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ABS brake sensor
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Haven’t seen one like that, but it is way better than the ones in the differential housing.
To access the sensor you may have to pull the wheels and the drum. Once the drum is off it should be completely visible.
To remove the drums you might have to struggle a little with the 5 big screws that hold the drum to the hub. Once they are off, back the slack adjuster off a little and the drum should slide right off. I use a rolling floor jack to slide the drum back. That drum is heavier than I care to lift.
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So you’re saying this is a type of external mount? Where do the wires come from if the sensors are mounted in the diff?
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The wires from the sensor ultimately go to the ABS “brain”. The sensor actually is generating voltage and frequency which the brain compares to other inputs. All inputs need to be approximately the same and when they differ without the brakes being engaged the brain sees that as a fault.
The sensor has to almost touching the part that is rotating and helping to create the voltage and frequency. Almost all the time we get an ABS light it is because the sensors are all not doing that. Obviously sensors can fail, wires can brake or crud can interfere with the operation of the sensing part of the system,
Generally you should be able to move a sensor closer to the pickup point and that cures the problem. But if not the sensors can be ohmed out and if the value is out of the range the sensor can be replaced. There will be a connector near the sensor, maybe 18″ of lead.
When the sensors are all reading properly and a difference in speed is detected at a wheel when brakes are applied, the ABS control module (the brain) opens a valve at the wheel that prevents brake system air pressure from entering the brake chamber, while exhausting air from the chamber, thus effectively allowing the wheel to unlock and spin back up to where its speed matches all others. If lock up continues it will alternately release air and allow it to reach the brake chamber to enable the wheel to stop skidding and match the speed of the other wheels. In your car you might feel that as a pulsing in the ABS system. I have not felt it in the bus but I assume it is similar.
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What I’m asking is where the sensor wires on buses equipped with in-diff sensors emerge from the axle?
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I’d be guessing. My 97 had that sensor location and I think the wires came from the top of the differential about 10″ from the pumpkin but that is a guess.
The mind don’t work so good any more.
1999 XLV X-6872, liberty #440 -
So I definitely have some sort of “externally” mounted sensors.
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The backing plate you refer to…could it be a simple dust shield? We used to get them as it kept a lot of crap out of the drum area. If it is a dust shield, it should be removable from the back side, unless the mounting fasteners are too rusty to get out. Then as Jon indicated, you may have to remove the wheel and drum.
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I guess I would characterize sensors you could access without opening up the differential as external.
If your access to the drive axle sensors is via the underside of the coach at the area of the hub and backing plate, even if it means wheel and drum removal you are far better off than the ones requiring access via the inside of the differential / axle assembly.
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