[R129 SL] automatic gearbox update

[Jan Kuylaars]

It is depending on the age of the car. In the beginning the sensors are
mounted inside the differential box, that is the part that let your
wheels make more turns on the right side than left when you make a curve
to the left. If the car has not this  differential box the axes should
be damaged after a while because they make different cycles in the
curve. By terrain vehicles you can block this to have power on both
wheels in mud and sand, but drive on the road without take of the block
will damage the axes or the cardan. So inside the cardanbox they can not
become dirty, but if there is a failure it cost a lot of labour to
replace. The cardanbox and drive axes must be disambled.  Maybe your car
has a automatically blocked differential box, what can make the trouble,
look in the accessories list in your delivery note ( manual ) 
If there is a difference in your front wheels against the rear wheels
the ASR light and the block will come on.
 
So later on mercedes dicide to set the sensors like in the frontwheels (
ABS) on the same manner on the rearwheels. They are mounted near the
both axes and the brake disks. Now there is a possebility that they
become dirty with small pieces iron, and then they are not counting the
cycles anymore. 
You can take them off and clean the center ( it is a coil with softiron
center, mounted near a tandwheel on the axe ) 
You also can measure the resistance, should be a couple of ohms.  And if
the wheels are of the road and turned by hand, you can make a measure
with a osciloscope or frecuency counter.  The front sensors often are
dirty, and also the cables are sometimes broken with yes and no
connection as result. But then the ABS light also goes on. 
 
BUT; in the ASR/ABS computer there is software what is calculating with
some difference, because that is necessay when you make a curve.
Only when there is a big difference in cycles between both wheels, the
computer reconize that there is wheelslip.
 
AND; you said the light comes on after some minuts of having the motor
turns without driving. So it cannot be the sensors.
 
I believe you must search in the computer itselfs, the overvoltage
protect relay, or the instrumentcluster or some wires and/or connectors.
If some connector is not making contact , the system indicates that it
is not safe to drive with the thougt that the ASR will work.
So the system light up the warninglight so you now you must drive
carefully because the ASR system wil not work when necesarry.
 
Jan
 

-----Oorspronkelijk bericht-----
Van: r129list-bounces at mbcoupes.com
[mailto:r129list-bounces at mbcoupes.com] Namens Oldbenz1 at aol.com
Verzonden: maandag 13 augustus 2007 18:56
Aan: r129list at mbcoupes.com
Onderwerp: Re: [R129 SL] automatic gearbox update



VERY INTERESTING!  This raises some obvious questions- since I am
convinced that my gear 
box is OK (properly filled, no leaks, no suspicious behavior, maintained
better than recommended)- now I wonder the following:  exactly where are
these sensors located and can they be tested?   If one or both of the
sensors is bad will this cause the ASR light to come on?  Are the
sensors expensive and can a do-it-yourself mechanic replace them?  Can
this system be disabled without causing other electronic problems?   My
rear  wheels are both the same size and I have matching Michelin tires
mounted.
 
 
In a message dated 8/12/2007 6:48:47 P.M. Eastern Daylight Time,
J.kuylaars at kpnplanet.nl writes:


At the rear wheels ther are two sensors wich are measure the cycles from
both wheels.
So only if there is a difference betwen them, the computer reacts.

 




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