Tachometer Circuit Board Going Out... Again

[Fishman]

For the third time in 6 years my tach circuit board appears to be going out... (1) when I gun it the needle flies back and forth, and (2) the RPMs never go higher than 3200. I have had to replace this board twice already. I bought the last one from Ecklers and forgot who I bought the first one from.

Does anyone know where to get a high quality board? Perhaps even a board that uses newer technology?

Thanks... Brian

 

[ruby76]

I can't offer an answer, but am interested in what responses you get. My tach on my 76 does the "jumping" thing as well.

 

[Bob Chadwick]

I got mine at The Last Detail 3 years ago and haven't had any problems.

 

[Fishman]

I got mine at The Last Detail 3 years ago and haven't had any problems.

Thanks Bob... I just called them. They are $60, which is .01 higher than Ecklers at $59.99. Price fixing old Vette ICBs? :L So I guess it doesn't really matter where you buy it... only a few cents difference between companies.

When I spoke with the techy at The Last Detail, he said they were all probably made by the same company that GM outsourced to years ago, he wasn't sure where from though.

I sure wish there was something out there a bit more realiable... so if anyone knows more than this...

 

[Bob Chadwick]

The boards shouldn't go out like this. Could there be an electrical issue somewhere else that is doing the damage?

 

[tom102]

Tach problems

Have you checked the tach filter? a bad one can cause the same problems

 

[Fishman]

Have you checked the tach filter? a bad one can cause the same problems

Check it :confused Guess I should get out the AIM and find it! Never heard of such a thing... thanks everyone (so far).

 

[tom102]

filter

it is located and bolted on the intake manifold on the left(drivers side) behind the carburetorit looks like a condenser with wires running to the distributor and tachometer. Hope this helps

 

[cesully]

would the tach cable cause this "jumping" ?? I thought that the tach was an analog type of unit with a relationship to a small gear inside the transmission on these older vettes.
Was is the function of the circuit board?

Thanks,

Sully

 

[tom102]

tach

Sully,

the circuit board is used on a electronic tach not the mechanical cable driven ones.

 

[George Black]

Good advice re the tach filter. I once replaced the tach on my 1980 L-82, only to find out later that it was the tach filter that had gone out. The above given description and location for the tach filter is correct. I replaced the filter and the tach unit was fixed! I now have an "extra" 1980 L-82 6000 RPM tach unit sitting on my shelf.

 

[81 Corvette]

i'm with tom...if its touching metal, i'll act funny

 

[joe1975]

Is there a way to check the filter?

 

[Fishman]

I have two wires coming from the distributor into the firewall, one is yellow and one is red. I imagine the red wire should have the filter... there is nothing there. There are two blue clips on the red wire that probably were intended for the filter assembly, but are just connected together to complete the circuit.

 

[81 Corvette]

two wires go to the distrubtor (all info from an 81), in my case the thicker wire (red) is for providing power to fire the plugs. On the other wire, is the filter. The filter is about 1/2 inch in diameter and an inch long. You can't miss it. if you don't have a filter, i'd find one before worrying about a circuit board.

 

[Fishman]

I sent my stock intake manifold off to a fellow CAC member (Culprit) a while back and now that I think about it... I think I sent him the tach filter as well. I went to the AIM (page 123) and that looks exactly like what was on the old manifold when I removed it (not sure why none of this didn't raise a red flag to me at the time... parts is parts, I guess). So... I'll need to go out and find one.

I noticed Ecklers (for example) has two types, the original OEM 'barrel' style replacement (1975-1989 models, part # 46137, $59.99), and the 'replacement' no barrel filter (1975-1989 models, part #45731, $29.99)... now for the part I do not understand. The OEM barrel style has two wires (that is what is shown in the AIM as well). The replacement has three wires. Anyone have any experience/ advice here?

 

[tom102]

Tach Filter

The reason for the two wire vs: three wire is because the oem style grounds by bolting to the manifold the case (barrel) is the ground, the three wire style has the same components inside except it is without the metal barrel case and does not attach to the manifold so that third wire is meant to be grounded on the engine. I hope this helps

 

[81 Corvette]

grounding....hmmm i swapped my intake and thus the bracket the holds the filter on mine. I tucked the filter up behind the distributor near the firewall. My tach seems to work fine without a ground.

 

[Fishman]

I hope this helps

It most certainly does! Thanks to everyone.

One last question however (I am not an electrical engineer): Do I need to use the three wire one as I now have an aluminum intake? I am unsure of the grounding properties of aluminum if I go back to the OEM two wire.

Later all... Brian

 

[tom102]

filter

Brian

There is no problem with aluminum, it is a good conducter and will work just fine.