Bendix to Volvo Speed Sensor Difference

I'm by no means a Volvo guy but being that you mention Bendix I'm going out on a limb and guessing that those speed numbers might be based off the ABS wheel speed sensors and the Volvo sensor is reading transmission output speed? Just a random thought and I could be completely wrong.

 

Also, the only time I have ever had a speedometer problem was deliberately set by FFE to show 65 when actual speed was 63. I think they discontinued this secret practice.

We kept testing for 65 against milemarkers and finally our laptop with GPS revealed the problem with the tractor, and we turned it in. This was back in 2001 to adjust the tractor to 65 or speedometer to 63 etc.

We were pulled into safety and given a talking to at that time. That was not for drivers to know. But the early forms of GPS at that time were beginning to be accurate enough in real time to show what a lie or truth (Depending on how you looked at it) it was getting to be with our appt times based on 65 which was not happening.

When you have a tractor or modern car or pickup on today's computers the input values need to be correct on the sensors for whatever required by the computer for it to run well at all. I remember my tahoe's coolant temp sensor was reporting -8 fluid inside a 50 degree shop and refused to start because it did not match the outside air so the computer refused to try and make a mixture based on that wild value. The sensor was replaced. (The computer was about itself to be replaced too.. HA...)

My post is not exactly on target with the OP's target question regarding his specific volvo etc. But Im pretty certain the faulty sensor or data will be corrected somewhere and she will be running right as rain soon enough when you have a qualified person with a big enough computer to work on the problem.

In the old days speedometer problems were induced by either too tall or too short wheels and tires in those days among other problems. And it's not good for it to be inaccurate when MSP aims a speed gun at you expecting 55 mph and come up with something else.

I remember another incident during a three day 4th of holiday ATS shut off the entire electronics suite inside the tractor so I had no information as to speed etc. I fell back to the good old stop watch against mile markers bobtailing around the area visiting friends without any of it. They were none to happy about it. But with a mechanical cat that does not need a computer to run it was not a problem in them days.

 

I had same problem about year ago. From the morning or after long enough park time speedometer was accurate. After first stop or slowdown it starts lie. The more speed is the more difference. Speed sensor change didn't cure it. Then it quit by itself.
Speed sensor connected to the VECU from there by J1939 speed value going to instrument cluster and ECM.
Try to check and clean all power supply connections and grounding.

 

buddy you are checking two seperate things you have a speed sensor issue but bendix you are reading tire speed that does not get used for truck speed, i would say either tone ring is loose or something is going on at the end of the trans thats where i would start.