1972 tachometer

[Jerome P.]

On acceleration the tachometer gauge bounces verses a smooth movement to the higher RPM numbers. On a steady speed the tach holds steady.


Should the movement of the tach gauge always be smooth during acceleration and deceleration?


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[Michael D.]

Re: 1972 tachometer

Should be smooth. Cable may need lube.

[Terry M.]

Re: 1972 tachometer

Or the tachometer drive gear in the distributor may be eating up itself and the mating distributor shaft gear.

[Ken A.]

Re: 1972 tachometer

Your tach is working correctly as you describe it's operation.

[Jerome P.]

Re: 1972 tachometer

In that I received various answers I will try to clarify my question and describe another condition/example of what I am experiencing.

The engine is running, the clutch is depressed, the engine is rev'd, and the tac gauge responds accordingly (smoothly) to the higher rev's. However, upon the engine returning to an idle speed of 800 RPM's the gauge bounces on it's return to the lower idle speed.


It may be functioning just fine, but I really don't remember it working this way or I am thinking the tac should respond the same as the one in my late model C5 (smooth on the way up and smooth on the way down) - Cable driven vs electrical?

[Paul O.]

Re: 1972 tachometer

Jerry

Your tach is having a problem and as others have stated start by checking the cable end at the distributor for wear the cable there should be squared. Then check your gear drive in the distributor as Terry posted for damage. The cable housing could also be worn or a good lubrication of the cable and housing my fix the problem. But you have to have a starting point and go to the easiest item in the assembly first and just do a through process of elimination.

[Ron G.]

Re: 1972 tachometer

Paul makes a valid point by having a starting point to begin. However, my own experience with this dilemma is the wear of the gear drive in the the distributor itself.

[Don L.]

Re: 1972 tachometer

Not to hijack this thread (I think this is related to the OP) but which should be expected to show wear first, the drive gear or the gearing that's cut into the distributor shaft? I think I recall my drive gear being steel and I know my shaft is steel.

[Jerome P.]

Re: 1972 tachometer

Don, What does OP mean?

Thanks to everyone for your input.

I guess I have a little investigating to do.

[Terry M.]

Re: 1972 tachometer

Not to hijack this thread (I think this is related to the OP) but which should be expected to show wear first, the drive gear or the gearing that's cut into the distributor shaft? I think I recall my drive gear being steel and I know my shaft is steel.

Once either gear begins to show damage the other will soon follow. The residue of the damaged gear churns with what lubricant there is and chews up the other gear. If the tachometer drive gear shows damage, just replacing that is a fools errand. If you need a quick fix to get you through a meet judging or PV, you may get lucky -- but you will revisit that location again in the long term.

Jerome, OP = Original Poster. In this case that is you.

[Don L.]

Re: 1972 tachometer

Sorry Jerry. As Terry says, "OP" = original post. I shoulda be more clear.

[Don L.]

Re: 1972 tachometer

Once either gear begins to show damage the other will soon follow. The residue of the damaged gear churns with what lubricant there is and chews up the other gear. If the tachometer drive gear shows damage, just replacing that is a fools errand. If you need a quick fix to get you through a meet judging or PV, you may get lucky -- but you will revisit that location again in the long term.

Jerome, OP = Original Poster. In this case that is you.

Thanks Terry. I had hoped that if not dis-similar metals (hopfully a bronze drive gear) they'd have at least used a harder or hardened steel for the shaft.

I was asking because my tach quit late last summer. I was worried that the gear(s) had been eaten, however, I replaced the cable 2 weeks ago and it's working now. While R&Ring the cable, I removed the drive gear and inspected it. All I found was lots of clean grease and clean teeth in the drive gear. I looked into the distributor casing as best I could to see the shaft, but couldn't see any damage. Hell, I could barely see the shaft. I greased her back up, set it in the case and re-assembled with success. I just hope it keeps working. When I disconnected the bad cable, I found a twisted mess of wire strands, all frayed around a then-loose drive tip.

Always something to learn on these cars...