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2010 ML350, 2010 SLK300
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Discussion Starter · #1 ·
ok, so several times now I have come across the quote from Bazzle: "..have you cleaned the tone ring?" and of course someone always asks...whats that? or where can I find it? So here is a elementary explanation and a common ABS pic of a sensor and tone ring:

The wheel speed sensor is built into the wheel bearing hub assembly.
A metal "tone ring" with a predetermined number of teeth sits between the inner and outer bearings. A Hall Effect sensor plugs into a carefully machined hole in the forging, locating it just above the tone ring.As the vehicle's wheelturns, the tone ring teeth pass by the sensor. The gaps between the teeth trigger the sensor in direct relationship to their speed. As the wheel turns faster, the teeth pass faster under the sensor. Under braking, the anti-lock computer compares the signals from the wheel speed sensors. If it sees the wheels are locked or turning at different speeds (skidding), it triggers the ABS braking system to modulate the brakes.

Since there is no direct mechanical contact between the tone ring and the sensor, the air gap between them must be precisely maintained or it will give false readings. The air gap in this type of system is normally in the range of 1mm.

NHTSA is investigating the likelihood that salt used on the roads in some states is working its way into the hub assembly via the sensor hole, contaminating the hub assembly, fouling the all-important air gap and corroding the sensor itself. When the gap is fouled in any way, the sensor can report a higher or lower speed than actual, or send a garbled, useless signal, any of which can confuse the ABS system into working when it should not, or not work when it should.

For example, coming to a low-speed stop, three of the wheel speed
sensors may be reading 50 RPM, while the contaminated sensor reports 500 RPM. The ABS braking computer compares signals and sees this situation as a vehicle out of control, one wheel turning 500 RPM and three wheels skidding at 50 RPM. Because the purpose of the ABS system is to prevent wheel lockup and skidding, it kicks in aggressively to pulse
the brakes. But when ABS triggers at too-low speeds, it significantly and
unsafely lengthens what should be a simple low-speed stop.

Ok, there ya have it. So look at your wheel hub and locate the Speed Sensor and then you will see that the sensor is pointing to the tone ring. Hope that helps. Class is adjourned. :D
 

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2001 SLK 320(217K Miles), 2002 E320 Special Edition(183K Miles)
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3,468 Posts
Thanks, it's good and precise info. Now we all know it's not something that you download to your cell phone. :D

PS. Is the NHTSA investigation a general one or specific for MB?
 

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2004 E320
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Excellent post.
I have a 2004 E320 that was reporting a ESP,ABS, errors. The errors cause the check engine light to come on, and of course the Speedtronic (cruise control) does not work under those conditions.

A 3rd party performed an analysis on the car. The mechanic went a step further and isolated the left rear speed sensor. We actually saw data coming from the seosor, but he was not a 100% that it was the problem and recommended that I take it to Mercedes Benz because they should have better equipment and a more complete knowledge base to diagnose this better than he.

I did as the mechanic recommended and took the car to XXX (dealer name redacted) – this is the closest dealer to me, here in XXX. I was charged for a diagnostic that recommend that I change the left rear wheel sensor, and possibly the wheel baring because that contains what they call a “Tone Wheel”.

According to the service manager, the tone wheel is what’s read by the wheel speed sensor, and it sometimes can develop imperfections that prevent reliable data from getting onto the car’s network. (Your post and some additional research, painted a more vivid picture of how the systems operates, and what can go wrong)

This sounded plausible, so I brought the car down last Monday to have the work done. The sensor was replaced, but I was told that baring that was ordered was the wrong part and that I actually need to change the axel because my specific model car have to “Tone Wheel” build on. This will cost 3 times as much (1,000 part, 500 labour) as the baring to repair, however.

After they change the wheel speed sensor, the errors no longer gos away periodically, as they did before the sensor was changed.

Now, after searching the part number I found:
- Part 2113500556 (axle assembly) will work with my car, and comes with a toothed ring. It also fits E 280 4MATIC 07-09, E 320 04-05, E 320 4MATIC 04-05, E 320 CDI 07-09, E 350 06-06, E 350 06-09, E 350 4MATIC 05-09, E 350 4MATIC 06-09, E 500 04-04, E 500 4MATIC 04-06, E 55 AMG 05-06, E 63 AMG 07-09
- Part 2033570382 is a toothed ring, and is part of the 2113500556 assembly.
- When searching on part 2033570382, a smooth ring is returned, and a note stating that if the toothed ring is desired, part 2113500556 must be ordered
My question is why not replace the existing ring with a smooth ring, or clean the existing ring? Its voodoo economics to pay $1,000 for an assembly that contains a $20 part that’s bad.
 

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reply to Davidw: Same thing happening here

2004 E320 Wagon. Mercedes shop recommending that I replace the rear left axle because the sensor is not reading the tone ring properly. Apparently on this car the tone ring is an integrated part of the axle - they moved it later. What a mess. Well-functioning axle, but some surface pitting on a small ring means its got to be replaced. Poor design. I am resenting it. Have you found any other fix or work-around? Thanks.
 

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Mercedes Benz E500 4Matic V8 5.0L 113.9692004 chassis 211.283
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I just bought new speed sensors and new magnetic rings - do I need to get this "toothed" ring too?
 

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2001 SLK230 Sport
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106 Posts
I just bought new speed sensors and new magnetic rings - do I need to get this "toothed" ring too?
I used to do general automotive maintenance for a living in an area of the country where rust is not prevalent. I don't recall replacing a toothed ring unless it was part of an assembly. I can see where corrosion could erode them to the point where the air gap would be too large for a reliable reading though. They don't wear and there is no electrical component to them, so unless they're badly rusted or damaged due to road debris (or a ham-handed mechanic) they should be fine. Best practice is to inspect and clean them and the sensors when ever a major brake service is performed.

IOW, eyeball 'em. If they look fine don't worry about them unless the new sensors don't solve the problem.

BTW, what's a "magnetic ring"?
 

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Mercedes Benz E500 4Matic V8 5.0L 113.9692004 chassis 211.283
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1. The magnetic ring is what goes on the axel side
2. The toothed ring goes into the hub

The rear axels are not for sale (with magnetic ring) so must chisel and replace

Hub is $130 (with toothed ring)

sound right?
 

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2001 SLK230 Sport
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I guess I've never seen the configuration you're talking about. All I recall seeing is a two piece setup as pictured in the first post.
 

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Mercedes Benz E500 4Matic V8 5.0L 113.9692004 chassis 211.283
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I used to do general automotive maintenance for a living in an area of the country where rust is not prevalent. I don't recall replacing a toothed ring unless it was part of an assembly. I can see where corrosion could erode them to the point where the air gap would be too large for a reliable reading though. They don't wear and there is no electrical component to them, so unless they're badly rusted or damaged due to road debris (or a ham-handed mechanic) they should be fine. Best practice is to inspect and clean them and the sensors when ever a major brake service is performed.

IOW, eyeball 'em. If they look fine don't worry about them unless the new sensors don't solve the problem.

BTW, what's a "magnetic ring"?
2631817

I have rear drivers side “toner ring” that’s bad

trying to figure everything I need
 

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Mercedes Benz E500 4Matic V8 5.0L 113.9692004 chassis 211.283
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I found this site - they come in all different shapes and sizes

 
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