Author Topic: Speedo Cable Color  (Read 1502 times)

dannystarr

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Speedo Cable Color
« on: August 28, 2023, 09:27:13 PM »
I was told by a friend that I was traveling 75mph. My speedo said 65. He used a satellite application on his cell phone for the speed and pulled up to match my speed. It was EXACTLY 10mph fast. What is the speedometer cable tooth/color. It has a black one I think with 22 teeth in it now.
 Transmission is a 4-speed M21 with 3.73 rear axle gears. Tires are Good-Year Wide Tread GT with 3.73 and only 100 miles on them. I see MANY colors and charts online ALL giving different teeth counts with the same color? ... Danny

dannystarr

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Re: Speedo Cable Gear Color
« Reply #1 on: August 30, 2023, 02:00:51 PM »
I forgot the word gear. I don't need the trans gear info. D

camaronut

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Re: Speedo Cable Color
« Reply #2 on: August 30, 2023, 04:40:52 PM »

x66 714

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Re: Speedo Cable Color
« Reply #3 on: August 30, 2023, 06:44:51 PM »
Danny, according to the factory parts book, it should be black, 23 tooth, pn# 3860346. You speedometer is off by percentages. It just happens to be 10 mph at that speed. No adapter used with that gear ratio....Joe
See America's First, Chevrolet

1968 Z/28 Corvette Bronze. Black Hounds Tooth. 02E Los Angeles born 3/13/1968 pnt OO. Purchased March 1976
1969 SS396 Yellow/Yellow 08E Norwood born 8/28/1969 pnt 76E. Purchased April 1981

dannystarr

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Re: Speedo Cable Color
« Reply #4 on: August 30, 2023, 08:25:28 PM »
WOW.. I would have thought after 80 or 100 MPH it would be off. That's the way those old cars worked. But reading 65 but actual speed is 75, that sucks. Any trick to make it more accurate between 50 and 75?  Less teeth or more teeth? 
Using that tire chart site   373 X 20.2 = 7,534.6   Divided X 26.73 = 28. Only 17 to 24 tooth gears on the chart... SSSOOO? No 28 or 3.73 on that chart... Just thought maybe someone knew that a certain gear with my set-up is more accurate. D

x66 714

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Re: Speedo Cable Color
« Reply #5 on: August 30, 2023, 08:57:17 PM »
We have speedometer calibration shops here. I would think you would also. Not really knowing how the speedometer works, could the problem be there?...Joe
See America's First, Chevrolet

1968 Z/28 Corvette Bronze. Black Hounds Tooth. 02E Los Angeles born 3/13/1968 pnt OO. Purchased March 1976
1969 SS396 Yellow/Yellow 08E Norwood born 8/28/1969 pnt 76E. Purchased April 1981

rare396bronze

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Re: Speedo Cable Color
« Reply #6 on: August 30, 2023, 11:59:33 PM »
When i worked in gm parts the rule of thumb was to add teeth to slow down speedometer. To speed up speedometer subtract teeth. Where  to 1 tooth for 5mph. So try  3987921 it is 21 teeth it might be still be available from GM.  Also see them on Ebay.  3987920 is 20 teeth . Hope this helps.

dannystarr

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Re: Speedo Cable Color
« Reply #7 on: August 31, 2023, 02:32:52 PM »
As far as I know the speedo is functioning properly. I installed a new cable a while back. Since I bought the car I have put about 5,000 miles on it. And the odometer shows that....

Thank you for the gear info, that is EXACTLY the info I was hoping for. I will start my gear experiment soon. D

GMAD_Van Nuys

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Re: Speedo Cable Color
« Reply #8 on: August 31, 2023, 04:15:37 PM »
You might consider getting a speedometer reducer as they are easy to install:

http://www.camaros.org/forum/index.php?topic=15107.0

dannystarr

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Re: Speedo Cable Color
« Reply #9 on: September 03, 2023, 02:18:43 PM »
Well, I am looking at that speedo gear number and it says it is for an automatic? Does it matter?... Danny

      GM ACDelco 3987921 Original Equipment Automatic Transmission Speedometer Driven Gear

David K

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Re: Speedo Cable Color
« Reply #10 on: September 03, 2023, 03:56:00 PM »
You could also drive slower…..75 is the new 65.

x66 714

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Re: Speedo Cable Color
« Reply #11 on: September 03, 2023, 04:43:35 PM »
Well, I am looking at that speedo gear number and it says it is for an automatic? Does it matter?... Danny

      GM ACDelco 3987921 Original Equipment Automatic Transmission Speedometer Driven Gear

Depends on what part of the catalog you're looking at. Here's the 4 speed section....Joe
http://www.gmpartswiki.com/getpage?pageid=12660

See America's First, Chevrolet

1968 Z/28 Corvette Bronze. Black Hounds Tooth. 02E Los Angeles born 3/13/1968 pnt OO. Purchased March 1976
1969 SS396 Yellow/Yellow 08E Norwood born 8/28/1969 pnt 76E. Purchased April 1981

rare396bronze

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Re: Speedo Cable Color
« Reply #12 on: September 03, 2023, 06:20:34 PM »
Was used on 3'4 speed and automatic!

Mike S

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Re: Speedo Cable Color
« Reply #13 on: September 04, 2023, 03:17:07 AM »
 I bought one of these kits for my Muncie and found the right gear color (I forget which one though):
 https://www.ebay.com/itm/134008901969?var=0&mkevt=1&mkcid=1&mkrid=711-53200-19255-0&campid=5338590836&toolid=10044&customid=5f9fc9133d5a1ee9c046ade676c27d66

Mike
67 04B LOS SS/RS L35 Hardtop - Original w/UOIT
67 05B NOR SS/RS L35 Convertible - Restored

David K

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Re: Speedo Cable Color
« Reply #14 on: September 04, 2023, 03:31:47 PM »
Maybe?
14 or 15” wheels?

 

anything