Recently purchased a 2005 F250 6.0. I noticed that sometimes when I break it feels strange...like ABS activating in rear or something. Usually at 15-30mph when breaking right after accelerating. Its a bit difficult to explain. I'm planning on getting a break inspection soon but just wondering if any ideas out there. Thanks.

Joe

 

Most likely the rear axle speed sensor is faulty as it's the most common problem. Sometimes you can just pull them and wipe off the iron wear particles that are attracted to it to fix it, but if the iron has been there too long the sensor goes bad. Can be a front wheel issue too, but it's usually 25% of the occurrence.

Attached is a image showing sensor wheel problems, but the lower image of the output signal is what I'm really trying to show. At high speeds the signal is strong enough that the ABS computer won't think there is a skidding wheel, but at lower speeds it's much easier for the decreased output to kick off the ABS. Enclosed tone wheels like on our trucks rarely have broken or damaged teeth.

 

Thanks for the diagram. Is this something pretty standard that any break shop can check for me?

 

Ford yes, others it depends on how sophisticated their test instrumentation is. If they just read codes it probably haven't set one otherwise your ABS yellow warning light would be on. And if they don't have a way to watch the voltage variance on a scope it will be "No problem found".

Taking it to a ford dealer will get you close to a $200 diagnostic charge, then the cost of replacement which is pretty easy for a mechanic in 5 min. An aftermarket Speed sensor runs about $10-15 wholesale, the Ford replacement should be around $30.

If you're not someone who does mechanical work on your vehicles considering the cost of the part vs the cost of the diagnosis, I would just change the part if the shop is not expensive. If I didn't have the instrumentation to check it, on my own truck I'd just replace. But there also have been a few cases where the wiring to the sensor has been an issue on older trucks that have seen commercial action.