I just aquired a 1981 in November. About a week ago my speedometer started going wacko on me, jumping all over the place. Just yesterday my odometer quit working and my milage counter also is not working. Any thoughts or ideas?
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Re: Help - 1981 odometer & speedometer problems
Susan------
Well, I can tell you that it's one of 3 things: (1) the speedometer drive/driven gears in the transmission; (2) the speedometer cable, or; (3) the speedometer head.
What I would recommend doing is starting with the easiest first, then progressing to the more difficult. Remove the speedometer cable at the transmission by removing the knurled nut which attaches the outer cable sheath to the transmission mounted adapter. Tug on the exposed end of the inner drive cable after you remove the nut. If it pulls out, that means that the cable is broken and will need to be replaced. Unfortunately, the cable can only be replaced from the dash end. In any event, if the cable is not obviously broken, then remove the adapter from the transmission. One bolt usually is all that has to be removed and the adapter will pull right out. Inspect the gear carefully for damage or wear. If it looks good, reinstall it.
If you haven't found the problem yet, then you'll have to next get behind the dash by removing the left side dash panel. This is NOT fun; follow the procedure described in your 1981 Chevrolet Corvette Shop Manual. When you get the dash pad pulled forward, unsnap the speedometer cable from the rear of the speedometer. A spring clip retains it. Pull the inner cable out from this end and inspect it for wear or damage. If damaged or worn, replace it. If not, lubricate and re-install it.
If you still have not found anything wrong, it means that your speedometer head is likely the problem. In that case, remove it from the dash and send it to a qualified instrument repair shop for service/rebuild.In Appreciation of John Hinckley -
Re: Help - 1981 odometer & speedometer problems
Susan, My speedometer did the same thing on my '80 up until a few years ago. It was a very worn speedometer cable. Needle would bounce up to 60mph and back down wildly when only driving less than 20mph. After 20mph, it'd smooth out. I replaced the cable and it's been perfect since. This most likely is your problem. The original GM cables are available through anyone like MidAmerica, Corvette Central, Zip, Dr.Rebuild,etc. I believe they are also less than $20. Takes an hour or two to install, not difficult to do either.Comment
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Re: Help - 1981 odometer & speedometer problems
Do you have cruise control? I don't know about 81's, but my 79 with cruise control went bad at the cruise control transducer. I had to replace the transducer and speedometer cable going from the transducer to the transmissionComment
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Re: Help - 1981 odometer & speedometer problems
Mike-----
Excellent point. I sometimes forget that later C3s had these "new fangled contraptions" like cruise control. But, for a car with cruise control, which most 81s DID have, the cruise control "transducer" is part of the "speedometer circuit".
The 1981 transducer, GM #25030876, is still available from GM but GM lists for a whopping $695.51. However, rebuilt or new units are likely available through Delco dealers for a lot less. I sure hope so, anyway.In Appreciation of John HinckleyComment
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Re: Help - 1981 odometer & speedometer problems
About 95% of the time its the cruise control.Comment
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Re: Help - 1981 odometer & speedometer problems
Susan,
You said in your message that your odometer and trip meter don't work at all. If this is the case and your speedometer still works, this means that the gauge has been damaged internally and usually needs to be serviced by a specialist.
If NONE of the three items work, then it's most likely the cable or cruise tranducer as others have mentioned.Comment
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Re: Help - 1981 odometer & speedometer problems
All good advice. If you rebuild the speedometer or if you need to replace the drive cable let me offer a warning. Make sure you match the fit of the dive cable end length to the speedometer very carefully. Specifically the length. If the drive cable end at the speedometer is too long to match the new speedometer rebuild or a new cable comes tool long you will be repairing the speedometer head in as little as 100 miles. The pressure applied to the speedometer head when the cable is tightened up from the drive cable being too long will destroy the speedometer head assembly. Usually will show up in the form of a possible squeak, followed by jumping then a needle that freezes, does not move correctly, or is stuck at one speed. When this happens the odometer will still work and the speedometer must be rebuilt again or a new busing made and installed. Also, from experience, I just got a new cable from a reputable supplier, the end length was too long and the cable was almost dry. The drive cable had to be lubed and the end shortened!!! Hope this helps. JoelComment
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Re: Help - 1981 odometer & speedometer problems
Thank you for your reply. From the responces I received I'm hoping it's just the cable. I've been told that if it's the cable that possibly the odometer has been tampered with and could have been turned back. Is this neccessarly true or can I assume that my odometer reading is true? It has just over 73500 miles on it.Comment
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Re: Help - 1981 odometer & speedometer problems
To all who have responed I thank you very much. Yes the car does have cruise control but it did not work when I aquired the car. When I try to set the cruise it would just keep excelerating. I did not need to hear that it may be well over $600.00 to fix but for the love of vettes I guess I'll have to do what I have to do. I live in Jacksonville, Florida close to Orange Park and could use a good vette mechanic if any one can help me out I would be ever so greatful. I don't want someone working on it that really has no clue as to what they are doing.Comment
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Re: Help - 1981 odometer & speedometer problems
Susan-----
I doubt that your problems are related to someone previously tampering with the odometer. It's possible, of course, but there are a lot of Corvettes of your car's era that suffer from speedometer problems without anyone ever tampering with the speedometer.
Even though your cruise control has not worked, your speedometer problems could still be linked to the transducer. On that score, I've got good news for you. The price I mentioned earlier was GM LIST price for a BRAND NEW transducer assembly. Whenever I provide prices I usually provide the GM LIST price since that's the maximum that anyone should have to pay and I can't predict what "discount" that folks might be able to get in the marketplace. So, the most "stable" information on prices is to provide the GM LIST price and that's what I do.
However, I've done a little more research on this one. It turns out that rebuilt, exchange transducers are available for your car for less than $100. A local Delco or auto parts dealer ought to be able to fix you right up. So, you're NOT looking at a $600 part. Unless, of course, you'll only settle for a brand new GM piece and would't think of paying anything less than GM list for it.In Appreciation of John HinckleyComment
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