[xj-s] ABS sensor cleaning and question about bleeding brakes

Well, as you may know I had this problem with the car
veering to the left when the ABS kicked in.

Yesterday, as well as replacing the flexible hoses, I
cleaned the front ABS sensors. They were both covered in
grease. It appears that the dodgy seals on the front wheel
bearings mean that grease is migrating up to the ABS ring,
and it is then scooped up by the ABS sensor! I’d expect all
ABS cars to have the same problem.

The result is that the problem appears to be fixed, if you
ignore the first hard brake I did last night when the car
veered to the right! Half a dozen subsequent stops resulted
in the car braking nice and straight with ABS working. So
I’ll tentatively say its fixed.

I’d say to anyone with ABS brakes, that they should clean
the ABS sensors routinely - how about whenever doing any
brake work or repacking the bearings?

Finally my question. I replaced the brake fluid and blead
the brakes. Now I’ve noticed that it is possible with a lot
of pressure to push the brake pedal down to the stop. Is
this normal? There is no problem with braking power.–
1990 XJ-S V12 Convertible, Glacier White, 59K miles
San Jose, CA, United States
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In reply to a message from Mark H sent Wed 30 Jan 2008:

If the brake pedel bottoms out, you most likely still have air in
the system.–
The original message included these comments:

Finally my question. I replaced the brake fluid and blead
the brakes. Now I’ve noticed that it is possible with a lot
of pressure to push the brake pedal down to the stop. Is
this normal? There is no problem with braking power.


Power
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In reply to a message from Mark H sent Wed 30 Jan 2008:

Can anyone explain why grease on the ABS sensor or reluctor ring
would be a problem, since it is non-magnetic and non-electrically
conductive??–
lockheed
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In reply to a message from lockheed sent Wed 30 Jan 2008:

I’m not sure either, unless it has graphite as an additive
or contains a lot of steel wear particles - in those cases
it would be conductive. (and magnetic in the case of the latter)

Of course at this stage its difficult to know whether the
brakes are really fixed - I’ll keep testing them for a few
weeks until I’m sure the problem has gone away.–
1990 XJ-S V12 Convertible, Glacier White, 59K miles
San Jose, CA, United States
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In reply to a message from lockheed sent Wed 30 Jan 2008:

Lockeed,

From what I’ve picked up by reading, there is a metallic content in
the pads. This dust mixes with the grease and bridges the gap of
the sensor. This, in turn, reduces the available AC output for the
ABS system to sense.

Noel–
The original message included these comments:

Can anyone explain why grease on the ABS sensor or reluctor ring
would be a problem, since it is non-magnetic and non-electrically
conductive??


'92 XJS Conv, '88 XJS, 68 XKE, 1914 &'15 Ford Model T’s
Edmond, OK, United States
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In reply to a message from Jags+30jugs sent Thu 31 Jan 2008:

Oh, interesting. Seems that there are plenty of candidates
to increase the conductivity of the grease. Maybe I should
go and measure the resistivity of some old grease?

Could someone try to see if it’s possible, with sufficient
force on the brake pedal, to push it to the stop? It hits
the stop long after the brakes would lock up, but still - I
can’t do this on my BMW. The brake pedal on the Jag does not
feel spongy, BTW.–
1990 XJ-S V12 Convertible, Glacier White, 59K miles
San Jose, CA, United States
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In reply to a message from Mark H sent Thu 31 Jan 2008:

Mark,

An electrical circuit is not being completed between the reluctor
and the sensor. It is strictly a magnetic field. Graphite is non-
magnetic as is steel of any quality - try sticking a magnet to your
stainless silverware or appliances. Iron particles are magnetic,
and if in the grease, could be a factor.–
lockheed
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In reply to a message from Mark H sent Thu 31 Jan 2008:

Mark,
What causes yellow soap based grease to turn black in use??
Metal!!

I can only hit bottom if the system is not bled fully.

BTW, Bleeding needs to NOT be done SLOWLY as some suggest. After
the initial purge of the master cylinder plus extras you need to
shove the bubbles of air OVER the top of high spots and pump again
ASAP to prevent the bubble from oozing back to the top of the high
spot and, therefore, remaining there due to the technique being
used by the bleeder.

I cannot stress how convenient and cheeep a set of 4 spring loaded
bleeders is. One such brand is ‘‘SPEEDBLEEDERS’’. Available at
Advance and other places. Check Google under ‘‘speedbleeders’’. They
make bleeding a one man job. They are also great for rapid movement
of fluid through the lines and over the above mentioned humps.

Noel–
The original message included these comments:

to increase the conductivity of the grease. Maybe I should
go and measure the resistivity of some old grease?
force on the brake pedal, to push it to the stop? It hits
the stop long after the brakes would lock up, but still - I


'92 XJS Conv, '88 XJS, 68 XKE, 1914 &'15 Ford Model T’s
Edmond, OK, United States
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In reply to a message from lockheed sent Thu 31 Jan 2008:

Normal carbon steel most definitely IS magnetic.

Some of the stainless steels are, and some aren’t.–
The original message included these comments:

An electrical circuit is not being completed between the reluctor
and the sensor. It is strictly a magnetic field. Graphite is non-
magnetic as is steel of any quality - try sticking a magnet to your
stainless silverware or appliances. Iron particles are magnetic,
and if in the grease, could be a factor.


1990 XJ-S V12 Convertible, Glacier White, 59K miles
San Jose, CA, United States
–Posted using Jag-lovers JagFORUM [forums.jag-lovers.org]–
–Support Jag-lovers - Donate at http://www.jag-lovers.org/donate04.php

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In reply to a message from Jags+30jugs sent Thu 31 Jan 2008:

I did do it with a cheap one man kit, but I think it may be
part of the problem and can admit a little air when the
pedal is released.

I would like to get some of the Speedbleeders you mentioned,
you wouldn’t happen to know the size for the XJS, would you?
That would be a great help.–
The original message included these comments:

I cannot stress how convenient and cheeep a set of 4 spring loaded
bleeders is. One such brand is ‘‘SPEEDBLEEDERS’’. Available at
Advance and other places. Check Google under ‘‘speedbleeders’’. They
make bleeding a one man job. They are also great for rapid movement
of fluid through the lines and over the above mentioned humps.


1990 XJ-S V12 Convertible, Glacier White, 59K miles
San Jose, CA, United States
–Posted using Jag-lovers JagFORUM [forums.jag-lovers.org]–
–Support Jag-lovers - Donate at http://www.jag-lovers.org/donate04.php

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