fixing a cable drive tach
Thread Starter
Burning Brakes
Joined: Dec 2005
Posts: 1,179
Likes: 100
From: cranford nj
fixing a cable drive tach
Ok, I've posted about my tach not working. I got a plastic button and a new gear,question how far in do you push the plastic button, so the gear lines up with the shaft gear.
Tech Contributor
Joined: Aug 1999
Posts: 14,380
Likes: 6,391
From: At my Bar drinking and wrenching in Lafayette Colorado
Blue -
I posted the answer in your last post in the topic. You can only use the plastic button if your distributor had one before - some distributors did not use the plastic button. You pop it into the existing hole and seat it. There is no alignment for the gear. The gear uses the wall of the housing and the button, if so equipped, as its thrust surface. Don't replace the crossgear without replacing the mainshaft. If the crossgear was damaged, the mainshaft is trash.
I posted the answer in your last post in the topic. You can only use the plastic button if your distributor had one before - some distributors did not use the plastic button. You pop it into the existing hole and seat it. There is no alignment for the gear. The gear uses the wall of the housing and the button, if so equipped, as its thrust surface. Don't replace the crossgear without replacing the mainshaft. If the crossgear was damaged, the mainshaft is trash.
Last edited by lars; Mar 13, 2007 at 03:16 PM.
Melting Slicks
Joined: Mar 2005
Posts: 2,095
Likes: 299
From: Midlothian VA
You know that button isn't gonna do anything to make your tach functional again. I see from your other post that you "got it working for a couple days". That rules out the tach itself so now you're down to the cable, the drive gear, and/or the main shaft in the dist.
It's rare that the drive gear goes without taking the main shaft with it.
Pull the dist and look carefully into the tach gear hole while turning the dist by hand to check ALL of the driven teeth. They either wear down into a valley all the way around (in which case you may get away with a new gear for a very short time) OR they break off in just one area.
You can easily test the cable by simply chucking a drill onto it and spinning it up. If the cable and tach are both working the results will be easily seen on the tach in the dash.
There's also a small washer in there that you may be missing but that won't stop the tach from functioning either.
It's rare that the drive gear goes without taking the main shaft with it.
Pull the dist and look carefully into the tach gear hole while turning the dist by hand to check ALL of the driven teeth. They either wear down into a valley all the way around (in which case you may get away with a new gear for a very short time) OR they break off in just one area.
You can easily test the cable by simply chucking a drill onto it and spinning it up. If the cable and tach are both working the results will be easily seen on the tach in the dash.
There's also a small washer in there that you may be missing but that won't stop the tach from functioning either.
Last edited by Hammerhead Fred; Mar 13, 2007 at 02:23 PM.
Safety Car
Joined: Jun 2004
Posts: 4,652
Likes: 80
From: Lakeland Florida
Hello,
If you replaced the cross gear, and the tach worked for a little while, then stopped working, you probably have a bad main distributor shaft gear. I would not replace the gear again until you pull the distributor out and inspect the drive gear.
Note. If you have not done this before, pay careful attention to where the rotor is pointing to before you remove your distributor. This will help you save some time and aggravation when you go to put the distributor back in.
kdf
If you replaced the cross gear, and the tach worked for a little while, then stopped working, you probably have a bad main distributor shaft gear. I would not replace the gear again until you pull the distributor out and inspect the drive gear.
Note. If you have not done this before, pay careful attention to where the rotor is pointing to before you remove your distributor. This will help you save some time and aggravation when you go to put the distributor back in.
kdf
Burning Brakes
Joined: Feb 2006
Posts: 1,024
Likes: 1
From: AL
the only time that a vette almost left me stranded was due to those little gears. i had walked about 50 feet before deciding to turn around and try it one more time; thankfully it started. if had the tools, i could have taken the tach gear out, but at the time i didn't have a clue what was wrong until i drove it the rest of the way home (the tach finally quit).
i got the best replacement parts i could find. and get both shafts new.
i got the best replacement parts i could find. and get both shafts new.
Instructor
Joined: Jun 2004
Posts: 118
Likes: 0
From: Cleona Pa
Blue -
I posted the answer in your last post in the topic. You can only use the plastic button if your distributor had one before - some distributors did not use the plastic button. You pop it into the existing hole and seat it. There is no alignment for the gear. The gear uses the wall of the housing and the button, if so equipped, as its thrust surface. Don't replace the crossgear without replacing the mainshaft. If the crossgear was damaged, the mainshaft is trash.
I posted the answer in your last post in the topic. You can only use the plastic button if your distributor had one before - some distributors did not use the plastic button. You pop it into the existing hole and seat it. There is no alignment for the gear. The gear uses the wall of the housing and the button, if so equipped, as its thrust surface. Don't replace the crossgear without replacing the mainshaft. If the crossgear was damaged, the mainshaft is trash.
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Melting Slicks
Joined: Mar 2005
Posts: 2,095
Likes: 299
From: Midlothian VA
I've read numerous posts regarding the large number of mainshafts used by GM over the years, how there is only one or two replacement shafts currently available, and how many problems one may have with using one of these replacements. So what is the best way to replace the main shaft?
Came with bushings, cross shaft, etc., and directions.
Rebuilt my distributor with that kit nearly 20 years and +100k miles ago and it still works perfectly. Only remove the brass coupler every 5-6 years to inspect and apply some grease with no visual wear last time I looked at it. The only thing I couldn't find was the the plastic cover for the grease cup located at the top of the distributor body (right where the main shaft slides in). Had to reuse my old one to complete the rebuild even though it was cracked....bothers me to this day.
Last edited by Hammerhead Fred; Mar 15, 2007 at 10:58 AM.
Tech Contributor
Joined: Aug 1999
Posts: 14,380
Likes: 6,391
From: At my Bar drinking and wrenching in Lafayette Colorado
Pull the distributor, pull the shaft out, install the new one. You then have to re-curve the distributor to verify length of timing curve and rpm. Most of the replacement shafts also have to be modified to install the chamfer on the end and to grind off burrs on the bottom of the advance cam.
The plastic seals are avilable brand new from GM. They come in packs of 10.
Melting Slicks
Joined: Mar 2005
Posts: 2,095
Likes: 299
From: Midlothian VA
Pull the distributor, pull the shaft out, install the new one. You then have to re-curve the distributor to verify length of timing curve and rpm. Most of the replacement shafts also have to be modified to install the chamfer on the end and to grind off burrs on the bottom of the advance cam.
The plastic seals are avilable brand new from GM. They come in packs of 10.
The plastic seals are avilable brand new from GM. They come in packs of 10.