Jaguar XJ-S. Service manual — part 115

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In a straight line with water or oil only on one side of the car, ABS offers a major benefit. If the conventional brakes
are applied hard, one side of the car will slide and the car will turn violently. Alternatively, if the brakes are not applied
that hard, it takes a long distance to stop. ABS allows the brakes on the dry side to be applied hard while the brakes on
the wet side are kept from sliding, and the car can be brought to a rapid halt in controlled fashion.

In a curve, ABS provides perhaps its greatest benefit. If conventional brakes are locked in a curve, the car will slide in
a straight line, which runs it off the side of the curve and into a tree or over a cliff. Skilled drivers know this and never
apply the brakes hard in a curve; they will aim the car straight, even if it’s aimed off the road, before applying the
brakes hard. With ABS, however, it is perfectly workable to apply the brakes hard in a curve, since the wheels won’t
lock and control will be maintained. Since the curve causes a weight shift to the outside, the outside brakes can be
applied forcefully without locking the lightly-loaded inside wheels. However, this is yet another possible reason that
ABS hasn’t lived up to its promise of increased safety; drivers may still refuse to apply the brakes hard in a curve.

Loose-packed snow, gravel, or the like, may be one of ABS’s most notorious shortcomings. On such surfaces, the
quickest way to stop a car is often to lock up the wheels and let them dig in. However, ABS prevents this from
happening, so the car seemed to roll along forever, pulsing all the way. If the car ahead doesn’t have ABS and has dug
its wheels in and stopped in short order, this can be a real problem.

Of course, stunt drivers don’t care for ABS. When you see those guys in the movies spin the car around backwards and
take off in the other direction, rest assured they do not have ABS; that 180º spin requires that the steering wheel be
turned first one way, then the other way hard and the brakes locked. With ABS, they’d probably just drive off the side
of the road.

ABS brakes were introduced on the XJ-S in mid-1989.

JAGUAR XJ-S ABS BRAKES (TEVES): Here’s a brief synopsis of how the ABS brakes work on this car: There is
an electric pump and a pressure accumulator that provide pressurized fluid. When the brake pedal is depressed, the
pedal linkage moves a piston within a chamber in the ABS master cylinder. This piston directly applies pressure to the
fluid leading to the front brakes, which means the front brakes will work even if the pump stops working.

This leads some to conclude that the front brakes are not assisted, but they are mistaken. The force applied to this
piston also actuates a valve that allows pressurized fluid to enter the chamber behind this piston, helping push it forward
and applying the front brakes. The result is a 4:1 power assist on the front brakes when the system is working properly.

The pressurized fluid applied behind that piston to assist the front brakes is also ported directly to the rear brakes. The
rear brakes are therefore actuated entirely by the power assist to the front brakes. If the pump fails, you will have no
rear brakes whatsoever, save for the handbrake. Combined with the loss of power assist on the front brakes, the fact
that something is very wrong with your brakes will be apparent immediately -- even without all those warning lights lit
up on the dashboard.

Now to the ABS operation. There are three systems here: the LF, the RF, and the rear. Each of these has two solenoid
valves within the valve block. If a wheel sensor detects that a wheel has stopped rotating, the first solenoid valve closes
off the line from the master cylinder so no further pressure can be applied to that caliper. Then the next solenoid valve
opens, relieving some of the pressure within that caliper back to the brake fluid reservoir. As soon as the wheel sensor
detects that the wheel has begun rotating again, the second valve closes and then the first valve opens, applying more
pressure to the caliper. In practice this all happens over and over very quickly, leading to the characteristic pulsing of
the pedal.

With the rear brakes that are fed entirely by the pump, that’s all there is to it. With the pedal-operated fronts, however,
this alternate relieving and repressurizing would quickly allow the brake pedal to fall to the floor. So there is one more
valve involved that applies pressurized fluid directly to the front brake circuits during ABS operation to keep the pedal
up.

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BLEEDING: Stefan Schulz points out that the bleeding procedure for ABS brakes is neither obvious nor similar to
normal brakes. “Details are in section 70.25.02 of the manual. Most ABS repair operations refer specifically to
these procedures, so I guess they're kinda important.”

RESERVOIR CLEANING: With a conventional brake system, the fluid in the reservoir just sits there. With an ABS
system, it is moving all the time -- and is subject to flow restrictions. Roger Calvert reports: “I cleaned out the brake
fluid reservoir because the outlet to the pump was blocked with sludge etc. After 18 years I guess that even with
regular fluid changes there will be some 'stuff' that remains at the bottom of that lower part of the reservoir. The clue
was that the pump whine would change as some fluid got through, then got noisier as it could only get air. It wasn't that
difficult a job to do, just a bit messy.”

ALWAYS USE DOT 4 FLUID: Greg Meboe clarifies: “ABS systems call for (and need) DOT 4 fluid. Not DOT 3,
not “DOT 5” (silicone). This is not the same thing as the early British systems. The fluid required in the 50/60’s cars
must be compatable with the rubber used. The fluid readily available in the US for this just so happens to be DOT 4
spec. ABS systems require the boiling point (wet) of DOT 4 fluid, and don’t care about being compatable with old
British rubber.”

Jeb Boyd elaborates: “Do not use anything but Castrol GT LMA DOT 4 fluid. As far as the earlier (non-ABS) cars go,
I have heard great reports on the Valvoline synthetic fluid. I feel that the risks involved in the Teves system if
something goes awry are so great that I would be afraid to use anything but what is specified. I have used the Castrol
fluid in every car I have owned for twenty years and have had zero problems. I feel it is the only fluid to use and it
works great, so I have never experimented with a replacement.

“I would never presume to tell anyone what they must do, but one of my customers just paid $4000 to have a new brake
actuator replaced on his '90 due to seal failure. The seals failed due to fluid contamination from the wrong brake fluid.
I don't know what kind of fluid, and I can't prove it, but I know that the local Jaguar dealer did it. They are a Ford store
with a Jaguar franchise; Tauruses and XK8s are worked on side by side in their shop. That, IMHO, is not a good thing.
So if a Jag dealer can poison a brake system by not being careful, I will not be the one to experiment with fluids. The
label says it is compatible but will they pay for your ABS system if it trashes it? Or will they say that it must have been
your fault? I'm not willing to take the chance.”

Reportedly, Pat Goss, the host of the TV show Motor Week, said the following: “Never use silicon brake fluid in an
ABS system! [Silicon] brake fluid doesn’t like the pumping action of the ABS pump. The pistons move so rapidly that
it causes the silicon to foam and all of a sudden you have aerated fluid and you have a pedal that’s on the floor.”

PAD CHANGE: If the car has ABS brakes and the calipers are pressed back, fluid within the calipers is forced back up
the lines and into the master control system. Since the fluid that has been within the calipers for some time often has a
high degree of contamination (wear particles from the cylinder walls, etc.), when this fluid is backed into the controls it
tends to cause problems -- and very expensive problems at that. It is suggested that when pressing the calipers back
(like when installing new pads) to open the bleed port and allow the fluid to drain rather than pushing it back up the
lines. In fact, cautious mechanics will actually clamp the hose to make sure none of the junk can back up into the ABS
system.

Perhaps this isn’t a bad idea with any brakes.

ABS TESTING: Michael Neal writes: “I do extreme situation ABS test on cars during major services. I get quite a
few surprises. Even from a moderate speed of 45 mph I’ve had cars yank the steering wheel out of my hands and the
car ends up rotating 30 or 40 degrees. This is usually caused by a sticking piston or slide on a caliper.”

Pat Goss, the host of the TV show Motor Week, reportedly advised to “exercise” the ABS at least once a month on a
gravel road or in a wet parking lot -- meaning, jam the brakes and let the ABS kick in.

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BLACK BALL REPLACEMENT: The ABS system includes a black ball that serves as a pressure reservoir to allow
the brakes to operate about a half dozen times after the pump has been shut off. This accumulator contains a diaphragm
and a charge of nitrogen. If the incidence of failure reports on the online discussion list is any indication, if you have an
ABS system you will be replacing this black ball sooner or later.

With a brand new accumulator, Stefan Schultz says the ABS pump “comes on about every eight to nine "normal" brake
uses or every three times I push the pedal down all the way and release.”

When the diaphragm charge is deteriorating, the pump will kick on more often. When it comes on every application or
runs constantly, you need a new accumulator. Rusty Beard: “This is a primary concern. I have had the brakes totally
fail due to my own negligence. The equipment gets hot, as the pump is not engineered for 100% duty. Please know
how active your brake pump is. If it is extremely active, call your favorite parts supplier and buy a new pressure bulb,
like right now.”

OK, so where do you buy a new black ball? It’s Jaguar part number JLM1907; the dealer will charge you about $200.
You could go to the source; Peter Cohen says, “The ABS Accumulator Ball is made by Lemfoerder Metallwaren
GmbH, 28036 Bremen, Germany. Part Number is 834 000 008 if you happen to be in a place where you can buy or
order Lemfoerder parts.”

But there are lots of cars that have ABS brakes, and there are even lots of cars that have Teves ABS brakes. Including
GM cars. Joe Calandriello says, “The original accumulator ball can be replaced with an AC Delco part #25528382. It
can be bought at any GM dealer for around $156.00, which is quite a bit cheaper than the original ball. Napa also said
they could order it, but their price was about $177.00. I replaced mine with the AC Delco and the #'s stamped on the
ball were the same and both said made in Germany; looked identical to me.”

Andrew Weinberg confirms it’s not just an interchangeable part, it’s the same part: “The GM part is identical to the
Jag; virtually every marking on the two parts (and there were about 4-5 different number sequences) are the same,
including a pressure rating- 210 Bar. I also checked the threads -- they are the same, and the GM part also has the same
hex drive in the top. It does have a spiffy yellow warning label on it that's different, but who cares? This is an original
part for the Buick Reatta. This was for my '89 convert, but I imagine it is the same for all XJ-S with the Teves system.
Check it out. And the price is only $87 or so.”

Bryan LaPlante says, “I not long ago replaced my ABS accumulator ball in the '90 XJ-S -- with a ball listed for the
Pontiac 6000. Probably same as the Reatta part, but a lot cheaper car! Took a bit of cross-number checking, but it
bolted up fine and looks identical.”

Hey, we’re talking Delco here; there are people selling parts cheap. Peter Cohen says, “You can buy the ABS
accumulator from Keltner's Automotive (800) 666-3311 (

http://www.keltners.com

) under AC Delco part number

25528382 for US $72.62.” Hey, don’t hold this book to the price, but clearly it pays to shop online.

Another option, believe it or not, is to have the original ball renovated. Alan Baker says, “I've recently had the sphere
re-charged by Pleiades UK (01487 831239) for about 1/3 cost of a new one. Note that they are more used to re-
working the XJ40 sphere which has a larger diameter thread, so be aware. The spheres lose around 10% pressure every
year. As long as they aren't completely de-pressurised they can usually be re-charged. Look into the sphere, the
diaphragm should be seen easily if there is pressure. If the diaphragm is all the way in, chances are the sphere is scrap.”

Beard described how to remove the ball; basically, you apply the brakes hard about 50 times with the ignition off to
bleed off any pressure in the system. Then you wrap a rag around the threads to catch fluid (it will leak some), then
unscrew the old ball and screw on the new one.

Peter Cohen says, “When I did mine, I mistakenly took it to mean "put a rag underneath the threads". Since what
happens is that fluid sprays out from 360 degrees, Rusty's instructions are spot on. Just don't misread them.”

Schulz feels the spray is due to inadequate pumping. “The ROM says to discharge the brake accumulator by stomping
on the pedal twenty times before attacking it. I stomped on the pedal forty times for good measure and still, when I
unscrewed it, brake fluid squirted out far and wide. Not good. Make that sixty full-pedal-travel stomps next time.”

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Cohen: “I don't think the number of times you pump the pedal has any effect. I think I pumped 50 times. The key is to
wrap the threaded portion of the ball in a rag to absorb the fluid.”

Schulz adds, “The ROM also says that the brake pedal should go hard when the accumulator is discharged. With the
new accumulator the transition from soft to hard on discharge is sudden and noticeable; with the old one it wasn't.”

Schulz also notes that discharging the accumulator will raise the fluid level in the reservoir. If it’s too high to begin
with, it “results in a nice little fountain of brake fluid out of the valve in the reservoir cap when you discharge the
accumulator.”

Do you need to bleed the system afterwards? Cohen: “Prior to changing my black ball, I put the question to the list
about whether or not bleeding was necessary. The answer was "not necessary". That didn't seem right to me, but,
following ball replacement, the brakes worked fine without bleeding.”

Schulz disagrees. “The repair procedure in the ROM does not suggest bleeding anything after replacing the
accumulator. Since the pedal was ridiculously spongy after I did the work, I bled pump, fronts and rears anyway.
Pedal was firm afterwards. Bleeding should be part of the job.” Of course, it’s possible that Schulz’s system would
have bled itself within a few minutes of running if he had left it alone.

WHEEL BEARING FLOAT: LaRue Boyce says, “If you have trouble with the ABS unit, check out the front wheel
bearing float; it will cause the sensor to report brake problems when it is working fine.”

ABS System Removal

ABS SYSTEM REMOVAL: Some people, faced with the prospect of paying serious dollars to repair an ABS system,
opt instead to simply remove it and convert the braking system to the far more reliable and easily repairable non-ABS
power brake system used on the pre-ABS cars. Sean McKee did this job on his '90:

“Parts list:
ƒ Complete master cylinder/ vacuum booster/ pedal assembly
ƒ Check valve and vacuum adapter for RH intake manifold.
ƒ front steel brake lines

“There are really no tricks in the installation. The rear brake line screws into the master cylinder. The steel lines for the
front simply replace the existing lines. I used the fluid supply line from reservoir to pump to be used as a vacuum line
RH manifold to booster. A tab needs to be welded to the pedal to push on the brake light switch.

“Note: the ABS/brake light will remain illuminated, less a rewire, the bulb needs to be pulled.

“Pedal feel is identical to the ABS unit with the free play distance maybe slightly shorter.”

Tom Hollingsworth did the same job: “The swap was not partially difficult. You do need to replace the entire unit,
pedal to master cylinder (the pedal/box is slightly different) you'll need a few metric pieces, and a small piece of
bubble, not doubled flared, brake line.”

Obviously, you’ll want to remove much of the ABS equipment such as the pump. Maybe you can get a good price on
EBay. The wheel sensors and associated wiring can be abandoned in place.