C3 Tach Sloppy
Thread Starter
Instructor
Joined: Mar 2005
Posts: 104
Likes: 0
From: Perkasie PA
C3 Tach Sloppy
I have had these crappy tachs for years and want to know if anyone has ever taken one apart and tried to tighen up the backlash? I have a new MSD billet distributor and new cable. The tach still flops around when you get on and off the gas. To me this indicates there is a lot of backlash in the tach gear head. Anyone been successful?
Instructor
Joined: Oct 2006
Posts: 219
Likes: 0
From: Jupiter FL
I have had these crappy tachs for years and want to know if anyone has ever taken one apart and tried to tighen up the backlash? I have a new MSD billet distributor and new cable. The tach still flops around when you get on and off the gas. To me this indicates there is a lot of backlash in the tach gear head. Anyone been successful?
Drifting
Joined: Feb 2000
Posts: 1,591
Likes: 53
From: Central MN
Although I'm not new to Corvettes (I've owned 5,) I am new to the C3 world - I just bought a '70 L46 coupe. I, too, noticed the "sloppy" tach and just assumed it was 1970's technology. Is the tach supposed to be "sloppy" or does the tach need fixing/adjusting? It doesn't really bother me (I shift according to sound not necessarily the tach anyway) However, if there is an easy fix for the tach, I'd be interested in knowing how to fix it. Thanks.
Last edited by Cosmo Kramer; Jul 20, 2007 at 10:52 AM.
Team Owner
Joined: Jul 1999
Posts: 65,492
Likes: 230
From: Orange Park Florida
All of the above, I may add that you can fix it yourself IF you really want to....pull it outta there, and sit down at a well lit kitchen table with cloth on it....pull the needle off very carefully, don't break the pin size shaft off or you are shafted....
then unscrew the face plate....note in back of the zinc housing there are two rather larger screws....take tham apart....now to get into the guts, I forget just exactly how, but when you examine it, i'ts self evident....the points you are looking for are the input where the cable goes....spot of oil, duh......then you are looking for the pivots on the sprung tach shaft the indicator went on....one is evident, the other is inside that aluminum cup that spins from the cable input....there is a tiney needle bearing inside that cup....it needs a dap of oil....I have used WD40 on a Q tip for years and never had a failure on a tach or speedo...same mechanical assemblies.... did this speedo here 12 years ago, and it still survives Florida heat just fine....
you gotta be careful, this is not a rocket science rebuild, but it's gotta be done carefully....common sense rules...
then unscrew the face plate....note in back of the zinc housing there are two rather larger screws....take tham apart....now to get into the guts, I forget just exactly how, but when you examine it, i'ts self evident....the points you are looking for are the input where the cable goes....spot of oil, duh......then you are looking for the pivots on the sprung tach shaft the indicator went on....one is evident, the other is inside that aluminum cup that spins from the cable input....there is a tiney needle bearing inside that cup....it needs a dap of oil....I have used WD40 on a Q tip for years and never had a failure on a tach or speedo...same mechanical assemblies.... did this speedo here 12 years ago, and it still survives Florida heat just fine....
you gotta be careful, this is not a rocket science rebuild, but it's gotta be done carefully....common sense rules...
Instructor
Joined: Oct 2006
Posts: 219
Likes: 0
From: Jupiter FL
All of the above, I may add that you can fix it yourself IF you really want to....pull it outta there, and sit down at a well lit kitchen table with cloth on it....pull the needle off very carefully, don't break the pin size shaft off or you are shafted....
then unscrew the face plate....note in back of the zinc housing there are two rather larger screws....take tham apart....now to get into the guts, I forget just exactly how, but when you examine it, i'ts self evident....the points you are looking for are the input where the cable goes....spot of oil, duh......then you are looking for the pivots on the sprung tach shaft the indicator went on....one is evident, the other is inside that aluminum cup that spins from the cable input....there is a tiney needle bearing inside that cup....it needs a dap of oil....I have used WD40 on a Q tip for years and never had a failure on a tach or speedo...same mechanical assemblies.... did this speedo here 12 years ago, and it still survives Florida heat just fine....
you gotta be careful, this is not a rocket science rebuild, but it's gotta be done carefully....common sense rules...
then unscrew the face plate....note in back of the zinc housing there are two rather larger screws....take tham apart....now to get into the guts, I forget just exactly how, but when you examine it, i'ts self evident....the points you are looking for are the input where the cable goes....spot of oil, duh......then you are looking for the pivots on the sprung tach shaft the indicator went on....one is evident, the other is inside that aluminum cup that spins from the cable input....there is a tiney needle bearing inside that cup....it needs a dap of oil....I have used WD40 on a Q tip for years and never had a failure on a tach or speedo...same mechanical assemblies.... did this speedo here 12 years ago, and it still survives Florida heat just fine....
you gotta be careful, this is not a rocket science rebuild, but it's gotta be done carefully....common sense rules...
The dap of oil is one of the secrets to smooth operation. I use a bearing oil, available at any hardware store for 4 bucks or so, (for a 2 ounce jar which is probably more than any of us will use in our lifetimes), or a synthetic clock oil, both work fine. Just a drop in the jewel in the center of the magnet. When the oil dries out that's the first thing that makes it jumpy. Depending on the condition, the fix can be more extensive, but this fixes many of them without the need for more.
Last edited by gldnkngt; Jul 20, 2007 at 06:16 PM.
