Topic: cable drive tach,72
in Forum: C3 Interior
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Lifetime MemberEquinunk, PA - USA
Joined: 10/31/2007
Posts: 2465
Vette(s): 1972 conv, 4-speed, 350, 200hp, numbers match, rally wheels, war bonnett yellow w/white top. good condition, nice driver.
Greetings, On the way home from HOT SPRINGS my tach started jumping mildly, read slow, then just gave up the ghost. Any secrets on the best way to get it out to replace it? I am inclined to think the steering column has to be dropped to get at the panel. I already replaced the cable, got to it from the center and fished it in to hook it. THANKS
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sounds like a--either the gear drive in the tach went kerput orrrr b-- the cable or trans gear went kerputt,,or c ,,,the tach died,, go up under the car and pull the cable out of the side of the tranny,,turn the cable and see if the tach moves,, if so,, must be the tranny gear,, if not either the cable or the tach,, if you cant figure it out,,sell the car and buy a 2008 zo6,,rd
Lifetime MemberEquinunk, PA - USA
Joined: 10/31/2007
Posts: 2465
Vette(s): 1972 conv, 4-speed, 350, 200hp, numbers match, rally wheels, war bonnett yellow w/white top. good condition, nice driver.
No tranny drive here, cable is only about 2-3 feet long. It drives from distrbutor.
My 72 works and doesn't work - I'm inclined to think its the gear drive in the distributer Takr the cable of the distributer and twist it - I used a power drill to spin the cable . My tack is fine - cable works - so I'm looking at the distributer gear drive.
Big Al
Mark,
Big Al has the right idea to determine if it is the cable, the tach or the distributor.
Have Shirly watch the tach while you spin the cable from the distributor end.
If it is the tach, I think it comes out from the front.
If it comes out from the rear, take the driver's seat out. You will be much more comfortable.
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Lifetime MemberEquinunk, PA - USA
Joined: 10/31/2007
Posts: 2465
Vette(s): 1972 conv, 4-speed, 350, 200hp, numbers match, rally wheels, war bonnett yellow w/white top. good condition, nice driver.
Thanks, for the input. Will give it a twirl this week-end.
The tach ONLY comes out from the rear. Taking the seat out is the best way, You can get the dash out without removing the steering column, but it is best to take the bolts loose inside.
MikeMc71 2008-05-02 05:30:03
If it turns out to be a frozen tach, you can sometimes loosen it up and oil it and you're good. Mine was frozen beyond repair, so I just got a used one on eBay, and replaced the guts. Its been working fine ever since.
If you do end up pulling the dash pad, fix everything you can while its out, because you will NEVER want to do it again!
OH, and have fun! 
[QUOTE=MikeMc71]...The tach ONLY comes out from the rear. ...[/QUOTE]
6880Mike 2008-05-02 09:10:49
Correct. Cable on the tranny is the speedo, not the tach. Test the tach cable from the distributor end before diving under the dash. Your problem might only be the cable (if you're lucky).
If the tach works when you test the cable, pull the drive gear housing from the distributor and check the cross gear for possible missing teeth. If the drive gear has been chewed up, you can bet the distributor main shaft teeth are also gone.
If the cable is good and the drive gear is good, the tach or the cable connection on the back of the tach is the problem.
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Mounds View, MN - USA
Joined: 5/24/2007
Posts: 1031
Vette(s): 70 LT1 coupe, 69 350 HP coupe, 69 390HP 427 coupe, 71 LS5 convert, 85 coupe, 93 coupe
The most common reason we see for this problem is the driven gear in the distributor. If it is bad, almost certainly the brass screw-in housing that holds it is also bad. And be sure to look inside the distributor to verify the main shaft is OK. Second most likely would be the cable, which can be tested as described above.
Larry
Larry
Lifetime MemberCOPPERAS COVE, TX - USA
Joined: 7/6/2002
Posts: 417
Vette(s): 1972 corvette stingray convertible
2007 coupe
My 72 did the same thing, it was the drive gear in the distibutor. Its an easy fix, you do need to check the shaft in the distributor also, mine was worn down any new gear I put in would end up doing the same thing in a short time.
You dont want to have to pull the dash panel if you dont need to. I'd rather change the heater core than to pull the dash ever again. My repair manuel for pulling the dash states if you dont have to dont.
Good luck!!
in Forum: C3 Interior
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