Diagnosing Tach Problems on a 1969
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Diagnosing Tach Problems on a 1969
Looking for advice on the best way to go about diagnosing tach problems on a 1969 4speed 350/350, stock distributor, no other crazy engine mods.
The tach doesn’t work at all, the needle is broken, but the dash lights work and dim with all the other dash lights just fine (I’m guessing these are unrelated anyway). Wondering if it’s just the coil/cable that goes to the distributor, or maybe the distributor itself?
Has as anyone else experienced the same thing previously? If so, what did you start testing first? Are there any key indicators I should be looking for before I start ripping the drivers side of the dash apart?
Thanks in advance!
The tach doesn’t work at all, the needle is broken, but the dash lights work and dim with all the other dash lights just fine (I’m guessing these are unrelated anyway). Wondering if it’s just the coil/cable that goes to the distributor, or maybe the distributor itself?
Has as anyone else experienced the same thing previously? If so, what did you start testing first? Are there any key indicators I should be looking for before I start ripping the drivers side of the dash apart?
Thanks in advance!
Tech Contributor
Joined: Aug 1999
Posts: 15,175
Likes: 3,990
From: Connecticut, USA
The Tach's were mechanical to 1974, went electric in 75.
First look to see you have a tach drive distributor, there should be a cable screwed into it. If not then someone replaced the distributor. If there a cable unscrew it and spin it, if the needle fell off then you won't see it move but if it broke and part of it is there have someone look close at it while you spin it. I use a drill, lower RPM. Sometimes the cable breaks if the angle is too tight into the distributor.
You can unscrew the brass bushing in the distributor body to check the gear. They often strip out and wreck the main shaft gear too. .
The dash has to come out to fix the tach needle. The needle just pulls off. The cable clips into the back of the tach, same as the speedo. Removing the dash pad is tricky the first time but doable, just take your time.
First look to see you have a tach drive distributor, there should be a cable screwed into it. If not then someone replaced the distributor. If there a cable unscrew it and spin it, if the needle fell off then you won't see it move but if it broke and part of it is there have someone look close at it while you spin it. I use a drill, lower RPM. Sometimes the cable breaks if the angle is too tight into the distributor.
You can unscrew the brass bushing in the distributor body to check the gear. They often strip out and wreck the main shaft gear too. .
The dash has to come out to fix the tach needle. The needle just pulls off. The cable clips into the back of the tach, same as the speedo. Removing the dash pad is tricky the first time but doable, just take your time.
Last edited by GTR1999; Jul 25, 2019 at 08:45 PM.
Thread Starter
Instructor
Joined: Jul 2019
Posts: 142
Likes: 10
From: Los Angeles, CA
The Tach's were mechanical to 1974, went electric in 75.
First look to see you have a tach drive distributor, there should be a cable screwed into it. If not then someone replaced the distributor. If there a cable unscrew it and spin it, if the needle fell off then you won't see it move but if it broke and part of it is there have someone look close at it while you spin it. I use a drill, lower RPM. Sometimes the cable breaks if the angle is too tight into the distributor.
You can unscrew the brass bushing in the distributor body to check the gear. They often strip out and wreck the main shaft gear too. .
The dash has to come out to fix the tach needle. The needle just pulls off. The cable clips into the back of the tach, same as the speedo. Removing the dash pad is tricky the first time but doable, just take your time.
First look to see you have a tach drive distributor, there should be a cable screwed into it. If not then someone replaced the distributor. If there a cable unscrew it and spin it, if the needle fell off then you won't see it move but if it broke and part of it is there have someone look close at it while you spin it. I use a drill, lower RPM. Sometimes the cable breaks if the angle is too tight into the distributor.
You can unscrew the brass bushing in the distributor body to check the gear. They often strip out and wreck the main shaft gear too. .
The dash has to come out to fix the tach needle. The needle just pulls off. The cable clips into the back of the tach, same as the speedo. Removing the dash pad is tricky the first time but doable, just take your time.
Thread Starter
Instructor
Joined: Jul 2019
Posts: 142
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From: Los Angeles, CA
Okay. I've noticed my speedometer trip reset twistie-button doesn't work either - would this be related? (I'm guessing not, and that it's probably just a bad switch or something)
Tech Contributor
Joined: Aug 1999
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From: Connecticut, USA
That is a spring loaded cable, if the gear is still good you have to push it up and turn it. The odometer plastic gears last about 60k miles and fail. If you end up pulling the speedo from the dash panel you can fix it.
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See image below:
