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Old 07-31-2006, 08:53 AM
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Help Speedometer Not Working (at all)

I just bought a 1978 Camaro. This vehicle had a cruise control unit on it that went in between the transmission and the speedometer. When I bought it the speedomter was not working. The previous owner had a standard speedo cable in the trunk (just from the tailhousing to the speedometer.

So I dissasembled the dash and removed the old speedocable and cruise unit under the hood. I then removed the cable from the cruise to the trans. I wasn't sure how to remove it from the transmission, so I loosened the 10mm bolt that was holding the retainer thinking that it was locking the speedometer knurled nut. When I tried to unscrew it it was just turning. I realized what was going on and rotated the speedometer housing back into place and locked down the retainer. I then easily removed the speedometer cable with channel locks and then by hand.

I checked the speedometer by spinning it by hand and there is nothing wrong with it. The needle goes up when you spin it and then drops back to 0. The cable that he had spins fine I checked it by turning it by hand.

Last night I reassembled the dash and attached the cable to the transmission. When looking at the cable end it is square in shape, but the hole it goes to in the transmission seems to be round. I didn't have to rotate it or anything to slip it in. I tightened it back down and test drove it and it is still not working. I don't here anything when I am driving. no clicking or whining.

My Questions so far:
Is the speedometer cable hole in the driven gear supposed to be square? Is it possible that it is stripped out? They are plastic right?
Can I replace the driven gear without having to remove the tail peice for the transmission?

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Old 07-31-2006, 09:38 AM
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speedo not working

Can't answer all your questions. But I had a similar problem. Dropped the tail piece and found the drive gear was missing. Installed a new one, and it worked. (About $11.00). [ I have also seen the driven gear installed in the wrong shaft location so it didn't line up with the bullet hole, either way it is the first thing to check] On mine the calibration was off the first time, so I just replaced both the drive and driven gears with a new combination to correct the error. If you have enough information, 1 - speedo ratio, for example 1,000 rpm equals 60 MPH 2. Rear end gearing, 3. rear tire size, etc. you can calculate the exact gearing you need and get the right combination the first time. good luck.
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Old 07-31-2006, 09:54 AM
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Pull the cable out of the speedo end and go for a little slow drive with somebody else watching and gently holding the cable into the outer ( I use a screwdriver handle) if it turns its the speedo head if it dont its the cable or drive. Like previous poster says the drive gears are often missed out or put on backwards or slip

enjoy
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Old 07-31-2006, 10:03 AM
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Thanks for the replies so far, more info please

I'll do this this afternoon...

If I find that it is the transmission side not the head or cable, is it possible that the driven gear is stripped and the drive gear is not? Or do they usually go togeather. I was just wondering because I may not have the special tools required to remove the drive gear. I have read an instruction on changing the gears on thirdgen.org (http://www.thirdgen.org/speedogear) and it seems like I need a special tool to remove the drive gear.
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Old 07-31-2006, 10:10 AM
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One more thing. Cordless Drill?

Could I also check the cable and head by removing the end from the transmission (very easily done) and attaching the square end to my small cordless drill and running the drill and see if the speedometer registers?

Like I said I checked the head by spinning it by hand and the needle goes up when I spin it and then falls back down like it should and I turned the speedometer cable by hand and it didn't feel like it was binding.

It is quite an undertaking to remove the cable from the speedometer because I have to remove the entire guage cluster and disassemble it in the car because there is no external clip holding the cable in it's actually behind the head inside the guage cluster housing.
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Old 08-01-2006, 12:41 AM
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If the dash is that much trouble, I'd just buy a new gear for $5 and see if it works.

As far as using a drill on the cable end, you can do that, but if it works by hand, it's gonna work with the drill.

While you have the gear housing out, look inside and see if the drive gear is in place, and securely clipped to the tailshaft.

Last edited by jimfulco; 08-01-2006 at 01:02 AM.
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Old 08-01-2006, 09:40 AM
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help speedometer not working

You can check the head by spinning the transmission end, but a couple of tips. To my knowledge, they turn backwards (counterclockwise) so you need a reversable drill. I have one that runs 500 rpm in reverse, so on a 1000rpm to 60 mph speedo head, it should register 30mph. Maybe you can confirm the RPM to speed ratio without pulling the head - dealer/website/??
Popping out the driven gear is simple. do that and look at it, if the teeth are all gone and you can see in the hole the drive gears are OK (not likely) that would be that. If the teeth are good, either the drive gear is missing or out of place, or someone took a shot and replaced the driven gear already.
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Old 08-01-2006, 02:13 PM
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speedo not working.

Just clicked that website you listed, to see what "special" tools were needed to pull the drive gear in the tranny. Must have been the 2 pound sledge??? LOL.
Sorry, couldn't help it. Do not hesitate to do this job. Drop the driveshaft, remove 4 bolts and tail piece comes off. The drive gear should be a tight fit on the shaft so it will take some nudging, but no big deal, it's plastic. The 2 pound sledge must be used to hit yourself in the head so you can say this was a bruising ordeal. The clip is easy to get out. When I am in doubt on a never before job, I like to get the new parts first. So when you have the tailpiece off note the color of the gear and style, also the width of the little clip. Assuming the teeth are bad and you have to replace it, go buy the gear and clip first to see how they go together. Once the driveshaft and tailpiece are off, You will swap the gear in 2 minutes. trust me. Personally, I would much rather swap the drive gear in the trans than pull the speedometer out of the dash. It's a no brainer.
[be sure to note the color of the gears. color indicates number of teeth.
If the rear end or gears or tire size has been changed, the speedo could be off. When it works, you can test it against one of those traffic speed indicators (or a friendly cops radar gun) and if it is off, it will be easy to
fix. IE; say you know you have a 10 tooth drive gear and a 20 tooth driven. If it reads 10% (not mph, but %) fast, change the driven to a 22. If it is 10% slow, drop the driven to an 18. etc. ]
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