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Technical Information (MGB 18)
Brake Modifications

Last Modified - 8/5/00

We still believe that our original statement that the MGB braking system can be improved at a reasonable cost still holds true. Unless you are racing, we see no reason to spend $1,000 to $2,000 on 4 pot calipers and thicker/vented brake rotor equipment.

This update brings you some new information (mainly brake pad material chooses) as well as retaining old information which we still believe to be applicable.

Brake Master Cylinder
A new brake master cylinder for the 63-67 MGB single line system is still relatively cheap, therefore, if your cylinder is beyond the simple rebuilding stage, replace it. New brake master cylinders for the 68 through 74, 75-76, and 77-80 MGBs are more expensive. Rebuilt cylinders for these models are readily available, also cheaper, through various vendors and are usually rebored and fitted with oversize seals.* Another rebuilding method is to have the unit resleeved with either stainless steel or brass sleeves, thereby retaining the original bore diameter, this obviously becomes a more expensive proposition. From the experts, brass has a more desirable finish than stainless steel and also has better seal bite characteristics.

Brake Master Cylinder Applications


Part Number

Part Number

Part Number








* 53-0972




* 53-1003BS




* 53-1003WS

Brake master cylinders applicable to the 75-76 and 77-80 models are basically not interchangeable. Yes they will fit, although, they do have different brake fluid reservoirs. The hidden problem lies with the difference in the internal floating pressure differential piston design and the activation of the brake failure warning light. The 75-76 brake master cylinder can be recognized by the wedge shape brake fluid reservoir and black brake pressure fail switch. This switch when grounded (see diagram 1) by the lateral movement of the floating piston (due to independent hydraulic line pressure loss in the front or rear brake system) the dash light bulb ground circuit is activated. When the brake pedal is released the floating piston self centers and the dash light goes out.

The 77-80 brake master cylinder can be recognized by the rectangular shaped brake fluid reservoir and white brake pressure failure switch. This switch is simply a make and break contact switch (see diagram 2). Again, with sufficient lateral movement of the floating piston, the switch probe will fall into the detent and complete the circuit to the brake failure light

This type of circuit is not self healing and the switch has to be removed to allow the floating piston to self center, until this is done, the brake failure warning light will remain on.

Brake Calipers
OEM brake calipers are more than adequate for street performance. Unfortunately, should they need resleeving, you will find it very expensive, in which case I would suggest locating a good used set, rebuilding and replacing the caliper pistons as necessary.

Wheel Cylinders
Currently, the 0.800" replacement wheel cylinders for the MGB roadsters are very cheap to replace, since the price is low it makes more sense to replace them rather than rekit them.

The 0.875" MGBGT replacement wheel cylinders command a higher price, but here again I prefer to replace than rekit. Trying to achieve the desired bore finish is a major drawback when honing out the existing wheel cylinder bore. A more expensive proposition is to have the cylinders resleeved as outlined above.

Rear Wheel Cylinder Sizes


OEM Part Number

Moss Part Number

All Roadsters

GWC1103 (L4241-575)



GWC1122 (L4241-942)


These two wheel cylinders fit their appropriate backplates, however, existing backplates can be modified to accept either cylinder.

If you are experiencing rear wheel lockup under heavy braking, smaller wheel cylinders are available which, will result in less lb/in 2 cylinder actuating pressure, however, as you will read later, a better approach is to increase the braking effort of the front disc brakes. More efficient braking up front will result in lower hydraulic line pressures with less chance of rear brake lock up.

Alternate Rear Wheel Cylinder Sizes

OEM Part Number

Moss Part Number


GWC1102 (L4241-596)



GWC1129 (L4241-193)

(Requires slight backplate modification)


GWC1101 (L4241-075)



Brake Hoses
Definitely replace front and rear brake hoses with stainless steel, teflon lined type (Moss Part # 182-228).

Brake Rotors
We do not recommend re-machining brake rotors. OEM thickness (0.345") should be maintained where possible. If you must re-machine (0.300" minimum thickness) your old brake rotors then they should be non-directional finished, simply machining the brake rotors the conventional way will result in a directional finish much like that of an old gramophone record, this type of finish will promote glazing and brake pad squeal. Be sure that the brake rotors are hand finished (usually 40-60 micro-inch) with No 120-grit sandpaper.

In 1994 British Automotive introduced angular grooved brake rotors, we continued to sell these into 1996, at that time we re-evaluated the situation and concluded that, besides serving as a brake pad wear indicator, that by simply machining a channel in the brake pad we could achieve the same results. During 1998 we were in a position to further evaluate this procedure and found, upon examination, that the channel in many of the brake pads, which we had previously installed, had become blocked over time with brake pad material. The more brake pad wear that was evident, the more the channel was blocked with transferred pad material.

Based upon the above, we have reintroduced brake rotor set part # BTB387/DG. The DG standing for "directional groove". Our original DG brake rotors had 6 grooves machined on both sides of each brake rotor. Current DG brake rotors have 4 grooves per side. These "Brembo" rotors are surface ground to 60 micro-inch. FYI the MGB factory workshop manual specifies that brake rotors be surface ground to 63 micro-inch. I have seen 3 methods of reading surface finishes: RA (roughness average), RMS (roughness mean surface), and AA (average area) all expressed in micro-inches. To convert RA to RMS multiply RA by 1.11. That is all I know.

These angular grooves are essential when using today's modern brake pads. They allow gas buildup, between the brake pad and rotor, to escape, as well as channeling away water, brake dust and debris. This kind of brake rotor is preferred over the cross-drilled type brake rotor. The brake pad channel is still retained, with its primary function serving as a wear indicator.

We would now like to present more information on MGB brake pad choices for both Street-Street Performance and Racing.

First of all, brake pads containing asbestos are a thing of the past. I only mention them here as a reminder of their past performance, rather like a belated obituary.

Brake pads containing asbestos were capable of absorbing lots of heat without burning, however, they would begin to glaze as low as 250 degrees F, thereby reducing their coefficient of fiction (COF), and as temperatures reached 350 degrees F, fading would become apparent. Sustained high temperatures would form a glaze deep enough into the pad material that they would, in many cases, never recover. On top of this we knew how inefficient this material became when wet. It is estimated that asbestos brake pads under these conditions lost almost 2/3 of their COF. "May they rest in peace."

We don't know how lucky we were (back in the early 60s) having OEM front brake disc systems on both the MGA and MGB as standard equipment. Numerous vehicle manufacturers offered this set up as an optional sports extra, while others continued on with regular brake drum systems well into the early 70s. Next time you are into replacing the front brake pads on your MGB, please don't compromise; use a quality brake pad set.

The modern performance brake pad choices of today are: 1) Carbon Metallic (a registered trademark of "Performance Friction Corporation"), 2) Carbon Kevlar, 3) Hawk Ferro Carbon (formally known as Carbotic), and 4) Ceramic.

British Automotive exclusively promotes and sells Carbon Kevlar RS-4 compound brake pads. With many years of sales and feedback from customers, we have decided to offer this brake pad material as the only choice. If you decide that you would prefer a different brake pad compound, you will have to contact one of the appropriate companies mentioned below.


1-Carbon Metallic is "Performance Friction Corporation's brand name for its brake pads. These are completely different from organic or semi-metallic pads. They offer superior braking pedal feel and longer life without fade at high temperatures. As the name implies, they are of Carbon Metallic composition as opposed to being organically based. Carbon Metallic contains no asbestos, no kevlar and no lead. Organic and semi-metallic pads use clay as a filler to cut costs which sacrifices performance.


Carbon Metallic brake pads meet Federal Motor Vehicle Safety Standard 105. Not all brake pads on the market meet these stringent standards. They are also Original Equipment on over 2,000,000 Ford and GM vehicles. Carbon Metallic is the safest pad you can buy. They are integrally molded using Ionic Fusion system and have the highest shear strength in the brake industry. Carbon Metallic pads are completely ABS compatible. A significant feature of Carbon Metallic pads is that brake force remains consistent throughout pad life.


Performance Friction Carbon Metallic pads are extremely strong, which offers superior brake pedal feel. Less strong organic/organic based or semi-metallic pads actually can compress especially when hot. Carbon Metallic pads continue to grip even when hot, offering consistent braking and pedal feel. There is no good, better or best grade. There is only one Carbon Metallic. This strength also makes Carbon Metallic more compatible with ABS.


Carbon Metallic pads are manufactured to the highest standards from the raw material to the finished product. With a well-maintained system, i.e., properly actuating calipers and brake rotors that are in spec., Carbon Metallic should not make noise.


No! In fleet use many users such as Federal Express, Pepsi Cola, Penske Truck, etc. have drastically reduced their rotor replacements. Rotor wear is reduced with Carbon Metallic pads.


The highest friction brake pads available for street vehicles, for customers who demand ultra high performance braking with low wear, rotor compatibility and fade resistance. Ideal for the driver who demands maximum friction while maintaining excellent everyday street use.

Performance Friction Z-rated High Performance Glycol Based Brake Fluid is an excellent replacement to OEM fluids with a dry boiling point of 550 degrees F. It has extremely low compressibility and excellent lubrication properties. Z-rated fluid is non-corrosive to brake system components and has been proven to be easier on both natural and synthetic rubber seals. Z-Rated Brake Fluid (16oz steel container). The preceding information is courtesy of "Porterfield Enterprises Ltd."

For the MGB we recommend the Z-Rated Compound with a COF in the low 40s. Operating temperatures for this compound are not published and there is no thermal heat barrier between the friction material and backing plate. Therefore, we recommend the use of Z-Rated Brake Fluid with these pads. Contact "Porterfield Enterprises Ltd." at (949)(949) 548-4470548-4470 for brake fluid and brake pads with this compound. The recommendation is for the use of non-directional finished brake rotors, 60RMS or smoother.


2-Carbon Kevlar R-4. A uniquely engineered composite brake pad. This precision design combines Kevlar, Carbon and an array of other high performance materials to make a better brake pad. R-4 Carbon Kevlar is a high COF material 0.485 and incorporated in its design a unique ceramic heat shield integrally molded and designed specifically for high temperature applications (75F to 1500F) to minimize heat transfer. NOT "PRE-BURNISHED."

R-4S: Street High-Performance & Limited Competition. Slightly different compound than R-4. This is the high performance street pad of choice. Very high COF 0.41. No dust*. No squeal (depends on brake disc condition and RMS finish). This is the fastest stopping road pad available (I definitely agree with that statement). Temperature limits 75 F to 1050 F. Thermal heat barrier designed. "PRE-BURNISHED."

R-4E: Endurance Racing Pads with Longer Life. This endurance pad, with special formulation for long races, runs cool and wears longer than our regular R-4. COF 0.475 Temperature limits 75F to 1350F. Great for extended time events. NOT "PRE-BURNISHED" Thermal heat barrier design. The preceding information is courtesy of "Porterfield Enterprises Limited" and edited for applicable content.

* Note: All brake pads emit dust as they wear. Lighter material colors are not as noticeable. Brake dust also has a tendency to adhere to aluminum/alloy wheels more readily and, if not washed from the wheel, will destroy the wheels finish. British Automotive can supply you with the following brake pads in R-4S compound only.

* Part # LD48/KEV.Designed for the factory MGB GTV8 brake caliper assembly, however, they will fit directly into the MGB brake caliper. This oversize pad gives approximately 20% more swept area than the OEM size.

* Part # MGB/KEVLAR. British Automotive custom brake pad. Specifically, designed for the MGB brake caliper with the largest pad size possible. Greater swept area than LD48/KEV.


3- Hawk Ferro Carbon. A Carbon-semi-metallic material offering high torque, low wear and excellent brake disc life. Carbotic materials exhibit stable COFs under hot and cold applications.

Black Y5 Compound. Medium torque and excellent stopping power with extra fade resistance. Provides good pad wear and is brake disc friendly. Recommended for low temperature applications. 200F to 900F. Vehicle weights 2400# or less. High COFs under cold and hot applications.

Blue Compound, HAWK 9012. High torque with superior stopping power. Will not fade. Provides excellent wear and braking at high temperatures 100F to 1000F. Slightly less brake rotor friendly than black compound. Recommended for all heavy brake applications with vehicle weights of 2,400 lbs. to 2,800 lbs. High COFs under cold and hot applications.

HPS. Street replacement high torque pad with temperatures of 75F to 700F. High COF, low dust, brake rotor friendly and silent running.

HP+. Street performance and Rally replacement much higher torque pad with temperatures of 100F to 800F. High COF, Dustier than HPS and brake rotor friendly. Ideal for the fast street driver.

It is recommended that the MGB brake rotors with their OEM 0.345" thickness be replaced rather than re-machined. The minimum thickness regrind is set at 0.300" a 0.045" difference.

When installing new Hawk brake pads and new brake rotors together as pairs, it is OK to use swirl finished rotors. However, if you ignore the recommendation about installing new brake rotors and decide that it is cheaper to have them re-machined, then they must be directionally cut with the surface finish being as smooth as possible, the emphasis being on smoother the better. Most Hawk brake pad compounds are "PRE-BURNISHED", however should additional burnishing be required for a particular compound, instructions will be supplied with the brake pad set.

Also, Removing brake pad material build-up on used brake rotor surfaces when changing compounds or brands of brake pads will assure the proper transfer of friction material on to the brake disc surface and increase the performance and wear life of both brake pad and brake rotor.

OEM sized brake pad no thermal heat barrier Part# HB132 (Black Y5 or Blue Compound)

OEM sized brake pad with thermal heat barrier Part# CT27TE (Blue Compound) The preceding information is provided courtesy of "CARBOTECH Engineering" and edited for applicable content. Please contact them at (954) 493-9669 for brake pads using these materials.


4- Ceramic. Ceramic filled brake pads are one of the newest friction materials being marketed. At the moment I know of no company offering this material choice for the MGB.

Ceramic based pads contain no steel wool or fibers. Instead, ceramic fillers and copper fibers are used to handle higher operating temperatures. Reported to be quieter, more durable, kinder (less abrasive) to rotors and almost dust free. However, all brake pads generate dust as they wear. With the light color of the materials used in this type of pad, brake dust is less visible.

The above information is provided courtesy of "IMPORT CAR"February 2000 issue and edited for applicable content.



Due to the better bite characteristics of modern brake pad materials, brake pedal modulation becomes of primary concern. With larger pad areas and higher coefficient of friction materials, the driver should be aware that front wheel lockup can occur more rapidly if proper pedal techniques, under heavy braking, are not applied.


For more effective rear braking, other than installing larger diameter wheel cylinders, the rear brake lining material can be updated. Presently we have brake shoe sets available lined with the R-4S compound PART # ES437/KEV @ $150.00 (not cheap). However, for street and street performance driving, we have found that the regular brake shoe replacement lining materials, supplied by various Vendors, when used in conjunction with upgraded brake pads, to be more than adequate.

Be sure to have your rear brake drums machined when changing rear brake shoes. To make sure that the brake drum is machined concentric, we use regular road wheel hubs from the tube axle MGB, with the brake drum attached. This setup requires Volkswagen brake drum adapters for machining. OEM brake drum size is 10" with a maximum oversize regrind set at 10.060"


What is the difference in brake fluids?

The most popular types of brake fluid are DOT3 and DOT4, both of which are inexpensive and readily available. Appearing clear to amber in color, DOT3 is a polyglycol fluid; DOT4 can often be a polyglycol, as well. These fluids cause rubber parts of the brake system to swell slightly, improving sealing and preventing leaks. Drawbacks include their high affinity for moisture, causing both a reduction of the boiling point as well as rust and corrosion in the brake system. Also, they have a higher viscosity at low temperature.

Recognized by their purple color, DOT5 fluids are typically silicone-based products, with extremely high boiling points, and have no affinity to moisture. DOT5 fluids are more expensive than polyglycol brake fluids. Due to their air retention properties DOT5 fluids make bleeding air from the braking system more difficult than DOT3 or DOT4 fluids. For this reason, DOT5 fluids cannot be used in ABS systems.

Hydraulic system mineral oil (HSMO), a blend of mineral oil and additives, is easily identified by its green color. This rare fluid is typically the most expensive. HSMOs have the highest boiling points and do not contribute to rust or corrosion. However, HSMOs are not compatible with silicone-based or polyglycol fluids.

Although developed for the consumer market, DOT4 brake fluid has found wide usage on the NASCAR racing circuit for its high boiling point (446 degrees F) and increased corrosion resistance.

We continue to use Castrol LMA. However, regardless of the type of brake fluid used, proper maintenance is the key to ensuring your brakes operate properly when you need them. It is recommended that the brake fluid be flushed out and changed at one to two year intervals. Always keep your brake master cylinder fully topped up.

Brake fade.
Brake fade in association with a firm brake pedal, especially under heavy braking, and with increasing brake pedal pressure, is usually the result of glazed brake rotors and or brake pads, either of these two conditions reduces the friction that is required between the brake pads and brake rotor to effectively bring the vehicle to a stop within a reasonable distance. However, we have found numerous MGBs that have had the following: Seized rear brake wheel cylinders, collapsed front brake hoses, hydraulic problems within the brake master cylinder, and seized brake caliper pistons (normally a retraction problem)

All of the above increase brake pedal pressures, relative to stopping the vehicle within a reasonable distance. So be sure to check these items out first.

Brake pedal fade.
This condition is a hydraulic related problem with either brake fluid loss, the inability of the brake master cylinder seals to maintain hydraulic line pressure or even brake fluid "boiling".












Brake Rotor (Set)





MGBGTV8 Brake Pad (Set)





Brake Pad Retaining Kit
Caliper Locking Plates





L/H Rebuilt Brake Caliper
Rebuildable Core Charge (Included)





R/H Rebuilt Brake Caliper
Rebuildable Core Charge (Included)





OEM Brake Shoe (Set)





Stainless Steel Brake Hose (Set)





All Roadster W/Cyl @ 17.95




180 645

All GT W/Cyl @ 40.46





63-67 Brake Master Cylinder





68-74 Brake Master Cylinder





75-76 Brake Master Cylinder
Use 53-1003BS





77-80 Brake Master Cylinder





68-74 Rebuilt Brake M/Cylinder
Rebuildable Core Charge





75-76 Rebuilt Brake M/Cylinder





77-80 Rebuilt Brake M/Cylinder
Rebuildable Core Charge





Hub Bearing Kit @ 19.75





Hub Bearing 2 of each
0.030", 0.010", 0.005", & 0.003"



We highly recommend that you carry out brake rotor and brake pad replacement using the appropriate workshop manual; i.e., Chilton, Haynes or Bentley etc. We also recommend that you service or replace front hub bearings at the same time.

The most convenient method for replacing or servicing front hub bearing or service is without the brake rotor attached to the hub and carried out as follows:

After thoroughly cleaning hub components, assemble the oil seal collar, inner bearing, tapered sleeve and shims 0.030" and 0.010" (2) on the spindle shaft. Apply a film of oil to the inner bearing, likewise the outer bearing, and assemble the hub along with the outer bearing, washer and nut. After tightening the nut, check for correct end float (0.002"-0.004"). To achieve this, use a selection of the provided shims, as well as your old shims, It is relatively easy to carry this out on a regular disc wheel hub, but is much more frustrating on a wire wheel hub. Assemble brake rotor to the hub and install on the spindle with the appropriate number of shims, fit outer bearing, washer and nut. Check for brake rotor "run out" (0.006"). Should this "run out" be greater than the specified amount, remove and reposition the brake rotor on the hub. Keep repositioning, if necessary, until the correct "run out", or the lowest figure, is achieved. If the brake rotor "run out" is still greater than the specified amount it will be necessary to have the brake rotors remachined (see previous information).

Follow the appropriate workshop manual instructions for brake rotor and brake pad replacement.