Jaguar XJ-S. Service manual — part 111

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INBOARD REAR BRAKE CALIPER REMOVAL (DANA): If you have a Dana final drive unit, trying to make sense
of the disassembly procedures in the ROM will only cause confusion. The manuals describe the Salisbury attachment
in which the brake calipers are bolted to the inside of the flange holding the output shaft bearings in the final drive unit,
and therefore the bolts back out towards the centerline of the car. On the Dana unit, however, the calipers are bolted to
the side of the final drive housing itself, so the bolts point the other direction -- they back out towards the sides of the
car.

There apparently are no Jaguar publications describing the removal of the brake calipers from the Dana differential.
Fortunately, it’s not difficult to figure out once you’re in there; in fact, it’s easier than working on the Salisbury. Jim
Moore says, “Bolt access holes exist in the rotors and you can see them if you slide back the dust covers on the axles.
Not mentioned in Haynes, not obvious whilst on your back with halogen lamp heating up the back of your head.” Use
these access holes to remove the two bolts holding the caliper in place. Once the caliper is off, you can then remove the
rotor.

If you’re ordering parts beforehand, make sure you get rotors with the access holes if you have the Dana final drive.
Such rotors are usable on the non-Dana cars as well, although the access holes won’t serve any purpose.

If you’ve ordered the wrong rotors and don’t have time to exchange them, Tony Bryant says, “you can use the non-
holed rotors on the Dana diff. It's just a royal PITA to juggle the caliper bolts into place, and then do them up with a
open ended spanner. But it can be and has been done...” Really, if you have the non-holed rotors you might be better
advised to take them to a local machine shop and pay them to put holes in them while you wait. There are dimensions
in Figure 24 that will help, even though the two-piece rotor hub looks different.

DANA VS. SALISBURY/BREMBO ACCESS HOLES: With OEM rotors, the difference between Dana and
Salisbury rotors is obvious: the Dana has access holes. With the aftermarket Brembo rotors, the difference is no longer
so obvious. John Wynne says, “I purchased both sets of rotors. Both sets had the access holes in them. The only
difference was the location of these holes.”

Charlie Welkie says, “Guess which (Brembo) rotors I got first! Yes, the ones with holes that didn't work -- they were
too close to the center of the rotor. They were completely on the flange surface. Try as I might I just couldn't get the
caliper bolts in. By now I had determined that I had a Dana and the rotors went back for exchange. The replacements
went in very smoothly (perhaps due to all the practice I had by now). They have access holes out further that are partly
on the flange and partly in the stepped portion of the rotor.

“The Altrom number for Brembo rotors for the Dana diff (hole spacing further apart) is 094-1106. The other - smaller
spacing - number is 094-1104.”

Both sets of access holes are shown in Figure 24; the holes closer to the center are for Salisbury diffs, and the holes
closer to the outer edge are for Dana. You can check the dimensions to determine which access holes you have -- or
you can just lay the rotor on the paper and see which holes line up.

5/8” SOCKET: Whether you are using the access holes to get at the caliper mounting bolts on a Dana final drive or to
get at the output shaft bearing bolts on a Salisbury, the tool is the same: a 5/8” socket. Various reports, probably
reflecting variations in hardware, describe the access holes as being anywhere from 7/8” to 1”. If they happen to be
7/8”, you will need the right socket to fit. A high-quality six-point socket will usually fit through a 7/8” hole with a bit
of wiggle room, but a clunky 12-point from Taiwan hasn’t got a chance. If the access hole happens to be located a hair
off so the bolt head isn’t perfectly centered under it, well, things just get harder.

I’d suggest you buy a thinwall socket, except that thinwall sockets are also usually deep sockets -- and you’d be better
off with a short socket here. It’s best to just shop around with a dial caliper in your hand and buy the smallest OD short
5/8” socket you can find.

Remember: 5/8” is functionally the same size as 16mm. So, check the other drawer in the toolbox for sockets that
might work before heading for the tool store. And while you’re at the tool store, that gives you more sockets to check
for a small OD.

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Of course, you could just make sure that the access holes on your rotors are large enough -- by boring them out, if
necessary. Going to 23mm, 15/16” or even all the way to 1” will provide enough clearance for the bulkiest of 5/8”
sockets.

ONE MORE DISASSEMBLY METHOD: In addition to the two disassembly methods for the Salisbury and one for
the Dana described above, there is one other method that should work for either: splitting the caliper. Remove the
bridge tube connecting the two halves of the caliper, and remove the pivot pin for the outboard handbrake caliper.
Remove the four large bolts holding the halves of the caliper together, which allows you to remove the outboard half of
the caliper from the car. Then you can remove the rotor, which will permit better access to the bolts holding the inner
half of the caliper in place -- whether Dana or Salisbury.

BRAKE COOLING: If you regularly drive your car hard enough to get the brakes hot, you would be well advised to
improve the cooling air flow to the final drive area. A scoop on the bottom of the car directing air up into this space
might help; the Series Three E-Type came with such scoops, and it was a lighter car.

UPGRADING TO VENTED ROTORS: Jeffrey Gram installed vented rear brake rotors in his car. The interesting
thing was his reason for doing so: to reduce the tendency for the brakes to cook the final drive seals. He expects that
the use of vented rotors, even if braking performance is insignificantly improved, will extend the life of his final drive
unit. Jan Wikström -- who drives a long, twisty mountain road to work -- also installed vented rotors: “They worked
well. The old brakes worked pretty well too, and I certainly never got them hot enough to induce fade, but the oil seals
didn't last, and they seem to last well with the ventilated disks.”

There is yet another possible reason for upgrading to vented rotors. The author noticed that the outboard pads were
much more worn than the inboard pads, and Andreas Boedenauer explained: “I owned a couple (about 15) of Citroens
with inboard front brakes. All of them had almost unworn inboard pads (lubed with oil from the diff) even when the
outboard pads where completely gone. You only had some wear on the inboard pads on a brand-new car (the first 2
years). I doubt that the differential -- especially the output shaft -- on a Jaguar is 100% dry and without any greasy
surface. Maybe I am wrong and there are Jags with immaculate bone-dry new or rebuilt differentials on the road -- if
yes, I want to see them.”

What does this oily brake situation have to do with vented rotors? Because vented rotors may avoid the problem.
When oil comes out of the differential output shaft seal, some of it runs along the shaft to the disc and ends up running
down the inboard disc surface. But with vented rotors, it will come to the inner end of the air passages through the
rotor before it gets to the inboard friction surface. The oil will then pass through the air passages all the way to the
outside edge of the disk, completely bypassing the friction surfaces. Hence, if your diff output seals leak, having
vented rotors can improve your braking considerably, even when cold.

If you’re interested in upgrading to vented rotors, there are kits available. See XK’s Unlimited (page 694), Terry’s
Jaguar (page 693), or Bob Greene Developments (page 714). All of these kits provide ventilated rotors (which
inherently must be thicker than the OEM solid rotors), spacers to put between the halves of each caliper to provide
clearance for the thicker rotors, and several small parts that are necessary as a result of the caliper widening.

Brian Schreurs says, “I talked to Terry's about their kit two days ago. According to them, their kit makes no
accommodation for the handbrake whatsoever; they assume you're not going to be using it.” So, if you’d like a
working handbrake, you might want to consider other kits -- or consider the possibilities described below for obtaining
the handbrake parts you need.

If you ask around, you may find negative reports on vented rear brake kits for Jaguars. This is because GT Jaguar (now
defunct) offered vented rear brake kits that were garbage -- they didn’t fit right, you had to grind on your final drive
output shafts to bolt them in, they came with distorted hubs that caused runout in new rotors, etc., etc. Perhaps this
helps explain why they are now defunct. Whatever, note that these problems have only been reported with the GTJ
kits; the kits from all other vendors reportedly fit and work well.

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If you wish, you can upgrade to vented rotors without a kit. All you really need are the rotors themselves and a few
minor knickknacks. This has the potential of saving a little money or a lot of money, depending on your abilities to
fabricate parts yourself as opposed to employing a machine shop to do the fabrication work.

This author has installed such a do-it-yourself rear brake upgrade (making small parts but hiring a machine shop for the
hubs), and will provide considerable detail here; if you’re not interested, skip the rest of this section.

The rotors described here are two-piece style -- as are the rotors in most (not all) of the kits mentioned above. Two-
piece rotors are largely unknown in production automobiles where obviously it is cheaper to set up a casting process to
create the entire rotor as a single part. However, two-piece rotors are very common in the performance and competition
arenas, where they are well proven. In their simplest incarnation, they provide a simple benefit: the outer portion of the
rotor, the part that has the cast-in ventilation passages, can be machined from a standardized casting (or even from
brake rotors designed for other cars) rather than requiring a custom casting for each application. The center hub portion
of the two-piece rotor assembly, commonly called a “hat” because that’s sorta what it looks like in most applications, is
a non-wear item that sports most of the unique features -- bolt patterns, offsets, pilot diameters, etc. -- that make a rotor
assembly a custom fit to one car or another. Not only does using a two-piece rotor make it cheaper to obtain the custom
rotor design needed, it also makes it considerably cheaper to maintain: when the rotors get worn, only the standardized
outer portion needs to be replaced.

There are other features often incorporated into two-piece brake rotor designs including aluminum hats to save weight,
“floating” attachment schemes to better deal with thermal expansion issues, carbon outer discs to save weight and work
at higher temperatures, etc. For our purposes, we’ll be sticking with a basic design to keep the costs within reason; the
ventilation is the feature we’re looking for here.

Alan Heartfield found a company that’ll provide special-order outer discs:

Essex Parts Services Inc.
2350 Industrial Park Blvd
Cumming, GA 30041-6460 (US)
770-889-4096
fax: 800-335-7223 or 770-889-5256

http://www.latemodel.com/essex/

There are other companies that can provide such discs, including Wilwood.

Ordering discs through Essex involves filling out a “Custom Brake Disc Order Form” which they can fax to you. In the
middle of the form there is a chart where you must fill in “Nominal Dimensions” of the discs you need. Fill the form in
as follows:

MOUNTING HOLES

ØA

OUTSIDE

DIAMETER

B

THICKNESS

ØC

EYE

DIAMETER

ØD

FLANGE

INSIDE

DIAMETER

E

OFFSET

NO. DIAMETER ØM

PCD

APPROX.

WEIGHT

10-3/8” 3/4” 6-3/4” 4-3/4” 3/8”

8 5/16” 5-3/8”

The rest of the form is fairly self-explanatory -- name, address, credit card number, etc. I recommend you opt for no
cross drilling and no face grooves. I also recommend opting for straight vanes, since curved vanes result in the left
rotor being different than the right, probably more expensive, and of dubious benefit in this application.

Essex will quote you a price once they get the form. I try to avoid quoting prices in this book, but you’ll be happy with
Essex’s quote.

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Next you need a pair of “hats” to mount the discs on. For the Jaguar with inboard rear brakes, the term “hat” is not
appropriate; they are basically a flat disc with a step machined in one side. Just take a copy of Figure 24 to your
friendly neighborhood machine shop and ask for two, please.