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  Chicagoland MG Club:Tech Tips

Compensation - For Your Handbrake

If you've decided to do something about a frozen or sticking handbrake on an MGB, you should know that the source of handbrake problems is not always in the cable itself. The handbrake cable passes through a "compensating" mechanism, attached to the differential back plate that is susceptible to corrosion and can cause the handbrake to stick or lock-up altogether. If pulling up the handbrake causes the rear brakes to engage, but releasing it releases only the driver's side rear brake, then the odds are that you have a malfunctioning compensator.

What's a compensator? The primary handbrake cable runs from the handbrake lever to the driver's side rear brake through the compensator. When you lift up the handbrake handle, the primary handbrake cable pulls the driver's side rear brake lever towards the center of the car, thus engaging the driver's side rear brake shoes. As the primary cable is pulled towards the center of the car, the cable housing, which abuts against the compensator, moves in the opposite direction. This opposite motion of the cable housing works through the compensator to pull the secondary cable, attached to the passenger side rear brake, towards the center of the car. Magic! You pull one cable and two cables move simultaneously. The compensator has translated the motion of the primary cable into an opposite motion of the secondary cable.

To function properly, the inner and outer compensating levers must be able to pivot freely on the compensator fulcrum. Unfortunately, the lever and fulcrum receive no regular lubrication. Greasing the handbrake cable does not lubricate the compensator! Eventually, even in the mildest climates, the compensator becomes corroded and frozen. Once the compensator stops moving the handbrake cable also seizes up, regardless of how much lubrication it has received.

When replacing the handbrake cable, test the compensator fulcrum for easy motion. If it is stuck, remove the small nut joining the two halves of the compensating lever, and the large nut at the bottom of the fulcrum. Pull the inner compensating lever from the fulcrum. Use emery paper to remove corrosion from the lever bush and fulcrum. Clean and apply a light grease of anti-seize compound before re-assembly.

If corrosion is so severe that it is impossible to dismantle the two halves of the compensating lever, you will have to unbolt the entire assembly from the axle back plate and replace the frozen parts. (It isn't a good idea to use heat to dismantle the compensator while it is bolted to the differential back plate - the fuel tank is just inches away!) The compensator fulcrum, inner and outer levers, and fulcrum bush should be replaced as necessary.

Since the bolt holding the compensator in place is also responsible for helping to secure the back plate to the differential, it is possible that a leak of differential fluid could develop after replacing the compensator. If so, it will be necessary to replace the differential back plate gasket.

Since the compensator is so important for the smooth functioning of the handbrake, it is a good idea to dismantle and lubricate it on a yearly basis.

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