Tach Jumping?
Thread Starter
Burning Brakes
Joined: Aug 2008
Posts: 845
Likes: 12
From: LAKE BARRINGTON IL
Tach Jumping?
Hi all,
Just bought my 69 vette convert, and have noticed the tach jumping.
There is a replacement small block in there, so not sure why this is happening...is this common?
How do I fix this?
Thanks,
The Factor
Just bought my 69 vette convert, and have noticed the tach jumping.
There is a replacement small block in there, so not sure why this is happening...is this common?
How do I fix this?
Thanks,
The Factor
Race Director
Joined: May 2006
Posts: 18,774
Likes: 2,597
start by unscrewing the tach cable from the distributor. Then remove the bronze fitting and gear the cable attached to. Examine for any excess wear on the gear. If all looks well pack grease into the distributor housing and reassemble. Try pulling the inner cable from the outer cable housing and apply grease or there is a graphite based lubricant that you can do a search on. Only apply the grease/lubricant a maximum of 2/3 of the way up the cable, you do not want the grease/lub getting into the tach.
Terrorizing Orange Cones
Joined: Oct 2007
Posts: 2,572
Likes: 17
From: Northern CO
Good item to check, from MelWff.
Depending on how many cycles your tach has delivered, worse case is that the tach itself is worn and may end up failing. That was my experience and caused a replacement to be ordered and installed.
Depending on how many cycles your tach has delivered, worse case is that the tach itself is worn and may end up failing. That was my experience and caused a replacement to be ordered and installed.
Former Vendor
Joined: Aug 2006
Posts: 76,656
Likes: 1,853
From: Jeffersonville Indiana 812-288-7103
St. Jude Donor '08-'09-'10-'11-'12-'13-'14-'15
start by unscrewing the tach cable from the distributor. Then remove the bronze fitting and gear the cable attached to. Examine for any excess wear on the gear. If all looks well pack grease into the distributor housing and reassemble. Try pulling the inner cable from the outer cable housing and apply grease or there is a graphite based lubricant that you can do a search on. Only apply the grease/lubricant a maximum of 2/3 of the way up the cable, you do not want the grease/lub getting into the tach.
Here is the GM procedure on this.
http://willcoxcorvette.com/repairand...lp.php?hID=283
If you do find the distributor gear worn, you'll need to replace both shafts and not just the cross gear. If it is damaged then the odds are against you that the main shaft gear is good.
Post back with what you find, I've got tons of good distributor pictures.
Drifting
Joined: Oct 2010
Posts: 1,972
Likes: 6
From: Chester Virginia
if it's electronic it might be from a later tach like my 76. Mine jumped a little then eventually stopped. I bought an aftermarket external tach and before installing a mechanic looked at my original and traced the signal wire from the distributor to the tack and when he unplugged the wire from the distributor it had broken inside the connection to the distributor and he simply re soldered it and it works perfectly. New tach on shelf!
When it jumped it was because the wire threads weren't always in solid contact where the break was. These are old cars and corroded, broken wires are not uncommon.
Lance P.
When it jumped it was because the wire threads weren't always in solid contact where the break was. These are old cars and corroded, broken wires are not uncommon.
Lance P.
Former Vendor
Joined: Aug 2006
Posts: 76,656
Likes: 1,853
From: Jeffersonville Indiana 812-288-7103
St. Jude Donor '08-'09-'10-'11-'12-'13-'14-'15
Factor: There is ton's of info on the electronic tach's on my web site... just search for Tach and you'll have a weeks worth or reading..
Willcox
Willcox
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