My speedometer hasnt worked since I bought the car 4 months ago. I am finally getting to fix it ('70 350/350 4 speed). I took the cable off and spun it and my speedo went up so it isn't that. Then I looked at the gear and it looked in good shape so I don't think it's that, then I looked at the worm gear in the tranny (the other gear) and it looked fine also. So, I'm baffled, but it is getting dark, so I put it all together and before I let the jack down, I start it and put it in gear just to see, and the speedo works for the first time since i bought it (it got to about 20mph) then it bottomed out back at zero and moved no more. I then lowered it back to the ground and went for a spin to test the brakes (which is why I had it jacked up in the first place) and again it worked till I hit 20 or so, then nothing. So I'm thinking that the gears are not touching all the time and are working themselves away from each other. I looked in a Paragon catalog and see they have a "speedometer gear seal" which I have no idea how it works. The site says, " Use only with fitting having I.D., which accommodates seal. Most original models prior to 1966 had no provision for this seal. We suggest purchase of entire 7188K if you are not sure." Is this like a spacer that will make my gears touch better? Is there something I'm missing. I would really like to fix this without having to drop the tranny if possible. Thanks in advance for any advice as always.
---Donnie

 

I have a '70 also and in my case it was the speedo itself - the gears in the speedo were well worn and did not mesh. Took to a speedo shop and they put in new. I knew I had the problem before I took out the dash for other things so it became "while you are there" - replace all bulbs, etc. Hope it's something simple for you.

 

my spedometer is not working also. How did you check if your spedometer was moving (needle)???? Because i spun the cable from the trany and my spedometer did not move at all. I spun it with my hands. Somebody told me that i cant check with with my hands becuse i cant spin it fast using my hand. So he told me to connect the cable to a drill and spin it. Im wondering how did you check it. Hope you can help. It sucks driving without a spedomeeter.

thanks

 

First, thanks for your posting. In responce to you both in one responce, I dont think it is the speedo, because when I spun it manually with my hand and the speedo went up (you can do it with your hand, but you need someone looking at the speedo to tell you if it is moving). It seems that the gears are not making good contact in the tranny. Is there room for wiggle inside the tranny and are there spacers that can ensure contact? Actually, I am still wondering if that part from Paragon is my answer, but I'm waiting on more responces before I start ordering stuff. Lastly I think the gear is right, 19 teeth (I have a 3.70 gear with 15" tires) but the guy before me may have messed with that too. But I don't think there are different "size" gears (in diameter), just different number of teeth, right?

 

I went to corvettecentral.com and they have different color for the gears. Everything is color coded so im guessing to try to match the color or the teeth. Also you can try to buy the speeodometer gear fitting in the tranny maybe its broken or lose . its only 13.50 on the website.

Sucks my spedometer did not move when i spun it with my hand. But im still gonn try to change the gear and the gear fitting. If all dont work i will just buy a seperate spedometer. Im dont want to pull out the spodometer cause i might crack it. ha ha ha

 

Any tips for removing the gear in the transmission?

 

I have EXACTLY the same issue on my 79. It didn't work when I bought it, I took the dash gauges off and the speedo works fine when rotating the cable input by hand. The cable is fine. The gears on the transmission were also good and once we re-tightened it, the speedo worked when I drove out from the garage and stopped working again right after. I haven't touched it since, but I thought that the problem might be in the gear which is connected to the cable - perhaps the slot where the cable goes into, is worn and the gear just rotates without pulling the cable together with it.

 

99 times out of a hundred, with the situation you describe, the cable end is worn or rounded and will not fully engage the driven gear or speedo head - depending on which end is worn. It's always a good idea to take a close look at the connections between the cable and the corresponding female parts.

 

I had no problems with my speedometer until about a week ago. I was just pulling of and heard a clicking noise coming from the speedometer when I looked down I saw the needle jumping from 5 to 30 mph I was doing maybe 20 mph. As I got going faster the needle an smooth and no noise then I looked down when I had gotten up to maybe 60 mph and it was on 0. It has not worked since from what forum members have posted it is the speedometer itself. The gears in the back of the speedometer I guess but I have not been able to find any post on repairing it or where to get the parts to do so. Any help from you all if you can.
Thanks

PS my odometer works just not the speedometer.

 

Hey everyone I just finished up working on my speedometer this weekend and the problem was a broken plastic fitting (red) on the end of the lower cable. When I originally checked it, it looked fine because the wear from the constant spinning had rounded it out to look stock. After much digging I pulled out the broken piece from the transducer. This might be your problem if the fitting is catching sometimes it might be making the speed jump around as it rounds out the plastic. Just a thought but I would definitely give it a look-see because $20 bucks isn’t much to get a working speedometer!