Should I be worried about the brake power assistance gremlin on my 54-plate Ford C-Max?

Q. The power assistance to the brakes on my 54-plate diesel Ford Focus C-Max sometimes stops functioning a few moments after starting up, only to return soon afterwards. My garage found no fault with the braking system, but mentioned that the power assistance is linked to the turbo and told me to come back if the fault recurs. Any thoughts? 

MD, Rotherham, West Yorkshire

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A. The link between your problem and the turbo is a red herring. We’d advise you to go to a different garage — perhaps a Ford specialist — that will take the time to properly diagnose the fault.

To understand the likely cause of your problem you need to understand how power-assisted brakes work. Power to the brakes is applied by the creation of a vacuum, which is used to boost the force you apply to the brake pedal with your foot. In diesel engines there is a valve inside the pump used to create the vacuum and another where it connects to the brake servo. These are supposed to stop air getting in.

There is a history of the valve in the pump sticking on the Focus and other Ford models, as well as some Peugeots with the same pump, when the engine is cold. However, as you found, because the servo has retained the vacuum created the last time you drove the car, for the first few brake applications the power assistance is provided as usual.

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Only once that vacuum has disappeared — usually after three or four pedal presses — does the power assistance fail and the brakes start to feel hard and unresponsive. Once the valve frees itself, the vacuum builds back up again and the brakes work normally.

Ford issued a recall for several models, including the C-Max, made between November 2005 and December 2006, and a similar one for Fords made in 2008-9, but neither of these applies to your vehicle. As the car is 10 years old it may simply be a worn component. A new vacuum pump could cost from £50-£250, plus about an hour’s labour.

TIM’LL FIX IT
Tim Shallcross used to train AA patrols to fix cars. Now he advises the Institute of Advanced Motoring – read more from Tim here.

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