84-86 tachs

[eaglescout526]

Anyone have any knowledge on them? I am starting to toy with them and so far they are resistors and two chips. I’m gonna try to see if there’s a difference in the resistors to make future conversions possible for 6 to 4 cyl engines. 

[Eagle]

3 hours ago, eaglescout526 said:

Anyone have any knowledge on them? I am starting to toy with them and so far they are resistors and two chips. I’m gonna try to see if there’s a difference in the resistors to make future conversions possible for 6 to 4 cyl engines. 

 

That's the way to convert them, but I don't have the specs on the resistor ratings.

[Eagle]

Just now, Eagle said:

 

That's the way to convert them, but I don't have the specs on the resistor ratings.

If you're comfortable doing board-level work, why not replace the resistor with a potentiometer so the tach can be used on either engine -- like the '87 and newer ones?

[eaglescout526]

23 minutes ago, Eagle said:

If you're comfortable doing board-level work, why not replace the resistor with a potentiometer so the tach can be used on either engine -- like the '87 and newer ones?

I might make an attempt to do just that. The tach that was in Chunk now has a bad resistor I’m going to replace.   I think the one resistor that went bad is what controls the pulses as the tach just pegs out wayyy past 7k. So I might give that a shot. 

[Green Mesa XJ]

I’ve had a few but only ever saw the 6cyl with the tach, I ended up running with the 1988-89 cluster because the printed circuits I had on the 84-86 kept pealing and failing. Tach was always wonky.

wasn’t there something on the early ones that could be adjusted to 4 or 6?


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[eaglescout526]

Yeah the printed circuits are known for that. 
 

I think the tachs have been weird probably due to cheap resistors on them. That’s my guess as I installed a NOS tach and it works just like the later years. 
 

I'm more or less also doing this for guys who want full blue face but can seem to only find the 6cyls around but can’t find the 4cyl tach. But I’d like to roll with eagles idea and add a pot to them for adjustability.