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Old 01-31-2005, 11:13 PM
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speedometer with its own mind????

ok guys I have a problem that just baffles me, hopefully some1 can help me out. the problem is on a 1966 chevy 3/4 ton fleetside with a TH350. the vehicle has a brand new speedometer cable (and well greased), speedometer drive gear can not slip (clip is in place)

ok, well the speedometer works for the most part in the summer when its hot out, however when it starts to get cold she tends to "hang up" I can leave home, with the motor hot, cab cold, get on the highway, floor it, and it still says I am going like 20 MPH when I am going near 60. weird thing is that all of a sudden it will say I am going 90+ mph, just like that, then hang their until I start driving real slow. however if I turn on my heater full bore she does not do it, or at least not very often.

-cable (driveshaft) was greased liberally at installation, no sharp bends, and kept clean.
-its your normal cable driven speedometer with a drag cup connected to the needle. (as stock)
-after having problems with it I took it out, blew all the dust of and checked the needle return spring and its NOT broken
-it has hung up on me in the summer time a cop has even seen it

the only thing I can think of is maybe the magnets magnetism is messed up or a spring thats kinda acting like a spring in a thermostat. since the goofy little thing is so simple I just cant figure out what could go wrong and cause this relationship with cold weather, however not always always in the cold, and the weird needle movements. So are they any gauge guys in here?

thanks for any ideas... 'cuz as this speedometer seams to have its own mind, I think I am loosing mine!


-Leo-

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Old 02-01-2005, 07:04 AM
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What kind of grease. Usually speedo cables use a dry graphite lube. It sounds to me like the cable is hanging up.
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Old 02-01-2005, 04:54 PM
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i just saw a new product that was a speedometer that worked of GPS, that would defently solve your problem. i think i saw it on the new Car Craft mag. ill put a link when i find it.
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Old 02-01-2005, 05:35 PM
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speedometer with its own mind.

Take a small nail & grind 1 end to fit in the speedometer ,put nail in drill & reverse the drill. it will tell you if speedometer works or not...---Take your drill & hook up to 1 end of cable & run your drill & check cable . this works for me.
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Old 02-01-2005, 06:55 PM
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You have to know how a speedo works. There is no direct connection between the cable and the needle. The cable spins a magnet, inside a cup connected to the needle. The cup and needle are mounted on jeweled bearings. The magnet drags the cup with it against a spring by magnetism only. When it does what you are describing, the jeweled bearings have hardened oil or grease on them, which is making it stick. You can clean out the speedo head, lube the jeweled bearings with light oil, and it will work ok.
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Old 02-01-2005, 08:58 PM
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thanks guys for your thoughts,

enjenjo, what kind of "light oil" should I use, I have thought about oiling the pivot points, but since I saw no sign of oil I left it as is. you are correct tho, in this model the speedometer needle is NOT connected directly to the cable. this is the typical drag cup design. (some gauges use a flyweight system so it is connected)
anyways, would a fine oil for like a sewing machine work???

-Leo-
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Old 02-01-2005, 10:09 PM
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The old standby 3 in 1 oil works good.
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Old 02-02-2005, 10:25 AM
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Quote:
Originally posted by enjenjo
The old standby 3 in 1 oil works good.
cool thanks
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Old 02-13-2005, 11:10 PM
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My '79 Suburban has a similarly lost mind. Reads anywhere between 60 & 95 when going 75 on cruise-control. Where are the bearings that I need to oil?
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Old 02-14-2005, 10:19 PM
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well you can start out by taking your speedometer back out, I didn't get around to doing it yet, but if you look directly under your needle you will see a small brass looking "bearing" that holds the needle into the speedometer housing. the needle's shaft continues through the bearing where a small calibrated spring is located. the spring is needed so that the drag cup does not peg the needle out. So the quality of this "bearing" must be in good condition. when I took mine apart it looked fine, guess I shoulda oiled it.

-Leo-
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Old 06-04-2008, 03:12 PM
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bouncing odie

Hi GUYS! My problem is the speedo jumps around all over the place and I was wondering if I need a new head or something??? the odometer doesnt seem to move either????
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Old 06-04-2008, 03:20 PM
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My 63 suburban was fine for years, then would erractically jump (at 50mph) from 30 to 100. I've got tons of spare parts so I just swapped it out. It is such a pain to pull the cluster out, so I saw no need to torment myself trying to fix that one.
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Old 06-04-2008, 07:26 PM
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Quote:
Originally Posted by 62Savoy
Hi GUYS! My problem is the speedo jumps around all over the place and I was wondering if I need a new head or something??? the odometer doesnt seem to move either????
This usually means that the speedo cable is bad or needs to be greased. The other possible problem is that the plastic speedo driven gear in the trans is worn. When this happens, the speedo works erratically.
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Old 06-04-2008, 09:58 PM
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wow i guess i am not the only one with a crazy speedo!

i agree a speedo that is constantly bouncing/jumping has cable problems

btw, the oil trick worked for about a year and a half, then it started acting up again, and now its making a ticking sound and the odometer isnt turning, so a gear in the odometer must be worn out (this 1966 chevy has ALOT of miles, and gets driven over an hour every day year round for many many years...)

-Leo-
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Old 06-06-2008, 07:49 AM
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Thanks guys for the info and I report back when I get time to pull this thing appart.
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