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Speedo Coupling @ trans for 75

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Ala75Vette

Guest
My speedometer stopped working not long after I bought my 75 comvertible about a year ago. I took it in to a mechanic, he fed me some line about a bushing being worn out, but got it working again. From talking to a local parts guy, I suspect my mechanic just squirted some glue on the end of the speedo cable at the transmission to get it to keep from slipping. The problem is back -- speedometer not working -- so I took it in to my local vette shop. The guy there says it's the coupling between the speedo cable and the (4 spd) trans. That part makes a 90 degree turn between the speedometer cable and the transmission. I've tried locating the part through Eckler's and Paragon, but no luck. I suspect a 73-76 vette, monte carlo, chevelle, or nova with a 4 spd manual trans may have the same coupling, but I haven't been able to find one yet. Any ideas?
 
Joined
Aug 29, 2001
Messages
3,235
Location
Norcross, Georgia, United Stat
Corvette
2017 Arctic White Grand Sport
I've got a similiar problem with my 77 in that the seals where the speedo cable goes into the trans are leaking. My mechanic suggested checking with a speedo shop, my local Chevrolet dealer recommended one, as they are tied into the parts for this type of work.

Bob
 
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Big Fish

Guest
All I can find on my 75 is a round adapter that is retained by a clip and single bolt. The cable attaches to one side, the other (inside) holds the driven gear against a gear on the transmission output shaft. You should be able to remove the adapter and inspect both gears for missing teeth, etc. If everything looks good you either need a new cable or speedometer, most likely the cable. You could also check the bushing and/or driven gear for wear when the adapter is out. Your local chevy dealer should be able to order these parts, they are not high dollar items.
 
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Ala75Vette

Guest
Thanks guys! It's been a perplexing problem, and I'd sure like to know how fast I'm going (although using the tach gives you a pretty good idea). Soon as I get it figured out I'll post what I wound up doing (I'll be checking with Chevy on Monday....).
 

69MyWay

Well-known member
Joined
Jul 3, 2001
Messages
4,364
Location
Auburndale, Florida
Corvette
1969 Killer Shark
Way off here, but just a suggestion. If this is not an all original car and you have some extra pocket change, look into an aftermarket speedo and tach. I dropped in a pair from Autometer. The trick is, they have no cables! That is the speedo feeds just like a new car. There is a small adapter that screws right onto the trans shaft and converts the spinning into an electric signal.

It is not cheap, but really trick looking. You can get gauges in black, silver, and white.

Just a thought if you keep hitting a dead end. In the meantime, I would suggest you just hunt for a used part. The trouble with speedo cables is old used ones that have been sitting up tend to freeze up. Frozen cables can do damage to the couplings, and or of course the inner cable snaps anyway.

Good luck. Let us know where you end up finding it.
 
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Ala75Vette

Guest
Thanks, 69MyWay! The car is not all original, so I don't really have any reservations about modifying it. The new speedo & tach would look great, however..... I'm a little embarrassed to admit that after checking with perhaps the most obvious parts supplier -- my local chevy dealer -- that particular part is still available from GM. Advance Auto Parts didn't have it, nor did AutoZone, Eckler's, or Paragon. Anyway, thanks for the advice, and I'll just be happy to know how badly I'm breaking the speed limit for a change!

Lesson Learned: Don't forget to check with chevy for hard to find parts.
 
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Big Fish

Guest
I talked to a friend today who has a 72 with a Muncie 4 speed. The speedometer drive gear in his trans was slipping on the output shaft causing his speedo to quit. He wound up having to remove the trans and buy a new gear which had to be heated for a tight press fit when cooled. Apparently there is not enough space to remove the tail shaft housing with the trans in the car. He had a heck of a time with that gear. I think if it wasn't too worn he could have corrected the problem with some loctite quick metal or permanent retaining compound. I suppose a quick check to see if you have the same problem would be to see if the gear will turn on the shaft, you could gain access through the hole that the speedo gear holder goes into.
 

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