I had the dreaded odometer not working problem. I pulled the dash off, and what a miserable job! I have the speedo apart and sure enough I need a new 2nd worm gear. I can purchase a worm gear, however according to Willcox, the first worm gear and magnetic bushing could be out of alignment (the cause of the worn 2nd worm gear). So, where can I buy either a speedo head or just the assembly with 1st and 2nd worm gear good and working, OR should I just buy an aftermarket speedo head? To send it out and rebuild is around $200, and to buy a reproduction is around $300. BUT if I can buy the 1st worm gear with magnetic bushing, and 2nd worm gear as use the current head, even better!

 

The worm gears must be available again- I found both of mine were bad a year ago, called everyone I could think of and the gears were "out of stock". Got a rebuilt head from one of the vendors and put my bad on in a box on the shelf.

 

The only vendor I can find that has the 1st, 2nd and 3rd worm gears in metal is Long Island Corvette. Only thing is, their 1st worm is funky looking, and does not come with a new bushing. One alternative is to remove your tachometer and press out the 1st worm, and swap it for the one in the speedo. The 1st worms are identical and the gears on the one in your tach will be pristine as there are no other gears in it. Unfortunately, you would then need to get both units recalibrated. Pictures and other info to follow since the forum software is being a *****. Again.

 

 

Hmmmm, that is sort of what I was looking for. I was considering swapping the tach and speedo first worm gear, but I would have to have both unit calibrated if I did that..... I'm going to look into this method as well. I will then only have to have speedo magnetized/calibrated. Thanks! I'll keep the thread up to date on what the decision is for this problem.

 

My experience with calibration is that it's easy to do yourself. The anchors were magnetized to saturation at the factory, so you just magnetize as much as you can and it will be right. As long as no one messed with the clock spring stop your speedo will be very accurate. I fixed mine up that way, then just hooked up the speedo in the car without the dash for testing. I compared the reading to a Garmin GPS and it was within 1 mph all the way to 70 mph.

My re-magnetizer tool. A stack of neodymium magnets from home depot and a piece of flat bar steel.

 

Swede, thanks for the reply. I just read your post from the past as well. Awesome might I add for putting that out there. I do have a question for you, when you made your tool you used 1/8" stock on each end. How come you just didn't use the magnets? I assume I will be able to magnetize the new bushing/first worm gear even though it's not stock and was not magnetized to saturation at the factory. I will be sure to test it before reinstalling everything obviously.

 

The factory anchor has up-swept ends making it U-shaped. The ends of the flat bars of my tool go against those up-swept ends. One side of the anchor will be north, the other south. You need to touch both N & S poles to the anchor at the same time to get the max magnetizing effect. Looking a buns picture above I don't like the looks of that replacement as it looks like just a flat piece of metal. No idea how well that will work and for how long.

 

Ok, thanks for the heads up. I ordered it and I'll take a look at it when it comes in. If I don't like the look of it I'll send it back. Actually I also just found and ordered a factory NOS AC Delco speedometer head unit with the first and second worm gear installed- as per factory specs. So, this might work out better!

 

The flat first worm gears were a GM replacement that came with no charge in them. They are easy to charge but I have the OEM borg electro magnetic charger that I use and you have to zap the flat first worm and magnets a bit longer then the original style. I'm not at the shop but we have a stop watch we have marked for the two different heads so we make sure we have enough charge in them.

The trick is the calibration... and the condition of the other parts. The first worm and magnet has a jewel bushing inside of it which the speed cup spindle rides inside... it also has one on what is called the jewel plate which is the plate that the spindle shaft goes through on the top of the speedometer.... if either of these are worn it could also cause a calibration issue. In the picture below you can see the bushing in the larger picture of the head assembly, and then if you look below it you'll see the jewel plate with the bushing installed in it.

1000 rpm's is 60 miles per hour +-/ 3mph at any given point so you can check this with a drill as long as you feel it's accurate. The issue is that the original GM calibration guide (I still have it) came with a not that anything within 3-5 mphs at a given point was considered calibrated... no kidding..

While the metal second worm gears are nice, I'd rather run the plastic replacements.... GM changed the second worm gear to the plastic replacements and down the road if the first worm magnet bushing fails and the first worm *****.... it takes out the plastic gear and not both.

Willcox