When the transmission is in park the speedometer goes up fast

Tiny
TREVORMCCASLIN
  • MEMBER
  • 1987 PONTIAC FIREBIRD
  • 5.7L
  • V8
  • 2WD
  • AUTOMATIC
  • 167,000 MILES
Okay, when my car is in park I rev the engine and the speedometer goes up and it goes up fast I can get to the max speed just by revving the car. Any idea what this would be?
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Saturday, October 17th, 2020 AT 7:47 PM

23 Replies

Tiny
KASEKENNY1
  • EXPERT
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?
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Sunday, October 18th, 2020 AT 7:25 AM
Tiny
TREVORMCCASLIN
  • MEMBER
This is all electric. I just recently bought the car and the wires where cut somewhere I could not find them, so I went to the buffer bot and ran new wires and bought the plugs for the speed sensor on the back of the transmission so the speedometer was never working. When I rewired it I can get my car to 80 mph in park just by revving the engine and when I put it in drive and tap on the gas it climes really fast.
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Monday, October 19th, 2020 AT 4:12 PM
Tiny
KASEKENNY1
  • EXPERT
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.
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Tuesday, October 20th, 2020 AT 8:14 PM
Tiny
TREVORMCCASLIN
  • MEMBER
This car has a buffer box and it goes from the buffer box to the cluster dash the speed sensor wires got cut somewhere by the last owner and when I rewired it not it does this before I had nothing because it was not wired. I was thinking maybe the speed sensor is going bad or the buffer box is acting up.
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Tuesday, October 20th, 2020 AT 8:48 PM
Tiny
KASEKENNY1
  • EXPERT
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.
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Wednesday, October 21st, 2020 AT 6:49 PM
Tiny
TREVORMCCASLIN
  • MEMBER
Possibly a short, but I don t think to because it moves just fine it does not glitch out and all the speed sensor is it s a box basically it does not have any gears on it or anything. I have a new sensor for it but I don t have the car currently because it had a blown head gasket.
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Wednesday, October 21st, 2020 AT 8:39 PM
Tiny
KASEKENNY1
  • EXPERT
Okay. Can you get a picture of the speed sensor and post it? Does the vehicle have a tachometer?
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Thursday, October 22nd, 2020 AT 12:37 PM
Tiny
TREVORMCCASLIN
  • MEMBER
When I get the car back yes I ll send a video and everything.
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Thursday, October 22nd, 2020 AT 6:20 PM
Tiny
KASEKENNY1
  • EXPERT
Awesome. Thanks. We will wait to hear back.
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Friday, October 23rd, 2020 AT 6:33 PM
Tiny
TREVORMCCASLIN
  • MEMBER
This is the video. Sorry it took me so long.
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Wednesday, November 25th, 2020 AT 12:48 PM
Tiny
DANNY L
  • EXPERT
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.
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Thursday, November 26th, 2020 AT 11:01 AM
Tiny
TREVORMCCASLIN
  • MEMBER
This did not do anything. But than you for the info I have a new VSS and I rewired it with all new plugs and the wires. I have a new speed buffer box put in and a new dash cluster. What else am I missing? What can mess up the speedometer other than the speed sensor in the back of the transmission? Or what?
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Saturday, November 28th, 2020 AT 8:26 AM
Tiny
KASEKENNY1
  • EXPERT
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?
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Sunday, November 29th, 2020 AT 7:42 PM
Tiny
TREVORMCCASLIN
  • MEMBER
That is the VSS that s in the back of my transmission. And yes it s been the same ever since I hooked it up.
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Monday, November 30th, 2020 AT 1:41 AM
Tiny
KASEKENNY1
  • EXPERT
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.
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Tuesday, December 1st, 2020 AT 2:41 PM
Tiny
TREVORMCCASLIN
  • MEMBER
I will check as soon as possible we are currently getting snow and I work on my vehicles outside.
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Wednesday, December 2nd, 2020 AT 7:46 AM
Tiny
KASEKENNY1
  • EXPERT
Got it. Thanks for the update. Just let us know whenever you get to it. Thanks
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Thursday, December 3rd, 2020 AT 12:12 PM
Tiny
DANNY L
  • EXPERT
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-
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Tuesday, December 8th, 2020 AT 9:10 PM
Tiny
TREVORMCCASLIN
  • MEMBER
Okay, I got the VSS out and there is like a bracket in the transmission the broke. How can I fix this?
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Saturday, January 2nd, 2021 AT 12:23 PM
Tiny
KASEKENNY1
  • EXPERT
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
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Sunday, January 3rd, 2021 AT 6:38 PM

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