Your questions answered: Haldex, cruise control, and brake fade

Freelander 2 locks up

Samuel, Germany: I have the following problem and would be very grateful if you could help me. I have a Freelander 2 diesel (148bhp) from 2013. When you drive, it locks on the rear axle. There are no error messages, but if you pull the plug from the Haldex, it drives normally.

Ed Evans replies: It is intended that the rear drive via the Haldex should pre-engage or lock up when starting off from a standstill, so the problem here seems to be that the Haldex is not disengaging when under way.

Oil from the Haldex’s sump is drawn through a filter to a pressure regulator and also to an accumulator. The pressure regulator, which is a solenoid valve, supplies hydraulic pressure to a piston which compresses a multi-plate clutch pack, which then transmits drive to the rear axle to give four-wheel drive. This valve operates gradually to apply the drive progressively. When rear drive is not required, the valve closes and oil diverts back to the sump, relieving the pressure from the clutch pack.

Drive will remain to the rear axle if the valve fails to fully close. Also, deposits in the oil can affect operation and restrict oil flow from the accumulator back to the sump, leaving the clutch under pressure.

With the unit on the bench, the filter can be renewed. This one shows how much debris can accumulate. Replace with a quality part

When repairing the Haldex, always use original parts, not cheap alternatives, including the special Haldex oil. The unit needs to be removed from the car and it’s worth changing the valve first, plus the filter, and cleaning the pump galleries using compressed air. Cleanliness is paramount; every aspect needs to be thoroughly cleaned. When reassembled, give the car a long drive and include conditions that will activate the rear drive to fully test the Haldex operation.

The oil pump also needs to be removed, cleaned and all accessible galleries and surfaces thoroughly cleaned and dried before refilling with the correct oil

​​​​​​If the problem isn’t fixed, there may be oil flow restriction in the accumulator, a part that can’t be dismantled, nor serviced. In that case, contact haldexrepairs.co.uk who can supply a modified control unit intended to overcome the problem with the accumulator, and is a cheaper fix than a new Haldex.

Cruise legalities

Exercise caution when using an app to measure road speed

Michael Secomb: Your correspondent in the June issue of LRM suggested using a phone app to measure road speed to enable Defender cruise control to work with overdrive. He may be wise to consider the law on this, as he may find it is illegal for a vehicle’s speedometer to show a speed which is less than the actual speed of the vehicle.

That is why the vehicle speedo always shows a speed slightly faster than the actual speed. A GPS is not an accepted alternative as there can be a lag before the actual speed is shown. The vehicle’s registration can be voided if the speedo shows less than the actual speed, which can also invalidate the insurance coverage. This could be an expensive exercise.

Slow stopper passes MoT test

Carl Gordon: I’ve just had my Td5 Defender MoT tested and it has passed, with no advisories. The garage did point out a brake pipe that is getting a bit rusty; it’s the one that runs up the front of the bulkhead from the chassis. They also pointed out that all the bleed nipples on the calipers are very corroded and the spanner flats rounded off to the extent that it may not be possible to bleed the brakes when that pipe, or any other, is renewed. Are there any tricks to getting the bleed valves open?

The garage measured the brake performance using a brakeometer placed on the floor in the cab, which gave an acceptable reading. However, during normal driving I’ve noticed that the brakes work okay when first applied, but each subsequent time I apply them they are progressively less effective. Sometimes, after repeated application in a short space of time, they are barely working. I guess my brakes need looking at, but can you suggest what may be causing them to become weaker after repeated applications in quick succession?

Cleaning the areas against which the pads move may cure brake imbalance, but sticking pistons are best sorted by fitting new calipers all-round, or at least in axle pairs

Ed Evans replies: This situation is obviously dangerous and needs rectifying right away. We can rule out the usual air in the system because this would cause sponginess at the first pedal application, which you don’t seem to have. There are several possible causes of your fading brake performance including leaking servo seals, distending master cylinder seals and, the most likely in this case, old brake fluid.

​​​​​​Brake fluid is hygroscopic: it absorbs moisture which gets in when deteriorating piston seals deflect, whenever the hydraulic system is opened for repair, and also via the master cylinder. This is less of a problem when the brakes are first applied and the system is cold, but after repeated applications the system heats up and the contained moisture can vaporise inside the system. Water vapour is far more easily compressed than hydraulic brake fluid is, so when you press the brake pedal the vapour is compressed, rather than the fluid, so relatively little pressure is applied to the brake caliper pistons, and the car rolls on.

Incidentally, the use of a brake fluid tester inserted into the fluid reservoir may suggest the fluid is good, because this is where fresh fluid is always added. It doesn’t necessarily confirm that old fluid further down inside the system towards the calipers is in good condition.

The Td5 braking system is easy to bleed using the conventional tube and bottle, assuming bleed nipples release. This old discoloured fluid was well overdue for replacement

So the first approach is to replace the brake fluid, and that will involve fitting new calipers or at least new bleed nipples if they can be removed leaving intact threads in the calipers. If the spanner flats are rounded off, you could try applying penetrating fluid to the threads for a day or two and then attempt to remove them with mole grips, before replacing them with new nipples. Don’t apply heat because it will damage the calipers’ internal seals.

But before doing this, test the brakes on an empty road when safe to do so. Hold the steering lightly and notice if it pulls to one side under varying degrees of braking. Then allow the truck to roll to a halt without touching the brake pedal, and note whether it stops with a very slight lurch. Both conditions suggest the brake pads are not being applied or released in a smooth and equal manner. If that’s the case, you probably have sticking pistons in the calipers (nothing to do with the brake fade), in which case, don’t bother trying to get the bleed nipples out, just replace the calipers. And if doing that, fit new pads too and, unless they are very good, replace the discs at the same time. This might be getting a bit expensive but, from your description, it sounds that a brake overhaul is due, and it will be reassuring to know all this part of the system is in first-class order.

By now, having also replaced that dodgy pipe and bled through with new fluid throughout, I expect your brake fade will be cured. If not, you could consider renewing the seals in the master cylinder and, lastly, having the brake servo tested. A very basic test for the servo can be made by holding the brake pedal down while starting the engine. When the engine fires, the pedal resistance should decrease if all is well. Also check the vacuum pipe between the pump and the servo for poor connections, splits and blockages – with the engine running, take the pipe off the servo and check it is drawing a vacuum.

Incidentally, Carl’s MoT experience is a great example of why a current MoT certificate should never be taken to imply the car is reliable or safe. By applying the brakes to get a reading on the decelerometer, the MoT tester would have complied with the testing requirement.

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