79 Calais Tach

hangar401

hangar401

Greasemonkey
Supporting Member
Oct 3, 2019
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My in dash tachometer has not worked properly for years.It works but readings are off by bunch,like at 30 mph it reads at 2500rpm.Is this tach run by the alternator or distributor?
 
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oldsmobile joe

Royal Smart Person
Nov 12, 2015
1,314
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distributor
 
H

hoffa65

Master Mechanic
Mar 11, 2019
286
63
Atlanta GA
My in dash tachometer has not worked properly for years.It works but readings are off by bunch,like at 30 mph it reads at 2500rpm.Is this tach run by the alternator or distributor?
There is a 6cyl/8cyl jumper on the back of the cluster. It has a spring type tab on it that after time cuts into the solder points it sits on after years of road vibrations the connection gets poor.
Pull cluster and solder a piece of wire or paper to the two connection points
It could a look so be the tach filter going bad, you should be able to remove the filter that is mounted to the fire wall to the left of the distributor
 
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oldsmobile joe

Royal Smart Person
Nov 12, 2015
1,314
113
mpls
thats good, neither can i. i checked my '78 and '79 factory service manuals, no diagrams or descriptions.

i did find these diagrams in my '80 manual. (see first pic)

and this from my 86 manual (see second pic)

then there is this from Al Gore's invention,

Setting the Tachometer:

The tachometer can be set to indicate RPM for a 6 or 8 cylinder engine by means of a jumper accessible from the rear of the gauge cluster housing.
Tach Jumper


1. Instrument Cluster Assembly2. Shorting Adapter
  • Calibrate the tachometer by installing the shorting adaptor in the hole that matches the number of engine cylinders (6 or 8).
or
  • This would be a good time to consider replacing the jumper with a soldered connection to eliminate possible future problems.







and this from you tube

 

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oldsmobile joe

Royal Smart Person
Nov 12, 2015
1,314
113
mpls
now i did find this on the monte ss forum.


i don't know if it pertains to an olds cutlass tach, but it may. i could see gm using the same components but on the tachs but on different circuit boards. so it the resistor on the monte tach has a high fail rate, so would the cutlass tach.

hope this helps you.
 
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hangar401

hangar401

Greasemonkey
Supporting Member
Oct 3, 2019
104
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Thankyou everyone
 
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