Tachometer question

[714Speed]

My cable is twisted at the distributor end, so I need a new cable. I'm trying to figure out if my existing cable is too long and if I need a 90 degree adaptor right now. I want to drive the car while I'm figuring all this out, but I'm afraid I'll damage the drive gears with it making such a terrible racket. In the meanwhile my question is this:

Can I cut the inner cable short and keep it plugged into the distributor so that the cable does not engage the drive gear? If so, I don't mind not having the tach working for awhile. :s

 

[Mike Carter]

I think yes for a short time, it can't rotate if not proper length. When you set up timing place distributor so you don't kink cable or stress it. You can set distro place as long as rotor position doesn't change. The adapter doesn't seem to right fix if distro is positioned correctly.

Mike

 

[Mike Carter]

And the cable is right length, many replacements you cut to lengtt. Forgot that on first post.

Mike

 

[jonstr]

Can I cut the inner cable short and keep it plugged into the distributor so that the cable does not engage the drive gear? If so, I don't mind not having the tach working for awhile. :s

You can just pull the inner cable out if you want. I'd re-connect the cable housing to keep dirt/dust out of it, but not having a cable in it should not cause any problems. Pulling it out makes it real easy to cut a replacement (just line them up, cut to length, and crimp the end on) - assuming your cable is the right length.

Speaking of which, what you describe is a pretty common place/way for those cables to fail. Is there something specific that makes you think the cable is the wrong length?

The 90 degree adapters look like a good idea (never tried one myself), but it should be possible to line up the distributor to minimize the stress on that cable. However, note that if your outer casing has been crimped or bent sharply at that point, it may wear through a new cable with or without the adapter. Make sure you check the cable casing for kinks before you re-assemble it.

 

[714Speed]

Yes, it comes out of the firewall and runs smack into the chrome plug wire protector. It does not kink, but is a sharp bend. The housing looks too long to me. Do you think I could cut the housing and recrimp the distributor fitting back on, and reuse the old cable by cropping it to fit?

My original question was: Can I unhook the cable from the distributor, cut the cable short so that it does not make contact with the drive gear, and just hook it back to the distributor? This would not let dirt get in, look stock, but not have the tach work. Could this hurt anything?

 

[Mike Carter]

Answer is no, it won't hurt anything.

Mike

 

[jonstr]

Yes, it comes out of the firewall and runs smack into the chrome plug wire protector. It does not kink, but is a sharp bend. The housing looks too long to me. Do you think I could cut the housing and recrimp the distributor fitting back on, and reuse the old cable by cropping it to fit?

I don't know if you can cut/recrimp the casing. I've never heard of anyone doing it, but it may be possible. They are also available from any of the usual suppliers (Ecklers, Corvette Central, Mid America, etc.). The inner cable could be cut and re-used, but both ends need to be square to engage the distributor and tach. The aftermarket replacements come one-size-fits-all and come with one end pressed/molded square and include a crimp-on piece for the other end. You cut it to length, less about 1 inch, and then crimp the end on, lube it up, and slide it into the casing. I don't know if that crimp-on end would be available separately, but the entire replacement cable is about $4 at any auto parts store.

My original question was: Can I unhook the cable from the distributor, cut the cable short so that it does not make contact with the drive gear, and just hook it back to the distributor? This would not let dirt get in, look stock, but not have the tach work. Could this hurt anything?

Sure. What I meant was you can cut the inner cable off, or just pull it out of the casing, then re-attach the casing to the distributor. Either way should be fine and should not cause any damage or other problem. One minor note on pulling the inner cable out - If the inner cable has been replaced before and the crimped-on end is at the tach-end of the cable, it won't pull through.

 

[714Speed]

You're right, I'd have to pull the cable out from the gauge end. By the way, I've got 7 different suppliers, some you mentioned, and some of them advertise 22 inches and others 23 inches in length.

As for the 90 degree adaptor, I'm finding it hard to see how that is going to reduce the bending action of the cable. Seems, at least on my application, the factory angle is the cleanest and most direct angle from the distributor to the gauge. I wonder if you can order a casing custom length? What I really need to do is pull mine out and measure it, but I'm a bit worried that I'll break a connection or worse with my hand up in the dash.

I sure do appreciate your advice and experiences.

 

[714Speed]

Oh, you mentioned one end of the cable being crimped....My cable does not have any crimped-on device on the end. It's just cut, and I looked at it the first time it made a noise and it was still square at the end. The second time I disconnected it, it was frayed. I'm assuming that the factory replacements are simply cut to fit without any special crimped-on piece on the end.

 

[jonstr]

Oh, you mentioned one end of the cable being crimped....My cable does not have any crimped-on device on the end. It's just cut, and I looked at it the first time it made a noise and it was still square at the end. The second time I disconnected it, it was frayed. I'm assuming that the factory replacements are simply cut to fit without any special crimped-on piece on the end.

Not sure. I've always just gone NAPA route and bought a generic cable, cut it, and crimped it.

For what it's worth, I just pulled out my old Chevy parts book that lists 53-74 and looked up the tach cable assembly. As luck would have it, the book lists lengths for each of the cable/casing assemblies up to '68, then stops showing the length. Bummer. It does, however list the replacement inner cable as 84" with a crimp on end that is cut to length. I guess that means if you find an NOS cable/casing assembly, it would have a made-to-fit inner cable. I'm not sure what the parts houses supply.

Jonstr

 

[luvmy73]

You never need a 90 degree tach adapter. If you install and orient your distributor properly the cable should enter the distrubtor housing without a bend. If you look closely of the picture below you can see under the ignition shielding the orientation of the vacum advance, if your vacume advance points this way then then there should be no bend in the cable. Due to the excessive bending of the tach drive cable in the C3 chassis, GM issued a Service Bulletin in late 1969 that allowed the dealers to rotate the distributor about 45 degrees clockwise, pointing the vacuum advance out from behind the distributor shielding instead of bringing it out in front of the shielding. The dealers were instructed to re-position the spark plug wires so they remained in their same position relative to the engine. This straightened out the tach drive cable to promote longer cable life. If you need help with the install, please private message me.

Mike.

Also this picture is of a NCRS 1973 LS-4 Corvette engine bay.

 

[714Speed]

My cable and housing are in very good condition with the exception of the frayed end. I don't think my cable has more than 500 miles on it. Just bad decisions on the part of prior owner. I think I will try recrimping the distributor end fitting and reuse the one I have to avoid messing around in my dash like a bull in a china shop. I'll let you know how it goes, hopefully for your benefit someday. Thanks, guys, and nice car, Mike.

Neil

 

[Mike Carter]

hey Neil,

You'll do more damage trying to crimp an end on a damaged cable than replacing cable with one cut to proper length with good ends. It's not that hard, and the cable at tach is not that hard to remove, you'll be surprised. I replaced the tach cable in my car in less than an hour, when my tach needle broke that took days.

mike