Jaguar XJ-S. Service manual - part 106

 
 

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Ed. note:  Speed Bleeders are offered by Griot’s Garage, page 708.  

Walter Acker IV notes that Speed Bleeders are made from 303 stainless steel.  He also provides internet source info: 

e-mail:  

Speedbleeder@ameritech.net

 

http://www.speedbleeder.com

 

 

BRAKE PAD WEAR WARNING SYSTEM:  The XJ-S doesn’t have one!  What a cheap car.  Even the author’s mid-
80’s Hondas have little warning squealers on the pads; when the lining gets too thin, the squealer contacts the spinning 
rotor, and the resulting racket is usually enough to get the owner to visit the shop and complain even if he has no idea 
what the squealer is for.  The Jaguar XJ40 goes a fancy-schmancy route, and actually has little electrical contacts in the 
pads connected to a warning light on the dash.  But the XJ-S has nothing, zilch, nada; the first indication the driver gets 
that the pads are worn is the expensive sound of steel pad backing plate against iron rotor.  Ray Thackeray says, “I was 
shocked to find my 1995 XJ-S didn't have pad warnings - I just had to replace the disks because I started grinding.” 

Of course, many Jaguar owners would replace the rotors when replacing pads as a matter of course, so saving the rotor 
may not be an issue.  But steel against iron also provides really lousy braking, so it is a good idea from a safety 
standpoint to replace the pads before the linings are gone.  Not only will steel on iron reduce braking effectiveness, but 
the fact that it will probably do it on one wheel before the others may also surprise you with a violent pull. 

The XJ-S owner would obviously be well-advised to inspect his linings every now and then -- even though it requires 
getting under the car to inspect the rear ones.  The lining on new pads is 3/8” thick.  The Jaguar literature specifies a 
wear limit of 1/8”; this is apparently conservative since the linings are only 2/3 used up, but they are cheap so replacing 
them at this point is a reasonable policy.  Note also that the rear pads could theoretically be used right up to just before 
the steel backing plates hit, but the fronts have anti-rattle clips that sit against the pad and will be the first thing that hits 
the rotor when the linings get thinner than the wire that clip is made of. 

Actually, there may be another reason to replace pads with that much thickness left on them.  Roger Bywater says the 
1/8” minimum thickness is “to retain adequate heat barrier to the fluid.”  In other words, the facing material itself serves 
as a layer of insulation to keep the heat generated at the friction surface from getting to the brake fluid.  Of course, if 
you always drive gently enough that the brakes never get very hot, you might not care. 

If you keep track of your pad wear rate and don’t change your driving style, you can usually predict fairly well when 
you need to start checking for worn pads.  Of course, it still wouldn’t hurt to check them every now and then; it’s a 
good way to catch other problems such as leaky calipers or sticking caliper pistons. 

 

CHOOSING NEW PADS:  Choosing new pads is largely a matter of matching the product to your driving style -- 
which means that you, as the owner of the car, should be involved in the decision.  Merely allowing a mechanic or 
dealer to install whatever pads they normally provide is not necessarily the best way to maximize your driving pleasure 
and safety. 

Much of the discussion of pads -- and brakes as a whole -- centers on the issues of how well they perform when hot vs. 
when cold.  So, the first thing that needs clarification is just what is meant by “hot” and “cold”.  We are talking about 
when the brakes are hot or cold, not the engine.  If you’ve been driving down the freeway at 70 mph for the past hour, 
your brakes are cold -- but if you just used them hard once coming to a stop on the exit ramp, they are now hot.  
Whether or not brakes are hot depends only on how hard you have been using them in the past few minutes.  And they 
cool down faster if you’ve been moving than if you’ve been parked. 

It’s simply amazing how many “experts” miss this very simple point.  If your brakes don’t work right the first time you 
apply them in the morning but work fine the rest of the day, that has nothing to do with hot vs. cold.  You have some 
other problem, possibly a sticking caliper, but very likely either your pads or rotors are rusting and the first application 
in the morning scrapes all the surface rust off. 

Obviously, if you are going fast enough, the first application of the brakes could result in hot brakes by the time the car 
comes to a stop.  The most severe test on level ground, though, is in accelerating to around 60 mph and coming to a halt 

 
 

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repeatedly.  If you accelerate to higher speeds, there is more time between applications to cool down, and more airflow 
around the car to help cool the brakes.  Of course, the real torture test for brakes is going down a mountain, where you 
can easily perform such a test without even using the engine -- or worse, using the engine to accelerate to 60 mph much 
faster than you could on level ground -- and then using the brakes repeatedly or constantly to limit speed.  It is not 
reasonable to expect Jaguar -- or any automobile company -- to design brakes that will withstand whatever downhill 
road you can possibly find.  If you are going down a hill that is clearly beyond the norm, either proceed slowly (which 
allows the brakes more time to dissipate heat), or downshift to a lower gear to use engine compression to absorb some 
of that energy. 

Just driving around town, gently applying the brakes when you come to a stoplight, etc., results in cold brakes at all 
times.  The only time Granny will ever experience hot brakes is if she goes down the mountain road, which of course 
makes it all the more dangerous since she probably has no idea what she’s doing nor what to do when her brakes begin 
to fade.  Driving that Cadillac at 25 mph may make some sense after all. 

From a safety standpoint, for street use it is of utmost importance that the brakes work well when cold.  Your typical 
panic stop is done with cold brakes.  This should be kept in mind when considering new pads. 

In simplest terms, people talk about three types of brake pads: organic, metallic, and semi-metallic.  Organics are best 
considered a cold-stop pad only.  They have four advantages:  1)  They generally require the least pedal pressure for a 
given braking action, making them popular with Granny and her arthritic legs;  2)  They wear themselves out without 
doing much damage at all to the rotors; when replacing organic pads, not only may you not need to replace rotors, you 
may actually get away without even having them turned!  3)  They are quiet; you basically cannot hear the brakes in 
operation; and 4)  They are cheap. 

Their disadvantages show as soon as they get hot, though.  Organic pads have a relatively low melting point, and the 
melting point is what results in “brake fade” -- the friction surface of the pad melts, lubricating the brake.  When this 
happens, the driver still feels a “hard” pedal, but the car doesn’t want to stop.  Organic pad materials don’t conduct heat 
very well, either, and this results in the fade being very sudden and complete; the brakes at one end of the car go from 
working properly to basically not working at all very suddenly and with little or no warning.  And when the brakes at 
one end quit, the other end (which is usually pretty hot by now already) takes up the additional load and promptly fades 
as well.  The suddenness of the transition from good brakes to no brakes is arguably as much of the danger as the fact 
that they fade at all. 

The other extreme is metallic pads.  The friction material on such pads is typically sintered iron or the like.  Having the 
melting point of iron, such pads are pretty much impervious to fade up to the point where iron melts -- at which point 
your rotors are in trouble!  This makes metallics the traditional choice for racing, but unfortunately they have 
disadvantages for street use.  First, they tend to build up a surface layer of rust -- which can cause really serious 
problems on that first stop in the morning.  Second, they require a good deal more pedal pressure to effect a stop -- 
which the racers actually consider an advantage, since the higher pedal force makes it easier for them to modulate their 
braking.  But Granny probably won’t like it.  It was a much larger problem prior to the advent of power brakes, of 
course.  Third, their coefficient of friction is generally higher when warm than when cold (the iron gets “softer” as it 
gets hotter, giving it more grip), so stopping the car when the brakes are cold -- which is basically every stop in typical 
street use -- requires that much more pedal effort.  Fourth, they make a considerable amount of noise.  We’re not talking 
about squealing here; squealing can be a problem with any pad, but is easily corrected with the proper application of 
anti-squeal compound to the back of the pad.  The noise we’re talking about here is a scraping sound, the sort of sound 
you’d expect from metal-on-metal.  Fifth, metallic pads play hell with the rotors; whenever the pads are replaced, you’ll 
be replacing the rotors as well. 

Semi-metallic pads have a friction material that is typically an organic material with particles of metal interspersed 
through it.  To a certain extent, this represents a cross between the organic and metallic pads; when the organic portion 
fades is just when the metallic portion is getting heated up enough to work best, so with any luck at all (or careful 
design on the part of the pad manufacturer) the pads will seem to work equivalently well either hot or cold.  There’s 
more to this than the simple mixture of friction materials, though: the metal particles -- which often look like shavings -
- help to conduct heat away from the contact surface, and therefore help keep the organic material cool and resist 
fading.  Some semi-mettallics appear to have copper in them instead of iron, apparently trying to maximize this effect -- 
or maybe just to avoid the rusting problems.  With either copper or iron, semi-metallic pads not only have far greater 

 
 

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resistance to fading than organic pads, but when they do fade they seem to do so gradually, telling the driver that he’s 
getting close to trouble and perhaps should take caution. 

Of course, in this day and age this discussion must be considered oversimplified at best.  There is also a type of pad 
referred to as “low-metal”, apparently similar to semi-metallic only leaning closer to organic.  Kevlar, basically a type 
of really strong plastic, is available in pads.  Asbestos is still around, but nowhere near as popular as it once was -- but 
you can get pads made with ceramic fibers which behave very similarly to asbestos, some suggest even to causing 
similar health problems.  You can now get pads with carbon in them; carbon has a much higher melting temperature 
than iron but doesn’t conduct heat well at all.  You can even get carbon-carbon pads (carbon fibers bonded together 
with a carbon substrate) which will hold together until the rotors melt -- which, of course, helps explain why many 
racing venues have gone to carbon rotors as well. 

In the US, the DOT now requires that new pads be marked with a pair of letters indicating their coefficient of friction 
(CF).  The first letter is the CF at room temperature, and the second letter is the CF at 600°F -- which is not really all 
that hot as brakes go, possibly indicating DOT’s concern with panic stops rather than performance under severe or 
racing conditions.  Whatever, if you have power brakes it’s probably of little concern to you just what the letters are; if 
the CF is low, you just push a little harder on the pedal to stop the car.  Your bigger concern should be that the two 
letters are the same.  If the first letter indicates a higher CF than the second, these pads fade a little by 600°F, which is a 
pretty low temp to be fading at.  If the first letter is lower than the second, these pads don’t work as well when cold as 
when hot.  Of course, being only one letter off or so is probably not a big deal. 

You might also note that the letter E in the DOT designation indicates a CF that is fairly close to bare steel-on-steel.  If 
you are the type that never checks for pad wear until disaster strikes, this might actually be important.  The XJ-S has no 
warnings of pad wear until the lining is gone, and when that happens you will be running steel-on-steel -- and probably 
on one wheel first.  If the linings have a CF a long ways from that of steel-on-steel, your brakes suddenly pull to one 
side -- if it’s the front brakes, probably pretty severely.  If the CF is E, though, it stops pretty well the same way it did 
before, it just makes a lot more noise.  Still, this is a minor point at best; the better idea is to be inspecting the pads 
periodically and replacing them before they’re gone.

 

You also want the front pads to match the rear pads to maintain brake balance (the importance of brake balance is 
discussed on page 430).  This important criteria is confirmed by Jaguar; with VIN 109447, the XJ-S switched from 
organic pads to semi-metallic pads from the factory, and notes in the parts list indicate clearly that if one end of an early 
car is upgraded to semi-metallics, the other end must be upgraded at the same time.  It is of considerable importance 
from a safety standpoint that the pads behave similarly both hot and cold.  At the very minimum, the CF letter 
designations on the pads should be the same for the front and rear; better yet, just use the exact same brand of pads on 
both ends of the car. 

It has come to this author’s attention that many so-called experts consider it a good idea to use semi-metallic pads at the 
front and organic pads at the rear, “since the fronts run hotter.”  This dangerous concept is apparently so popular that 
many shops don’t even discuss it with their customers, they just go ahead and install the pads accordingly!  For your 
safety, this is one place where you need to have a discussion with the shop working on your car.  If they subscribe to 
this idea, tell them in no uncertain terms that you do not, and insist upon matching pads front and rear.  If they have a 
problem with that, take your business elsewhere. 

 

REPLACING BRAKE PADS:  Replacing brake pads in Girling brake systems -- if you don’t need to turn or replace 
the rotors -- is pretty easy:  Just remove the retaining pins, slide an old pad out, squeeze the piston back into the caliper 
to make room for the thicker new pad, slide the new pad in, repeat with the other pads, and reinstall the retaining pins.  
There are a couple of tips to add here, though. 

First, although you can just squeeze those pistons back and push the brake fluid back into the master cylinder, it’s a 
better idea to open the brake bleeder and squeeze that fluid out of the system instead.  This tip goes from being merely a 
good idea to absolutely imperative if you have ABS brakes. 

Second, it is recommended that you remove and replace one pad at a time.  When pushing that piston back, even with 
the bleed screw open, you may push another piston out if there isn’t a pad in its way. 

 
 

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BEDDING IN NEW BRAKE PADS:  The frequency of this complaint, on Jaguars as well as other cars, indicates that 
the following advice should be followed closely.  Allan Charlton explains:  “My son works in a car parts firm, and they 
have had disk pad bedding-in problems.  It seems that the new asbestos-free pads need to be bedded-in properly or they 
can cause damage.  In their experience (mostly VW Golf, but also BMW and M-B) disks were blued and warped, but 
the following procedure has eliminated the problem entirely. 

“Accelerate to 60 km/h.  Use moderate brake pedal pressure to slow to 5 km/h.  Do not stop the vehicle, but accelerate 
to 60 km/h again.  Repeat ten times, with about 500 metres between applications, then stop and let the brakes cool.”  
Note: it’s probably not really a good idea to stop.  A better idea would be to continue driving for at least ten more 
minutes or so, allowing the rotors to cool while turning rather than while parked. 

“Use the brakes moderately for the next 300 km, and do not get them hot.  After that, they should be OK.  The 
procedure is intended to be used when you first install the disks--it won’t repair damage already done.” 

Peter Cohen adds, “Jaguar actually includes a paper with approximately these instructions in the box with their brake 
pads.” 

It’s not entirely clear just what this is supposed to accomplish.  The iron rotors are not the problem.  The cast iron either 
has casting stresses, or it doesn’t; if it does, they’re gonna warp the first time they get hot, and a bedding-in procedure 
won’t stop that.  If they run straight and true, you can warp them by overheating them and then parking or otherwise 
abusing them, but under normal circumstances they will work fine for their life -- even if used hard. 

The problem is apparently in the pads themselves.  One idea may be that the pads are not perfectly flat and mated to the 
surface of the rotor to begin with, and such a procedure is needed to get them applying consistent friction across the 
surface -- but it’s not clear why you couldn’t get there by just using them for a while rather than needing to do this 
bedding-in procedure. 

There is something about new pads that isn’t good.  Apparently, the manufacturing process results in the surface of a 
new pad that is different than the interior of the pad, in much the same way that the surface of concrete is smooth while 
the interior is full of rocks.  This virgin surface may not only result in different braking characteristics when new than 
after bedding in, but it may cause some other detrimental effects.  Apparently one problem is that this new surface may 
deposit substances on the rotor, and only in some places rather than all over.  Then, with continued light use, the areas 
where the deposits are are protected from rotor wear while the uncoated areas wear, and from then on the inconsistent 
wear patterns result in pulsing brakes -- even after the deposits are gone. 

Starting with VIN 125760, the XJ-S came fitted with “scorched” pads.  It is unknown whether or not this was intended 
to address the new pad problems, but it’s not likely they did it for nothing!  Various aftermarket brake pad companies 
offer “burnished” pads or “machined” pads, either of which may be methods of getting rid of the virgin surface before 
installation. 

 

BRAKE HOSES:  All automobiles have flexible hoses connecting the hard metal brake lines on the car out to the brake 
calipers that are bouncing up and down with the wheels.  Most cars have one hose per wheel, but Jaguars with inboard 
rear brakes are a little different; since the brakes are at the final drive unit rather that bouncing up and down with the 
wheels, a flexible hose to each rear wheel is not required.  However, since the entire subframe is attached to the car 
with rubber mounts, a single flexible hose is used to connect from the car to the subframe.  Hence, there are three hoses 
on the XJ-S with inboard rear brakes: two front and one rear. 

As one might expect, such hoses won’t last forever.  Like other items made of rubber in the car, they need to be 
replaced periodically -- preferably before they fail in this case. 

The OEM brake hoses come with a stripe down the side.  It’s there for a reason: so you can tell if you’re twisting the 
hose as you install it.  Make sure you don’t. 

The front brake hoses on the XJ-S come with a coil around them.  This helps prevent kinking as the steering and 
suspension move, and it also help protect the hose from abrasion if a tire manages to rub against it.  On some of the