Speedometer interchange 1975-1974
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Joined: Mar 2014
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Speedometer interchange 1975-1974
Hi guys, I have a 75. My odometer went out. I managed to find a fully functional 1974 speedometer I was looking to interchange. The needle rate seems to be different however. The needle on the 75 seems to take a much faster turn rate to get spinning compared to the 74. Is this because the 75 has different internal gearing; or is it just worn?
Thanks!
Thanks!
Race Director
Joined: Apr 2009
Posts: 19,294
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From: Charlotte NC
I honestly do not think that GM changed the internal design of the speedometers that you are describing. they should be the same. But if in doubt...call company that restores them.
DUB
DUB
Melting Slicks
Joined: Jul 2009
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74 was last year for cable distributor driven mechanical drive tach....cast iron housing distributor with gear driven cable to Tach .....old school...lol
1975 would have used the electronic HEI tach gauge and the new HEI aluminum distributor.
Completely different systems
1975 would have used the electronic HEI tach gauge and the new HEI aluminum distributor.
Completely different systems
Last edited by LS4 PILOT; Dec 10, 2015 at 07:57 PM.
Race Director
Joined: Apr 2009
Posts: 19,294
Likes: 2,754
From: Charlotte NC
74 was last year for cable distributor driven mechanical drive tach....cast iron housing distributor with gear driven cable to Tach .....old school...lol
1975 would have used the electronic HEI tach gauge and the new HEI aluminum distributor.
Completely different systems
1975 would have used the electronic HEI tach gauge and the new HEI aluminum distributor.
Completely different systems
...but he was talking about a speedometer...not a tachometer.DUB
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Joined: Mar 2014
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Yep. Speedometer. So I ended up breaking down the 74 speedometer I have. Couple of points of interest. Looks like they're built exactily the same. There's a return spring to bring the needle to 0 that seems to also provide resistance against the needle spinning, so if this spring is more tightly wound, it'll be more resistant to turning. Unfortunately I muckered up my good one, so my speedo will now forever be off several mph using the old spring 
Last edited by NothingSpecial; Dec 11, 2015 at 10:00 PM.
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Race Director
Joined: Apr 2009
Posts: 19,294
Likes: 2,754
From: Charlotte NC
Yep. Speedometer. So I ended up breaking down the 74 speedometer I have. Couple of points of interest. Looks like they're built exactily the same. There's a return spring to bring the needle to 0 that seems to also provide resistance against the needle spinning, so if this spring is more tightly wound, it'll be more resistant to turning. Unfortunately I muckered up my good one, so my speedo will now forever be off several mph using the old spring
DUB