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 ABS questions 
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Joined: Mon Apr 13, 2009 7:42 pm
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Location: Mill Hall, Pa
Post ABS questions
I know I started a thread back in the fall that kind of touched on this but I have a few questions to ask. So here we go:


1. I remember I believe it was nick saying that the transmission has a part in the abs. My question is how exactly? Does it compare tail shaft speed vs the sensor speeds? What information does the ecu use to determine how the abs will function?

2. Will a change in tire size throw readings off?


3. If I can get the car hooked up to a diagnostic machine or scan tool. What factors should I be looking for? Also will it tell me outright which sensor, if any, are bad?

Thanks ahead of time guys

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Mon Jul 29, 2013 8:08 pm
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Post Re: ABS questions
I don't know too much abt the abs but I would think that the speedometer would be what the ecu is using. Tire size should have no effect on it. The ecu reads the tire speed (by the reluctor and eye) or more of the tire speed rate of change. Meaning if the tires are moving at say 50 mph and the rate of change is say 0 or even 10 mph in a determined time, it triggers the abs to activate. I'm sure there are other factors like rpm come into play also. I do know 4 channel is way more sensitive than the 3 channel.
Like I said though I don't know too much abt abs systems so I could be way off.

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Mon Jul 29, 2013 9:05 pm
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Post Re: ABS questions
If you change tie size drastically you can cause issues, especially if you have more than one size. But ABS works with a magnet and a reluctor ring. The magnet is fixed and the reluctor ring turns with the hub or axle. If the magnet reads a rapid deceleration of the ring it triggers the ABS system. I believe more modern vehicles with stab control also compare between the individual wheels and can recognize if one wheel is decelerating and the others are not and can actuate ABS on individual wheels to increase stability. To the best of my knowledge the speedo has nothing to do with it. ABS diagnostics is normally a stand alone tool, most handheld/pocket scanners can not read their codes. If you get an ABS scanner it will tell you exactly what is wrong. Most of the time it is a bad sensor or a cracked/broken reluctor ring. On rare occasions it can be the EBCM. Off the top of my head I cannot think of a way the transmission affects ABS directly so I don't think I was the one who told you that, unless we were trying to figure out a symptom that could have been either. But maybe I had read something at that point I have since forgotten

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Thu Aug 01, 2013 7:16 pm
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Post Re: ABS questions
Try to keep your overall tire diameter within 1" front to back on an f-body, too.

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Thu Aug 01, 2013 8:04 pm
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Joined: Mon Apr 13, 2009 7:42 pm
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Location: Mill Hall, Pa
Post Re: ABS questions
Sorry for the delayed response guys. I have been stupid busy with work and my girl being home finally I haven't looked at much electronic.

Thanks for the info and now I need to find an ABS scan tool.

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'92 K1500
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Wed Aug 21, 2013 5:50 pm
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