Expert advice and readers’ tips

ED EVANS REPLIES: There has always been concern among owners about testing the hand-operated transmission brake, though MOT inspectors are aware of the accepted practice of applying the brake carefully and measuring the deceleration. I have only once seen a beam axle Land Rover tested on the brake roller and, straight afterwards, it produced a noise and vibration from the rear which was found to be caused by a seized sliding joint on the propshaft. I doubt the roller test would have caused this on its own, though it may have been the last straw for an already defective prop.

I contacted the Driver and Vehicle Services Agency (DVSA) who confirmed that decelerometer testing has been carried out for many years without concern or damage. The transmission brake is applied gently and slowly while driving the vehicle until the minimum acceptable brake efficiency is reached, at which point the brake is released and the test is completed. This would involve keeping the button held in so the ratchet is not engaged.

DUAL BRAKES

Ian also asks about the Discovery’s dual brake system. This is a separate safety feature operating on the wheel brakes during normal driving. The Discovery has a tandem brake master cylinder, in that it has two separate fluid reservoirs, each operating on a separate brake pipe system known as the primary and secondary circuits. When the brake pedal is pressed, both circuits operate simultaneously, but if one circuit fails, the other will still work so, in the case of a pipe leak or a burst hose, the car still has working brakes, though not with the original overall braking efficiency.

Only the front brakes benefit from the dual system. The front calipers have four pistons. The primary brake circuit operates the two upper pistons, and the secondary circuit operates the two lower pistons. So, if one circuit fails, the other will still operate the front brakes. The rear brakes are supplied only by the secondary hydraulic circuit so, if that fails, the primary circuit will continue to operate only the front brakes. On the other hand, if the primary circuit fails, the secondary circuit will continue to serve all four wheels, but with the front brakes on reduced efficiency.

NICK SPEARMAN SUGGESTS: Any garage should be capable of reading diagnostic trouble codes on the engine ECU so, as your garage hasn’t found anything, we’ll assume the ECU is all clear. So, we’re left with something that causes the engine to stop when the revs drop below 1500, but isn’t registering as a fault. I’ll assume your engine malfunction warning lamp is working – this will illuminate when the ignition is first switched on, and extinguish after a few seconds when the self-checking is completed satisfactorily.

The crankcase breather problem you mention is a common fault and it’s caused by blockage of the crankcase breather filter inside the depression control valve assembly. That’s fixed by fitting a new one. But the symptoms for this are usually that the engine will not rev so well, black or blue exhaust smoke, low power and increased oil consumption. You don’t seem to have any of these symptoms, so we’ll rule that out.

There was an early problem with chafing of the engine wiring harness on the nearby suspension turret, but I don’t think it would cause your symptoms and all affected models would have been modified long ago by Land Rover.

So I suggest you have an injector problem, and this would not show as a fault code. Your best course is to take the car to a Land Rover specialist or a diesel specialist to have the fuel system pressure tested or to check for leak-back to identify any injector problems. It’s usually possible to identify individual faulty injectors and replace only what’s needed – they are quite expensive. But if one is failing, others can be expected to follow suit.

MODERN KIT: When placed in the driven vehicle, this Brakecheck electronic decelerometer displays the efficiency of the transmission brake as it is gently applied

TRADITIONAL KIT: This is an old-school Tapley meter with steel handle and a heavy base weight to keep it in place on the vehicle floor. This was the common tool for testing Land Rover brakes

DUAL HYDRAULICS: The primary hydraulic circuit (green) works only on the front brakes. The secondary circuit (red) works on the front and rear brakes. The blue section is a pressure-reducing valve to the rear brakes

EASY BLEEDER: Because the systems are independent, it’s necessary only to bleed the system that’s been worked on. But it can get a tad confusing... If in doubt, bleed everything to be on the safe side

TRICKY REMOVAL: Once you’ve reached the injectors, it’s a simple matter of unbolting the retainer and easing them out without damage, but they are often – and irritatingly – well stuck