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Why are the tachometer cables different lengths between the '68 with screw-on fitting on the back side tachometer gauge and the '69 that's snaps on? The reason for my question I have changed the speedometer and tachometer in my '68 to '69 gauges. I ordered a '69 cable and it around 23 inches long I found the old cable from a '68 its around 19 1/2 inches long. The '69 is too long!!
Had my tach cable out of my '69 recently, but never measured the length as there was no problem with the cable. The dash was in pieces. Don't know why there would be different lenghts.
I am wondering if the routing of the cable is different for '68 to '69. This image is from the '69 AIM and shows the cable routing for a '69.
Does your cable route that way?
Cable routing is the same as I can tell from the ‘68 AIM the cable goes through the grommet that also has the reverse back up light wiring and the tubing for the oil pressure gauge going through from engine compartment to under the dash. The question is the location of the opening for that grommet are the different between ‘68 and ‘69?
I have installed the drivers dash back in the car everything went in as it should (always a pain in the rear) the speedometer cable fits fine but when trying to connect the tach cable it to long best guess a couple inches. There’s more room for the speedometer cable to move around in the engine bay area.
Couple things I notice first the speedometer cable shown in the picture is for an automatic in both pictures. Second the view E shows a brace I think is in convertibles only.
If I still had my dash apart I would measure the length of my original tach cable. '68-'70 dashes are such a pain to put back together because of how GM routed the harness makes that very difficult.
I know that when I put the dash back together I had a difficult time getting the tach cable plugged back in correctly. Doing the speedo cable was easy as there is plenty of length and can be plugged in before sliding the panel into position.
I did some online research about tach cables and found some strange info. Apparently, the companies that make tach cables do not know the exact length the cables should be.
I went to Zip Corvette and they say that the '68 cable is 19.5" and the '69 cable is 24".
Corvette Central says '68 is 23" and '69 is 23".
Several others do not give lengths, but Top Flight says their '69 cable is 22"
Don't know if they can't measure their cables lengths correctly or that there are cables with various lengths. Very Confusing.
Agree I did some research on cable deign and length and came up with the same. I have 2 different '69 cables there about 1/2" difference in length. The picture attached is the shorter.
Update, rerouted the tachometer cable through the same hole as the speedometer cable and the longer length of the '69 was OK. It looks like I will need to locate a new grommet that will work for both of the cables. The original speedometer grommet was a strange design had metal and rubber deign hard to snap in place.
If anyone out there has a '69 with 4 speed and you get a little time could you check the routing of the tach and speedometer cables in your car and let me know what you find out I would apricate it.
Attached is pictures of what I have at this time.
If I remember right, only on small block 68's (327), they told you to clock the distributer one position clockwise to give you the room for the tach cable without being kinked. I think that this is in the "MOTOR" car manual.
You have to understand that everything was rushed to bring out the new 68's. The 63-67 tach and speedometer cables have the same screw on type. This is also why the way too small 68 radiator support, that my company made, was a direct copy of a 67.
And the miserable gigantic 68 steering wheel that kills your right leg when you try to get into the car is a direct copy of the 67 wheel, except that the "dish" is smaller. Lou Palfy...68 owner for fifty years.
Looking at your pictures I can't see your vacuum advance and I think that perhaps your distributor might be rotated too far clockwise. This would push the direction of the tach drive closer to the tach making the cable seem too long.
The original documentation said to set the vacuum advance at the 7 o'clock position and then there was a service bulletin to rotate the distributor so that it was a 9 o'clock position to reduce the curve in the tach cable and then to reposition the ignition wires in the cap.
I tried to get a decent picture of mine, but I has the Chrome box installed and it makes it almost impossible to get a decent picture.
This is where my vacuum advance is located.
This is where my tach cable goes thru the firewall.
Thanks, for the pictures, I’m not using a stock distributor but the direction of the pickup for the tachometer is aimed in the right direction for a straight pickup from the firewall where the cable goes through at. What year and what engine and transmission do you have?
Per GM parts manual 1968 cable listed as 19" 3928769
1969 6480240 or 25032874 listed in 525.0mm equals 20.6"
The first item is the change to the connection at the tach to a spring type. Then the distributor reposition to allow the cable to be a straighter alignment with the distributor connection.
Agree with the changes spring type connection was a great improvement. The old screw type was a pain either tighten it or trying to disconnect while the dash is in place. As far as distributor that more common sense then anything. But my question is where can you get a 20 1/2” cable for a ‘69 that would be a perfect length.
68 and 69 Tachometer cables
