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MG MGB Technical - Brake Upgrade

Hi

I am thinking of upgrading the front brakes. can anyone offer advises?

I am thinking of replacing the disks as they are warped and also uprating the pads to V8 pads or greenstuff. Also going to braided hoses

anyone got any comments/ advantages/disadvantages/ recommended brands
Mr Motor

V8 size green stuff will fit in the normal MGB caliper and work with the normal MGB brake discs. It is a good cheap upgrade.

Do you have a servo? If you swop between driving a modern car and your MGB you may find a servo worth while as it will give a similar pedal effort.
DJ Witham


I have put on new standard disks and standard V8 pads, which work well.

However, 3,000 miles on and the V8 pads have worn over the intended area (ie- over the step on to the lower bit in the middle) on the disk. I'm going to leave them as they are though as they still work fine. Just thourght I'd mention it...
Carwyn Beswick

thanks guys

does upgrading the front alter the brake balance enough to warrant upgrading the rear brakes too? are there any recommended shoes that are a 'bolt on' alternative?

I've seen mintex ones for sale for example. Are these made just for racing or will they be ok for road use?
Mr Motor

The MGB's braking system was highly advanced when it was introduced in 1962, consisting of solid 10 3/4" cast iron rotors on the front wheels and 10" X 1 3/4" cast iron drums with single leading shoes on the rear wheels. Properly upgraded, it is fully capable of locking the wheels at high speeds, even against the traction of modern V-rated high-performance tires. Although obviously still adequate for normal driving by today's standards, they can be improved for satisfactory function in high performance driving without resorting to the expense of adapting of an exotic all-wheel vented disc braking system. Installing vented rotors will dissipate heat more quickly and thus forestall brake fade, but will increase undesirable unsprung weight, thus hampering roadholding. Remember, it is not the intention of this article to create an exotic braking system suitable for competition on a race track.
There are several things that can be done to enhance the performance of the original system for use on the street. First, rebuild the brake master cylinder, slave cylinders, and calipers. Be sure to use stainless steel pistons as they will not rust or pit, thus ruining the seals. If you do not wish to do this yourself, White Post Restorations does this using stainless steel pistons, brass sleeves which give a better bite to the seals, and gives a lifetime warranty on their products. They have a website at http://www.whitepost.com . Be aware that US market MGBs used different models of Master Cylinders. The first model (1962-early 1968) had provision for only a single-circuit system, while the subsequent models had provision for safer dual-circuit systems. The 1975-1976 and 1977-1980 models used two different Master Cylinders that were servo-boosted to provide power brakes. These servo-boosted models did not produce more braking power, they simply required less effort at the brake pedal.
Converting a 1974 or earlier car to the later dual circuit servo-boosted Master Cylinder is difficult due to the mounting flange having been turned 90 degrees. The fitting of a modified later pedal box (the pattern of the pedal box mounting holes on the sheet metal flange is different), complete with servo booster that matches this Master Cylinder mounting flange pattern will solve this problem, but be advised that you will also need the later version pedals that were designed to be used with it or the clutch pedal will not depress far enough to disengage the clutch! You will also need to enlarge the pedal hole in the bulkhead. In addition to the aforementioned items, you will need the clutch slave cylinder line from a servo-boosted car, plus the engine compartment brake lines that run from the brake master cylinder to the front wheels and the brake lines that run to the connector under the passenger seat from servo-boosted car. Unfortunately, these later systems are not without their liabilities. Many owners complain that they interfere with the "feel" of the system, producing a somewhat "numb" feel at the pedal. In addition, they project so far into the engine compartment that they make the mounting of dual carburetors difficult and force the mounting of small, restrictive conical air filters.
Next, install a set of Teflon-lined braided stainless steel brake lines. These will not expand under pressure and will result in a firm brake pedal with greater "feel," enabling you to more precisely modulate the braking forces and more easily tell when the brakes are about to lock up. They can be obtained from Brit Tek at http://www.brittek.com (Part # ABK103). Although it is common practice amongst track racers to remove the dust covers to promote greater airflow to the brakes, this is not recommended for a street car as the dust covers protect the rotors and pads from road debris. If you are reconditioning your original rotors, take them to a competent automotive machine shop and have them surface ground to a non-directional 60 microinch finish. Do not use rotors that have a thickness of less than .300". Having them lathe-turned and finished with sandpaper is highly inadvisable as this will promote glazing and squealing.
In recent years much has been made of the use of drilled rotors. They were developed primarily for racing use. Some people think that they're intended to facilitate cooling, but rust quickly builds up in the holes, acting as insulation. Other people think that the holes are for water to be displaced into by the brake pads. The primary purpose of the holes is to reduce unsprung weight in the suspension system. While their reduced unsprung weight makes them a useful modification for the race track, the tendency of the holes to become coated with rust and clogged with brake material make it questionable as to whether or not they are a worthwhile investment for a car intended for use on the street. Since drilling creates stress lines in the vicinity of the holes, they have a tendency to develop a cracking problem. In addition, the more holes drilled into the rotor, the weaker it becomes. To make the reduction in unsprung weight worthwhile, well over a hundred holes have to be drilled ($$), which results in lots of stress lines. All of these holes should be chamfered slightly after surface grinding, then the surface reground (more $$), then the rotor has to be stress-relieved in a furnace (more $$). That's why racing rotors are so expensive. The majority of aftermarket rotors that have far fewer holes drilled in them remain sufficiently strong after drilling so that the stress-relieving process isn't necessary and can be eliminated (thus saving $$$), and are surface-ground afterwards to reduce the need for chamfering (thus saving more $), but in practical terms the total reduction of unsprung weight is insignificant. The brutal truth is that the fewer holes in such rotors are in effect nothing but a cosmetic sales gimmick aimed at the "monkey see, monkey do" market niche. The cross-drilled rotors used by racers have so many holes in them that few would buy them for street use because they'd be too expensive. Directionally grooved slotted rotors offer the advantage of being less prone to becoming clogged with brake pad material and are far more efficient to use centrifugal force to duct water off of the surface, making them the superior choice for street use. They are also far less prone to glazing the brake material. The rotors manufactured by Tarox and Red Dot are of exceptionally good quality, so much so that warpage even at the highest temperatures is a quite rare experience. These are available from the MG Owners Club in the UK. They have a website at http://www.mgownersclub.co.uk/ . They also sell slotted brake drums as well.
Today's brake pads and shoes are available in a wide variety of materials. Materials intended for racing applications are unsuitable for street use as they perform well only when hot. At the temperatures incurred outside of a race track their performance is actually inferior to that of materials intended for street use. Rather than use racing brake material, install a set of MGB GT V8 brake pads in the calipers. They will fit without modification and, due to their larger surface area dissipating heat more easily, are more fade-resistant. Avoid the use of pads made of the Original Equipment organic compounds as they are the least heat resistant, have the poorest coefficient of friction of .32mu, and produce more brake dust.
There are essentially three options for high performance brake friction material. The first and perhaps the most commonly available material marketed for a high performance street application are the Carbon Metallic compounds such as those marketed by Hawk. These seem to come in two categories: those suitable only for racing and those suitable for only street use. Those suitable for street use have a coefficient of friction of .36mu, which is too small an increase in performance (11%) over that of stock materials to make them worth the additional expense. The second choice is the Semi-Organic/Semi-Metallic type. Being more heat resistant than organic compounds, they also have a superior coefficient of friction of .48 mu, a fifty percent improvement over that of stock materials. These are available from Carbotech Engineering. They have a website at http://www.carbotecheng.com . While these may be popular, there is another material which has an equivalent coefficient of friction but yet an even greater resistance to heat: the Carbon Kevlar type (F 1,050). These are available from TSI Automotive (Pads- Part # CKPMGA/B, Shoes- Part # CKSMGA/B). They have a website at http://www.tsimportedautomotive.com . Be advised that whatever material that you choose for the front brakes should also be used on the rear brakes as well so that the coefficients of friction will be equal, otherwise one pair will prematurely lock up under heavy braking.
It is possible that under the heavy braking loads generated by stronger brakes the rear brakes may lock up prematurely, creating tail drift. This can be tuned out of the braking system by installing a proportioning valve or by changing the slave cylinders to ones with a smaller size piston. The latter change may require modifying the rear brake backplate in order to fit the different size slave cylinders. Another solution is the fitting of tires with more grip, although this can be said to be treating the symptom rather than the cause.
Amongst the brake fluids presently available there are three possible candidates. The first, DOT 3, is a poor choice for high performance driving due to its low wet boiling point of F284 (dry boiling point F401) and is now generally considered to be obsolete. Be advised the American DOT 3 brake fluid is formulated differently than British DOT 3 and is incompatible with the Original Equipment natural rubber seals used throughout the brake system. It will slowly but surely dissolve them! The second candidate, DOT 4, is much better with a wet boiling point of (dry boiling point F446). Of the different Brands of DOT 4 brake fluid on the market today, Castrol LMA appears to be the best. The third choice is a synthetic fluid, Valvolene SynPower, which wins with a wet boiling point of F343 (dry boiling point of F513). DOT 5 Silicone-based brake fluid is a poor choice for any automobile as it has problems with air retention, making bleeding of the brake system a real bear, and poor lubrication, sometimes allowing the pistons of calipers and/or slave cylinders to bind in their bores and lock up the wheels. With a boiling point of F500, its performance is inferior to that of Valvolene SynPower. While it is true that silicone-based brake fluid does not absorb water, water still gets into the system through condensation. Because water is heavier than silicone fluid, it will ultimately sink and gather in the lowest point in the system. Should it freeze, line blockage and brake failure becomes possible. Should you decide to use silicone-based brake fluid, be sure that all of the seals are in excellent condition as it will easily find its way past a leaky seal and air will get into the system. Be sure to flush the system with denatured alcohol prior to refilling it with the silicone fluid. Failure to do so will result in the residual glycol-based fluid interacting with the silicone fluid to form a sludge which will destroy the seals in the system, resulting in catastrophic brake failure.
Steve S.

thanks steve, very comprehensive answer and very very useful

I have checked out the midget/sprite general board on their thread regarding green stuff pads. Seems there are alot of boo boys for greenstuff pads and mintex seem to be the order of the day.

also seems all hoses are not the same. Goodridge a name you can trust?
mr motor

on suppliers

has anyone experience of brembo brakes?

cambridge motorsport do disks (rotors) for £20 as a straight swap for original mg ones?
matt

Brembo has always made a good quality product. They supply several F1 (and other) race teams. However, as with many other manufacturers, they have apparently aligned themselves with Asian suppliers for some of their retail products. I recently got a set of rotors for my son's VW which were allegedly Brembo. But stamped on the box was "China".
Bill Boorse

I have Brembo rotors on my GT. Although I replaced them a couple years ago the box was marked "made in EC" or European Community, wherever that is. Which in my opinion probably means some former Eastern Block country and they were too embarreseed to say exactly where. Or they have several manufactering plants and they make their parts in many countries, but only have one sticker for the box? Of course I'm a bit of a sceptic. No problems with them though.

-Jared
Jared Snider

Jared,

Members of the European Community are:
Austria
Belgium
Denmark
Finland
France
Germany
Greece
Italy
Luxembourg
Netherlands
Portugal
Republic of Ireland
Spain
Sweden
United Kingdom of Great Britain and Northern Ireland

Geoff
Geoff King

Let me make one clarification. The primary reason for cross drilling rotors was not for weight reduction - rather it was for out-gassing of the brake pads which could cause a boundry layer to form between the rotor and pad (back in ye old days when cross drilling became popular brake compounds did out-gas). It was also thought to help in the rain, giving water a place to go rather than to stay on the rotor and forming a boundry layer. Moreover, it was to help in cooling the rotor. Of course the engineers had to make a choice knowing that adding mass to the rotor enabled it to absorb more heat and decreasing the mass did the opposite which resulted in brake fade. FWIW, the Brembo rotors used by Porsche, Ferrari and the like have cast-in holes and are stress relieved, but then again the rotors aren't cheap like the ones you can buy for the MGs.
Mike MaGee

This thread was discussed between 19/08/2003 and 21/08/2003

MG MGB Technical index

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