Having trouble with tach not registering at all. Have examined gears, look o.k. Have attached a drill to end of tach cable at the distributor, when drill energized, tach read o.k. Varied speed on drill, tach responded. Reconnected cable to distributor, tach worked for about 5 seconds. Is there supposed to be a bronze or plastic button somewhere? Any help will be appreciated!
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Re: C3 1971 Tach Question
How does the bronze bushing look that holds the driven gear? These get worn oblong and let the gears seperate. -
Re: C3 1971 Tach Question
As Wayne mentions, the bronze coupling does wear and cause problems, and you should also set up the cross gear for minimal end play and use new grease in the crossgear cavity inside the coupling. You also should check both the mainshaft gear and crossgear for chips and nicks, hopefully you have none. The plastic button started somewhere around 70-71 if I recall, and was GM's attempt to fix the endplay wear issues with this design. This button "plugs" into the housing body in a hole inside the crossshaft gear housing. They also make brass replacements for this, which in my opinion is better than the plastic but the idea is dissimilar metal bearing surfaces. I use a good grade of grease, like Valvoline Syntec grease...CraigComment
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Re: C3 1971 Tach Question
Dale-----
I suggest that you check the tach gears more closely. Given the symptoms that you described and the tachometer check that you made using the drill, it sure sounds to me like bad gears. Usually, if one is gone, the other will be, too.
When you examine the gears, make sure that you examine the FULL CIRCUMFERENCE of the gears.In Appreciation of John HinckleyComment
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Re: C3 1971 Tach Question
Joe,
can you give me some actual dimsional data (or a source to obtain same) .. I can then use a set of calipers to check for correctness of the gears .. what I do know is the car is a true 24k mile car .. with all correct orginal parts .. in talking to previous owner the tach only ever worked once in a great while and never for very long ( a few minutes at best) and only when the engine was first started after it had been sitted for a few days ..Comment
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Re: C3 1971 Tach Question
Dale----
I don't have gear dimensional data handy, but it should not be necessary. If there is a problem with the gears, it will be quite obvious on careful inspection. Usually, there will be a "chunk" out of both gears. That, and, perhaps, fitting wear are the only 2 reasons that I can imagine that the distributor tach drive would be disfunctional.
There could be an excessive end-play problem which would cause the gears to mesh incorrectly. However, that usually always causes the gears to fail as described above. Your 1971 tachometer should have the nylon thrust button installed in the distributor housing opposite the inner end of the driven gear.In Appreciation of John HinckleyComment
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Re: C3 1971 Tach Question
Dale,
I have had several problems with mine - 71 sb, mine is now fixed as it has been working for over a year. Pull the distributor to check the end play and to check out the main shaft. You can find out how to take it apart in the service manual - if needed. The teeth should show no wear and be vertical with out any inward curve, which indicates wear. The cross shaft should be the same - showing no wear. If it does, replace both. A lot of times a tooth will be missing and the tach will ork hit or miss. I found that my problem was too much slop in the end play of the main shaft. Too much up and down when spun fast. So it was eatting up my main shaft with the cross shaft. As the main shaft rises when its spinning it was causing too much friction with the cross shaft and thats where the wear and tear ruined the main shaft. also, don't put the cross gear housing in too tight. It will bind up the gears. I fond this was best to do with the distributor out of the car so you can spin the shaft with your hands to feel if its not binding or too loose. I used lockout to keep the coupler in place after I was happy with its position. As the other people have chimmed in, lube it up with a good quality grease before you lock it in place. Sorry so wordy, hope this helps.Comment
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