PASSAT B6 ELECTRIC PARK BRAKE (S)

The Passat B6 park brake has rear calipers operated by an electric motor.

Pressing the EPB (Electric Park Brake) button on the dash activates the Electric Park Brake control unit.

The Electric Park Brake control activates the rear caliper motors.

The rear caliper motors apply the Park Brake.

The Rear caliper & motor assembly looks like this:

And like this in real life. (The caliper mounting bracket is not present in this picture).

The Brake Disc, Caliper, Pads, Slide pins, Piston and Seal are similar to a traditional set up.

In a traditional set up the piston would be pushed out onto the pads by a lever operated by a cable.

So the main difference is the use of an electric motor to push the Piston out.

The piston has a fixed thrust nut inside it on a threaded bar attached to the motor drive.

e.g

When the threaded bar turns, the thrust nut winds along the bar.

The thrust nut pushes the piston out.

The Piston presses on the pads and applies the park brake.

*Note: Now that the brake is on (motor wound out), it will remain on even if the battery is disconnected.

To release the EPC the button is pressed again.

The electric motor now winds the other way.

The thrust nut is not fixed to the caliper piston so it DOES NOT retract the caliper piston.

Distortion of the piston seal and disc run-out, cause the piston to move back.

Sounds Simple.

BUT

How does the motor know how far to wind the piston out ?

The EPB control module measures the current drawn by the motor.

As the motor strains to squeeze the piston onto the pads, the current rises. This current rise is detected and the motor is switched off

How can a small electric motor produce enough piston pressure ?

The motor is connected to the piston’s thrust nut by a 1 : 150 gear drive.

This has two effects.

1. It allows a small motor to produce a high pressure.

2. It allows fine control of the piston as 150 turns of the motor are needed to turn the thrust nut drive by one turn.

How does Auto-release of the EPB work.

The EPB control module takes information from an inclination sensor, clutch position sender and accelerator position sender. The EPB remains engaged until the control module calculates that engine torque is great enough to overcome “roll-back”. At this point the EPB is released.

Emergency braking.

Emergency braking at speeds above 7 kph (4 mph) IS NOT by the Electric Park Brake. This will only operate below 7 kph.

Pressing the EPB button at speeds above 7 kph activates the ABS unit which pulses brake fluid pressure and applies all four brakes for a controlled stop.

Changing the rear brake pads.

The caliper piston MUST be retracted to the service position using a diagnostic tool such as VCDS.

The caliper piston can now be pushed back in.

The pads can now be changed as on previous VW cars.

After fitting the brake pads, the motor must be reset with VCDS or similar.

NEVER attempt to push the rear piston in, without retracting the motor first. You will be pushing against a gear ratio of 150 : 1 and something will break.

Rear caliper strip down.

This is the complete caliper with electric motor attached.

The first thing I did was remove the two torx bolts holding the motor housing onto the caliper. The motor housing then pulled off,

looking like this

and this.

There is an o-ring seal between the caliper and the motor housing which can be seen in the caliper picture.

In this picture you can clearly see the caliper piston and the dust seal.

The bleed nipple, brake hose mounting bracket and short metal brake pipe are just visible.

The next picture shows the caliper viewed from the motor housing end.

You can see the two caliper mounting holes and the two motor housing threaded mounting holes.

The o - ring seal is just visible as is the central socket for the motor drive shaft and the circlip holding it.

This is a close up view.

I have removed the o- ring which runs round the outside edge of the circular housing.

You can clearly see the circlip and the central socket for the motor drive shaft.

(A Torx T45 bit fits it perfectly.)

Winding the motor drive socket ANTICLOCKWISE moves the caliper piston outwards as if putting

the brake on.

Winding the motor drive socket CLOCKWISE seems to do nothing because the thrust nut is winding back but not pulling the piston in.

When the thrust nut is completely back you can hear and feel it hit home. At this point you can push the piston in with a G cramp or your fingers,

if you are strong enough.

There is no point in dismantling the motor housing further as it cannot be repaired as no spares are available.

I have stripped it further just to show what it looks like.

Dismantling the electric park brake motor housing.

I clamped the electric motor housing in the soft jaws of a vice. Next I gently heated the joint on the gear housing using a hot air gun.

Then I used a blunt cold chisel to hit against the end casing cover until it moved. I slowly worked my way round the flange joint until the

end cover was free to pull off.

The gear cluster actually stayed in the housing as the motor pulled out. I have reassembled it for the picture below.

The 12v electric motor is a "Johnson" motor as used in cordless drills. This has a small drive cog on the end which drives a toothed band.

The toothed drive band drives a much larger cog on the gear cluster.

You can't see it in the picture, but there is a crack running from left to right along the top of the gear drive housing, exactly where the red

arrow is pointing. On this example the gear cluster was siezed so the drive band couldn't turn it.

Putting 12v on the motor showed that the motor was ok.

My best guess is that the seal between the gear housing and the caliper was not good enough and let some water in.

The water caused the gear cluster to sieze.

Every epb that I have examined has had this crack in its casing. I now believe this is a stress crack caused by the design of the epb system.

Each time the epb is applied the motor tuns until it stalls at which point the controller detects peak current draw and switches off the motor.

When the motor stalls it cannot turn the caliper drive so the force is transmitted to the wobble gear pegs instead. These try to rotate in the casing which is only made of plastic, so it cracks. I guess that this is a design fault.

In this picture you can clearly see the gear assembly with its drive cog on the right, the drive belt is still attached to the motor drive cog.

The gear assembly is an odd design.

The driven cog is turned by the drive band. As it turns, the central wobble gear cannot turn because it has two pegs (top & bottom)

holding it in the gear housing. Instead of turning it wobbles in and out (left and right as viewed in the picture)

It has teeth on its left hand face and the output gear has teeth on its right hand face.

As the driven cog turns the top of the wobble gear moves left, engages its teeth with the output gear teeth and turns it a fraction.

As the driven cog continues to turn the top of the wobble gear moves right and disengages with the out put gear BUT

because it is tilted, the bottom of the wobble gear is now engaged with the output gear, so it turns it a fraction.

Sounds daft but this system allows two same size gear wheels to have very slightly different numbers of teeth.

This is presumably to allowed the designers to get the exact gear ratio that they wanted.

The end result of this is, the motor turns about 150 times to tun the caliper piston drive shaft, once.

ELECTRIC PARK BRAKE GEAR CLUSTER STRIP DOWN.

(Thanks to Vince and David for providing these parts)

This is a diagram of how the parts are assembled

The caliper drive pinion, output drive gear and gear shaft are all one piece.

The central wobble gear sits over the nose of the drive belt cog. There are two wobble gear bearings

between the wobble gear and the drive belt cog nose. So the wobble gear can rotate freely on the drive belt cog nose.

The drive belt cog contains a needle bearing in the nose and a larger bearing in the cog. These allow it to rotate freely on the gear shaft.

This is the EPB drive gear cluster once it has been removed form the EPB housing.

This is the part that always seems to seize.

It is not designed to be taken apart and as such can’t really be overhauled.

The gear cluster assembly is held together by a pressed on collar just behind the drive belt cog on the support shaft.

The only way I could remove this was to rest the shaft on the almost closed jaws of a vice and hit the collar with a small

8mm cold chisel to split it.

This is the gear cluster assembly shaft with the cogs removed to show the remains of the collar after splitting it.

You can see a groove on the gear shaft where the collar was clamped on.

It took a lot of soaking in WD40, Oil etc to get everything loose enough to come apart.

This is all of the parts disassembled in order. You can see all of the parts except for one small needle roller bearing

which is in the nose of the drive belt cog.

Having stripped a number of these EPB gear clusters I can confirm that the Drive belt cog bearing and it’s nose needle

bearing do not seem to seize.

In every EPB gear cluster I have examined, the wobble gear bearings (x2) have been seized.

This is a closer view of the wobble gear and its two bearings. The bearings fit in the centre of the wobble gear. One on top of the other(like a sandwich). The drive belt cog nose, fits into the center of the bearings.

This is what the motor looked like freed from its mounting cover. I wouldn't advise doing this as the electrical connectors

had to be forced out of the connector housing by breaking it. They should pop out with the right tool, but they wouldn't

Anyone attempting to replace a motor would be better off cutting and soldering the motor wires.

Dismantling the rear caliper

Spares are availabe for reconditioning a rear caliper.

For safety sake, please don't try this unless you have previous experience with caliper repairs.

Caliper reconditioners can pressure test the finished item. DIYers can't.

Turning the piston drive anticlockwise with a T45 torx bit winds the caliper piston, out as shown in the picture.

The ratchet wasn't needed, fingers worked fine.

With the piston right out you can just pull it away, no force required.

You just need to free the dust seal from the groove in the piston.

The dust seal remained firmly fixed at the other end, in a groove in the piston bore.

It simply pulls out once the piston is removed.

With the piston out, the thrust nut fell out. The thrust nut sits inside the piston but is not fixed to the piston.

This is why it can push the piston out but cannot pull it back.

You can see the piston and thrust nut in the picture.

This is a view of the piston bore with the dust seal and piston removed.

You can see the piston threaded drive and just about see the piston fluid seal near the top edge.

Removing the circlip on the threaded drive shaft, allows the shaft to lift out of the bore. It is made up of 5 pieces

so you have to be careful nothing falls off as you lift it out.

This is the assembly as lifted out

And this is the 5 pieces laid out, plus the circlip that holds it in.

The two thrust washers and roller bearing make up a very thin bearing for the threaded drive collar to press against.

An o-ring seal sits behind this and is pressed against the back of the piston bore.

This picture shows a view of the piston bore with the thread drive removed.

You can just see the piston fluid seal near the top. This is very easy to hook out.

The threaded drive shaft bearing is a brass insert at the bottom.

That's it....One stripped electric park brake rear caliper.

EPB motor - Production changes.

During 2007 the Passat rear caliper/epb motor was redesigned. The exact chassis number change point is unknown as far as I can tell.

For the EPB motor the old ‘wobble gear’ system was dropped in favour of a planetary gear system.

The output drive was changed from a torx shape to a spline shape.

This means that a ‘new’ design epb motor will not fit on an old design caliper. So swapping an old epb motor for a newer one is impossible.

To stop the fitting of the wrong epb motor and caliper the epb manufacturers changed the design of the electrical connector as shown below;

The later style motor and caliper connector will not fit the early style wiring connector on the car.

DO NOT FEEL TEMPTED TO CHANGE THE CONNECTORS TO FIT A LATER CALIPER/MOTOR.

The control unit will not allow this so you can’t do it.

So you can’t fit a later caliper and motor to an earlier car and you can’t fit a later design motor to an earlier design caliper.

To upgrade an early car to the later epb you need to change both rear calipers and the control unit.

Thanks to Chrisman of vwaudiforum for supplying the caliper.