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  #1  
Old 12-29-2007, 03:58 PM
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WSS Resistance Values?

On my 124 I have been trying to trobleshoot the abs for quite some time now, getting to one thing at a time. I have checked all the WSS's and they all have connectivity but the resistance values are different. The front ones were about 1500 or 1800 ohms , i can't remember, but they were the same. The rear one was 680 ohms. So my question is what are they supposed to be? Does anybody have what these should be from the shop manual?

Thanks in advance

Kurt Kiefer

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  #2  
Old 12-30-2007, 01:25 AM
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My FSM for US models 1986 126 chassis says -
front .85k - 2.3k
rear .6k - 1.6k .
Would think this would be about right.
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  #3  
Old 12-30-2007, 05:48 PM
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Pull the sensor, clean all of the iron and rust from it, re-install. Often cures the problem.
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  #4  
Old 12-30-2007, 05:54 PM
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Testing, testing....

Does the factory have any special tests for ABS? My ('87) system apparently has some kind of problem although not enough to light the lamp. My mechanic says I may need to replace the RF sensor (I'll try the cleaning route first) and/or the pump ($$$).

Jeremy
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Our all-Diesel family
1996 E300D (W210) . .338,000 miles Wife's car
2005 E320 CDI . . 113,000 miles My car
Santa Rosa population 176,762 (2022)
Total. . . . . . . . . . . . 627,762
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  #5  
Old 12-30-2007, 06:30 PM
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What is the failure mode? If the light doesn't light, what indication do you have that it is not working properly? Does the lamp light when you first start the car?

Used pumps are available, don't ever seem to fail. I think I have three, ...
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  #6  
Old 12-30-2007, 08:10 PM
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Learning as we go...

When coasting to a stop (at a light or sign, for example) the brake pedal sometimes shudders slightly, as if the ABS were functioning to stop a skid [but the speed is too slow and there is not actually any slipping of the wheels]. My mechanic says that the ABS electronic package goes through a self-test every time it is powered up (when you start the car). The problem (whatever it is) in mine causes the ABS to continually recycle, that the self-test is what I am feeling in the pedal.

My concern (in part) is that the mechanic seems less interested in really fixing the problem and more in just throwing money (his time plus parts) at the problem. I suppose that's not uncommon. I'd rather figure out what's wrong, save some bucks, maybe learn something along the way, but I've never owned a car with ABS before the '87, much less worked on one. There may not actually be anything wrong with the pump but I wouldn't know one way or another. The brakes do seem to work.

Jeremy
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"Buster" in the '95

Our all-Diesel family
1996 E300D (W210) . .338,000 miles Wife's car
2005 E320 CDI . . 113,000 miles My car
Santa Rosa population 176,762 (2022)
Total. . . . . . . . . . . . 627,762
"Oh lord won't you buy me a Mercedes Benz."
-- Janis Joplin, October 1, 1970
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  #7  
Old 12-30-2007, 09:00 PM
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Check the ground to the pump, just for grins.

Are all of the tires the same size/make/inflation?
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  #8  
Old 12-31-2007, 08:31 PM
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Good advice

Good idea, I'll check the ground wire. The tires are all the same size, type, brand, style, color, inflation, and age (miles).

I plan to change the brake fluid and clean the front wheel sensors before doing anything else. The fluid is old and dark, hasn't been changed for quite awhile. I have a homemade pressure bleeder, worked great on my 123 car, haven't tried it on an ABS-equipped model yet -- more pressure needed or so I've read here.

In case all else fails, I scored the ABS pump from a 1988 420SEL while at Pick-and-Pull's half-price sale today. It's a Bosch 0 265 200 043. I'd like to use it in place of the unit on my '87 300D, which has a Bosch 0 265 200 026. As the attached pictures show, the two units appear identical except that the 300D's has two extra ports with plugs in them. The unit with attached piping is in my 300D; the other one is from the 420SEL.

I can't find any ABS details in EPC and the Bosch numbers don't mean anything to EPC. Anyone know whether these two units are interchangeable?

Tomorrow I'll return to P&P for the front wheel ABS sensors (forgot to bring Allen wrenches today ).

Jeremy
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WSS Resistance Values?-img_2397.jpg   WSS Resistance Values?-img_2398.jpg  
__________________

"Buster" in the '95

Our all-Diesel family
1996 E300D (W210) . .338,000 miles Wife's car
2005 E320 CDI . . 113,000 miles My car
Santa Rosa population 176,762 (2022)
Total. . . . . . . . . . . . 627,762
"Oh lord won't you buy me a Mercedes Benz."
-- Janis Joplin, October 1, 1970
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  #9  
Old 01-01-2008, 02:36 PM
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If it isn't a direct fit let me know, I might have a good used one on the shelf.

I really need to organize that stuff so I know what I have, ...
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  #10  
Old 01-01-2008, 11:14 PM
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from experience if you have different tire sizes, it will take a certain speed to set the light off. i.e. mine before would do it when I had rear snow tires on, the light came on after going above 55mph.
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  #11  
Old 01-01-2008, 11:31 PM
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Quote:
Originally Posted by wgilmore View Post
My FSM for US models 1986 126 chassis says -
front .85k - 2.3k
rear .6k - 1.6k .
Would think this would be about right.
The front sensors that I pulled off of an '88 E420 at Pick and Pull today ($3.00 each due to the half-price sale ) measured almost exactly 1.3k ohms. I'll check the ones on my '87 300DT tomorrow.

Jeremy

__________________

"Buster" in the '95

Our all-Diesel family
1996 E300D (W210) . .338,000 miles Wife's car
2005 E320 CDI . . 113,000 miles My car
Santa Rosa population 176,762 (2022)
Total. . . . . . . . . . . . 627,762
"Oh lord won't you buy me a Mercedes Benz."
-- Janis Joplin, October 1, 1970
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