ELCO Forum - Now ABS problems

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Chas
| I have had a slight problem with my brakes too, When coming to a halt
after
| slow moving (in a traffic jam), at the last moment, just as the
Cruiser
| comes to a halt I get a very slight pulse, just one, from the pedal
and the
| brakes pull to the right, this ONLY happens after slow movement NEVER
when
| driving faster.
| I assume it is something to do with the ABS but why does it only seem
to
| effect one wheel, I would have thought it would effect the whole
braking
| system?
This is absolutely normal for an ABS problem, and I had very nearly
identical symptoms.
What is happening is that a sensor has either failed, or is getting a
poor signal, and it thinks that its wheel has stopped turning when in
fact it is still moving. It occurs just before a halt because that is
when the signal to noise ratio is worst. I found that the symptoms were
provoked when coming to a gradual halt, as you describe, or when
trickling v. slowly downhill on the brakes.
The fact that you get a pull to one side suggests that it is a front
sensor, and it will be on the opposite side to the pull. (Since the
failed side will be pulsing and giving less braking effort.)
First check the wiring at the sensors, looking for dislocation or
damage. It's worth checking the wiring all the way up to the ABS
actuator (LHS of engine compartment next to windscreen washer bottle if
you have a diesel).
However it's more likely either that the sensor has failed or - quite
common - that it has a build up of gunge and iron filings on its tip
that is reducing the magnetic field at that wheel.
If the wiring looks OK then - carefully - remove the sensor, clear any
gunge out of the hole & the toothed ring, and make sure it is screwed
fully back in when replaced to give the correct gap between sensor tip
and toothed wheel.
If none of this works, or it breaks when you remove it (according to the
Toyota mechanic who did mine this can happen if the old sensor has got
corroded into the hole) then you need new front sensors. Unfortunately
you can't buy separate ones and you have to get the front pair plus
wiring harness from Toyota - not cheap. If you get to this point I
suggest taking it to a Toyota agent and getting them to plug their
computer thingy into the ABS diagnostic port to check the system.
In my case I got the pulsing you describe, but no pull to one side. It
was a back sensor that had been pushed away from its toothed ring by a
build-up of crud. However yours sounds like a front one.
Finally I'm afraid that while I can describe the problem and the
solution I can't give you a blow by blow mechanic's account of how to
fix it, since I paid Mr Toyota to do it for me. However it took a year
and repeated attempts to get to the bottom of it all, and I ended up
understanding far more about ABS than I really wanted to!
I hope this helps
Christopher Bell
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Guest
Ah,
A much better reply than mine, sounds like some hard won knowledge, nice to
know my reasoning might be right.
If I were diagnosing it (without Mr Toy's system) I would go to an empty car
park and connect my protable two channel scope up to the outputs and go for
drive - question then is what happens if all the wheel sensors are
disconnected?
I bought the scope a while ago and sometime forget I have it but it is
really good for intermittent faults in sensors & wiring, as well as digital
inputs.
Malcolm Bagley
Stafford UK
FJ45 '75 & FJ45 '76
-----Original Message-----
From: [Email address removed] [mailto:[Email address removed]] On
Behalf Of Christopher Bell
Sent: 04 June 2007 14:03
To: [Email address removed]
Subject: RE: [ELCO] ELCO Forum - Now ABS problems
Chas
| I have had a slight problem with my brakes too, When coming to a halt
after
| slow moving (in a traffic jam), at the last moment, just as the
Cruiser
| comes to a halt I get a very slight pulse, just one, from the pedal
and the
| brakes pull to the right, this ONLY happens after slow movement NEVER
when
| driving faster.
| I assume it is something to do with the ABS but why does it only seem
to
| effect one wheel, I would have thought it would effect the whole
braking
| system?
This is absolutely normal for an ABS problem, and I had very nearly
identical symptoms.
What is happening is that a sensor has either failed, or is getting a
poor signal, and it thinks that its wheel has stopped turning when in
fact it is still moving. It occurs just before a halt because that is
when the signal to noise ratio is worst. I found that the symptoms were
provoked when coming to a gradual halt, as you describe, or when
trickling v. slowly downhill on the brakes.
The fact that you get a pull to one side suggests that it is a front
sensor, and it will be on the opposite side to the pull. (Since the
failed side will be pulsing and giving less braking effort.)
First check the wiring at the sensors, looking for dislocation or
damage. It's worth checking the wiring all the way up to the ABS
actuator (LHS of engine compartment next to windscreen washer bottle if
you have a diesel).
However it's more likely either that the sensor has failed or - quite
common - that it has a build up of gunge and iron filings on its tip
that is reducing the magnetic field at that wheel.
If the wiring looks OK then - carefully - remove the sensor, clear any
gunge out of the hole & the toothed ring, and make sure it is screwed
fully back in when replaced to give the correct gap between sensor tip
and toothed wheel.
If none of this works, or it breaks when you remove it (according to the
Toyota mechanic who did mine this can happen if the old sensor has got
corroded into the hole) then you need new front sensors. Unfortunately
you can't buy separate ones and you have to get the front pair plus
wiring harness from Toyota - not cheap. If you get to this point I
suggest taking it to a Toyota agent and getting them to plug their
computer thingy into the ABS diagnostic port to check the system.
In my case I got the pulsing you describe, but no pull to one side. It
was a back sensor that had been pushed away from its toothed ring by a
build-up of crud. However yours sounds like a front one.
Finally I'm afraid that while I can describe the problem and the
solution I can't give you a blow by blow mechanic's account of how to
fix it, since I paid Mr Toyota to do it for me. However it took a year
and repeated attempts to get to the bottom of it all, and I ended up
understanding far more about ABS than I really wanted to!
I hope this helps
Christopher Bell
____________________________________________________________
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Guest
|
| Ah,
|
| A much better reply than mine, sounds like some hard won knowledge,
nice to
| know my reasoning might be right.
|
| If I were diagnosing it (without Mr Toy's system) I would go to an
empty car
| park and connect my protable two channel scope up to the outputs and
go for
| drive - question then is what happens if all the wheel sensors are
| disconnected?
|
| I bought the scope a while ago and sometime forget I have it but it is
| really good for intermittent faults in sensors & wiring, as well as
digital
| inputs.
|
That is more or less how I finally forced Mr Toyota to find the problem.
There is a diagnostic routine somewhere in the manuals - but sadly not
in the RM184E one posted last week - that involves measuring the
(static) resistance of each sensor to check for outright failure. If
they are within tolerance then you spin the wheels and measure the
voltage coming off each sensor.
I thought of the oscilloscope method, but decided not to mention it to
the nice people at Toyota in Exeter since even the idea of putting a
multimeter on it spooked them! To be fair they got there in the end.
I should think a sensitive AC meter would be good enough as one isn't
really interested in the pulse frequency, just the amplitude.
Incidentally I never had the ABS light come in fault mode, and the
Toyota diagnostic computer thingy was hopeless for pin-pointing the
fault.
I lived with it for a year until one day I was towing the horses very
slowly down a steep little slope in the village and needed to stop ...
and couldn't because the blasted ABS just kept buzzing away, and the
truck just kept on rolling. Fortunately I'd left more than enough room
to stop, and we did eventually grind to a halt about 10 yards further on
from where we should have done, but it was pretty scary at the time. I
must have been in the exact low speed regime that triggered it, and the
extra weight of trailer & horses prolonged the agony as it were.
Moral of the story: get it fixed, but in the meantime pull out the ABS
fuse as Julian has done.
As long as your ABS warning light doesn't come on you can get it through
an MoT (mine did twice) because you can restore the fuse and the heavy
braking they use in the test won't trigger the situation. You can't
leave the fuse out because they check the light against a chart showing
"should come on for <n> seconds when ignition turned on."
CB
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Jon
You're a star! I wish I'd had that manual 5 years ago.
It shows (page BR-46) that the static resistance of the front sensors
should be in the range 870 - 1270 ohms. And - yahoo!! - it shows the
use of an oscilloscope to measure the dynamic response.
More critically (page BR-49) it shows how to adjust the air gap by
changing the spacers - clearly trial and error is acceptable here. If
your sensor is OK electrically I'd say it was a dead cert that you could
fix the problem by fiddling with the air gap.
Christopher Bell
| > There is a diagnostic routine somewhere in the manuals
|
| ABS is covered in RM315E (1992) which Julian lent me for copying. I
| haven't OCR'd that section yet but there's a none OCR'd version of
just
| that section at www.mudtoys.com/manuals/RM315E-BRAKE-SYSTEM.pdf
(20.5MB).
|
| There's a short update section on ABS in RM434E (1995) but I can't
tell
| what it adds to RM315E which has lots of diagnostics information. I've
not
| yet scanned RM434E but as its a short section if you decide to do a
DIY
| investigation / repair I can scan it and pass it on.
|
| RM534E (1996) has a brake section but nothing for ABS.
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I've just printed off pages BR46-50 to show to my friendly mechanic.
TTFN
Chas
London UK 1HDT 80 Safari snorkel, Custom Winch bumper and Rear bumper
with spare wheel carrier.
----- Original Message -----
From: "Christopher Bell" <[Email address removed]>
To: <[Email address removed]>
Sent: Monday, June 04, 2007 4:35 PM
Subject: RE: [ELCO] ELCO Forum - Now ABS problems
Jon
You're a star! I wish I'd had that manual 5 years ago.
It shows (page BR-46) that the static resistance of the front sensors
should be in the range 870 - 1270 ohms. And - yahoo!! - it shows the
use of an oscilloscope to measure the dynamic response.
More critically (page BR-49) it shows how to adjust the air gap by
changing the spacers - clearly trial and error is acceptable here. If
your sensor is OK electrically I'd say it was a dead cert that you could
fix the problem by fiddling with the air gap.
Christopher Bell
| > There is a diagnostic routine somewhere in the manuals
|
| ABS is covered in RM315E (1992) which Julian lent me for copying. I
| haven't OCR'd that section yet but there's a none OCR'd version of
just
| that section at www.mudtoys.com/manuals/RM315E-BRAKE-SYSTEM.pdf
(20.5MB).
|
| There's a short update section on ABS in RM434E (1995) but I can't
tell
| what it adds to RM315E which has lots of diagnostics information. I've
not
| yet scanned RM434E but as its a short section if you decide to do a
DIY
| investigation / repair I can scan it and pass it on.
|
| RM534E (1996) has a brake section but nothing for ABS.
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Christopher,
"If your sensor is OK electrically I'd say it was a dead cert that you could
fix the problem by fiddling with the air gap."
This has got me thinking about what could change the sensor air gap (aside
from physical damage or fiddling).
Maybe an intermittent front wheel ABS fault under gentle breaking at low
speed could be a sign of loose wheel bearings; if the hub is sitting at
slightly the wrong angle because the bearings are loose then the drive plate
may be pushing the abs toothed ring on the CV joint away from the sensor
altering the air gap. I can't see it moving much as the bush or bearing
inside the spindle would limit it, but then again it may not need to move
far...
Putting the brakes on harder might move the hub into its correct alignment
making the fault hard to replicate.
Clutching at straws, I know - but easily checked.
Toby
1990 HDJ80
 
G

Guest

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Toby
With mine it was the build-up of junk that had physically forced the sensor outwards a bit. But I guess it could be a sign of incipient bearing failure - "lift wheel and waggle" seems indicated!
I've had a front wheel bearing failure (bearing inner sleeve turning on stub axle) and while it produced some truly horrible noises, and cost a new stub axle, it didn't produce any ABS problems. I can't help feeling that a bearing failure serious enough to produce 0.5 to 1mm movement at the ABS sensor location is going to produce lots of other horrible symptoms too - not least about 30x as much movement at the wheel rim ... assuming that the wheel is still attached to the vehicle!
It could also be "iron filings on the end of the sensor", a hint I picked up from a similar discussion in the USA a few years back on the 80s-Cool list=2E But if it is I'd be keen to know where the "iron filings" come from....
As I said before I wish I'd had that manual: it would have saved me a year of grief, =A3350 or so for a set of unneeded new front sensors, and repeated trips to see Mr Toyota. They must have been terminally brain-dead not to diagnose the problem given the amount of information listed in those pages.
CB
| Christopher,
|
| "If your sensor is OK electrically I'd say it was a dead cert that you could
| fix the problem by fiddling with the air gap."
|
| This has got me thinking about what could change the sensor air gap (aside
| from physical damage or fiddling).
|
| Maybe an intermittent front wheel ABS fault under gentle breaking at low
| speed could be a sign of loose wheel bearings; if the hub is sitting at
| slightly the wrong angle because the bearings are loose then the drive plate
| may be pushing the abs toothed ring on the CV joint away from the sensor
| altering the air gap. I can't see it moving much as the bush or bearing
| inside the spindle would limit it, but then again it may not need to move
| far...
|
| Putting the brakes on harder might move the hub into its correct alignment
| making the fault hard to replicate.
|
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