Understanding electric park brakes

Need to know

Models: Discovery 3 and 4, Range Rover Sport 1.
New components illustrated: The following part numbers apply to Britpart supply:
• LR 031947F, Ferodo park brake shoe kit for D3/RRS.
• LR 019223, genuine Land Rover park brake module assembly. 
• DA9223, Britpart repair kit including new gears.
• LR 134696DT, TRW rear disc brake pad kit for D3/4/RRS.
When ordering parts, always quote the VIN and registration number of the vehicle to ensure they are correct for the model.

 

Electric park brakes have a bad reputation, not so much for reliability, but for the huge cost and length of time taken to replace the components on the Discovery 3 and 4 and Range Rover Sport 1 when they do go wrong. Plenty of other Land Rovers and Range Rovers have them, but in a more simplified and logical form, and those don’t really cause any concerns.

I’m calling them electric, rather than electronic because the brake mechanism that we’re concerned with here is electrically operated – it’s the control system that is electronic and this part doesn’t give trouble. Either way, electric or electronic park brake, the initials are the same, so from now on we’ll refer to its abbreviation of EPB.

The advantages of an EPB are that the absence of a conventional handbrake lever in the cab saves space and looks nicer to some buyers, and it’s one less protrusion to cause injury during an accident. An EPB is also lighter in weight, theoretically contributing to cumulative fuel and emissions savings, though given the size of the EPB actuator module hidden up on the chassis of the D3/4 and Sport, the weight advantage is debatable, as is the complexity and impracticality from a maintenance and repair viewpoint. There’s another advantage in that if you drive away with the park brake still on, it’ll automatically release for you. Later systems automatically apply it for you when you stop (though I’m not sure any motorist ever complained about having to apply a handbrake, nor even to release it).

So we’re talking about the D3/4/Sport system here. Instead of a handbrake lever, we have a simple switch to flick up and down. And if we’re not sure what to do, the electronic system will work it out for us and apply power as necessary to the actuator module mounted on top of the chassis. The actuator module is a large box containing an electric motor, a gearbox and electronic sensors with the sole purpose of pulling the cables to apply the park brake shoes at each rear wheel. The park brakes at the wheels comprise a pair of traditional brake shoes inside a drum; and that’s it. The slightly interesting bit is that the drums are actually the inside face of the rear brake discs, making it all compact, but complex.

It also means that adjustment of the park brake shoes within the drums needs to be accurate, and stay that way. It’s so critical that fitting a new disc/drum and/or park brake shoes of dubious quality could adversely affect the shoe-to-drum clearance. Incorrectly set shoes can introduce brake drag, leading to higher fuel consumption, overheating of the disc/drum and to the accumulation of brake dust which further restricts the internal operations and increases the loading on the operating mechanism.

Incorrectly set brake shoes can also put extra load on the two operating cables. As it is, these cables can become stiff through lack of use, such as by relying on an auto transmission’s park position or by leaving a manual transmission in gear instead of using the EPB when parking on a hill. As with most things that move, time, moisture, dirt and wear can all stiffen them up. And when that happens, the plastic gear system in the module which is trying to drive the cables is burdened with extra load, at least until the sensors and ECU decide it’s a bad idea and switch off the power. But, in order to sense that extra load, the electric motor has to initially drive the gears, and such continual attempts by an unknowing driver to apply a defective EPB will eventually take their toll and components will fail – probably leading to a new actuator module, resulting in a £1600 garage bill.

There is a kit available for around £86 to renew the gears in the actuator module, which is tempting, given that a new module assembly alone will cost around £850. But you still have to remove the actuator module from the car to fit the gear kit, and the old cables and module internals, such as the electric motor, will still be the well used originals. Might as well bite the bullet and do the full job.

Case in point

A failed system can sometimes be re-booted, cleared and be back in satisfactory operation again. But it’s only a matter of time before it goes seriously pear-shaped, as illustrated by this incident with my own Range Rover Sport.

When I applied the EPB, there was a screech, the dash light came on and the park brake would not release. I was on the sloping slipway onto a ferry in the Outer Hebrides – not the ideal position or geographical location to become immobile. I could have removed the interior trim to reach the emergency release cable, but it seemed marginally less embarrassing to get out and direct the queue of cars around me. When I climbed back in and re-booted the ignition, the light went out, the brake released and I drove on board, but didn’t dare re-apply it.

The pandemic prevented me getting it fixed, but each time I used the EPB I listened for the screech and immediately switched to the release position if I heard it. No problem: it became one of those endearing quirks of Land Rover life and, given that I no longer have facilities for this type of job, it meant I was delaying a huge garage bill. A few weeks ago, my MoT inspector tried the EPB, but he wasn’t listening for a screech, so he left the brake on. The brake stopped working and the red light came on and he handed the car back to me with a fail sheet. To rub salt into the wound, the MoT station would not do the repair work (too complicated), and that’s something else to bear in mind – many garages avoid working on these systems, so you need a good Land Rover specialist. So let’s take a look through the system in detail to see how it all works, what can go wrong, and what’s involved in repair.

 

HOW IT WORKS

Basic components

Driver control: The driver’s switch powers the control module which drives the cables to apply the brakes, but only if the electronic control unit deems it appropriate (Discovery 4 shown).

On top of chassis: This Discovery 3 EPB actuator module is visible with the body lifted off, otherwise access is through wheelarches and spare wheel recess.

Cable operation: Two Bowden cables running forward from the actuator module, drop and curve back through guides on the lower suspension arms before connecting into the rear drum/disc assemblies.

Disc and drum: The rear brake discs are recessed on the inside to provide a drum for the park brake shoes – similar to earlier drum brakes, though considerably more sophisticated.

Inside the drum: Removing the rear brake disc/drum (and caliper) exposes the park brake shoes on the back plate. Note toothed adjuster at top of this RH brake (at bottom on LH).

 

The park brake module assembly

The EPB module (sitting above the chassis) is the heart of the system. It controls the tension on the two park brake cables to correctly apply and release the brake shoes inside the rear drums, even accounting for gradient.

New part: The EPB actuator module is supplied as an assembly with the two wheel brake cables pre-fitted, and also a new emergency release cable, seen with silver wrap.

Cables: Bowden cables have a nipple which engages into a brake shoe lever in each drum. The black screwed connector locates and seals the cable to the brake back plate.

Mountings: Looking at the rear of the actuator module, two rubber feet engage in the bottom of the chassis mounting bracket, and two studs locate at the top with nuts.

 

Failure modes

We know the EPB system as a whole failed on my Range Rover Sport but, despite now having the complete assembly renewed, it’s always interesting to discover exactly what failed, and perhaps how, by dismantling the old parts. The cover is off, so here goes:

Getting inside: The casing front cover will lift off after removing the Torx screws, but it still takes some shifting because it’s very well sealed against dust and moisture ingress.

Internal components: The electric motor drives the gearbox which rotates the splined shaft. This shaft has a screwed connector rod through it so that, as it rotates, the screw thread causes the rod to move out or in. The cable to the left wheel brake (right of picture) is attached to this screwed connector and, thus, the wheel brake is applied or released. Because the splined shaft can slide axially through the gearbox, and is linked via the force sensor to the right wheel brake cable (left of pic), the movement is equalised between the two cables to give the correct pull on each brake. The loading on the system is detected by the force sensor.

Strip-down: The dismantling starts by de-coupling the RH wheel brake cable assembly from the body of the module, and withdrawing the screwed connector from the hollow splined shaft.

Instant issue: With the RH wheel brake cable assembly now disconnected, its inner cable should be free, but is completely seized and is a likely cause of the failure.

Releasing the gearbox: The motor and gearbox is unscrewed as a unit from the casing, and the white plastic gearbox is slid out over the splined shaft, before opening its casing.

Opened up: The gearbox casing splits into two (with the motor still attached at the back), allowing full access to the gears, and simple replacement if choosing that route.

Damage evident: The serrated teeth (blue arrow) of this clutch are rounded off. They mesh with radial teeth (red arrow) inside the gear wheel below, where some are broken off.

And more: Dislodged spring clip in the gearbox base casing is available new – no clue as to why it’s loose. Note keyways in bearing (left), in which the splined shaft slides.

New gears kit: The replacement gears kit includes fixing screws and rubber mounts for the module, but the remainder of the system has to be serviceable for this to be viable.

 

Repair work

When there are signs of problems with the EPB system, it’s worth having it electronically diagnosed by a professional rather than jumping to conclusions. The system is linked by sensors to several other systems around the vehicle (such as the clutch position on manual Discovery models), so an issue could be outside of the EPB system, as well as among the many components within it.

As we saw above, the actuator module gear set can be renewed, and the cables can be renewed individually but, given the labour time for accessing components, plus the fact that all components will have deteriorated, it’s usually best to replace the complete module assembly. If replacing a single failed component, it’s important to confirm that no other parts are defective, otherwise the considerable labour time could be in vain.

Complete replacement is a big job and not something to be attempted without the relevant workshop manual. The electrical system needs to be deactivated before any work (including removal of the brake discs) to prevent the module overrunning and to avoid automatic re-application of the brake.

Access to the module is difficult through the rear wheelarches with the road wheels removed and, mainly, from underneath with the spare wheel removed. Fittings are likely to be corroded and seized. Adjustment and setting of the park brake shoes in relation to the drum can take a couple of hours. Then the new shoes need to be bedded in while driving the vehicle slowly and using the park brake, after first entering a ‘bedding mode’ which temporarily disables the ABS stability functions. The whole operation of setting and bedding the brake shoes is critical, and incorrect settings will eventually cause further damage.

Good practice: Ideally, discs/pads are renewed with the EPB assembly so the new shoes work against a new drum. Shoes are set and adjusted through the hole in the drum.

New kit: The park brake shoes are basically conventional, though with specific operating levers, cable attachments and critical methods of setting and adjustment.

 

Avoiding trouble

Faults on the EPB system won’t necessarily flag up a warning lamp right away, so it’s worth checking in other ways for faults before they fully develop. Typical Diagnostic Trouble Codes (DTCs) include C1A:34-00, 53-68 and 46-62, but often the first sign is a screech from the actuator module which can be easily heard when applying the park brake with the door open and the engine off. There will be a normal whirr as the brake is applied and released, but a screech means something is seized and/or the actuator has overrun. Either way, it hasn’t long to live. If you hear a screech, press the switch to the release position instantly. It might be safe to then switch it back on again, but things aren’t going to get any better. If the warning lamp appears on the dashboard, try switching the ignition off and removing the key for a few seconds to clear it. If the lamp stays on, it’s an MoT failure and there won’t be an effective park brake.

Failure causes include seized cables, incorrectly adjusted brake shoes, worn shoes, corroded brake shoe mechanisms, accumulation of brake dust inside the drum and damaged shoe linings. So a check and reset of these components, plus cleaning the drum and shoes may cure the problem, if caught  early.

Maintenance

There’s little that can be done other than to ensure the drums are clean inside whenever the brakes are serviced (more frequently if off-roading in dusty or especially wet conditions where water and grit can enter the brake drums), that the shoes are correctly adjusted and that quality parts are fitted. The EPB actuator module is watertight, and electrical connections on Land Rovers are first-class, but deep wading brings with it the possibility of moisture and silt entering between moving surfaces with the potential to cause stickiness, adding to motor and gear loading. The two cables enter each brake via the back plate using a watertight screwed connection, so check the condition of these, and the cable guides on the suspension arm at service times.

By using the park brake regularly so that parts don’t have time to seize, the cables are more likely to stay free and easily operable without risking overloading the tensioning system. Release the EPB with the switch before driving off rather than relying on the system to do it automatically. In fairness though, correct use and maintenance should keep the system serviceable and trouble-free for the long term – the trouble is that, given their age, many of these vehicles have actually exceeded the ‘long term’ in respect of average car life.

Critical adjustment: One of two setting devices, this adjuster sets shoe-to-drum clearance. Note the build-up of brake dust on these shoes, and grab marks on the friction faces.

Break-up: Maladjustment of the shoes in the drum leads to overheating, overloading and, as seen here, break-up of the shoe friction faces inside the drum.

Wipe-out: The friction faces on these brake shoes have overheated, broken up and been completely wiped off the shoes in a cloud of dust, letting the actuator module overrun.

Reasons to maintain: The crack across the face of this drum was because of a park brake locking up at 70mph. Fortunately, Land Rover parts are designed with strength to spare.

Check spare wheel winch: If seized, it will need renewing to remove the spare to access the actuator module, adding more cost, as well as being inconvenient when a flat tyre occurs.

 

Emergency release

If the EPB becomes locked on and the shoes and their mechanism are not seized, or low battery charge prevents the EPB from being released, the emergency release cable behind the centre console switch panel can be used to allow the vehicle to be moved. Inside the actuator module, the release cable disconnects the force sensor from the splined shaft, thus releasing the cables. When the EPB is next switched on, the splined shaft will move and reconnect with the force sensor ready to operate normally. A subsequent switch-on will then apply the brake, if all else is well.

The emergency release cable on this D3 is reached after removing the console. Extra purchase, such as from a large screwdriver, is needed to pull it.

 

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