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Tachometer sticking when cold


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My EA81 Turbo Wagon's tach is sticking when cold. I'll start the car, and the tach will read 0, and the engine is obviously running. I'll start driving the car, and it'll bounce up to 2k and stay there. Sometimes it goes back to 0. If I drive it for about 20 minutes, it unsticks itself and starts operating normally. On warmer days, it didn't do this.

 

Is this a common problem? Is there a way I can remedy this? If I need to replace the tach, is the unit itself replaceable without having to replace the whole dash?

 

Thanks!

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Mine's been doing that for years. Not been a problem, but sometimes to unstick the needle, I'll whack the top of the dash with the palm of my hand (not too hard) after warmed up. Sometimes it works, sometimes not.

 

Just my 2 bucks

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A few drops of Tri-Flow where the needle connects?

Maybe, I think that's the right idea, anyways. My theory was that a slight bit of moisture was in the tach head, and cold enough weather would freeze it temporarily. Never did take it apart, but moisture-chasing lube may fix it.

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My '84 wagon did that too -- on really cold days, you could drive a few miles before the tach would get above 0. Then all of a sudden it would work fine. I thought it was a electrical connection problem down by the coil getting moisture in it or something, but maybe lubrication or moisture in the tach head? Could it possibly be the same problem source as with the slow speedometer response? The speedo on my 89 GL only vaguely indicates road speed when it's cold out.

 

And, always check to see if the pack rats haven't chewed almost completely through the tach wire -- that's what they did on my truck.

 

One "solution" Drill a small hole in the y-pipe, then the engine will be loud enough to have an audio tachometer.... That's the reason I never worried about the tach on the '84 wagon -- I could hear it. The 89 is so quiet that I do need the tach though.

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The greese or lube on the needle gets really thick when cold, and it may have some dirt in it. My 1987GL would do it too untill the inside of the car warmed up.

As somone who would calibrate gauges for a living, the tach in a car is rather delicate, especially where the shaft is for the needle (being electronic) One of two things is happening, either its the lube, or the coil that moves the needle is getting weak. Either way its very hard to fix. Three drops of lube is probably 2.80 drops too many.

 

nipper

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It's ironic that you would post this. Today I noticed this problem for the first time on my new to me 84 BRAT. It has been "cold" here in SoCal, close to freezing. Once I drove for a few miles it started working again. I will see if it does it again tomorrow morning.

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Its not the point of whether or not I need it. I want it. I like to be able to verify that the fast idle is working when I first start it up. I like to have everything on my dash functioning properly. I don't like to see a needle pointing to 0.

 

Also, mine doesn't always pick back up. On a 10 minute drive to work, it usually hasn't started working again. Kinda bugs me.

 

But since it doesn't sound like there really is an easy fix, I'll live with it.

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Thats exactly how I feel about a check engine light. Everyone says:"just put some tape over it". Thats not the point, its on for a reason not just to bug the crap out of you.

 

Some of these charter members has gotta have a sure fire way to fix this.

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See if you can get one from a junkyard, it doesnt have to work. Take it apart and see how it works, then decide if you can tackle the problem.

 

And i agree about the tpae on the CEL, it can do more harm then good.

 

nipper

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  • 2 years later...

Is there any noise associated with it? A hatchback I had did this when it was cold, then it would jump around. But there was a screetching from the distributor. The shaft and bushings were worn enough that the shaft would chatter while spinning.

Edited by Frank B
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  • 3 weeks later...

I don't know about the tach, but I do know about the speedometer. The cable that comes up from the transaxle has seals that routinely fail, and the gear oil from the transaxle case will work it's way up the cable and into the speedo housing. It's also why your car can start smelling like gear oil for no real reason... Dash pulling fun, and a fair bit of electrical cleaner can change the sticky speedo, I'd guess that the oil can get into everything in the instrument cluster and muck it all up. Never had a tach fail me yet, though.

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I don't know about the tach, but I do know about the speedometer. The cable that comes up from the transaxle has seals that routinely fail, and the gear oil from the transaxle case will work it's way up the cable and into the speedo housing. It's also why your car can start smelling like gear oil for no real reason... Dash pulling fun, and a fair bit of electrical cleaner can change the sticky speedo, I'd guess that the oil can get into everything in the instrument cluster and muck it all up. Never had a tach fail me yet, though.

 

 

Gotta love the gear oil smell. I never would have thought it came from that. We should have a thread on suby only smells.

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