Basic Service Guide Part 6
Inspecting your brakes
The MGB is equipped with hydraulically operated disc brakes on the front wheels and 10in diameter drum brakes at the rear. The cable operated hand-brake controls the rear wheels only. When properly maintained in good condition the standard braking system of all MG models will provide effective and safe stopping power. The only major changes to the MGB system occurred in February 1970 when a brake servo was offered as an optional extra and in May 1977 when a dual-circuit system with a direct acting in-line servo was introduced. The MG Midget was never offered with a brake servo and dual-circuit brakes were not introduced on the 1500 MG Midget until May 1978.
Over time or with excessive use, brakes will wear out and this gradual process is all too easily overlooked, especially when their performance deteriorates over a long period. It is therefore essential that you make it a regular habit to inspect your braking system and take note of any changes or reduction in the performance of your brakes when driving.
Wear in disc pads
To make a visual inspection, turn the front wheels on to full lock and look at the pad and calliper assemblies. If the disc pads are worn they will be appear thin, when new, the pads are around 10cm thick, once half of this material has worn away it is a good idea to replace the pads. If you allow the pads to wear right down they will damage the discs which are much more expensive to replace.
The pads shown here are so badly worn and have become so thin that the chrome piston in the calliper is fully extended and clearly visible.
Make it a regular habit to remove the cap of the brake master cylinder reservoir to check the fluid level. If you notice a drop in the brake fluid level then investigate the hydraulic system, the disappearance of fluid indicates a problem with seals, brake pipes, wheel cylinders or even fluid leaking into the servo (if fitted).
If the fluid level is found to have dropped significantly, there is a possibility that the seals are perished or there is leak in the system. Often the first sign of a leaking master cylinder will be brake fluid seeping down the side of the brake pedal inside the foot well. Touching the side of the pedal will result in a brake fluid stain on the fingers. A leaking master cylinder must be replaced or removed and fitted with new rubber seals.
Regularly check brake fluid the level in the master cylinder.
Rear wheel cylinders
Fluid leaking from the rear wheel cylinder will often leave a tell-tale stain around the inside of the brake back plates or even around wheel nuts. Leaking wheel cylinders are best replaced especially if they are already old but you can fit a repair kit of new rubber seals.
The staining around the wheel nuts gives a clue to a rear wheel cylinder leak.
Removal of the road wheel confirms the problem.
Brake pipes and flexible hose
Steel brake pipes can corrode and the unions may become damaged and subsequently leak. Examine brake lines and check that unions are fitted correctly and that no fluid is seeping past. The flexible rubber brake hose to the front callipers and to the rear axle can also deteriorate over time, bend the hose and examine it for any sign of cracking or splits. If the flexible hose is damaged or perished in any way it must be replaced. The flexible hose fitted to the front callipers must be twisted to ensure that it does not come in contact with the chassis, suspension or wheel rims. Sometimes when wider wheels have been fitted and the flexible hose has not been reset correctly the wheel rims have rubbed onto the flexible pipes and worn grooves into them.
Callipers tend to seize, causing the brakes to bind-on and over-heat. If the pads have been allowed to wear right down until they become extremely thin, the chrome pistons will become fully extended and their surfaces exposed to corrosive dirt and winter salt. This will damage the pistons and when new pads are fitted and the pistons pressed back into place the corrosion on the surface can then cause the pistons to seize. The only cure is to replace the chrome pistons or renew the callipers.
To inspect the rear brakes it will necessary to remove the rear drum. The soft cross-head screws are easily damaged if you try to undo them with a screwdriver that is too small. It is well worth investing in a large Phillips screwdriver to remove the screws on the rear drums. Once the screws are out and the handbrake is off you can withdraw the brake drum by tapping it on each side with a wire wheel hammer and prising away each side until the drum comes free. With the drum off make a thorough inspection of the rear shoes. If they have been allowed to wear down too much the rivets will score the inside surface of the brake drums, if the drums are badly scored they will have to be replaced.
Removing the retaining screws with a large Phillips screwdriver.
The handbrake on the MGB is often criticised as being ineffective but if it is properly set up and correctly maintained it is perfectly adequate. The handbrake should hold the car firmly after being pulled up by to the third or fourth position on the ratchet. The handbrake will only work correctly if the adjusters on the back-plates are set properly, the cable is correctly tensioned and all the linkages are working freely.
Bleeding the hydraulic brake system
Over time the condition of the brake fluid can deteriorate and it will need to be replaced. If there has been any disturbance to the braking system such as fitting new pads, shoes or replacing a master cylinder or wheel cylinder, then it will be necessary to bleed the brakes. This is normally a job for two people, one to pump the brake pedal, while the other person maintains the fluid level in the master cylinder and operates the bleed screw on each of the wheel cylinders and callipers in turn. Always make sure you have the correct specification brake fluid. Never re-use old brake fluid which has been bled from the system. Keep brake fluid away from paintwork.
- For best access to the wheel cylinders and callipers you need to jack up the car and support the body securely on axle stands. The process of bleeding the brakes is easier with all the road wheels removed but this is not strictly necessary.
- Before you start it is essential to top up the brake fluid in the master cylinder and ensure that the level is kept topped up, because if the level falls too low air will be pumped around the system.
- Starting at the wheel furthest away from the master cylinder attach a length of clear plastic tubing to the bleed screw and feed the other end of the tube into a jam jar. You need clear tubing to be able to observe the air bubbles as they emerge from the bleed screw. It is helpful to buy a purpose designed bleed tube complete with a non-return valve.
- Using the correct size spanner undo the bleed screw by half a turn. Then instruct your assistant in the driving seat to depress the brake pedal slowly and evenly. This pumping action should be repeated pausing between each stoke while you observe the fluid coming through. When the fluid is free of air bubbles, instruct your assistant to fully depress the brake pedal while you tighten the bleed screw.
- Move on to the next rear wheel cylinder and repeat the process. Working your way all around the car, bleed each cylinder and calliper in turn. Once all the air has been successfully expelled the brake pedal should be firm with very little travel and no feeling of sponginess.
Undoing the offside rear wheel cylinder bleed screw after attaching the plastic bleed hose.
Bleeding brakes on your own
If you do not have the services of an assistant you may find a special tool such as the Gunson's Eezi-bleed pressure bleeder very useful. This enables you to bleed the brakes on your own, by pressurising the hydraulic system with the air from a spare tyre. The kit consists of a special reservoir to hold the new brake fluid - a pipe with a choice of caps to fit the master cylinder and a pipe to fit onto a spare tyre. With the system connected the brake bleeding process is exactly the same but you don't have to worry about topping up the master cylinder and you don't need an assistant to pump the brake pedal. As soon as you open a bleed screw the pressure from the spare tyre will force the fluid through and you can observe the air bubbles passing down the bleed tube. As soon as the bubbles cease you can tighten up the bleed screw and move on to the next wheel.
Bleeding the front calliper using the Eezi-bleed system. The spanner is attached to the bleed screw and the collection jar is placed on top of a tin of household paint to keep it at a convenient working height. The tyre of the old spare wheel on the left is being used to provide the pressure.
The Eezi-bleed connected to the master cylinder. The remote reservoir is filled with new brake fluid so that the master cylinder is automatically topped up as the system is bled.
If you at all unhappy about the performance of your brakes and not confident to tackle them yourself, do not hesitate to take them to a professional mechanic for attention.