Greetings,

I just purchased my first Vette about 3 weeks ago, and this my first post on this forum. It's a Black '79 with a light beige interior. The car is in great condition, and I'm very happy with it. I would like to post pictures of it, but I'm not sure how...

I just took the kids for a ride (with the t-tops out), and the speedometer started jumping around at low speads. For example, when I was doing 30mph, it jumped between 20-40. When I got up to about 50, smoothed out...

...As I was coming up to my house, it stopped working all together. I think it's the cable, which would make it jump. The car has cruse control, so I looked up the cables on Ecklers, and there are 2 of them, an upper and a lower.

My question is, how difficult are these to change? What are chances it's just the upper one, and I don't have craw under the car?

Thanks in advance!!!

 

1 in a 1000 -Sorry those dont go bad very often.

 

I think the upper one would be the harder of the two to replace. The upper one requires you to actually get under the dashboard - and that area is a huge jumble of wires and stuff. Trying to position yourself so that you can use both of your hands to disconnect the cable from the speedometer is impossible.

However, the lower one isn't nearly as big of a deal. The speedo cable connects to the driver's side of the back of the transmission. It should be just a quick unscrew and reattach job.

My speedo cable broke a few years back, just before I started my restoration project on my '79. I've since removed the cruise control, but I can't seem to get the cable off the the back of the speedometer. Once I get the car on the road for the first time in two years by the end of this week, I'm just going to bring the car to a local mechanic and have him replace the speedo cable for me.

I can rebuild my transmission but I can't swap a simple speedo cable

 

The cruise control transducer has a series of plastic gears on it. I;ve had two of these go bad, one of which gave similar symptoms. When I upgraded to TPI I got rid of the old cruise contrpl (used onr that ran off of the TPI's pulse generator) and ran a single cable. Much better.

 

Agreed. Removal of the upper cable is simple if you pull the speedo/tach lens and then pull the speedometer out. When you do, be very careful with the speedo needle, they are fragile.

 

Thanks for your responses. I will order a single cable tonight.

 

Sounds like the cruise transducer is going bad. While you do this job, regardless of whether you replace the transducer or go with a single cable, I would replace the driven gear in the transmission-and the bullet. If the cable has been dragging it will eventually cause the square slot in the driven gear to round out. Also the aluminum bullets wear and should be replaced with a steel one.

 

Before ordering anything I'd suggest first identifying the problem, or you will be throwing money at the problem. I went through this with my 79 recently. Our problem my not be the same, but you might go through a similar trouble shooting procedure. First, you need to identify if the problem is located in the lower or upper cable. This is best done disconnecting the cables from the speed control transducer. I found the weak link on mine was the cable end that went into the tranducer from the transmission. If this is you problem, save yourself some cash and buy a universal inner cable from Autozone for about $7. GM will charge about $35 for the same thing. You probably don't need to replace the outer sheath and that is the most expensive.

Same thing for the upper cable if it is broken. Disconnect it from the transducer and see if the speedometer registers speed when you turn the cable. You can also use the same universal inner cable to replace it if broken.

If you need to replace the inner cable, you will need to crimp the metal end on the cable after cutting to length. I'd recommend putting a dab of JB Weld on the end before placing and crimping the square end. NOTE: I went and bought an entire upper cable, only to find it was about an inch too long and couldn't be used. Unless the outer sheath is broken, just replace the inner cable, but lube before replacing. Hope this helps.

 

I was thinking about it some more, and I didn't order anything yet... I should probably figure out what is wrong first before throwing parts at it.

I'm going to take it back to the dealer where I got so he can take a look at is. It's a corvette only place, but I can't get there until the end of the week, so I will live with it as is until then.

 

Hey blk79nj...welcome to the fun! I too bought a black 79 with Oyster interior, in the summer of 2005. My speedo didn't work at all which I traced to the drive gear in the transmission extension housing. I fixed the drive gear then replaced the driven gear and seals at the trans. It worked for a few miles until I got it up to highway speed, then stopped again. The cable had sheared off where the lower cable enters the crusie control transducer. I replaced the whole lower cable and all is well, although I have a little bounce at highway speed. I'll be working forward now from the transducer to the rear of the speedo to cure it once and for all. Point is, it's worth getting your hands dirty to find where the problem exists, then go after it. Put the wallet away for now.

BTW, lots of great Vette-folks in Jersey. Fill out your profile..maybe there's someone nearby that can take a peak and save you the pricey labor fees.

Enjoy,
Steve

 

definitely fill out your profile.

if you're close enough to us central NJ
guys you will have some help with the car

 

Thanks, you guys are great.

I'm going to start by disconnecting the top cable, and spinning it to see if the speedo works. If it does, I will reconnect, and disconnect the bottom cable from the cruise control, and attempt to spin the cruise control to see if the speedo works... if it does I will reconnect it, and craw under and try it from the bottom.

If the cruise control is bad, I'm just going to get the single cable, and bypass it. If it's either of the other cables, I will replace/fix them seperately. If it's gear in the trans, I will have the dealer fix it.

I filled out the profile, I live in Pitman, which is in southern New Jersey.

The car is almost perfect, everything works even the clock and AC.
(except the speedo and cruise control)

I will post pictures as soon as I can.

 

It might make it easier to reach the transducer if you unfasten the one bolt that holds the washer bottle filler neck to the fender and turn it out of your way. You can also remove the neck if you turn it out about 45 degrees and pull it up and out of the reservoir. Don't connect the top cable until you are finished with the bottom. These two things will help make your life a little easier.

 

I checked it out, and it was the lower cable. The dealer told me that when the transducer goes bad, it gets tighter and tighter and puts more and more pressure on the lower cable until it dies. He also said the replacement ones are junk, so putting in a single cable is the way to go...

The good thing is that he gave me the single cable, which I will install this weekend.

Thanks to everyone for your help. I'm sure I will have more questions/problems in the future.

 

Its easier to do the top cable with a helper.You push the release inside and they pull the cable housing from outside.