MOT says EPB 'only just sufficient'

[GaryJEdwards]

Hi all - first post so hope you can share some of your experience!

The MOT says that the electronic park brake is only just sufficient to hold the car. It does move a little after the car is switched off but does seem to hold. I've had all new discs and pads - any suggestions why it will move after applying the EPB (and turning off the engine)? Manual handbrakes wouldn't do this. Is it just a quirk of EPB's?

Many thanks!

Gary

[J44EAG]

One one occasion I had this on my early non electronic hand brake car. It turned out to be just one of the four calliper carrier slider pins which was seized solid. Freed off, cleaned up and copper grease applied, full hand brake efficiency returned.

Oldtimer may be able to offer more detailed advice on electronic versions although I believe there are similar parts as regards the calliper carrier and the sliding pins.

Seized pins stop the opposite and equal reactions of the calliper hand brake mechanism which can lead to unequal wear on pads and discs and what my MOT man described as a "high load`handbrake. The effect was I had to pull the hand brake up high to gain any parking brake action.

Mike

[GaryJEdwards]

Thanks Mike

I'm not much good with the mechanics. Wondered if anyone had experienced the same thing? I'd read about re calibrating the epb and wondered if that might help?

Gary

[J44EAG]

The golden rule is to check out the basics first before going in deep.

I`d suggest you strip out the back callipers before touching the electronic (electric) motor unit. Stiff and dirty calliper lever arm mechanisms and slider pins are the main culprits with sluggish hand brake mechanisms. Check to see the discs are not overly thinned through wear and the same with the pads. The Laser 1413 tool is useful for winding calliper pistons in and out of calliper bores during servicing operations.

With the electronic hand brake unit, this will be needed to be set to the off position before you begin maintenance operations. Check out other posts on this BB in the braking section for details. Oldtimers posts on the subject give a good insight into the electronic handbrake operation and maintenance procedures.

Mike

[oldtimer]

Hi Gary / Mike,
Only just finished in the garage so too "nacked" to respond tonight. Off to BB's breakfast at Kemble in the morning so will add my peneth later.

Agree with Mike but will add a little later, in the meantime try and dig out JEC Mag Dec 2013.
there is an article which describes things and may help you to understand

Oldtimer

[GaryJEdwards]

Thanks Mike

I've had all new brake lines, discs and pads, even new servo etc fitted as part of my planned maintenance since buying it a year ago. Like you said, the caliper pins were causing problems but these have all been rewound and greased front and back. Even after all this it still moves noticeably when applied and the engine turned off. A little movement doesn't really worry me but the fact the MOT says its insufficient after their tests is a bit of a mystery

Gary

[oldtimer]

Hi Gary,
I don't understand your enquiry. What exactly moves even after it's switched off, kindly explain.
With the Park Brake selected "on" the vehicle should be rock solid. Failure to achieve this indicates a serious mal-function in the braking system.

The S Type does not have an inherent Park Brake problem regardless if it is applied manually or electrically. This is confirmed by way of holding both the car and a ton and a half of caravan on some very steep inclines.

You tell us that you have had new brake pipes, brake discs and brake pads fitted.

This model of Jaguar does not employ an addition set of brake pads for parking brake purposes as certain earlier models did. The S Type has one set of brake pads which are either operated when the foot brake is applied or the park brake is selected on, it is one in the same device activated by two methods.

Taking the above into account I don't quite understand why the MOT tester has passed comment about the hand brake efficiency but not the foot brake efficiency, this needs looking into.

Trying to diagnose a problem from a distance is a dubious art form and accuracy is a bit subjective so try giving us a little more information

Oldtimer

[GaryJEdwards]

Hello

On a hill (even a slight hill) I would stop, put it in park and then apply the epb (although I'm told that putting it in park applies the epb anyway). Then when I turn the engine off the car will feel like it moves down the slope about half a foot before the brakes bite. I would expect the car to stay where it is once the brake is applied! Difficult to know what its like on the flat but the fact that the MOT is on the flat and says its insufficient using their equipment is a bit of a worry.

Given that all the pads and discs etc have been replaced I was wondering if the epb could simply need resetting and if anyone else has experienced similar.

Gary

[davidr]

Hi Gary - as far as I know, putting the car into "Park" does not apply the brake. What it does is lock the transmission and I would suggest that the slight movement you are feeling is the transmission moving round until the pawl engages and locks.

[J44EAG]

Start by jacking rear wheels off the ground. This should be done on a hard, level surface.

With the car in neutral gear, hand brake off, rotate each rear wheel and feel for no resistance to turning. Apply the hand brake and check that both rear wheels are locked. If one does not lock up, that would imply a fault on that calliper, calliper pins or brake pads. There are location pegs on the pad backings that must engage with the detents in the calliper pistons.

Common faults are as previously discussed in relation to seized calliper pins, seized calliper pistons or corroded/seized ramp and ball hand brake lever arms on the callipers themselves. To check full and free action of the calliper lever action, you can pull on the levers or cables and you should be able to lock up the rear brakes. If that is satisfactory, make use of an assistant and have them operate the electronic/electric switch whilst you lay under the car and watch to see if the mechanism operates and tensions the individual calliper cross cables and the electric motor with the single cable running down the car. If you see no movement at all, then the fault would appear to be with the hand brake cable and motor unit or the switch gear or electronic module controller.

On a hill it is wise to apply a working hand brake to hold a car on an incline. The P position on the gear select lever should only be used as final security once the hand brake is successfully holding the weight of the car. P engages a transmission lock pawl which is primarily designed to help stop a car being stolen. Although it is moderately strong, it should NEVER be used to hold a car on a gradient on a regular basis. Possible ok in an emergency but not as a general practice.

Mike

[GaryJEdwards]

Thanks everyone I didn't know what a pawl was till today

Worried that the car might be relying on the pawl rather than handbrake to hold it.

Will take it to our local specialist to see if they can check it out for me.

Thanks again. Gary

[oldtimer]

Hi Gary,
Your thread earlier today reveals a lot. As David said, the movement taking place is probably the transmission lock engaging when Park is selected. I suspect that the parking brake is not functioning at all.

Where as I agree with Mike K suggestions, there might be a simpler way to determine where the problem is. I would suggest you find a stretch of road with a downhill slope. Stop the car with the footbrake, select neutral, release the footbrake and allow the car to roll forward for a cars length or less and apply the park brake. The car should stop immediately with a bit of a jolt.

If there is no reaction when the Park brake is selected "on" and the car fails to stop, another check can be carried out to establish if the Park Brake electric motor is working. The electric motor operates a winch mounted on the rear suspension sub-frame. With quiet surroundings and windows closed, the motor can be heard to run for about two seconds and the red, brake on, light will illuminate. I would suggest you use the ignition key for this check. Switch the engine off, it is the action of pulling the key out that activates the brake motor, at this point the motor should be heard to run.

If the motor can be heard to run then we have gone full circle and come back to the rear brake calipers

I've only done it about a thousand times but I am sure you have to start the engine before the park brake can be released. You may need to repeat this process more than once until attuned to the motor noise.

Hope this helps

Oldtimer

[GaryJEdwards]

Hi all

I put it in neutral and let it roll at low speed (walking pace) and then applied the epb - nothing happened it just beeped at me and the epb light flashed a couple of times.

But, when I have it in Drive and apply the epb I can feel it bite and then when I drive away there is a little resistance from the epb so it is working.

Not sure how they test the epb for the MOT which was why I was wondering if it needed recalibrating?

Gary

[J44EAG]

Best to get the car diagnosed at a well equipped and competent Jaguar specialist. There comes a time when precise analysis is needed. Then you know what you are dealing with and can go from there.

Mike

[oldtimer]

I entirely agree with Mikes comment above