I just had my XK which has 17,780 miles serviced and was told that the rear brake pads are nearly worn out. I enquired as to why they would be worn out with so few miles on the car and was told by the mechanic that Jaguar has designed the brake activation system to apply the rear brakes before the front brakes are activated thus putting more stress on the rear brakes which wears them out before the front brake pads. I have never heard of such a thing as past Jaguar XKs that we have owned have never had this problem. Anyone out there know anything about this?

 

Welcome to the forum jdzubas,

I've moved your question from General Tech Help to X150 forum. Members here with the same model will be able to help.

Please follow this link New Member Area - Intro a MUST - Jaguar Forums - Jaguar Enthusiasts Forum to the New Member Area - Intro a MUST forum and post some info about yourself and your vehicle for all members to see. In return you'll get a proper welcome and some useful advice about posting to the forum.

Graham

 

Hi jdzubas,

Don't know if the reason given is valid but mine was the same -
XKR at 17000 miles, front brake wear 50%, rear brake wear 75%.

regards

Rod

 

I learned the same application is employed on my Venza. The rear pads had to be replaced before the front on my Venza with 32K. It's for "anti-dive" deployment, as I've learned.

 

Yeah, that is backwards to conventional mechanical brakes, the fronts always wear quicker than the rears for those of us that brake hard. The anti-dive explanation makes sense where the electronic braking system applies more force to the rear. If that is the case then they are just reversing the wear, so now the backs go quicker than the fronts.

17,000 miles still sounds pretty quick!

 

I'm not sure I buy the 'anti-dive' explanation - I've never heard of it, and there's nothing listed in the Owners and Workshop Manuals.
There is reference to the ABS system boosting pressure to the rear under hard braking - up the wheel lockup limit. However, in that case all wheels are braking hard (and all the pads are wearing).

I suspect the Traction Control (aka Stability Assist / DSC) system is causing this rear pad wear. This system uses the compares the wheel rotation speeds from the ABS sensors, together with a steering sensor and a Yaw Accelerometer (and a lot of software magic) to determine if the car is understeering or oversteering in a corner.
It then applies one of the rear brakes to correct the trajectory. (inside rear brake if understeering, outside rear if oversteering).
Have you seen the indicator light (looks like a rear outline of a car on an angle, with 2 wavy lines coming from the tires) ??

 

OK, so "anti-dive" may be a very simplistic explanation as to why rear pads have accelerated wear. Today, the modulation of individual wheels has gone well beyond what I employed in the 60s for rear brake pressure modulation...the "prop" valve, or, proportioning valve. This valve you adjusted pressure to the rear brakes, manually. Typically approx. 600-800 PSI to the rear and approximately 1000-1200 PSI to the front. Obviously, very archaic based on today's standards.
It's not surprising, Jag, Benz, Toy, Lexus, and numerous others are employing it.

 

Interesting discussion and what surprises me is with the braking technology why aren't the rear brake pads as large as the front pads. Other then cost it seems it would provide better overall braking . My 2 cents

 

XK rear brake pads are from S type sedan...........so your right it's cost!!!

Hope this helps you understand.............

Cheers, Adrian

 

I just had my XKR rear brake pads changed at 17k miles too. The dealer also said it was to prevent dive.

 

I can understand even though the XKR is a $100K car but if you have this independent brake technology why not go all out. What I was thinking is why not mount a set of front calipers on the rear too. Just an interesting thought . Would it work , I don't know . Is it an improvement , maybe not. Just thinking out loud.

 

Let's be thankful that we no longer have to deal with inboard rear brakes, they are not fun...
Front brake discs are big and heavy to deal with the heat from hard braking, when weight transfer unloads the rear of the car, at which point you cannot use much rear brake, which is why they do not need to be very big, (having heavy things out there with the wheels does nothing good for handling).
I don't believe XKs, at least the base models, have limited slip diffs, so I would expect that they use "traction control", braking of the wheel losing traction, to minimise wheel spin.
This "may" explain the feeling of the rear end stepping out that has been discussed.. and the need for rear pad relacements before the fronts.
I suspect that many here use hard acceleration way more than they stand on the brakes??
This is a very crude system, if I am correct, differential design has come a long way, with active torque biasing systems available on Audis, Lexus' etc..
As to the original comment, applying rear brakes to reduce front end dive sounds like a crock of ... (it, anti-dive / anti-squat, has been incorporated into suspension geometry design for decades), but I could wrong, again...
Just some thoughts for you.
Trevor

 

The cars do have anti-dive and traction control tied into the brakes but neither has anything more than minimal effect on pad durability. If the caution light for the traction control is not flashing, it's not activated. The brakes are not being applied secretly in the background as some believe.

The anti-dive engages the rear brakes milliseconds before the fronts. This slight difference in time is meaningless for pad wear.

Fitting bigger brakes on the rear or more aggressive pads is just asking for trouble by upsetting the front/rear bias.