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1981 Trans am Turbo
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18 Posts
Discussion Starter · #1 ·
Hi all. I’m looking to replace the speedo wire since the needle is jumping all over the place. I can’t find a diagram that specifically shows where it goes and color. Anyone have one?
 

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15,958 Posts
You will get better results with topics like this if you add your vehicle information to your ”profile”. The info will appear in your post, on the left hand side right below your avatar and member name. That way people can see year/engine/etc. about the car, so they don’t have to ask.

Click on your avatar in the upper right corner of any screen. On the drop down select “Account Settings“, scroll down and complete “Vehicle Details”.

In the meantime - what year is the vehicle you are asking about? Older models use a cable to drive the speedo, newer models use wired vehicle speed sensors. We can assume it’s an 81, but let’s be sure.
 

· Registered
1981 Trans am Turbo
Joined
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18 Posts
Discussion Starter · #3 ·
You will get better results with topics like this if you add your vehicle information to your ”profile”. The info will appear in your post, on the left hand side right below your avatar and member name. That way people can see year/engine/etc. about the car, so they don’t have to ask.

Click on your avatar in the upper right corner of any screen. On the drop down select “Account Settings“, scroll down and complete “Vehicle Details”.

In the meantime - what year is the vehicle you are asking about? Older models use a cable to drive the speedo, newer models use wired vehicle speed sensors. We can assume it’s an 81, but let’s be sure.
Oh! I didn’t know you could
Do that. Great suggestion. Ill
Do that. Yes it’s an 81
 

· Registered
1977 Trans Am W72 400/4speed (swapped)
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478 Posts
You’ll have two cables with cruise. A lower, from trans to the cruise control transducer which is mounted on the drivers side inner fender in the engine compartment. Then from the transducer to the speedometer is the upper cable.

First thing I’d do is check the routing of the cable. Poor routing caused mine to jump also which I believe is mainly from bends that are too sharp. Next thing I’d consider is remove the cable from the transmission end and use a drill to turn the end counterclockwise to see if the speedometer still bounces. If not, the speedometer gears in the transmission could be the culprit. If it does, I’d remove the upper cable from the transducer and use a drill again. If it still bounces you’ll know it’s either that cable or possibly (but less likely) the speedo. If it doesn’t bounce it is either the lower cable or the transducer.
 

· Registered
1981 Trans am Turbo
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18 Posts
Discussion Starter · #9 ·
You’ll have two cables with cruise. A lower, from trans to the cruise control transducer which is mounted on the drivers side inner fender in the engine compartment. Then from the transducer to the speedometer is the upper cable.

First thing I’d do is check the routing of the cable. Poor routing caused mine to jump also which I believe is mainly from bends that are too sharp. Next thing I’d consider is remove the cable from the transmission end and use a drill to turn the end counterclockwise to see if the speedometer still bounces. If not, the speedometer gears in the transmission could be the culprit. If it does, I’d remove the upper cable from the transducer and use a drill again. If it still bounces you’ll know it’s either that cable or possibly (but less likely) the speedo. If it doesn’t bounce it is either the lower cable or the transducer.
Thanks Brian! It does need a new gear box. Would that be something that might help?
 

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1977 Trans Am W72 400/4speed (swapped)
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478 Posts
Only in the sense that there would likely be a new speedometer drive gear in the new transmission otherwise no. I did have a worn drive gear in my transmission at one point and compiled with a small diameter driven gear needed to achieve the proper ratio it caused me issues with the needle bouncing but in a different way than when my cable was routed poorly.
 
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