Speedometer
Thread Starter
Heel & Toe
Joined: Sep 2022
Posts: 20
Likes: 2
Speedometer
I have a 1965 with a 327. The speedometer has been recalibrate this past winter and when it was reinstalled it only worked for a mile or so then dropped down to zero. I removed the blue transmission gear I noticed it was lightly worn so I replaced it and again when I took the car for a test the gauge was bouncing and registering less than actual speed and stopped working again (used a phone app). Could the cable be worn out and only working partially? Any help would be greatly appreciated. Regards Giulio
Le Mans Master
Joined: Dec 2004
Posts: 5,394
Likes: 2,769
From: Pittsburgh
2024 C2 of the Year Finalist - Modified
2023 C2 of the Year Finalist - Modified
2022 C2 of the Year Finalist - Unmodified
2019 C1 of Year Finalist (appearance mods)
Knowing that the speedo has been worked on, it would seem that it would be the cable. Is the cable hand nut on the back of the speedometer tight? If so, I would guess Cable issue! You might want to contact the party that worked on the unit last prior to spending any money!
Good Luck!
Good Luck!
Le Mans Master
Joined: Feb 2014
Posts: 8,924
Likes: 5,472
From: Richardson Texas
And, if it turns out that the cable is bad...there's only one place to buy one (if you don't feel like changing it twice).
https://deluxespeedometer.com/
https://deluxespeedometer.com/
Le Mans Master
Joined: Dec 2004
Posts: 5,394
Likes: 2,769
From: Pittsburgh
2024 C2 of the Year Finalist - Modified
2023 C2 of the Year Finalist - Modified
2022 C2 of the Year Finalist - Unmodified
2019 C1 of Year Finalist (appearance mods)
Actualy I called it a "hand nut" for a lack of the proper word. In other words it can be tighten by hand! AND re read post #3 in case the previous owner bought a inferior cable....which happens a lot!!!
Last edited by dcamick; Feb 26, 2024 at 06:39 PM.
Melting Slicks
Joined: Aug 2004
Posts: 2,056
Likes: 553
From: Sun Prairie WI
I have a 1965 with a 327. The speedometer has been recalibrate this past winter and when it was reinstalled it only worked for a mile or so then dropped down to zero. I removed the blue transmission gear I noticed it was lightly worn so I replaced it and again when I took the car for a test the gauge was bouncing and registering less than actual speed and stopped working again (used a phone app). Could the cable be worn out and only working partially? Any help would be greatly appreciated. Regards Giulio
Could you elaborate somewhat on the speedometer recalibration services you mention? Perhaps you mean that the instrument was calibrated via benchwork, repair, restoration then reinstalled in the cluster.
If so, it could follow that your transmission shaft's press-fit DRIVE gear is incompatible with your blue nylon DRIVEN gear.
There are two matching "families" of drive & driven gears, and they can't be interchanged:
* "large" (1.85" O.D.) drive gear only works with "small" (0.80" O.D.) nylon driven gears, color coded, 17 thru 22 teeth. Your 'blue' 20T lies herein.
* "small" (1.76" O.D.) drive gear only works with "large" (0.87" O.D.) driven gears, color coded, 22 thru 25 teeth.
* Large w/large will quickly tear up the nylon driven gear.
* Small w/small either won't work at all, or perhaps work briefly before skimming the teeth OD from the driven gear.
Thread Starter
Heel & Toe
Joined: Sep 2022
Posts: 20
Likes: 2
The speedometer was bench tested at 30 miles per hour @ 500 rpm and 62 miles per hour @ 1000 rpm. I contacted the previous owner and he said he didn't replace the cable but did try to play with the plastic gear because it was registering about 10 miles less he also changed the rear gears from 411s to he believes 3.23. I will remove the cable to see if it is spinning incorrectly. Is there a way to check what color gear should be in the transmission? Regards Giulio
Corvette Stories
The Best of Corvette for Corvette Enthusiasts
Top 10 Most Expensive Corvettes Ever Sold on Bring A Trailer
Brett Foote
10 Things Every Corvette Owner Needs (2026 Edition)
Michael S. Palmer
8 Most "Only Corvette Owners Understand" Quirks and Problems
Pouria Savadkouei
10 Reasons the C6 Z06 is Still A Performance Benchmark After 20 Years
Joe Kucinski
How Much Horsepower Every Corvette Engine "LOST" in 1972
Joe Kucinski
Top 10 DOs and DON'Ts for Protecting Your Convertible Top!
Michael S. Palmer
Top 10 Most Explosive Corvettes Ever Made: Power-to-Weight Ratio Ranked!
Joe Kucinski
150 hp to 1,250 hp: Every Corvette Generation Compared by the Specs That Matter
Joe Kucinski
8 Coolest Corvette Pace Cars (and Replicas) of All Time
Verdad Gallardo
Melting Slicks
Joined: Aug 2004
Posts: 2,056
Likes: 553
From: Sun Prairie WI
" ... I would guess that to change the metal gear the transmission has to be removed?..."
That would be a correct guess.
Note that each 1-tooth change is worth ~/nominal 4-5% for correcting speedo reading. If you could score/install a 22T green large 0.87" dia nylon driven gear (3860345) -- and this results in a functioning (likely somewhat inaccurate) speedo, that would demonstrate that you indeed have the small 1.76" metal press fit drive gear in the trans tailshaft.
small nylon driven gears (use with 1.85" metal, press fit, drive gear):
3987917-purple-17T
3987918-brown-18T
3987919-neutral-19T
3987920-blue-20T
3987921-red-21T
3987922-gray-22T
The large nylon driven gears (use with 1.76" metal, press fit drive gear):
3860345-green-22T
3860346-black-23T
3860347-yellow-24T
3860348-orange-25T
That would be a correct guess.
Note that each 1-tooth change is worth ~/nominal 4-5% for correcting speedo reading. If you could score/install a 22T green large 0.87" dia nylon driven gear (3860345) -- and this results in a functioning (likely somewhat inaccurate) speedo, that would demonstrate that you indeed have the small 1.76" metal press fit drive gear in the trans tailshaft.
small nylon driven gears (use with 1.85" metal, press fit, drive gear):
3987917-purple-17T
3987918-brown-18T
3987919-neutral-19T
3987920-blue-20T
3987921-red-21T
3987922-gray-22T
The large nylon driven gears (use with 1.76" metal, press fit drive gear):
3860345-green-22T
3860346-black-23T
3860347-yellow-24T
3860348-orange-25T