Tech Utopia

PROJECT USED KIT SPECIAL - Brake Upgrade

John Rutter gave a general overview of braking systems and how they work in issue 2 of totalkitcar magazine. Now Graham Bell uses his Quantum project to follow-up with a practical hands-on look at brake system upgrades.

Subjecting your car’s brakes to heavy use generates a lot of heat.

Repeated heavy use that doesn’t give the brakes chance to cool off can result in their temperature rising above the friction material’s operating range, leading to the dreaded brake fade as the overheating brakes loose their ability to slow the car.

Uprated front brakes looking the business and bedded in ready for some rapid retardation.

So what you basically need to do in order to upgrade the brakes to deal with this is to use friction materials that will stand higher temperatures and/or improve the brakes’ ability to cool. And if you use friction materials that have a higher coefficient of friction (µ) even at ‘normal’ temperatures than the 0.3 to 0.4 typical in standard materials you’ll have more powerful brakes in normal use too.

mintex C-Tech discs and pads. Reconditioned calipers and braided brake hose.

These days it’s easy – if you have the money – to get carried away with massive disc conversions and multi-pot alloy calipers, but here we’ll stick to showing the easy, inexpensive way to give your brakes a mild upgrade using direct replacement parts.

DISC WORLD

The first and easiest way of upgrading the performance of disc brakes is to fit some pads that both provide more friction and can withstand higher temperatures than standard pads.

There are lots on the market, but for the Quantum I went to one of the biggest and oldest names in the business - Mintex.

Drilled back plates

With competition success ranging from Le Mans winning Bentleys in the 1920s, through F1, rallying, NASCAR and GT racing, Mintex have a long and distinguished history of high performance braking, and it was Mintex pads that helped an Ultima set a new 0-100-0 world record of 9.8 seconds by stopping it in just 3.6 seconds.

For direct replacement brake upgrades Mintex have their C-Tech range, which caters for a wide variety of cars and offers a range of materials, starting with the M1144 I’ve fitted. The replacement for Mintex’s legendary M171 - widely regarded for many years as the material for fast road and clubman use - M1144 is ideal for fast road and trackday fun, offering quiet operation, good performance from cold and high friction stability (µ around 0.45) up to 450°C.

Segmented nature of Carbotech re-lined brake shoes clearly visible

GROOVY BABY!

Next step up from high performance pads is to fit some discs that will enable you to make better use of them, and here again I was able to upgrade my Quantum’s XR2 brakes thanks to Mintex’s C-Tech range, which offers direct replacement grooved and dimpled discs for a wide variety of cars. And they just happen to come in a nice blue finish that matches my Quantum’s paintwork…

The grooves improve braking both by de-glazing the pads to ensure good initial bite and by allowing easy expulsion of hot gases resulting from the braking process, thereby improving both cooling and frictional contact between pad and disc.

Fully reconditioned and uprated rear brakes waiting for drums.

They also help get rid of water from the brakes in wet conditions, which can be a big advantage on cars whose front brakes are very exposed to spray, such as Sevens, especially if no backplates/stoneguards are fitted. (Incidentally, removing backplates from disc set ups is another cheap and easy way to help get more cooling air to the brakes.)

As for the dimples, these are a safer substitute for the full holes you get in drilled discs, and while they aren’t as efficient at improving cooling they eliminate the problem of stress cracks that can occur round the holes of drilled discs.

Nice black brake drum. Shame about the furry brown suspension components!

HEAT THAT DRUM

These days the trend for uprating a drum braked rear axle is to convert to discs. However, this can involve a lot of work and expense. Consider also that the rear brakes only do about 25% of the braking on front engined/rear drive cars and just 10% on front wheel drive cars and you might prefer to stick with those humble old drums.

That doesn’t stop you from getting better braking though...

PAINT IT BLACK

One easy way to maximise the performance of your drum brakes is to paint them black. Why black? Because of a phenomenon known as black body radiation.

The gist of this is that dark coloured bodies both absorb and dissipate heat more readily that light coloured ones. That’s why the bodywork of a black car gets hotter on sunny days than that of a white car next to it. It’s also why black drums cool quickest.

Red calipers so last year! This year's hot fashion is colour co-ordinating discs.....

Obviously you need paint that will stand the heat, so I sprayed my shiny new drums with VHT caliper paint supplied by Frost, which provides a corrosion resistant finish rated to 900°F/490°C. Frost are currently letting totalkitcar readers have a free copy of their latest catalogue, and it’s packed with stuff useful for kit car builders. Just remember to mention totalkitcar when you ask for it.

HOLY BACKPLATES BATMAN!

Apparently one old performance trick people used with drum brakes was to drill them to improve cooling.

Drilling brake drums requires proper machining to ensure the holes are equally spaced to maintain even balancing, and it’s not something I’d recommend on a road car.

Drilling backplates however is a different matter as it won’t affect strength or balancing, and the place to drill is the channel that runs round them to provide clearance for the inner edge of the drum.

A series of holes (sized to suit the channel) spaced about 25mm apart around this will make it easier for hot gases to escape from the drum/shoe interface during braking and improve air flow to help cooling between times.

Leastways that’s the theory. How much difference it’ll make in practice I don’t know, especially on the Quantum where there’s quite a gap between drum and backplate which should allow some airflow anyway. Probably be more useful on those cars with virtually no gap between drum and backplate, but either way it can’t harm and costs nothing apart from a little time and effort so it’s worth a go.

IF THE SHOE FITS…

One thing that should certainly make a difference is fitting high performance brake shoes. At one time these were as easy to get as high performance pads, but not now. Even Mintex can’t supply them these days, so having gone to one of the largest manufacturers of high performance brakes for the front, for the back I went to one of the smallest, namely Carbotech.

Like the company, Carbotech’s range of ‘off the shelf’ pads and shoes is quite small, but because they offer a relining service they can supply high performance brakes for virtually anything – just so long as you can provide a set of old brakes.

As a result, Carbotech brakes are very big in historic racing, being fitted to a number of race winners including a championship winning DB4, while at the time of writing it looked like Carbotech was also set to be the brake material supplier of choice for the MX5 series.

Carbotech offer a range of lining materials right up to full race, though for the rear of the Quantum they recommended their mildest 912 compound, which combines low noise and dusting with a high coefficient of friction (0.46 to 0.48) from cold up to the sort of temperatures reached during fast road driving and trackday fun.

Although understandably more expensive than standard items, Carbotech shoes provide a way of uprating your drum brakes that’s far easier and cheaper than converting to discs.

THE BRAIDY BUNCH

Standard flexible brake hoses are made using fabric reinforced rubber tube, and when subjected to the pressures generated under heavy braking they expand slightly, meaning some of the effort you put into the brake pedal to move those pistons is wasted in expanding the hoses.

The simple solution is to upgrade to flexibles made with PTFE tubing covered by braided stainless steel, which, because they don’t expand under heavy braking, give you a firmer brake pedal. So considering how soggy the brakes on my Quantum felt it was a surprise to discover it already had these fitted…

A word of warning here regarding braided brake hoses on new kit cars. Many braided hoses aren’t SVA compliant due to having screwed compression joints, but the swaged type are now available so make sure you fit those if you want to keep the SVA men happy.

FLUID MECHANICS

Because most brake fluids are hygroscopic (they absorb moisture from the atmosphere) old brake fluid has a reduced boiling point and under heavy braking can produce a brake pedal that at best feels spongy and at worst goes all the way to the floor without producing any braking. Obviously not a desirable situation...

This is why it’s recommended that brake fluid be replaced every two years, though if you’re going to drive your car hard it makes sense to both replace it more often and to use a brake fluid with a higher boiling point.

The most readily available ‘high performance’ brake fluid is DOT5.1, which is fully compatible with normal DOT 3 & 4 fluids and not much more expensive. DOT5.1 is fine for fast road use and a bit of trackday fun, but for serious track use racing brake fluids such as Castrol SRF are better, though these are far more expensive (£30+ per litre!) and must not be mixed with other fluids.

LATE BRAKING NEWS.

Having had chance to bed everything in and live with my rebuilt and uprated brakes for a few weeks I can report the following.

The once soggy brake pedal is now noticeably firmer and more confidence inspiring.

As is often the case with high performance brake materials and grooved discs, the brakes are now slightly noisier in low speed town use than standard brakes, but you really have to be listening to notice and they’re probably still quieter than the old brakes with their scored discs.

In higher speed use the brakes now have a much keener initial bite once you start applying anything more than gentle pressure, while even from stone cold, high pressure, emergency stop applications result in very impressive deceleration, with those higher coefficients of friction clearly paying dividends.

Braking remained impressive following a few heavy applications in rapid succession, after which it was the back brakes that started to lock up first during a full-on stop, whereas when braking from cold it had been the fronts.

Overall, a definite improvement in braking, and in view of the straightforward fit and modest increase in cost over standard replacement parts I’d say a worthwhile upgrade for anyone building a sporty kit car that’s going to see some spirited driving.

CONTACT INFO

MINTEX.

TMD Friction UK Ltd
PO Box 18,

Hunsworth Lane
Cleckheaton
West Yorkshire
BD19 3UJ
Tel : 01274 854029

www.mintex.co.uk

CARBOTECH

Carbotech-Europe Ltd,

Greenways,

Plumpton,

Penrith,

Cumbria,

CA11 9PA