Has your Tachometer ever done this ?
Thread Starter
Instructor
Joined: Jul 2000
Posts: 115
Likes: 0
From: stockport Cheshire
Has your Tachometer ever done this ?
I went for a blast in my vette yesterday for first time in a few weeks. I got the engine up to temp then hit the gas pedel at 5500 revs the needle on the tach went crazy jumping off the scale and bouncing all over the place. It was also making a horrible noise, I backed off and at 3000 revs it went back to normal, but every time I went over 3500 it went crazy again. I took the car home and checked the drive cable and it seemed ok, I went out in the car later on and it was fine I could rev upto 5500 and it worked as normal.
Has anyone had this happen to them or any idea what may be causing it to happen.
Thanks Mark......
Has anyone had this happen to them or any idea what may be causing it to happen.
Thanks Mark......
Melting Slicks
Joined: Nov 2000
Posts: 2,112
Likes: 3
From: Kingston, TN
St. Jude Donor '06
Re: Has your Tachometer ever done this ? (British Mark)
Was it cold? This can happen if its lubed with grease or maybe has moisture in the cable. Usually much better afer warmed up. :chevy
Team Owner
Joined: Jul 1999
Posts: 65,492
Likes: 230
From: Orange Park Florida
Re: Has your Tachometer ever done this ? (British Mark)
The tach head and the speedo are nearly identical in construction....what heppens to either one when the needles go crazy is either the cable and driven gears on the distributor or tranny.....OR...most likely....
you need take the heads down for a complete disassembly and just a touch of oil in the pin bearing hidden way down in the device...hense you need take it all the way apart.....compass card off, needle pulled, two screws in the support frame taken off the casting, then you will see the hidden bearing which is dried out after decades....worse when cold of course....
that and the obvious bronze/oil lite bearing on the input section.....
it's an all day job...not so hard really, but not easy to get to....
GENE
you need take the heads down for a complete disassembly and just a touch of oil in the pin bearing hidden way down in the device...hense you need take it all the way apart.....compass card off, needle pulled, two screws in the support frame taken off the casting, then you will see the hidden bearing which is dried out after decades....worse when cold of course....
that and the obvious bronze/oil lite bearing on the input section.....
it's an all day job...not so hard really, but not easy to get to....
GENE
Safety Car
Joined: Apr 2002
Posts: 4,653
Likes: 6
From: North Royalton, OH
St. Jude Donor '06-'07
Re: Has your Tachometer ever done this ? (British Mark)
I had a similar situation a few years ago. Seemed fine when the car was sitting, even revving, but under load it went crazy, just like you described. And it didn't always do it - only when the engine was warmed up. My solution was the tach cable. New cable, no problem. Not sure exactly why, but it was an easy repair. Good luck!
Safety Car
Joined: May 2001
Posts: 3,758
Likes: 3
From: Surrey
Re: Has your Tachometer ever done this ? (BSiegPaint)
Mark,
I've seen this several times due to clapped out cables or cables that have dried out & then got rusty inside. What happens is that the inner snags on the outer but, as the cable is still being driven, the inner below the snag starts twisting until it either breaks or the twisting force overcomes the snag. If that happens then the cable rotates much faster than it's being driven to get rid of all the stored twists (hope that makes sense!). The result is that the tacho/speedo at the other end is suddenly driven very fast briefly, then slows to the correct speed, then the cable snags, etc. Hope it's your cable & not the tacho!
Paul
I've seen this several times due to clapped out cables or cables that have dried out & then got rusty inside. What happens is that the inner snags on the outer but, as the cable is still being driven, the inner below the snag starts twisting until it either breaks or the twisting force overcomes the snag. If that happens then the cable rotates much faster than it's being driven to get rid of all the stored twists (hope that makes sense!). The result is that the tacho/speedo at the other end is suddenly driven very fast briefly, then slows to the correct speed, then the cable snags, etc. Hope it's your cable & not the tacho!
Paul
Thread Starter
Instructor
Joined: Jul 2000
Posts: 115
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From: stockport Cheshire
Re: Has your Tachometer ever done this ? (mrvette)
I have had all my interior out for a refurb recentley and I had to strip down the speedo to replace a gear to get the odometer working. Why couldn't the tach have been playing up before I had done this, I was hoping it may just need a new cable so I don't have to pull all the console apart again.
I will be taking the car off the road soon to replace the engine and do some detail work on the engine bay, so I will look at the tach then.
Thanks Mark..
I will be taking the car off the road soon to replace the engine and do some detail work on the engine bay, so I will look at the tach then.
Thanks Mark..
Team Owner
Joined: Feb 2001
Posts: 49,198
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From: All in!
Cruise-In IV Veteran
St. Jude Donor '03-'10
Re: Has your Tachometer ever done this ? (British Mark)
I have this exact problem with my speedometer.
I just haven't gotten around to replacing the cable.
How difficult of a job is it? :(
I just haven't gotten around to replacing the cable.
How difficult of a job is it? :(
