The intermittent tach fix guide

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yottabit
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The intermittent tach fix guide

Post by yottabit »

I just soldered the red wire in my tach and I thought I'd take pictures since we need a FAQ on this. This is for intermittent tach failure, or a tach that doesn't work at all.

To get the instrument panel out first take out the screws holding on the outer trim piece that also holds the gauge brightness and wiper speed dials. Then shimmy it out a little bit and disattach the wiring from those dials. Pull that piece all the way out (I took off the plastic on top of my steering wheel column around the hazard flasher too). Then you have 4 screws that take off the actual instrument panel. Shimmy it out a little bit and reach behind to unhook the speedo cable. It should just pull off. Then pinch or pry the tab off the wiring and disconnect that from the instrument panel. Last but not least is the hose to the boost gauge, that I had to pry off with a screwdriver.

My cars a 1988, so I have the gas anti-slosh board. Thats what that board on the top left is with all the wires. Some people take it off if their gas gauge isn't working very well, and have reported that it helps. Other's put in new capacitors. It's held on with velcro. Mine works fine, so I left it.

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1) Remove the 5 perimeter screws and loosen two of the bolts circled in green. These hold the tach/boost gauge panel to the rest of the instrument panel. Then hold the tach panel as you undo the last bolt. If you're using the slosh board, make sure you remember where the wire went to.
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2) Pick off your needles and remember where they were. Be careful, they come off hard and I wouldn't pry them with anything because you might bend the teeny shaft. Be smart.
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3)You'll want to take off the two screws circled in red. These hold the face of the panel. Then undo the bolt holding on the boost thingy.
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4)This photo doesnt really show it but this board is held in by three tabs. I took it out by gently prying on one of the upper tabs at a time with a screwdriver and lifting the board up at the same time.
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5)Flipping the board over look for any loose connections. It seems like the most common one is this red wire, as you can see in the picture. All I did was hit it with a soldering iron and added a little bit of solder and voila. Good as new.
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Reverse is the opposite of assembly. Just remember to put your needles where they were.

Also, I believe this is the potentiometer many people have talked about giving them success with their tachometer. Some say to work it back and forth a little bit, then set it back to its original setting. Mine had some kind of weird glue on it.
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After doing this I had full function of my tach back. All you need is a soldering iron and a little solder on hand just to be safe. I touched up some of the other connections while I was in there too.

Comparing the stock tach to my Autometer, when it is perfectly calibrated they are dead equal while cruising/slowly accelerating, but if I rev it fast or floor it the stock tach will spike a lot higher than the Autometer, and it won't return as fast. So the stock tach is fine for cruising but I'm still going to keep my Autometer around.

Feel free to post back with any other tach/boost gauge/instrument panel info, or if I made any errors, but please keep it on topic!!
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DPDISXR4Ti
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Post by DPDISXR4Ti »

Nicely done! Highly FAQ-able! :thumb

Over the years it's been suggested that a failing component of some sort was the common cause of a failed/intermittent tach. I'm questioning that now.
Brad
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Mike McCreight
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?

Post by Mike McCreight »

I've seen it go both ways, Brad... Some tach modules have responded well to a bit of solder, others needed tweaking of the little potentiometer, others have been best served with a firm crushing under the heel of my shoe... :shock:
The last "fix" doesn't help the tach work, but after re-and-re'ing them a few times trying the different fixes, it sure makes me feel better... :wink:
It's not a hobby, it's an obsession!
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EVIL_XR4
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Post by EVIL_XR4 »

I really need to do this....my gauges all come and go but i think i missed some screws when i tried to take my cluster out and couldn't get it out.
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salukixr4ti
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Terrific Write Up

Post by salukixr4ti »

That is a great how to. I'm certain there are lots of owners out there to benefit from this. However, I 2nd the sticking to my autometer notion - It's so much more accurate.
This ain't no disco...It's Wichita.
jake
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Post by jake »

I just attempted this repair. Sure enough, there was a cold solder at the red wire. After fixing this, I managed to crack the circuit board while trying to secure it under the mounting tabs. So be careful, the tabs are tight and these old circuit boards are fragile.

PS please p-mail me if you have a tach for sale.
Jake
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xr4man
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Post by xr4man »

hey jake, i can fix you tach for you.


this is a nice write up, but the red wire is not the only one that can have a bad solder joint. when i refurb the tach, i go and resolder every connection on teh board and lube the pin for the needle too.
i've also found that some tachs are just unfixable. but i think that has more to do with the mechanical portions like the springs have gotten weak or something.
ian the re-animator
jake
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Post by jake »

Hey XRman,

Thanks for the offer, but I may give it one more shot. Merkur Midwest has a used circuit board that I am considering purchasing.

I have a question for you. After I removed the needle, the pin that the needle seats on moved a bit. Do I have to worry about getting the pin back in the original positon before putting the needle back on, or does the pin automatically come back to the original position?

thanks
Jake
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xr4man
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Post by xr4man »

yeah the pin is spring loaded. all i do is put the needle on and then turn it on the pin until it sits at the 0 rpm mark.
ian the re-animator
anglin
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Post by anglin »

Nice. Didn't even know about this thread. I thought I had done a FAQ on it myself, but it turns out that I just added it to my Road Car work thread. Here's a link to the page it is on:

http://forum.merkurclub.com/forum/viewt ... c&start=30
Anglin email: - anglin at mc2racing.com
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my8950
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Re: The intermittent tach fix guide

Post by my8950 »

Old post I know, but I'm working on the cluster issues now. If anyone here is still on the forum, do you know where we can find these photos anymore?
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Spaldino
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Re: The intermittent tach fix guide

Post by Spaldino »

Hey... that's my old 88 monowhite XR! Ryan is a good kid. thanks for bumping this old post and allowing me to feel some nostalgia!
88 Mono-white XR: Side exhaust, Walbro, MC2 Front Adjustable Coilovers, Rear Bilsteins, Full Poly bushings, MC2 Diff Mount, Rapido intercooler, Some sort of mild cam(?), Rear Disc conversion, 225s on 17x8 wheels.