When the transmission is in park the speedometer goes up fast

What I suspect what is happening if the speedometer is moving in park is there is an issue in the cluster. Did you just purchase this vehicle or did this issue just start? Does the speedometer work properly when driving?

This vehicle has a driven cable for the speedometer that is run off the tail shaft of the transmission. So if the vehicle is not moving this gear should not be moving.

I would disconnect the cable and then retest to see if it still moves. Can you get a video of this as well?

So this is a direct feed from the speed sensor through the gauge and direct to ground. Did you run a new ground wire or at least check to make sure it is a good ground? Then we need to monitor the voltage on that wire when in park and you are reving the engine. If you have voltage spikes then I would think the speed sensor is the issue. If not then the cluster must be the issue.

Okay. Clearly the wiring diagrams are not matching your vehicle so based on that information, I would think the buffer box is the issue and not the speed sensor. Assume this is the speed sensor that they are showing as your vehicle having, it is a driven gear. So if that is not spinning then there is no voltage generated. The box however, could have a short causing the issue.

Okay. Can you get a picture of the speed sensor and post it? Does the vehicle have a tachometer?

Awesome. Thanks. We will wait to hear back.

Hello, I'm Danny.

Just here to add my 2 cents. Clean connector on the gauges with alcohol and Q-tip they corrode and sometimes allow low current to jump circuit, also check and clean all your grounds. Hope this helps and thanks for using 2CarPros.

Has this issue been the same the entire time and it has never changed? You are not missing any components so the only thing I can think is we have a faulty part or like Danny said, we have dirty contacts or something like this.

To answer your question, there isn't anything else that would cause this other then one of these parts. The only other question that I have is, what gear do you have in the vehicle or do you have the speed sensor? Can you get a picture of the sensor that you have?

Okay. Can I dig a little deeper into what you mean by it has been the same "since you hooked it up"? Does that mean that you recently bought this car or whenever you got the car the speedometer was not hooked up and as soon as you hooked it up, this is what it was doing?

If that is the case, then it is safe to assume this is why it was unhooked. Which means we may be dealing with something the previous owner messed up.

I am trying to find it but there should be a driven gear that attaches to the sensor where I circled.

I am not finding the gear options but there are normally other sizes for when you change the wheel or gearing size then you can adjust the speedometer gear so that it is accurate.

This would all make sense as to what you are seeing because if that gear is wrong then the speedometer climbs too fast.

Can you remove the sensor again and see if there is a removable gear inside the unit? This is what I am not finding in the manual so we are going to have to just see if we can figure this out. As this is the way most all other vehicles of this era operated.

Got it. Thanks for the update. Just let us know whenever you get to it. Thanks

Hello again.

Just checking to see if you have any updated information for us weather permitting. Keep us updated and we'll get this issue solved. Thanks again for using 2CarPros

Danny-

Sorry, but I am not seeing the broken part? If it is inside the transmission then the only way you are going to fix that is to take it apart. Let me know if I am missing something. Thanks