ensure its done on a brake lathe. Many cheapo brake places (like brake depot, etc will swirl rotors to make for a quick resurfacing. It basically involves using a high speed abrasive wheel to make the rotors smooth. This is not what you want. A resurfaced rotor has a rough finish to it, but is perfectly even. For breakin of pads, you want the rough pad to come in contact with a rough rotor, otherwise you'll glaze them.
Glazing is when your pads (and the transferred material onto the rotor) get shiny and smooth. It's basically the pad material melting. Not a good thing for stopping, because it makes the two surfaces smooth.
Brake fluid getting low:
Could be caused by a leaky system (usually the beginnings of a MC failure), or just from the wear of the pads.
Fix: none. look for leaks & monitor the level of your pads.
Brake light on:
Low fluid, ebrake on (or handle relay touching), short at brake fluid level connector.
Figure it out.
Improving your braking:
The MOST important aspect of ANY braking system is the tires.
Go back and read that last line 2 more times.
You can have the trickest Brembo/Alcon/Baer brakes with 14" rotors, project Mu pads, stainless braided lines, etc, but if your tires are 13 year old cracking 165/80R12s (let's assume for the sake of demonstration that the tire/wheel is connected outside of the brakes), then you'll be outstopped by a Geo Metro.
The wider (to a point) and stickier the tire, the better you will stop. Ask anyone who's done a wheel upgrade while keeping their brakes the same(assuming brakes were in good shape).
To brake better, the following things are good to have for the following reasons:
Stainless braided brake lines- replacing stock rubber lines with these reduces the slop in the pedal and gives you a better feel for your brakes. The reason for this is that the stock rubber lines tend to flex when pressure is applied to them. Stainless lines can't flex.
Larger diameter, vented, crossdrilled/slotted, 2 piece, cryotreated or composite rotors.
Larger diameter means less effort needed to stop them. (example: stopping a spinning bike wheel by the tire versus the inner spokes).
Vented is something we have already (for the front), and it allows the rotor to cool more effectively.
Crossdrilling and slotting are popular these days as performance braking upgrades. They can have side effects such as premature pad wear, or rotor cracking, but the upsides are things like improved pad grip and pad ventilation (and cooling).
2 piece rotors are basically rotor outer pieces (which come in contact with pads) that are bolted to aluminum hats (where they slide onto the lugstuds). These are great because they reduce unsprung weight and rotational mass.
Cryotreating basically just makes rotors stronger and more heat & wear resistant.
Composite rotors (usually carbon fiber or some such) are much more exotic, but with price, comes performance.
Lightweight wheels: Also good in reducing rotational mass.
High performance brake pads:
Easily the best upgrade for an otherwide stock system, barring tires. Aftermarket pads range from cheap & useless to exotic and awesome. Racing pads can be too much for the street, as many need to be heated to a certain temperature to be most effective, and many throw off way too much dust to be user friendly for most drivers. There are many pads that make a good compromise between price, performance, and hassle.
Calipers:
the reason everyone likes switching to multi-piston fixed calipers is because they can provide more clamping force, spread more evenly onto the rotor, giving a better feel of the brakes, and more control during braking.
These tend to be the most expensive thing to upgrade, and require the most extra stuff to install (be it new rotors & pads, adapters or otherwise).
Master cylinder: useful for big brake upgrades, esp when using the entire braking system from another car on the S-chassis. (i.e. Z32 MC). Bigger MC bore diameter = more fluid pushed thru.
Caliper Upgrades:
Probably the most common upgrades done on S-chassis braking systems are 180sx/Altima brakes and Z32 fixed-caliper systems.
With the former, simply changing out the front caliper and rotor are sufficient to increase stopping power without compromising brake bias.
With the installation of the Z32 system, it is
vital to install the complete system. Installing only the front calipers will significantly throw off the brake bias of the car and make it more dangerous to drive.
Spacer kits are available for Z32/BNR32 brakes for repositioning of the caliper to accommodate for larger diameter rotors.
-Kevin
this info is intended solely for the users of Zilvia, and is copyrighted 2003 by me, Kevin Pratt. Any use for the purposes of monetary gain and/or reproduction outside of Zilvia.net is prohibited by me without prior approval and/or compensation.