Tachometer will reverse...what's up with that
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Joined: Jan 2006
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From: Saint Augustine Florida
Tachometer will reverse...what's up with that
The tachometer in my '78 is resting on 5500 and will wind in a reverse direction when I am around 6000 or so. Any advice here???
Thread Starter
Advanced
Joined: Jan 2006
Posts: 52
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From: Saint Augustine Florida
OK I pulled out the tach/speedo and lens, etc. I flipped the tach back to zero and started it up to see what would happen. At idle there seems to be no power but if I rev it up the tach will max out and bounce back and forth. Is there a simple contact clean if I pull the tach out??
Safety Car
Joined: Oct 1999
Posts: 4,101
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From: NorCal
I don't know about your area, but there's a great place out here (Commercial Speedometer) that fixes all my gauge issues. I'd bet there is a vendor there that could help you, and that stuff is usually inexpensive to fix...
Hans
Hans
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Joined: Jan 2006
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From: Saint Augustine Florida
Check th filter? What filter should I check? I realized that the tach was not reversing but was trying to wind down and zero'd back to 5500. Anyway, I did notice that one of the contact strips was bent a little and tried to straighten it out. I put the assembly back together and now I have now tach at all. I'll give it another shot today, I guess. FUN! FUN! FUN!
Racer
Joined: Jul 2005
Posts: 499
Likes: 1
From: Winnipeg Manitoba
Lucky76 has a good picture of the Tach filter that can be found on this thread.
http://forums.corvetteforum.com/show...ter&forum_id=3
The tach filter is for radio noise suppression.
You can bypass it to see if that's your problem.
(Short it out from end to end)
EDIT:
Your problem is unusual. Does it work OK if your running below 5000?
When you say "Resting on 5500", do you mean:
a) the tach is always at 5500? Even with the engine idle?
or
b) that when the engine is at running at 5500, and you go to 6000,
the tach starts going backwards.
(My engine doesn't get up there...)
http://forums.corvetteforum.com/show...ter&forum_id=3
The tach filter is for radio noise suppression.
You can bypass it to see if that's your problem.
(Short it out from end to end)
EDIT:
Your problem is unusual. Does it work OK if your running below 5000?
When you say "Resting on 5500", do you mean:
a) the tach is always at 5500? Even with the engine idle?
or
b) that when the engine is at running at 5500, and you go to 6000,
the tach starts going backwards.
(My engine doesn't get up there...)
Last edited by Kilroy1024; Feb 19, 2006 at 11:33 AM.
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Racer
Joined: Jul 2005
Posts: 499
Likes: 1
From: Winnipeg Manitoba
Well, theres only a few things to check...
1) I would assume the power and ground connections are good if its looks like its swinging to zero.
2) Turn the ignition key to RUN, but do not start the engine.
Does the tach return to zero?
If no, then this rules out a problem related to your tach filter.
When the engine running (and key in RUN),
__a) the tach should zero out.
__b) The filter has no affect (No noise to filter coming from the ignition)
3) Check your battery voltage.
There was a thread a while back about an erratic tach being linked to low voltage. (Not likely, but easy to check)
Other than this, it sounds like the Tach PCB is toast.
1) I would assume the power and ground connections are good if its looks like its swinging to zero.
2) Turn the ignition key to RUN, but do not start the engine.
Does the tach return to zero?
If no, then this rules out a problem related to your tach filter.
When the engine running (and key in RUN),
__a) the tach should zero out.
__b) The filter has no affect (No noise to filter coming from the ignition)
3) Check your battery voltage.
There was a thread a while back about an erratic tach being linked to low voltage. (Not likely, but easy to check)
Other than this, it sounds like the Tach PCB is toast.
