Wacky speedometer 1956

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bfdinardo

Member
I have a 1956 Fairlane 292 with fordomatic transmission. The previous owner didn't have a driven gear into the transmission housing. I recently installed a 19 tooth gear and took it for a drive. The speedometer was working great until about 45 mph and then the needle shot to 90-95 mph (bounced around) and became noisy until I slowed down to about 25mph and it worked again. I can't seem to get above about 45/50 without the needle shooting up and making a bunch of noise. Any ideas? I removed the cable and it's still square, not rounded off or stripped.
 
I’m assuming you pulled the cable out, lubed it, and put it back in. If not, that’s the first step. If you did, it’s probably not the cable, but a problem in the head unit. The jumping and bouncing is normally a lube or kinked housing problem. After that it’s the head unit.

Even with the right gears the speedo may be off a bit by 60mph.
 
bfdinardo said:
The speedometer was working great until about 45 mph and then the needle shot to 90-95 mph (bounced around) and became noisy until I slowed down to about 25mph and it worked again.
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Ummmm....that's why your previous owner removed the nylon gear out of the rear extension housing.
Usually, the speedo cable core needs to be lubricated, but sometimes the speedo mechanism itself is dried out and/or clogged up.
For the speedo cable, you can disconnect it at the back of the speedo mechanism and pull the cable "core" all the way out. Put newspaper down on your car floor so as not to get grease on your floorcovering.
Now you can lubricate the core with speedo cable graphite grease found at most local chain auto parts stores, then push the cable core back in to the housing (conduit). Wipe away any excess grease at the head of the cable before re-connecting to the speedo mechanism.
I have taken several speedo mechanisms apart before in the past and carefully cleaned and re-lubricated them successfully, but you gotta be careful with your cleaning solution and apparatus, not to get any on the dial faces or it could ruin them. I used 3-in-1 oil to re-lube the mechanism inner gears and moving parts. Don't squirt a ton in there or it will make a big mess.
 
I had a 67 Cadillac that did that. It would happen at random, usually at freeway speeds. It was kind of funny. It would go TWANG! and the pointer would wag from one end of the scale to the other. And as suddenly it would happen, it would fix itself after a minute or two of continued freeway speed. I never did try to figure it out. The odometer was unaffected.
 
I had sort of same problem on my '41. removed speedo and thee was a small hole above where the cable attaches that oil could be added to lub the bearing. did so and good for 10 yrs or so. don't know if '56s are the same but worth a look
 
The speedo needle it attached to a drag cup in its shafting that is separate from the drive. This assembly has a clock spring to regulate needle movement. On the driven end, the cable from the trans drives a magnet that fits relatively close inside of the drag cup previously mentioned. The faster the magnet rotates, the more needle movement you get. If the bearings (or bushings) on either the magnet shaft or the needle shaft get worn or allow too much movement on either item, the magnet can stick to the cup and cause a full needle indication plus the noise of the magnet slippage inside the cup. They can squeal pretty loud when this happens. Lubricating all of the bearings involved may halt this discrepancy but it depends on how much wear has take place over the years.
 
rotorwrench said:
the magnet can stick to the cup and cause a full needle indication plus the noise of the magnet slippage inside the cup. They can squeal pretty loud when this happens.
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I've had this happen to a couple of my speedo's. Yes it is a concern about the amount of wear there might be in the bearings, but if you service the speedo in a timely manner you can prevent further wear. Cleaning of dust and fuzz and adding new lubrication has proven to eliminate the problem on both my speedo's for many years and many thousands of miles.
 
Thanks everyone. I have the speedometer head unit out on the workbench now and see what you're all talking about with the magnet and cup. To be honest things move pretty smooth when I twist the input by hand but I suppose it's different when it's turning much faster. I'll clean things up and oil the bearings and put it back in to see what happens. I have already removed the cable and will use graphite powder/grease on it. I'll let you all know what happens when I re-assemble!
 
If you’ve got a short piece of cable, or just square stock, a variable speed drill will give you a look at how it works while it’s out. Might take a second set of hands to hold everything in line.
 
Update: All fixed! I removed the speedometer gauge from the dash and put some 3-1 oil into the little hole with what looked like a piece of fiber to lubricate the shaft bearings of the gauge. I did the drill trick which took the needle up to about 70 mph with no skipping thus the gauge looked to be in good shape. I then took the cable core out of the sleeve, soaked in kerosene for a few minutes, wiped it with a cloth and let air dry over night. Finally I applied graphite powder to the cable as I fed it back into the sleeve spinning it as I fed. Buttoned it all up and took a drive on the highway at 65mph with a nice and steady needle! Thanks for all of the insight.
 
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