Hello all

I have a question. Do you need a computer to tell the Electronic Parking Brakes that you want to change the rear brake pads? Or just as normal use the wind back tool after releasing the EPB?

Thank you
​​​​​​​Rav

 

Unless the existing pads are very new (which is unlikely if you are changing them) you will struggle to get the park brake cable released from the caliper to allow you to fit the new ones into the block. There are two ways to release the cable - reset through software (SDD/Pathfinder or a bespoke tool that sends the relevant messages to the EPB module), or by switching polarity on the DC motor to run it backwards (hard to access, make sure it is disconnected from the EPB module).

Once the cable is released you can wind back the pistons as normal. Resetting the park brake is easy as the car will prompt you when you next start the ignition.

If the cable won't come off the caliper bracket but is loose enough then WD40 the hell of it and try again as it can be a pita to remove if dirty. Be careful not to break the round plastic guide clip which can be removed to make it easier.

Both sides must be done together. If you forget and reapply half way through you can release again and then physically pull or push the cable through to realign them.

 

No. Manual release works perfectly


Yes.

 

Thank you all for your reply.

​​​​​​​Rav

 

Proof that ask online and you will get two conflicting answers!

If the pads are well worn then a simple release from the switch will not retract the pistons far enough to replace the caliper over two new pads. You get a little under 2mm of retraction on the pistons alone and can only rewind them a few more mm before the park brake cable will be taught against the lever again and you will struggle to get more than 5mm without unlinking the cable if you have the typical 10-12mm of piston to rewind. I struggled to do this when my SDD decided it would not connect to the car until 2 hours of updates where installed and I had already removed the old brakes ready to go and ended up having to wait till it was ready.

I'd be interested to hear why Mikey feels otherwise, and if it was on his own car how worn were the pads he was removing?

I guess it could work if you wound back both sides together and then applied (reset) and released the park brake again, then rinse and repeat until it was fully retracted. Logically that makes sense, but the brake force could break a poor quality rewind tool and I would be worried about blowing out a piston if it slipped. It seems like a lot of pain for a simple resolution with a cheap Mongoose or similar and an older copy of SDD on a spare laptop. If you are servicing the X351 yourself you will need SDD sooner or later anyway for things like the service message reset.

 

I'm going on my own experience with my own car, albeit an S-type but I know of no difference with XJ EPB mechanisms. In my case there was almost no pad material left.

If the EPB can be released manually and the caliper can be lifted clear of the rotor to remove the old pads, the tool should be able to retract the piston fully. Not quite sure in your case why it caused a problem with the cable and lever.

 

The system is largely unchanged between the later XJ X350s (2006 onwards) and the X351, with many identical parts, but the earlier X350s did have different calipers. I'm not sure about a 2003 S-Type, but I would expect that to have the earlier style brakes fitted to the launch X350 unless it is the SC version?

Calipers aside, the EPB side looks to be slightly different between the X350/X200 as the X350/X351 parts are stamped with 2W93 engineering references which was the code for the launch X350 parts, and the S-Type was engineered first. The system was probably adapted from the S-Type though as most of the other parts are shared.

Although I did change the rear brake pads on my X350 with the earlier brakes, I don't remember if they could be wound in further with just a manual cable release, and it now has the later larger brakes fitted as I had a spare set and the consumables are cheaper going forward. (They bolt straight onto the original hub carriers.) On the latter ones I tried both sides and it would not wind any more than at most 5mm but probably a bit less. The pistons need to be fully wound back (flush) to clear a new set of pads. At the extreme it was pulling hard on the park brake cables and I could get no more slack on them. (As noted in my last reply, I did not attempt to reapply and release which may give more slack to work with.)

 

Pardon my ignorance, but as the Parking Brake on the x351 are electronically applied I have not seen where there is a cable.

 

The parking brake is only electric between the switch, module and motor, the rest is basically the same as a manual parking brake setup. The motor pulls two 'bike cables' which force each rear calliper piston to engage, and slacks them off when disengaged.

The motor sits centrally above the fuel tank. The cables are easily visible s thick black cables looping onto the callipers from the rear of the wheels.

 

xdave , hello

It would be interesting to know what you think happens inside the caliper when the handbrake is applied .

Cheers ,

 

Referring to the attached picture, when applied the cable pulls the lever which forces the piston onto the rear pad. When released the cable is slackened and the spring and pressure in the caliper moves the lever back to its resting position. The former is hydraulically assisted.

I suspect if the piston moves enough to wind on it will do (if the foot brake was not applied first to move it out). Having handled a few of the calipers now (on my workbench) they are fairly simple assemblies.

[ edited ]

Added picture of motor and cables as requested. In normal operation the cables are only moved enough to disengage allow the normal minimal play between the piston and screw which is why you need to run the release routine (or power the motor) to fully extend the cables and allow you to wind them back fully.

 

I thought the caliper innards were purely mechanical for the parking brake, not hydraulic. (?)

 

Correct Mickey , the handbrake mechanism in the caliper is purely mechanical .

xdave , with all due respect , I think your well conversant of the model , but as far as the brakes go , I would sit this one out .

As I said with all due respect .

Cheers .

 

Semantics maybe; they are assisted by but not dependent on the hydraulics. They use a mechanical adjuster screw which is forced tight against the piston and held under the cable tension when the lever is applied. That basic approach is the same in almost all (if not all?) caliper brands whether cable-driven or motor-on-caliper, evident by the need to wind back the pistons to retract the screw, and the requirement to have a mechanical fallback. (Whether you can call an electronically activated brake a mechanical fallback is another topic - if you suddenly lose hydraulic pressure and electrical power -or a gremlin- then you will have no functional brakes.)

My understanding is that the hydraulic pressure is utilised to help set the piston against the pad and pull the adjuster screw out (it is attached with a clip in the ATE ones, unsure about the earlier ones), as well as lock in the retaining nut when the pressure is released and flows out of the caliper. As you helpfully have all due respect then if that is incorrect then please can you provide a correction so I can learn? I am unsure how the nut would lock if there was no fluid back flowing out of the caliper - wouldn't you be effectively locking the brake in that scenario similar to taking a torque wrench to it, requiring pad/disc wear or winding back the adjuster screw and piston manually as there would no longer be any play when the lever/cable is released? Or does the nut lock against the corresponding end of the lever and not the inside of the caliper itself? (If it does, doesn't that make it dependent on the compressibility of a long steel wire?) None of that would affect emergency braking (the primary function) but could affect parking?

If you apply the electronic park brake without first using the foot brake it will run through a speed-determined engage routine of on, hold, and repeat until the motor feedback tells the EPB module it either failed, or has engaged. It's quite simple - it just monitors the current drawn to determine if it is under load. If you do that at a reasonable speed (e.g. 70mph but must be above 20mph) and watch or gently rest your foot on your brake pedal while that is happening you will feel it move up and down as the vacuum draws the fluid through during the 'on' phase. IIRC it is on 500ms cycles (1 second total) that get shorter with each iteration, but it's late so I may have that figure wrong? I'm unsure if the ABS module is adjusting the pressure as a boost or if it is solely down to the vacuum. I think the latter as the system seems quite simple, but I don't know.

As an aside, if there is no hydraulic pressure surely the motor has to push the screw and piston all the way from the last rest position till the piston is fully extended? The system on the X351/X350/etc. is not intelligent enough to detect when one piston has engaged and one hasn't which causes the system to fail if one of the calipers gets stuck, the cable gets stuck (it is quite common for them to wear through the outer sleeve and rust), or the lever to jam. And sometimes even just because it feels like it. That's why it gets confused if you apply the park brake with one caliper not restrained by pads+discs. (There was a revision in 2013/14 across all the models and a service action to install redesigned springs to try and drag the problem out of warranty resolve the issue.)


As a general comment only, online forums like this one exist for the sharing and discussion of information. I believe it is far more useful to post "this is what I think" and invite comment, than to simply lead and disagree.

 

xdave , the only paragraph that makes any sense is the last one , and even that's wrong !

Like you , I agree that sharing and exchanging information and experiences is a good thing , ( and there are some really good posters out there ) however , when a member asks a question to something he or she really knows little about and telling them " this is what I think " doesn't really help and it was another member who couldn't understand what you were saying .

My intent was not to offend (or educate ) but to point out that you are just simply wrong about the topic in that post .

xdave , " experience is what you know of the subject "

Cheers ,

 

Extremely helpful, thank you.

The question was, very simply:
To which I answered:
Is that answer in contention? That is based on my experience of changing the pads on these and the X350 with the same calipers around half a dozen times across those in my signature (of which I gave an actual example of why I found it to be necessary) and the published service information provided by Jaguar to prevent the OP needing to pay for their own subscription to access it.

Given the OP understood that the park brake adjuster screw needs to be rewound to retract the piston it would appear a concise answer was perfectly adequate. The only improvement I can find reading it back now is to add the word enough (added in italics above).

The only question to do with the inner workings of the calipers has been from you Sid, no one else? I have to assume your comment is only related to that - if not it would be of benefit to the forum if you would post what you believe to be the correct procedure for releasing the park brake to the service position and why you disagree.

But again you have not actually provided any information. I find it most bizare that you would enrol for and post on a forum, on which you are a valued contributor, to post "my intent is not not offend or educate, but just to point out your are wrong." (Of which you have done neither of the former.) Why bother asking your question if you have no interest in providing or engaging with the answer? Very odd.

 

The op's question was answered by Mikey in post #3

The thread was ended by the op in post #4

My question was directed to you in order to understand why you think the handbrake cable needs to be removed from the caliper in order to wind the piston back to replace the disc pads .

Cheers xdave , have a good day .

 

FWIW, when I changed the pads/rotors on my '09 XF, equipped with electrically actuated parking brakes, I did not disconnect the p/brake cables when I "wound in" the pistons.....

 

I think there may be some misunderstanding there - I am not aware that I said the park brake cable needs to be removed from the caliper. Perhaps you took "released" to mean "removed"? It doesn't, at least not here in the UK. The use of release here means the opposite of engage (i.e. releasing the tension). That is why I added the comment about "enough" to clarify that. As I am not a mind reader, it would have been far more helpful had you simply asked the question as I quoted you above in the first instance.

I also explained how to remove the cable if needed because it makes moving the caliper out of the way of the discs much, much easier so you can tie it to the suspension out of the way rather than leave it supported by the brake hoses, as well as how to recalibrate the park brake afterwards. Both are actions the OP may, and will (respectively) encounter when elbow deep in a road-used caliper that won't retract for whatever reason while trying to prevent the pad sensor cable from being pinched by the bracket or the retaining spring from coming loose.

For the avoidance of any misunderstanding, this will hopefully be very clear:

You do not need to remove the park brake cable (unless you plan to remove the calipers from the car, or want to tie them up out of the way) but you do need to release it if replacing worn pads or discs. You must not attempt to force the park brake cable back directly as it can damage winding the adjuster screw and piston back against the cable tension and the gears in the actuator which is a great way to get "Park brake fault" messages on your instrument cluster. Jaguar didn't just add that restriction for the sake of it, or to sell diagnostic software. The warnings are prominently and repeatedly given at every step, and you can read them below.

For comparison, I've also attached the instructions for leadfoot's 2009 XF which are essentially the same.

 

[QUOTE=xdave;1600393]

" If the cable won't come off the caliper bracket but is loose enough then WD40 the hell of it and try again as it can be a pita to remove if dirty. Be careful not to break the round plastic guide clip which can be removed to make it easier. "


Misunderstanding , I don't think so

I would also think that most people know you need to RELEASE the handbrake in order to replace the disc pads . ( are you that dumb over there )

By the way , release means the opposite of engage even here in Aus .