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240 240 Tach issues

B

bumblebeeman

New member
Joined
Sep 26, 2012
Location
Petaluma
Yo Everyone!

So years ago I took out the giant clock and swapped a tach and small clock in.. Its an '86 245 N/A. The cluster was a bit funky but I broke all the seals and completely cleaned it, went through the whole thing in the evenings as I was doing the Ending wiring Harness....

so six months back, tach sometimes won't run, until now the tach does absolutely nothing... snagged another form the yard the other day. tested the tach wire, it had a signal that went up and down when I pressed the gas... put the different tach in, Still nothing..

I should also tell you that this cluster sometimes has an issues where the temp gauge starts to go up, both blinker lights come on, and high beams are illuminated. gas still works, speedo shows ~35 during this time.. if I reach around the underside and wiggle the little white connector on the Speedo it usually stops..

Haha ok guys, ideas or leads to chase?? It must be the cluster right?? but how to diagnose it and make sure I get a new one that works well???

Thanks!
BBman
 
Get a good used one from someone like Redwood chair so they will back up what they sell you. Electrical stuff can get flaky and it may be worth it to get another cluster.

However, be sure to take apart that cluster. It's worth a bit of time to go over that cluster looking for loose pins, cracked or broken conductors, and bad connections in general. Sometimes solder connections crack from the years of use and a quick little touch up with an iron may be all it is.
 
Sounds like you've got some cracked solder joints or traces in the PCB on the back of the cluster. If poking and tugging on things causes it to react then you have a mechanical connection problem somewhere. I find a lot of cracked solder joints in these cars so I usually touch up anything that looks suspicious.
 
I'm pretty sure the tach operates independently of the cluster, only requiring that red and white wire to work. It doesn't need a power and ground in other words, it just passes those through to the connector for the small clock.

You said you were able to measure a signal on that wire? It is connected to the coil with a spade connector- how corroded does that look? You could try cleaning up its connection with a wire brush and emery board. You could also try to follow that wire and make sure its insulation is intact and it is not intermittently shorting to ground anywhere. It sounds unlikely to me, but not impossible, that you have 2 broken tachs. There isn't much to them to go wrong.
 
cleanflametrap said:
The tach needs power and ground from the cluster.
Click to expand...

:oops: I thought it was just a simple ac voltmeter, but that still needs 2 connections doesn't it. Derp

02224.png
 
There's more to the tach than that, it has an electronic circuit in it, essentially it's an integrator that converts a string of pulses into a DC voltage proportional to the average rate of the pulses. It also has some basic means of calibrating it so that the reading on the tach corresponds to the RPM.
 
It is powered and grounds through the panel.

'basic means of calibration' means a little adjustable pot on a circuit board that converts 12v and a pulsing ground into a variable voltage that moves the needle.

P1190012.jpg
 
Power for the instrument cluster comes through the connector on the back of the speedo. There's a one time use clip that holds the connector to the speedo and without it, the connector can wiggle and make a poor contact.

I have a few in stock if anybody needs one, but they aren't expensive from the dealer and you'll save the shipping costs.

The white one is the original clip. You can see the tabs are broken on the back side.

SpeedoWireRetainer1.jpg


SpeedoWireRetainer2.jpg
 
Lots of good suggestions above. I don't have any to add, except that something is definitely f'ed.

[hijack] So, as long as you guys are discussing how tachs work, consider this: I bought a large 240 tach from an upstanding TB'er and it worked fine for a while, then it started reading 1000 less than the actual rpm's. For example, at idle it read zero. What do you all think of that? fix-able?
 
YEs the tach definitely gets ground and positive from the cluster... I too think my cluster may be Fuked, but was hoping that someone had seen the blinker high beam thing happen before, one thing I forgot to add, this ONLY happens when the lights are switched on.. anyways, I am searching for a better cluster..

HiperfAuto- Yes I have herd that those connectors are one of Volvos infamous "One way Only" this well may be my issue. do you have any pics of that part installed. having a hard time picturing it.. Its funny they put those kinda one way clips on there because cluster issues require it to be uninstalled and reinstalled with such frequency...

Thanks for the Ideas everyone!
 
hiperfauto said:
Power for the instrument cluster comes through the connector on the back of the speedo. There's a one time use clip that holds the connector to the speedo and without it, the connector can wiggle and make a poor contact.

I have a few in stock if anybody needs one, but they aren't expensive from the dealer and you'll save the shipping costs.

The white one is the original clip. You can see the tabs are broken on the back side.
Click to expand...

If there is an intermittent open at this point, the entire cluster would react?

Thx.
 
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