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Old 01-02-2013, 10:27 PM   #1
manofwar
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Tachometer

My gauge isn't working. I see where it screws into the distributer, and I pulled the instrument panel off enough to get my hand behind it and it appears to be screwed in there too. So is that the only cable? Or is there a wire as well that could be cut? It worked before I had my engine rebuilt and hasn't worked since.

If there aren't additional wires how the heck am I supposed to get that gauge out to replace it?

1972 coupe with a 350

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Old 01-02-2013, 10:46 PM   #2
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The tack is driven off a short cable to the distributor. If it was working before the rebuild I would say the tack is OK. The cable clips to the back of the tack unhook it and make sure every thing is good back to the distributor.
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Old 01-03-2013, 11:16 AM   #3
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The Tach operates by mechanical means, not electric. Forgive me if this seems simplistic, just want to cover all the bases.

There are a number of things that could be wrong. Let's discount the engine rebuild for now and discuss how it works.

If the engine runs then the distributor gear is operational, the tach drive gears in the distributor are cut into the distributor shaft and into the tach drive shaft. As the distributor rotates it drives (rotates) the tach drive shaft.

The tach gear in turn drives the internal tach cable. It's a short version of a speedo cable connected between the tach drive gear and the back of the tach. The cable has squared ends that slip into a square drive housing, one on the end of the tach gear the other on the back of the speedo.

Pretty straight forward operation..... tach gear drives the tach cable, tach cable drives the tach.

There can be a stripped distributor shaft gear or tach drive gear in the distributor. There can be a stripped square drive housing or rounded cable. There can also be a broken or missing internal tach cable. The most likely issue is that one end of the tach cable has slipped out of the drive housing.

Since the distributor end has a screw cap I would suspect the back of the tach. The back of the tach is a slip on type of connection held there by a metal clip. Alternatively it is possible that the cable could have been removed or slid out of the cable housing during the engine swap and not reinstalled.

Start at the distributor drive, pull the cable housing off and check to see if you have an internal drive cable, that the cable end is square and that the drive housing on the end of the tach drive shaft is square.

Next disconnect from back of the tach by pushing the clip toward the tach and pulling on the tach cable housing. If stuck wiggle it a little bit, it should slide right off. This would be a good time to remove the internal drive cable and check both ends for square, for any fraying and lubricate it. Most cables will have a brass collar around one end that allows removal in only one direction.

Reattach to the distributor and verify you have rotation of the internal drive cable when engine is turning over. If not it would likely be the distributor and/or the tach drive shaft gears.

Stick it back on the tach all the way, keep in mind you may have to rotate the drive housing to align the square drive. Once reattached test for operation. If all the mechanical pieces are in place and functional then the instrument itself is the problem.

I think you will most likely find a disconnected, severed or missing drive cable. The gears do go out sometimes but not near as often as other issues.

Hope I haven't confused you and that this helps.
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Old 01-04-2013, 02:24 PM   #4
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You can also disconnect the tach cable from the distributor, figure out which way it turns, then put your cordless drill on the cable run it the proper direction, and run it that way. If the tach reads you can go from there.
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Old 01-04-2013, 10:43 PM   #5
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Appreciate the help. This is what I came up with.


IMG_5205 by vette.wife, on Flickr


IMG_5209 by vette.wife, on Flickr


IMG_5211 by vette.wife, on Flickr

Im guessing its not supposed to look like that?

easier to buy the drive cable already in the exterior housing? And once I get it in does it have to be lubed or something?
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Old 01-04-2013, 11:15 PM   #6
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You are correct that is not supposed to look like that.
I would suggest a new cable and housing, it should come ready to install.

So was the cable housing kinked or did it have a real sharp like 90 degree bend in it? That can cause what happened to your internal drive cable. If so the distributor should be rotated to a location where the tach drive cable housing is not bent and the spark plug wires moved to match as close as possible. Reset the timing of course.

If your not familiar with what to do to accomplish this we can discuss further.
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Old 01-05-2013, 12:01 AM   #7
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I think I can get the cable back in without kinking it, if I cant Ill get back with you. Ive tried timing it in the past with crappy results.

I took the cap off, and I am sure I knocked the distributer around a little getting all that off of there is that going to jack anything up? Like will I have to retime?

Thanks again for the help.
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Old 01-05-2013, 07:38 AM   #8
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You can buy a universal speedo cable from AutoZone or I'm sure other big box auto parts stores. About $4.00. I believe mine was Pioneer brand if that makes a difference. Then buy some graphite speedo oil to lube the new cable. Don't use chassis grease or other oil that can dry out and get stiff. Cut to proper length and crimp on the square drive end with the little tool provided.
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Old 01-05-2013, 10:08 AM   #9
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Quote:
Originally Posted by manofwar View Post
I think I can get the cable back in without kinking it, if I cant Ill get back with you. Ive tried timing it in the past with crappy results.

I took the cap off, and I am sure I knocked the distributer around a little getting all that off of there is that going to jack anything up? Like will I have to retime?

Thanks again for the help.

If you rotated the distributer, you changed the time. Once you get it back together, if it runs funny or is hard to start, then that's 99% the likely suspect.
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Old 01-05-2013, 12:02 PM   #10
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The existing timing should remain unless the distributor itself rotated while you were removing the tach cable housing. It is usually locked tight enough not to move by a bolt and clamp right at the base of distributor. Where it goes down into the engine through the back of the intake.

If you loosened that lock clamp then yes you will need to time the engine or have it timed. My $.02 here......It might cost a little more but my advice is to get the proper cable and housing for your car. The universal ones will work but in my experience don't last as long or operate as cleanly as good quality.

Keep us posted.
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Old 01-05-2013, 12:08 PM   #11
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Yeah Id already ordered the correct replacement from Ecklers last night.
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Old 01-13-2013, 12:41 AM   #12
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Got it all put back together with the new cable. All my guages work now thanks for the help.
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