Jaguar XJ-S. Manual - part 107

 
 

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original hoses, this coil was plastic.  On replacement hoses, it’s often steel.  Either seems to work fine.  However, it’s a 
simple matter to unwind the plastic ones off the old hoses, while the steel ones get thrown out with the hoses.  If your 
old hoses have plastic coils, you might want to keep them just in case you ever need to install them on replacement 
hoses. 

 

BRAIDED BRAKE HOSES:  When replacing hoses, owners often seek something better than the OEM -- usually 
deciding right off that braided stainless steel hoses simply must be better.  Unfortunately, that is usually false; the OEM 
hoses may look plain, but they are excellent and safe, and one should be very careful indeed that replacing with 
something prettier isn’t taking a serious risk. 

Mike Morrin says, “In this country (New Zealand), stainless steel braided flexible brake hoses are illegal.”  Brian 
Schreurs adds, “They were in the US as well, until quite recently, for the simple reason that they could not be made (or 
no one was willing to make them) to federal DOT standards.  Just in the last couple of years a company has started 
making DOT-legal steel braided brake hose.” 

Jim Downes explains:  “I have seen steel braided lines being the cause of the suspension of an aircraft's airworthiness 
certificate.  This resulted from specific, documented cases of the line flexing due to movement and vibration.  In turn 
the braiding cut the internal material.  The other argument against steel braid is that its presence is useless as a means of 
containing any liquid, yet it prevents any kind of inspection of the internal components.” 

Apparently, the DOT-approved lines are teflon tubing surrounded by braiding.  The teflon tubing is fully capable of 
holding the fluid pressure without the braiding, but is susceptible to stone damage so the braiding serves as physical 
protection.  The stainless steel braiding won’t chafe the teflon, either, it will simply slide back and forth on it without 
discernable damage. 

When ordering aftermarket brake lines, you need to double-check that what you are ordering will fit -- see 

 

 

http://www.jag-lovers.org/xj-s/book/SSBrakeHoses.html

 

for details on why.  For the front of the XJ-S, each of the two front hoses needs to be about 18” long tip-to-tip and have 
10mm x 1.0 threads on both ends.  For the rear of the pre-1994 XJ-S, the single hose used needs to be 10” tip-to-tip and 
has the same 10mm x 1.0 threads.  Besides the thread requirements, the fittings also must be “bulkhead” fittings, 
meaning they must have the extra length necessary to insert them through a bracket and thread a nut down to hold them 
securely and still have enough thread left to attach the rigid line without the coupling nut bottoming on the mounting 
nut.  Of course, if you plan to replace the hard lines that these hoses connect to or change the mounting scheme, you 
can end up with whatever fittings and lengths you wish. 

Note also that some suppliers provide braided brake hoses with AN fittings on the ends and some screw-on adapters to 
connect to the fittings on the car.  This is not really a problem as AN fittings are quite reliable, but nevertheless it would 
obviously be preferable to get hoses with the correct fittings so adapters are not necessary.  Walter Acker IV found a 
company that will provide such hoses custom-made: 

Baker Precision Bearing Company 
1-800-959-7757 
e-mail:  

Baker16@ix.netcom.com

 

http://www.bakerprecision.com

 

“The cost of the hose was less than the price of a new rubber hose.”  In order to get them right, Baker Precision wants 
you to ship them one of your old hoses. 

Either the OEM rubber hose (which actually is a very tiny plastic tube surrounded by a very thick rubber casing) or the 
teflon surrounded by braiding is probably an excellent hose material for the application, but the attachment schemes 
used to fasten these hoses to the fittings seem to differ.  Of the braided hose assemblies I have seen, the braid/hose is 
slid over a barb and a separate sleeve is crimped down onto the outside of the braid to secure the hose to the barb.  As a 
result, the entire weight of the hose is supported by the barb itself -- and the barb is pretty tiny on a brake line.  One 
could easily envision this barb snapping off if the hose has been bouncing around for a while or something yanks on it 
hard enough.  One could also envision the hose pulling off of that barb, or being blown off by high pressure.  The 

 
 

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chances of these problems occurring may be small, and nobody has reported such problems, but nevertheless it’s 
something to think about. 

Conversely, the OEM hose has a vastly superior attachment scheme.  The hose is once again crimped onto the barb, but 
the sleeve that is crimped around the hose is not a separate item -- it is part of the fitting itself.  Hence, the crimped 
sleeve provides mechanical support for the hose and securely prevents it from being pulled off the fitting or blowing 
off.  If you hooked a tractor to this hose, you’d probably rip the hose apart before you got it to come off the fitting. 

If you can find a braided hose made with the same type fittings as those used on the OEM hose, go for it.  If you can’t 
but nevertheless insist on replacing the OEM hoses with braided hoses, don’t try to use hoses that mount the same way 
the OEM hoses mount.  Instead, find a way to support the braided hoses by installing support clamps around the hose 
itself rather than holding it by the fittings at the end.  This may require devising some custom support brackets, bending 
or replacing some of the OEM hard lines, and getting braided hoses a little longer than the OEM hoses. 

 

BRAKE CALIPER JAMMING:  Supposedly a fairly common problem on Jaguars, even though looking at the way the 
calipers are designed it’s difficult to imagine how the pistons could jam.  Jan Wikström says, “Crud in the cylinders.  I 
think the mechanism is that the crud settles to the bottom and gets sticky, so when pressure is applied the piston tilts and 
jams -- and once it's jammed, more crud settles in the baps and keeps it that way.  I had that on both front brakes, as I 
discovered when the brakes started pulling to the right.  I had to use the Big Bad-Assed Pry Bar to shift one inside 
piston on the right and three out of four on the left.  Once I had managed to shove them in, compressed air would 
(reluctantly) move them back out, but to restore them fully I had to split the calipers and clean the bores as well as the 
pistons.  Mega-gunge, collected since 1977...” 

I’d like to suggest that regular flushing of the brake fluid -- bleeding old fluid out and new fluid in -- would keep the 
calipers free of this mega-gunge, but it is clear from the configuration of the calipers and ports that the stuff won’t come 
out without a rebuild; the bleed port is at the top, so it will clear air, not mega-gunge.  However, what regular brake 
fluid flushing will do is help keep moisture out of the calipers.  Moisture, absorbed in brake fluid that’s been in there 
too long, causes the insides of the iron calipers to rust, and the rust particles undoubtedly contribute to the mega-gunge. 

 

BRAKE CALIPER DETERIORATION:  The author had a brake caliper fail after 17 years.  Obviously, therefore, it 
would be a good idea to rebuild the calipers before they are 17 years old to avoid nasty surprises while driving.  I can 
confirm that when the one failed, the other three on the car wouldn’t have been far behind if I hadn’t gone ahead and 
addressed them all. 

The pistons are chrome-plated steel, so the recess in the side facing the pads rusts big time -- but who cares?  The 
outside surface of the piston, which is where the seal rides, is completely enclosed behind a boot, and hopefully coated 
with some red grease besides.  Between the boot and grease outside the seal and the brake fluid (flushed regularly) 
inside the seal, the piston should stay functional forever. 

The boot, however, will not.  Either from age or from the brakes running hot (or just from being British rubber!), the 
boot will eventually deteriorate.  Once it is old and rotten, it still might work a good long while if it never moves -- 
meaning the pads don’t wear so the pistons don’t come too far out of their cylinders.  Once the pads wear close to their 
1/8” service limits, the pistons protrude from the cylinders a bit, stretching the boots -- and pulling open tears in them if 
they are old and rotten.  Once opened to the elements, water gets in and washes the grease out.  This, in itself, is not 
noticed by the driver, since the seal keeps the water out of the fluid and the brakes continue to work fine.  However, the 
chrome-plated pistons start to deteriorate on the important outside surface; the chrome starts to flake off and the steel 
underneath starts to rust, causing more chrome to flake off.  If it doesn’t cause brake failure out on the road, it most 
certainly will cause brake failure the next time the pads are replaced and the rusty exposed portion of the piston is 
pushed back in past the seal. 

If you rebuild your calipers and replace the boots before they tear open and expose the pistons to the elements, the 
pistons might last forever -- which makes that caliper rebuild significantly cheaper.  So, learn from my mistakes and 
subtract a few years from 17 and plan on a caliper rebuild when the boots still look good. 

 
 

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If you replace your pads before they get anywhere near their wear limits, you may be able to go longer between caliper 
overhauls because you’re not stressing the boots as much.  It’s probably not worth it, though; the boots probably won’t 
last much longer, and pad changing isn’t that minor an operation since you need to remove the rotor and turn or replace 
it each time. 

 

BRAKE PAD RETAINING PIN CLIPS:  Now that you are fully aware of the importance of the boots on the caliper 
pistons, note that the little clips on the brake pad retaining pins tend to poke holes in those boots!  Aaaaaargh!  
Basically, the ends of the clip can hang over the edge of the boot, and then as the pads wear and the pistons protrude 
farther, the boot is pulled into the ends of the clip. 

At first blush, it seems easy enough to install the clips turned either this way or that and thereby avoid problems.  
However, whichever way the clips are installed, the pins can still rotate far enough to poke holes in the boots.  The only 
way the clips could be installed to avoid boot damage is from the inside out, and that appears to be either difficult or 
impossible to do. 

Here’s the simplest solution:  Take some steel wire, 16 gauge seems about right, and form a ring that fits snugly around 
the pin.  Slide it onto the pin and up against the head prior to installing the pin.  Now, when the clip is installed, it will 
be held close to the inner surface of the caliper.  It will be held close enough that it will be beside the edge of the boot 
rather than over it.  Hence, you will have to turn the pin to the correct position to install the clip, and once installed the 
pin will not be free to rotate. 

Richard Dowling came up with another fix:  After installing the clips, he tied the loops on the two clips to each other 
with a thin piece of wire.  By  pulling those loops towards each other, the pointy ends are kept away from the boots. 

Another idea might be to simply toss the clips and use lockwire in those holes.  Or perhaps tiny cotter pins, if you can 
figure out how to install them properly without damaging the boots. 

On the rear calipers, there is yet one more possibility, and that is to buy or make longer pins and drill holes in the 
opposite end from the head.  Then you can install the clips on the outside of the caliper where they can’t do any 
damage.  Unfortunately, this idea isn’t as workable for the front calipers due to the configuration of the outside surface 
of the caliper. 

 

BRAKE CALIPER DISASSEMBLY:  The repair manuals suggest using compressed air to get the pistons out.  This 
works pretty well on the first piston -- provided the pistons are not seized in the cylinders.  Unfortunately, when a 
piston is seized, the non-seized pistons will be the first to move, and you’ll be left with a piston stuck in a caliper and 
open cylinders where the compressed air blows out.  To get the stuck piston to move, you would need to securely plug 
the empty cylinders (with the pistons) and plug all but one of the brake fluid passages while applying air to the one 
remaining. 

If you get into such problems, you’re probably going to want to separate the caliper halves anyway.  If so, forget about 
the compressed air trick.  Once separated, turn a caliper half over and clamp the lip of the piston in a vice.  Then 
carefully twist the caliper back and forth as you slide it off of the piston. 

The ROM says: “CAUTION: Under no circumstances must the caliper halves be separated.”  The page of directions 
that comes with the Lucas rebuild kits says the same thing, and since this appears to be a generic set of directions 
(“Publication XZB214”), it probably indicates a general rule that you shouldn’t separate the halves of any brake caliper. 
 Nobody seems to know where this rule comes from, but it is clearly BS -- at least as applied to the calipers on the XJ-S. 
 Many people have chosen to ignore this warning because separating the halves is obviously necessary to properly clean 
up the cylinders, and there have been no reports of problems.  There is a seal issue on the front calipers, however -- see 
page 435. 

The tool of choice for removing the old seals from their grooves in the cylinders is a dental probe with a slightly curved 
 needle point -- but a straight pin is almost as good.  Just stick the point into the rubber itself and use it to peel the ring 
out of the groove; you’re just throwing the seal away anyway.  This method cannot possibly damage the surface of the 

 
 

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metal in the caliper unless you really screw up with the pin and scratch something, so with any care at all it’ll be perfect. 
 The same cannot be said for using a screwdriver or some such to try to get under it and pry it out. 

 

BRAKE CALIPER RESTORATION:  Old brake calipers are commonly restored to usable condition by the fitting of 
brass or stainless steel sleeves.  However, notice that this will serve no purpose on an XJ-S.  First, sleeving is normally 
done on aluminum cylinders where wear can be a concern in long-term use, but the Jaguar calipers are cast iron.  
Second, sleeving is normally only called for when the caliper is NLA, because buying a new caliper generally costs less 
than sleeving.  At least as late as 2000, Jaguar XJ-S calipers were still readily available and reasonably priced. 

However, the most compelling reason not to bother sleeving XJ-S calipers is because of their design!  As Chad Bolles 
points out, “Take a look at the design of the caliper.  You will note the piston has no seal on it, the seal is in the body of 
the caliper itself.  Therefore if the bore of the caliper is rusted and pitted it would make no difference, 'cause the seal 
rides on the piston not the bore.”  As a result, the sealing surfaces in these calipers can be completely renewed by 
simply replacing the pistons -- and the pistons are available separately for this purpose.  Just ream any big chunks of 
corrosion out of the caliper so the piston doesn’t hang up on them and reassemble; pitting or the like inside the cylinder 
does no harm. 

 

STAINLESS STEEL CALIPER PISTONS:  The caliper pistons that come in the XJ-S are chrome-plated steel.  On this 
author’s ’83, a brake failure resulted when these pistons rusted and the chrome flaked off, causing a fluid leak past a 
seal -- but the car was 17 years old when this happened, so it’s hard to fault the chrome-plated steel pistons for lacking 
durability.  Just the same, I will be using stainless steel pistons from now on, so I never have to worry about that 
particular cause of brake failures again. 

Greg Wells points out that calipers assembled with stainless steel pistons seem to go through seals quicker, though.  An 
investigation soon revealed the reason why.  The chrome-plated steel pistons are as smooth as a baby’s bottom; they 
have a ground finish, not commonly seen on chrome-plated parts (chrome is usually polished, not ground).  The 
stainless steel items, on the other hand, have an as-machined finish that, although very pretty, is quite rough; if you run 
your fingernail down the side of the piston, it “sings” to you as the nail runs across all those tiny machining ridges.  As 
these pistons slide back and forth as the brakes are applied and released, they will file away at the seal. 

At P&WA where this author once worked, the finish on parts that rubber seals moved against was considered critical, 
requiring essentially a mirror finish.  It is therefore recommended that, if you plan to install stainless steel pistons, take 
the time to polish the outside diameter on them before installation.  This will require a buffing wheel and some buffing 
compound suitable for use on stainless steel; using a hand cloth and a jar of household silver polish won’t get it.  When 
buffing, hold the piston against the wheel so that the wheel is buffing either axially or diagonally along the surface of 
the piston, not circumferentially; you want to polish those machining grooves out, not enlarge them! 

About 30 seconds on the wheel makes the surface feel considerably different, although it doesn’t look much different.  
The fingernail still sings, but it doesn’t sing anywhere near as loudly and it somehow seems less harsh -- sorta like the 
difference between a new file and a worn file.  This 30 seconds of work per piston would probably triple the lifespan of 
seals in the caliper. 

With perhaps ten minutes per piston, they actually look a bunch smoother; maybe not mirror finish yet, but the singing 
when a fingernail is run down it is almost gone.  The problem here is that the job takes patience, because the pistons get 
too hot to touch after a couple minutes on the buffing wheel, so you’ve gotta set them down and go check your e-mail 
or something.  You could just dunk them in water to cool them, but I chose not to mix water with the polishing 
compound. 

I have been unable to measure any diameter change associated with this polishing. 

Obviously, when done these pistons must be cleaned very thoroughly to remove all traces of that polishing compound.  
Wouldn’t be good in a brake system.