Help! Tach cable broken?

[eoseitz]

I finally installed my new hei tach drive distributor. Considering the last guy that owned the car had removed the timing chain cover and put one on without marks, I managed to install it pretty easily and it runs far better than it used to. However, when I went to hook up the tach drive cable, it didn't want to go on. After looking down in the part that screws on I noticed that there was no gear in it. Does this use vacuum or is it gear driven? It appears to be a vaccum hose unless something is broken. It comes out of the firewall where the wiring harness does and it has a screw on type thing. Any info? I can post pics for confirmation or if you have some could somebody post one?

 

[Vettehead Mikey]

Sounds like you're missing the inner cable.

 

[Bob Heine]

I noticed that there was no gear in it. Does this use vacuum or is it gear driven? It appears to be a vaccum hose unless something is broken. It comes out of the firewall where the wiring harness does and it has a screw on type thing. Any info? I can post pics for confirmation or if you have some could somebody post one?

The thing that screws onto your tach drive is a cable housing and is supposed to have an inner cable. The cable has square ends on it and it feeds into that cable housing from the tachometer end under the dash. For around $10 you can buy a universal repair kit and cut the inner cable to the correct length (whatever that is). For around $20 you can buy the complete housing and cable ready to swap into your car. Getting to the back of the tach is a pain and you may want to remove the driver seat to gain better access.
Here's what you are looking for:
http://www.parts123.com/parts123/yb.dll?parta~dyndetail~Z5Z5Z50000050g~Z5Z5Z516435~P18.95~~~~S39E0IT79771196771924d~Z5Z5Z5~Z5Z5Z50000050G#

 

[eoseitz]

How does the cable insert into the distributor and gauge. My new cable has a screw on piece only on one side.

 

[6880 Mike]

Stock 74 distributors mechanically drive the tach with a cable and using a distributor mainshaft cross gear. What type of distributor did you install? Distributor end of the tach cable screws to the fitting on the distributor. Other end of the cable routes through the firewall and attaches to the rear of the tachometer.

Purchase the 74 assembly instruction manual (AIM) and take a look at the factory installation.

 

[Bob Heine]

How does the cable insert into the distributor and gauge. My new cable has a screw on piece only on one side.

The cable has a square end that inserts into the distributor. The distributor end of an original cable looks like this with a little more than an inch formed into a square.

The other end of the cable also has a square end but its part of a nylon piece attached to the round cable. I assume you purchased a universal cable so this piece has to be screwed on. The tape measure shows that the overall length of the cable from square end to square end is 20.5 inches.

If the cable isn't already cut to the proper length, cut it and attach the screw-on piece so the overall length is 20.5 inches. Remove the cable housing and cable from the behind the tachometer and reach in with small needlenose pliers and pull the old cable out. Re-install the new cable and push it in all the way.

Re-connect the cable housing to the tachometer. You should now have a square cable sticking out of the distributor end of the housing. The square drive goes into the distributor and the collar clamps it in place.

 

[TimAT]

Some of the MSD distributors use a different size square drive than the cable is. They supply a little sleeve that goes on the end of the cable. Without that sleeve, the cable rattles around inside the gear and won't drive the tach.

 

[eoseitz]

Thanks for the instructions. I bought the cable from corvette central. Would it already be cut to the correct size? The distributor is an ebay one. It looks pretty well made. I've drove it a few times and it seems to be working perfectly. My only question is, how do I get the dash loose. I've took out the center gauge bezel and removed all the securing screws on the dash. It moves freely but I cant get it out. Something appears to be hitting. Do I need to remove the steering column? I really hope not. I think I can get to the tach from behind the bezel, but I don't know how hard it will be to pull the cable loose and insert the new one in such closed space. Is there a clip on the tach or does it unscrew? I can see the plastic piece, but not real well. I have a haines manual. I'll check that, but I don't know how much detail it will provide me. I don't think I even saw it last time I looked. I really wanted to switch the drivers speaker while it's out. The speaker is blown. I've already switched the passenger side.

 

[eoseitz]

I was missing the little release switch in the back. I've got the tach cable out now without removing the dash any further. How do I get the plastic piece off? It appears to be made on

 

[Vettehead Mikey]

That piece is permanently molded to the cable. Why do you want to remove it?

 

[eoseitz]

actually it unscrewed. The new cable I got from corvette central didn't have it on there. I've switched it over to my new cable. There is a metal adjuster piece on my new cable. It appears to be preventing the metal house from going far enough on to connect to the clip on the gauge. can this be moved. I'm assuming this screws up and down too. My old cable doesn't have it. Could corvette central have put it there to pre-adjust the cable. I'll put a pic below.

 

[eoseitz]

Are you sure the cable is supposed to be 20. inches long? My new cable is the same length as my old one and the housing alone is longer than 20.5. There is room to trip some off on either side. I've noticed the metal piece inside it doesn't move to adjust it. On the gauge side of the cable there is a metal piece that separates the square part of the cable from the round. How much of the square part of the cable should I trip? Right now the nylon piece sticks out past the housing about a quarter to a half an inch. The distributor side the square part of the cable sticks out about the same distance as the nylon part. I know the cable is the correct corvette central part. I double checked the numbers. I have a picture of the nylon piece and the metal piece separating the round and square cable in the picture in my last post.

 

[Vettehead Mikey]

I don't believe you need the red plastic piece from the old cable- the new one should be good to go as-is out of the box.

 

[eoseitz]

I've got it working now. I trimmed the cable down on the gauge side. Thanks for everybody's help.

 

[Bob Heine]

I'm glad you got it working. I missed your post about the tip unscrewing. Looks like someone installed a repair tip on that cable. Apparently they are supposed to be crimped on and if yours unscrewed, the crimp was probably bad. Might have been your problem all along. Replacing the entire cable is a much more reliable fix but if you really want to do it on the cheap I found this repair piece for $4:

 

[eoseitz]

wow. I'll keep that in mind if I ever need to replace my tach cable again. It probably wouldn't have helped me too much this time. The inner cable was broken and I'd judge at least 5 inches of it was gone. I'm not sure what the guy before me did. He chopped a lot of things up. I'm slowly fixing everything, but it's definitely a slow proccess.

 

[Vettehead Mikey]

Saw this on another board:

Corvette Forum - View Single Post - mechanical tach cable install