76 speedo question
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Joined: Oct 2012
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From: Lucas TX
76 speedo question
The speedometer on my 76 almost works. That is it moves, but is jumpy especially at lower speeds. The odometer (both trip and main) do not work. Is it possible just lubricating the cable would fix the speedo? Why would the speedo needle move but not the odometer(s)? Would a stuck odometer mess up the speedo?
Drifting
Joined: Aug 2010
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From: nassau co. new york
for me the jumpy at low speed lasted only a few trips.my cable is split with a coupling by the tranny shift linkage.i disconnected at that point and ran it with my drill in reverse to determine which side had snapped.it was the 24" cable from the tranny to the coupling available at corvette central for $30.not sure about your odometer issue and how that relates.i believe they only recommend a dry type lubricant on the cable but i did not put any on mine.
Former Vendor
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From: Jeffersonville Indiana 812-288-7103
St. Jude Donor '08-'09-'10-'11-'12-'13-'14-'15
On any speedometer.. 1953-1977....
If the odometer is not working.. the speedometer needs to come out and be serviced.
When the first worm bushing wears out.. it puts the first worm A in a bind with the second worm B. The first, second, third and fourth gears are what drive the odometer and the trip odometer.
Once the bushing gets worn enough the first worm magnet will start hitting (scrapping) the speed cup... The speed cup has a shaft on it that the needle attaches to. This scrapping is what makes the needle jumpy..
Replacing (and they are available) the second worm gear with the plastic replacement is only a band-aide and actually a huge waste of time considering how hard it is to remove the speedometer from the car.
The cable can cause bouncing but again if the odometer is not working there is an issue in the speedometer.
I'd also like to remind everyone to NEVER put grease, wd-40 or other types of grease (lube) on a speedo cable. The cables are reverse wound and this will pack the grease in the speedo head.. The first worm bushing is made from oylite and the lube will cause premature failure.
If the odometer is not working.. the speedometer needs to come out and be serviced.
When the first worm bushing wears out.. it puts the first worm A in a bind with the second worm B. The first, second, third and fourth gears are what drive the odometer and the trip odometer.
Once the bushing gets worn enough the first worm magnet will start hitting (scrapping) the speed cup... The speed cup has a shaft on it that the needle attaches to. This scrapping is what makes the needle jumpy..
Replacing (and they are available) the second worm gear with the plastic replacement is only a band-aide and actually a huge waste of time considering how hard it is to remove the speedometer from the car.
The cable can cause bouncing but again if the odometer is not working there is an issue in the speedometer.
I'd also like to remind everyone to NEVER put grease, wd-40 or other types of grease (lube) on a speedo cable. The cables are reverse wound and this will pack the grease in the speedo head.. The first worm bushing is made from oylite and the lube will cause premature failure.
Last edited by Willcox Corvette; Nov 18, 2012 at 10:13 AM.
Had a 1976 L-82, 4-sp
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From: Some days your the dog and some days your the hydrant.
Royal Canadian Navy
I had a similar problem. I disconnected the speedo cable from the tranny and spun the inner cable with my fingers while the wife observed the speedometer. The speedo was working fine. The culprit was the nylon driven gear in the tranny. Easy replacement and it now works just fine.
Former Vendor
Joined: Aug 2006
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From: Jeffersonville Indiana 812-288-7103
St. Jude Donor '08-'09-'10-'11-'12-'13-'14-'15
I had a similar problem. I disconnected the speedo cable from the tranny and spun the inner cable with my fingers while the wife observed the speedometer. The speedo was working fine. The culprit was the nylon driven gear in the tranny. Easy replacement and it now works just fine.
When the odo and the speedo are both working and you have bounce then by all means you should check the gear in the tranny and the cable. The odometer not working is the key sign the head is failing.
Melting Slicks
Joined: Sep 2011
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From: Peoria Arizona
My problem is slightly different. I think it's the cable. Speedo does not work at all, expect once in a while as I take off from a dead stop. Works a little up until about 10 or 15 mph then drops back to zero. My odometer and trip may be working, but I can't tell that for sure until I get the speedo working. 4spd car so the cable is pretty cheap to replace and not horrible to replace (I hope) 
.
Adam
.Adam
Former Vendor
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From: Jeffersonville Indiana 812-288-7103
St. Jude Donor '08-'09-'10-'11-'12-'13-'14-'15
If you have cruise remove the cable form the transducer and put a drill on it.
If you don't have cruise pull the cable from the tranny and put a drill on it.
See if the speedo works.
If so, then you have a gearing problem in the tranny.
If it fails to work then I would replace the cable first and try again.
If you don't have cruise pull the cable from the tranny and put a drill on it.
See if the speedo works.
If so, then you have a gearing problem in the tranny.
If it fails to work then I would replace the cable first and try again.
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Thread Starter
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Joined: Oct 2012
Posts: 86
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From: Lucas TX
I forgot to mention that I have a standard transmission, so I only have one cable. I will try to reset the trip odometer and pay close attention if it moves at all. Are there any rebuild parts other than the plastic second worm gear or is that too much to tackle?
Melting Slicks
Joined: Aug 2012
Posts: 3,487
Likes: 83
From: Titusville Florida
If you have cruise remove the cable form the transducer and put a drill on it.
If you don't have cruise pull the cable from the tranny and put a drill on it.
See if the speedo works.
If so, then you have a gearing problem in the tranny.
If it fails to work then I would replace the cable first and try again.
If you don't have cruise pull the cable from the tranny and put a drill on it.
See if the speedo works.
If so, then you have a gearing problem in the tranny.
If it fails to work then I would replace the cable first and try again.
thank you
Former Vendor
Joined: Aug 2006
Posts: 76,656
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From: Jeffersonville Indiana 812-288-7103
St. Jude Donor '08-'09-'10-'11-'12-'13-'14-'15
If the odometer isn't working then the trip probably isn't either. There are no serviceable parts out there... A new plastic gear can be used, but you must first fix the issue of the bushing and possibly the first worm being ate up too.
Former Vendor
Joined: Aug 2006
Posts: 76,656
Likes: 1,853
From: Jeffersonville Indiana 812-288-7103
St. Jude Donor '08-'09-'10-'11-'12-'13-'14-'15
Willcox
Willcox Corvette
Attn: Service
123 E. Maple Street
Jeffersonville, In 47130.
Last edited by Willcox Corvette; Nov 18, 2012 at 02:55 PM.
Melting Slicks
Joined: Aug 2012
Posts: 3,487
Likes: 83
From: Titusville Florida
Absolutely! We do everything in-house.. And if you send these in to our shop please make sure you leave the metal can on the back.. it makes it easier to ship. And remove the forward bezel and the plastic bezel. The plastic bezel will be broken before it can arrive here..
Willcox
Willcox Corvette
Attn: Service
123 E. Maple Street
Jeffersonville, In 47130.
Willcox
Willcox Corvette
Attn: Service
123 E. Maple Street
Jeffersonville, In 47130.
I hope to have my dash apart early spring, if all goes well that is