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I have a question relating to the speedometer in my car. I bought a 1970 GT 1900 only a few days ago. But I am having a minor problem. The speedometer has stopped working for all practical purposes. The magnets on both the tach and speedo were weak, it seemed, when I bought the car, because the needles would always bounce when first accelerating from a stop. Now the speedo only occasionally moves, and when it does, it gives an inaccurate speed reading. Does anyone know of a solution that does not involve installing a new speedo?
 

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GTAlex1900 said:
The speedometer has stopped working for all practical purposes. The magnets on both the tach and speedo were weak, it seemed, when I bought the car, because the needles would always bounce when first accelerating from a stop. Now the speedo only occasionally moves, and when it does, it gives an inaccurate speed reading. Does anyone know of a solution that does not involve installing a new speedo?
First check to make sure that the speedo cable is completly screwed into your unit. This involves following the cable from the floor to the speedo and manually by hand turning the threaded locking ring. Mine would bounce when my threads were either cross threaded or not threaded on tight. The rest of the possible maintenence involves removing the cable from your tranny and cheching to be sure it is well lubricated.
BTW- if your unit is bad, you might as well get REAL familiar with the instrument panel removal procedure as it will become a necessity sometimes down the restoration and repair highway. I can remove mine in a little under 15 minutes- putting it back in 30 minutes
ALSO- if you have a bad unit, many members have several of the gauges in their private stash and they also come up regularly on EBay :cool:
 

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GTAlex1900 said:
I have a question relating to the speedometer in my car. I bought a 1970 GT 1900 only a few days ago. <SNIP> The magnets on both the tach and speedo were weak, it seemed, when I bought the car, because the needles would always bounce when first accelerating from a stop. Now the speedo only occasionally moves, and when it does, it gives an inaccurate speed reading. Does anyone know of a solution that does not involve installing a new speedo?
As noted, you may have to open up the dash ... Good idea to find a Factory Service Manual (usually eBay) for future references.

My 71 GT Speedometer would bounce from 0 mph to approx 35 mph. Installed new cable from www.opelgtsource.com (lubricated before installation).

NOTE: ONLY ACCOMPLISH ON DESERTED ROAD FOR SAFETY!!
While driving, found out that I could reach behind speedometer where cable is attached. Was able to tweak cable alignment, so that speedo needle bouncing almost went away. Not the safest task, but accomplished on deserted road traveling under 35 mph. You could park GT, tweak cable, drive, and see if bouncing decreases. Repeat process ...

Eventually I will find another speedometer with odometer of 4X,000 miles and will will swap when miles approx. match.
 

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different speedo problem

after doing the dash tear down, rewire, redo window rubber etc. dance of joy, i got everything back together and took it out for a ride only to discover that now the speedo doesn't register at all. no bouncing or anything. i've redone the cable connection 3 times and still have nothing. could the cable have gotten screwed up somehow during the 3 months it sat "idle" or is there something i'm overlooking...?

bob
 

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Having chased down this problem on a Manta, I would think it could be the same in a GT. I found that the Speedo "Drive" gear INSIDE the tranny to be completely stripped. This gear is a plastic worm gear which mates to the "Driven" gear. The Driven gear is the one that is removable from the outisde and the one the cable screws in to.

I had to disassemble the tranny to replace it with a good used one. I wasn't "that" difficult.

HTH
 

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Sounds like a broken speedo cable. To check, disconnect the cable from the speedo and let it hang out from under the dash. Go for a short ride and observe if the inner square cable drive turns while accelerating. If not and you are sure it is hooked up to the tranny the inner drive is broken. Not to uncommon when considering the age of the item.
 

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i'll have to give the "let it hang out" idea a try. what's confusing is that it was working pre-dash redo and suddenly, upon reconnection, it stopped. that's why i thought it was just a connection problem at first. wish that had panned out...

bob
 

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Another method to determine if your cable is good or bad is to disconnect the cable at the transmission. Hook a drill to the cable and start the drill(try both directions, I forget which is correct.) Have someone check the speedo. If it moves, your cable is OK, if not then it is the cable. Caution, don't pull the cable when installing the drill. If you do, you might pull it enough so it is not "connected" to the speedo. You can also disconnect it on both ends, hook one end to the drill and then have someone look at the other end when you are running the drill to see if it is spinning.

HTH

Jeff
 

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My 1970 GT speedo stopped working.
I guess it couldn't take the extra rpm from the performance engine.
I disconnected the speedometer cable at the transmission, it seemed OK.
Then I unbolted the angle drive unit off, the gears seemed fine.
The square flex shaft was a little worn and the square hole in the transmission fitting was worn on the end, the flex shaft could spin.
For a quick fix, I cut a .100" dia nail about an 1/8" long to use a spacer to push the flex shaft farther into the good part of the transmission square hole.
Greased everything and put it back together.
Speedo is working again!!!
For a better repair I would like to replace the worn square flex shaft, is it available? It checks about .103" across the flats.
Maybe I could braze the ends of the flex shaft to increase the size a little?
Any ideas?
Thanks
Lyle
 

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Lyle , NAPA has a universal cable that you cut to size .
HTH John
 

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Since I have the bouncing, sometimes not working, and noisy as all get out, speedo issue, I thought I'd revive this thread.

I know my speedo is faulty because sometimes it sits at 30mph. Sometimes it doesn't go up until I reach 70 and then it's sluggish.
And the cable makes a horrible chatter all the time but gets much louder between 40 and up... The chatter drives me nuts cuz it's almost as loud as the engine/exhaust with no sound deadener.

My cable is old. My speedo is old. Hell, the whole car is old.

I have new speedo cables for the GT and the Manta in my hoard and was wondering which was the longer one?

My GT is a 71 and if I need the right angle adapter I have one or two laying around. I might even have one on the car. I can't remember.

Anyhow, does anyone know which length goes to which?
 

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I have a question relating to the speedometer in my car. I bought a 1970 GT 1900 only a few days ago. But I am having a minor problem. The speedometer has stopped working for all practical purposes. The magnets on both the tach and speedo were weak, it seemed, when I bought the car, because the needles would always bounce when first accelerating from a stop. Now the speedo only occasionally moves, and when it does, it gives an inaccurate speed reading. Does anyone know of a solution that does not involve installing a new speedo?
The 1970 uses the early transmission, which means it has a right angle adapter. Remove the adapter and make sure that the cable is sticking out far enough to engage the speedometer gear inside the transmission.

I had this problem on mine. I slid the short piece of cable out farther and it has not reoccurred. That was 4,000 miles ago.
 
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