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Rat baby

Lack of tach.

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Tach was working fine and then just pooped out one day. I have checked the resistor but it appears to be fine. Every other gauge is working perfectly. I attempted to pull out the combination meter to inspect connection. It didn’t want to pull out more then a half inch or so and I didn’t want to force it or start unplugging with out checking with yall. It appears that the plug is securely connected. What else can I check? I was reading that an aftermarket tach won’t work with the coils so I would really like to get the original working. 

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You have to get your hand up in the dash and release the speedometer cable, then you will be able to get your hand in behind the cluster to release the wiring plugs from the back of the dash.

Edited by Charlie69
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The tach gets the signal from the coil. Start from that end because those connections are exposed to the elements and fail much more frequently than in cab connections.

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5 hours ago, bottomwatcher said:

The tach gets the signal from the coil. Start from that end because those connections are exposed to the elements and fail much more frequently than in cab connections.

 

 

Thank you. I’ll check and clean connections on coils and continue to inspect. 

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Can I run new wire and just hook the tach up like it’s an aftermarket to see if it works?  

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It needs the resistor. Just looked briefly at an 82 wiring diagram wire goes to a terminal and changes color I would put a meter on those conections starting at the blue one on the coil. Test the resistor, there isn't much to this circuit. 

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Well a couple of things. The tach is run off the intake side coil but after 45 years who knows if it hasn't been disconnected and accidentally switched? So check for spark on the high tension lead of both coils first. One (exhaust) is actually run through a fuse in the fuse box and if blown, is an easy fix.

 

Can't see the resistor being the problem, but they are just a 2.2K ohm resister..... 10 for a dolla on Amazon.

 

The tach simply plugs into the existing dash gauge unit so easy enough to replace it. You need a Nov. '83 and up round tach

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16 hours ago, datzenmike said:

Well a couple of things. The tach is run off the intake side coil but after 45 years who knows if it hasn't been disconnected and accidentally switched? So check for spark on the high tension lead of both coils first. One (exhaust) is actually run through a fuse in the fuse box and if blown, is an easy fix.

 

Can't see the resistor being the problem, but they are just a 2.2K ohm resister..... 10 for a dolla on Amazon.

 

The tach simply plugs into the existing dash gauge unit so easy enough to replace it. You need a Nov. '83 and up round tach

 

 

Thank you. I see the white wire with a blue stripe on negative post of ignition coil. same wire going to resistor. I’m going to go check for spark now. Is it possible to have a bad coil and not know it? I’ll see if I can wake up the tach but sounds like a replacement would be prettty easy. 

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Pulled a square tach out of a 81 720 today. hooked right up and works fine. Of course it doesn’t fit but at least I know that’s all I need. Thanks for the help 

 

A132-CBE9-FEA5-4-F04-94-DA-76952-AB9-DE9

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I don't suppose you can swap the guts from the square into the round?????

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14 hours ago, datzenmike said:

I don't suppose you can swap the guts from the square into the round?????

  

I was wondering the same thing! The two small screws look to line up. That would be great. 

 

 

**Edit**

 

Guts swapped! Tach looking and working amazing! Had to channel my inner Macgyver to make it work, but hot damn am I feeling good about this one. The 81 square tach was about an 1.5” taller then my 84 round. They had the circuit board mounted right behind the tach and some tall brass posts. I was able to snip a few wires, and screw it in to my combo meter with zero alterations to the meter box. Ran wire through the plug hole and mounted the circuit board on the back or the meter box. The 84 tach had the circuit board BELOW the tach so it would fit in a more shallow box. I did not think I would be able to pull it off but oh man was I happy to see it work!8-B1-F6-B49-32-E0-49-F5-A58-D-19-DC0-BF8C427-B341-71-D6-4-A85-8534-FDA187453-FC36-D3-CB569-DCCD-407-E-A3-F4-6-B01-ED5-AF0787-AB00-8257-4-DAC-A584-0-E2-CF175-EED

Edited by Rat baby
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Looks like I’ll have to open her up again to adjust the needle slightly. I put it right on 0 when I assembled it but it must hang a little below that when off. Hooked up a tach dwell and it’s a few hundred rpms off. That said I’m still idling a little high. I have been fixing some vac. hose and it seemed to pick up the idle. Can I just adjust at the carb? 

Edited by Rat baby
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Yes.

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14 hours ago, Charlie69 said:

Yes.

 

 

Hooked up the tach dwell meter to coil. Says I’m idling right around 1k. Sticker on my hood says 800 is money. When turning my idle adjustment screw it didn’t want to come down any lower. 

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Was your truck up to operating temperature when you tried adjusting idle speed?

 

If it was make sure your choke is adjusted correctly.

 

Also the AC has to be off to adjust the idle speed.

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1 hour ago, Charlie69 said:

Was your truck up to operating temperature when you tried adjusting idle speed?

 

If it was make sure your choke is adjusted correctly.

 

Also the AC has to be off to adjust the idle speed.

 

 

She was up to temp. I don’t have AC. I will check my choke. I’m sure some of my vacuum lines are cracked. Been trying to replace them all. Could this be a factor? Thanks for the help. 

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Vacuum leak either makes rough idle or will not idle.

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12 hours ago, Charlie69 said:

Vacuum leak either makes rough idle or will not idle.

 

 Ok right on. I’m doing a carb inspection today. Cleaned it a week ago and man it sure liked that. 

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Sprayed down the whole carb big time with cleaner. Lots of gunk came off and right away she was idling at 700. It’s been about a week and I notice the idle is creeping back up to the 1k mark. Still purring nice though. 

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See if it is resting on the idle set screw. Your cleaning loosened the gunk now the solvent is gone and things are getting sticky again. Lube attracts dirt but things get sticky dry so kind of a catch 22 but a little oil on the shafts and other moving bits go a long way on making the carb operate smoothly. Make sure your return spring is in good shape and it doesn't hurt to clean and lube or replace the throttle cable. Even the pedal pivot points in the cab like a little lube now and then 

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After I clean my Weber I use a dry silicone spray to lube the mechanical linkage.  The dry silicone lubricant goes on wet and quickly drys off.

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