time to tackle the Tachometer

[Zedyone_kenobi]

I have always had a partially sketchy tach. Now let me say that my tach works. Most of the time anyway. If I never rev my car past 5500rpm it would be a perfect tach. However, when I rev past 5500 rpm my tach sort of goes on strike. This was not a problem with my original motor (L24) as I never really pushed it that hard, as there was not really that much power past 6000 to be had. So it was a non issue for as long as I had the car. Below 5500 rpm it is dead reliable and smooth.

Now fast forward to a higher revving L28, that likes to live between 3500-6500 rpm and now I have a tach I canont trust beyond 5000 rpm really. So my quandry is this. I have a dash cap on my car. A full cap. Been on there since I bought the car. The prospect of removing a tach with the dash cap on is daunting. As I think the tach came out of the dash toward the driver, not back to the firewall. I could be wrong. I will check the FSM. I have a spare tach in my box of spares, but I have no way of knowing if what I have in the car is a 3 wire or a 4 wire. I have to assume it is the original tach.

So my questions are:

1) Has anybody removed a tach by removing it toward the firewall? Not through the steering wheel?

2) Is there a way to test my spare tach for continuity?

You see what can happen here is this can go from a simple swap to a case of while I am at its. I may be inspired to pull out the entire dash and get a new one or get mine restored. I have already replaced/restored all my other gages. I really have no time to do that to be honest.

Any tach removal stories?

[beermanpete]

The tach comes out toward the cockpit, not the firewall. Getting to the fasteners and wiring is a lesson in flexibility and clairvoyance. The dash cap will likely need to be removed first.

I repaired my tach (4-wire type). There are 2 transistors that seem to get shaky with age. Search for info on the Smith meters used in English sports cars. The Z tach is a close copy. This link is to a schematic for the Smith tach. The Z 4-wire tach is essentially the same.

Google Image Result for http://www.sw-em.com/1800_Smtihs_tach_schematic.gif

Some of the websites discussing the Smith meters indicate the timing capacitor (C2) also ages and should be replaced.

My complaint about the Z tach is that it bounces too much and takes too long to settle after a gear change. A small cap across the meter movement might help, I have not tried that however.

[FastWoman]

I've read of some people having success removing the tach through a full cap by using thin, metal shims (e.g. softdrink can material?) to shoehorn the tach past the dash cap ridge. It supposedly takes quite a bit of patience and finesse, but apparently it can be done -- at least sometimes.

[colinc]

I've read of some people having success removing the tach through a full cap by using thin, metal shims (e.g. softdrink can material?) to shoehorn the tach past the dash cap ridge. It supposedly takes quite a bit of patience and finesse, but apparently it can be done -- at least sometimes.

I removed my tach this past weekend and was not able to get it through my full dash cap. Luckily the dash cap was not glued down so I was able to remove it. I could see how shims may help but you may need someone else to push it from behind while you insert the shims. Also, you would have to shim the entire circumference to make it work.

Good luck.

[Zedyone_kenobi]

Removing my dash cap does not sound... um... fun.

But if I do, I know what is going to happen. I am going to start saving up for one of those uber rare uncracked dashes. I know myself too well. But I want my tach to work, so I will give it a go.

[Darrel]

look up kenz240, he has a thread on refurbishing his dash. I have seen it and he did a great job. Mine is next on his list. ;-)

[Captain Obvious]

Removing my dash cap does not sound... um... fun.

If the cap is free floating and isn't glued down, taking it out isn't bad at all. I don't remember if it's necessary, but taking the steering wheel off first makes it easier. A warm day helps too.

If it's glued down, you're on your own.

[Travel'n Man]

Stephen -

I sent my tach off about 2 years ago - works dead on perfect - no bounce.

APT Instruments International Inc

[tlorber]

Stephen -

I sent my tach off about 2 years ago - works dead on perfect - no bounce.

APT Instruments International Inc

I did the same with my tach but sent it to North Hollywood speedometer. They replace the guts with modern components.

Stephen, if you think you will be replacing your dash cap or cover eventually, then if you can't shoehorn the tach through the dash cap perhaps you could use a dremmel to cut the off the part of the cap that goes into the tach recess. Nothing to lose.

[Travel'n Man]

Remember, you car will not start without a tach connected - since you have two tachs (it sounds like) send off one and keep one in so you can keep on driving while it is out. Be ready to lay on your back like a pretzel - great time to change out some of your lightbulbs if needed while your at it............the speedo is the hardest.

[Zedyone_kenobi]

Travel'n Man, did they rebuild your OEM tack to OEM specifications. Our cars ignition power goes through the tach on its way to the coil as you know, so replacing the tach with one with modern guts worries me a bit. I will check out your link. THANKS guys for these ideas and link. I like the dremel idea, as I can always add a new dash cap if I have to later. That cost is trivial compared to getting my dashboard refurbished!

also can you give me an idea of the cost of the service.

EDIT: I just called them up and they were very nice Mitchell. I will pull mine out and have them repair it. As my OEM gage aesthetically is near perfect. Mechanically it just needs some TLC.

Edited March 12, 2013 by Zedyone_kenobi