Tach Needle jumping on high acceleration
Thread Starter
Drifting
Joined: Oct 2010
Posts: 1,972
Likes: 6
From: Chester Virginia
Tach Needle jumping on high acceleration
I have a 76 L48 four speed stock and just had new plugs and wires on it and they put a new rotor and cap on the distrib. Now when I accelerate the tach which seems about right in readings when I accelerate hard above 2500 rpm's goes immediately up higher and jumps around a bit. If I keep the rpms up it stabilizes and does not jump.
Any suggestions?
Thanks.
lance
Any suggestions?
Thanks.
lance
Safety Car
Joined: Sep 1999
Posts: 4,930
Likes: 11
From: AnyTown NJ
St. Jude Donor '08-'09-'10-'11-'12-'13-'14-'15
In playing with the dist did you/they move/reroute the tach cable? What your describing can be caused by the tach cable binding causing the needle to skip/bounce around. I'm assuming you have a mechanical tach and not an electronic one.
Thread Starter
Drifting
Joined: Oct 2010
Posts: 1,972
Likes: 6
From: Chester Virginia
I am not sure but that is something I'll check this week. Car's in garage hibernating as it left a dusting of snow here last night and it's too cold anyway. Next time hood is up I'll see if there is any binding and adjust if so. Thanks for a starting place.
Le Mans Master
Joined: Dec 2003
Posts: 5,727
Likes: 38
From: Fremont CA
76 has an electric tach last time I looked at one. My guess is the grounding wire from the HEI mounting plate to the distributor housing is broken causing feedback through the tach circuit. You should check inot this as it can cause module failure too. To check you will have to remove disributor and disassemble (remove drive gear and pull shaft out of the housing) to get to the bottom side of the module mounting plate where this wire is located.
Thread Starter
Drifting
Joined: Oct 2010
Posts: 1,972
Likes: 6
From: Chester Virginia
I think you are right now that I remember the manuals that it is an electric tach but I haven't checked or opened the hood yet. when I do I won't remove the distributor but I will check all the tach wire connections as the only thing that happened was new rotor and cap, new plug wires and plugs and perhaps timing adj. It always worked a little this way..just seems more so. I have a sneaking suspicion the connection at the tach contact isn't seated full well or has some oil on them from dirty fingers from p.o. or something on it. I also have a spring kit to change or advance the centrifugal timing curve a notch to perhaps put in lighter weight springs by one spring and new weights so will deal with all of it then. Right now the car is hibernating in the garage at the house so I can do it at my leisure. Have a new radio to put in and remove the non functioning non oem radio first. Have plenty of time this winter it looks like. Thanks for all the inputs.
Le Mans Master
Joined: Sep 2002
Posts: 5,236
Likes: 898
From: Myrtle Beach SC
I think you are right now that I remember the manuals that it is an electric tach but I haven't checked or opened the hood yet. when I do I won't remove the distributor but I will check all the tach wire connections as the only thing that happened was new rotor and cap, new plug wires and plugs and perhaps timing adj. It always worked a little this way..just seems more so. I have a sneaking suspicion the connection at the tach contact isn't seated full well or has some oil on them from dirty fingers from p.o. or something on it. Have plenty of time this winter it looks like. Thanks for all the inputs.
Tach Boards
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