Speedometer And Rear ABS Sensor

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Oct 23, 2005 | 06:25 AM

TexasGuy001

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Speedometer And Rear ABS Sensor

I have replaced this sensor on my 95 F150 before. It is located on the rear axle housing. I was just curious if it can be cleaned, or if it should just be replaced. Any opinions. My ABS light is NOT on as it was last time about 5 years ago, but my speedometer jumps about 5 mph or so at speeds above 55 or 60. Sometimes it wont do it and other times it does. This really is a pain because it messes with the cruise control.

Oct 23, 2005 | 07:46 AM

subford

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From: Easton,Ks

Yes it can be removed and wiped off with a rag.
You could also have something in the rear end oil, I think I would pull the rear cover and change the oil. You might be able to wipe it off while you change the oil and then you would not have to remove it. It can be broken while removing it.

Oct 23, 2005 | 08:45 AM

alz

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From: Michigan

I had a similar problem and I had to set the gap between the tone ring and the sensor very close. I believe it was less than .002 in. I think I have a bad tooth or some thing on the tone ring and the psom catches it periodically. The psom(speedo) only samples from the sensor, so it doesn't jump all the time. I even picked up another gauge cluster and it does the same thing so I know it is a problem in the rear end. Pull the diff cover off and check your tone ring for bent or broken teeth. That's probably where your problem is.

Oct 23, 2005 | 11:26 AM

FGS

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Even a small dent in the tone ring (I have also seen it called a reluctor gear) will cause spikes or dips in the speedometer and cause the ABS to act up.
When I had the rear end of my truck rebuilt, the mechanic inadvertedly put a small dent in 3 teeth with the effects described above. They had to change the ring (which meant disassembling the rear end almost completely again) to fix it.

Oct 25, 2005 | 02:37 AM

TexasGuy001

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I have heard it referred to as the excitor ring. I wonder if that is what is wrong with mine. I keep the rear LS diff fluid clean. I service that along with the tranny every 20-25K. I really don't think there is anything in the fluid. I do know that these sensors tend to fail fairly often because of all the trash that blows up on them while driving esp in the rain. I'll pull the diff cover and take a look at that ring. That could be the problem. If the sensor was the problem, wouldn't the ABS light be on or some idiot light? For 6 years or something like that my trucks speedometer has fluctuated just ever so slightly at higher speeds. I would say about 1 mph. In the last couple months it does this jumping 10-15 mph above the speed you are going. This only happens above around 60 though. I wonder if that 1 mph fluctuation is the excitor ring. I really think this is the sensor.

Last edited by TexasGuy001; Oct 25, 2005 at 02:41 AM.

Oct 25, 2005 | 08:35 AM

FGS

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As I see it, there are 2 ways of checking it. The Ideal one would be lifting the truck up, unbolting the differential cover, and with the transmission or transfer case in neutral, slowly turn the driveshaft in order to make the ring gear turn. In this way, you will be able to check the teeth of the excitor ring for damage. The other way would be jacking up the truck , unbolting the differential ABS sensor, and turn the driveshaft to see the teeth through the sensor hole in the differential housing. I would honestly go with the first one.

Take into consideration while checking the excitor ring, that even the slightest inperfections on the surface of the teeth will make a difference Do not think upon this ring as a gear. Gears can be slightly worn or dented and they will still work in most cases. This ring works through magnetic influence between it and the sensor. If the magnetic field between the two is altered, the readings will be affected. All this simply means that if you find any imperfection at all, you will need to change the ring.

Last edited by FGS; Oct 25, 2005 at 09:09 AM.

Oct 25, 2005 | 02:20 PM

alz

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From: Michigan

I had the cover off mine and could not see anything wrong with the ring. But I know that is where my problem lies. I put an oscilliscope on the speed sensor leads and could see the spike while I was driving. It repeated itself on every revolution. Visually with the naked eye or by touch there was nothing wrong with the ring. When the rear end goes I will be replacing the exciter ring along with the rebuild.