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Retro Cars - Ask The Experts

ASK THE EXPERTS

YOUR QUESTIONS ANSWERED...

Slamming on the Anchors

This month we head over to Taiwan to ask Dan Newton, boss of PB Brakes, all your questions...

What are brake pads made of?

Brake pads can be made from a variety of different materials. Your standard street compound pads are usually a non-metallic composite of various synthetic materials. They offer great cold bite and very low noise, but the drawbacks are they lack friction and will start to fade at relatively low temperatures. At the other end of the scale you have race compounds, which are either fully metallic or ceramic in composition. They offer much higher levels of friction and are a lot less susceptible to fade, but usually need warming up to optimal temperature in order to work properly. The cold bite is poor, they munch down your discs like there's no tomorrow, can be quite noisy, and you'll be lucky to get 1000 miles out of them. Great on the track, awful on the street. A good middle-ground option is a sport compound pad. Made from semi-metallic materials, the cold bite is good, and the warm bite is even better. You may or may not get a little noise depending on the application, but it's a small price to pay for big gains in friction and reduced fade.

 

What does the DOT mean in brake fluid and what should I look for?

DOT is a system created by the Department Of Transport in the US to arade brake fluids based on their boiling points. DOT4 is the one you want to go for as it's minimum boiling point is 230°C, more than enough for street applications. DOT5 has a higher boiling point, but it's silicone based, which isn't suitable for most braking systems.

 

Why do all cars have bigger brakes on the front than on the back even when they're rear wheel drive?

The reason for that is the front of the car is usually where the oily bit goes, so it's already heavier than the rear without passengers. Then combine that with the fact that the weight of the vehicle shifts to the front when you brake, and it means you need more stopping power on the front end to slow the car down effectively. This is why the brake bias on most front-engine cars is around about 70-percent front and 30--percent rear.

 

Can you get uprated drum brakes?

Not really. Drum brakes on passenger cars are pretty much obsolete these days, so they aren't really worth upgrading. You're best off with a disc brake conversion kit instead.

 

Why is it important to change your brake fluid regularly?

Glycol-based brake fluid is hydroscopic so it loves to absorb moisture, which is always going to find a way into the brake system via micro pores in the cap, lines and seals. This is a bad thing since it dramatically reduces the boiling temperature of the brake fluid - 3-percent water in DOT4 fluid can reduce the boiling point by up to 50-percent! That's dangerous because bubbles are compressible, which causes at best a spongy pedal feeling, and in extreme cases it may go all the way to the floor without actually stopping the car!

 

Why are bigger discs better than smaller discs?

One word - torque! When you increase the diameter of the disc, the amount of braking torque also exponentially increases. So in theory the bigger the disc, the faster you'll stop. However, there is a limit as to how big you can go. You're limited by how much grip your tyres allow, once your discs are over a certain size you'll brake so hard that the ABS will initiate in order to prevent the tyres from losing traction, and whatever gains you made are out the window. Brake pads can also be a limiting factor as your bog-standard street compound will just melt if subjected to more torque than it can handle. You also need to consider that brake discs are fairly heavy items, and increasing the weight that each wheel needs to rotate is going to have a noticeable effect on your acceleration. This maximum recommend size of discs depends on the car, but generally speaking, heavier cars require larger discs for effective heavier cars require larger discs for effective braking, and lighter cars can get away with running smaller discs.

 

Why do performance brake discs have grooves and holes in them?

There are a couple of reasons for having drilled holes or slots (or both) in your discs. The friction created between the pads and disc produces a lot of heat, which leads to brake fade. The holes and grooves help the heat to escape and keep the discs nice and cool. They also help to channel water and other unwanted material away from the contact surface to maintain maximum friction. The discs are actually cast plain, then once they have been milled down to a smooth surface the pattern is engraved onto them by CNC machine.

 

Why do people fit braided hoses?

Braided hoses comprise of a Teflon inner wall, with strands of stainless steel braided on the outside for increased durability. One advantage is that they expand a lot less than your OEM rubber hoses, which allows you a much firmer brake pedal. A firmer brake pedal means more feedback and ultimately better braking. The other big advantage is safety - they're almost bulletproof!

 

Why are some rotors 1-piece items and others 2-piece?

It all comes down to cost really. Your bog-standard OEM discs are usually cast in one solid piece as this is most cost effective way to manufacture them. 1-piece discs are fine for popping down the shops to pick up some milk, but push them too hard or take them on the track and they will fade within a couple of laps at race speed. When you're flying down the straight at 130mph and you hit the brake pedal, the last thing you want is for it to sink right down to the floor because of fade. The best solution is to upgrade to a set of 2-piece discs with billet aluminium centre caps. The contact area between the actual disc and centre cap is minimal, which greatly improves dissipation by allowing the heat to escape, whereas 1-piece discs tend to retain it. Another advantage of having centre caps is aluminium dissipates heat more effectively than steel, and it's a lot lighter too. The next step up would be 2-piece floating rotors. The centre caps on these have even less contact area with the disc, allowing ridiculously efficient cooling. A little overkill for most street cars, but worth every penny for many a full-blown race weapon.

 

Why are ceramic brakes silly money?

Ceramic brake discs are made from a compound of carbon and ceramic. The manufacturing process is complicated and lengthy, with one disc taking around a month to produce. That accounts for some of the cost, and the rest? Well, ceramic brakes are usually sold as add-ons for supercars so they're bound to be over-priced - it's not unusual to be charged 3-grand for an electric window motor on these right?

 

Why are fixed calipers supposed to be better than floating calipers?

Most cars as standard come with floating/ slider calipers that have one, or if you're lucky, two pistons on the inner side of the caliper. So when the hydraulic pressure from the master cylinder forces the piston(s) against the pad, the whole caliper is pulled inward as the pads clamp down on the disc, hence the name 'floating'. One downside of this is the pads on the outer side of the caliper tend to wear unevenly and you end up with something that resembles a door wedge. Another is that since the piston(s) needs to travel so much, the brake pedal can feel spongy and unresponsive. They can also become a bit sticky as they age. On the other hand you have fixed calipers with multiple pistons on either side. Since the pistons are clamping from both sides, the caliper doesn't move and remains 'fixed' in place. This allows for much more even pad wear and a firmer, more responsive pedal feel.

 

What's a hydraulic handbrake?

A hydraulic handbrake replaces the conventional cable operated unit, connects directly to the main brake system, and uses the same hydraulic pressure to clamp the rear calipers. The advantage of that is it's a lot more powerful than the standard part, but they're illegal for street use and an automatic MOT failure. That's because handbrakes are sometimes referred to as 'emergency brakes', if your main brakes fail it acts as a backup device. The law states that the handbrake must be cable operated and fully independent from the main hydraulic brake system.

 

How do I perform the perfect handbrake turn to impress the ladies?

I've often pondered the same question. Ask Ken Block and let me know what he says.

 

What is bleeding brakes and why does it have to be done?

Over time air will find it's way into the brake system, so it needs to be released every couple of years. The problem with having air in the system is, unlike brake fluid, it's compressible. This cause your pedal to become spongy, and if too serious can lead to complete brake failure, so it's really important to bleed the brake lines before it gets to that stage.  

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