dp320 Posted April 21, 2014 Report Share Posted April 21, 2014 The title is a bit misleading. I found that may speedometer worked but that my odometer didn't. So finally yesterday I took it out and today opened it up. Turns out one of the worms was worn and not engaging the worm gear. At the bottom of the photo you can see the worn worm, I don't have a good camera for this kind of close up small image. I managed to get the needle and face off the speedometer that had been in my truck. I thought I would just switch out the bad gear, since my face was nicer than my backup gauge. I then started dismantling my backup. This is where things didn't go well. The first gauge I was able to twist the needle off, it's just an interference fit on a tiny shaft. The backup gauge I managed to become impatient and careless and bent my needle and bent the little watch spring that returns the needle to 0. I took no photos of the disassembly, so I'll try to reconstruct the steps in the assembly photos. 1 Quote Link to comment
dp320 Posted April 21, 2014 Author Report Share Posted April 21, 2014 Remove the three tiny screws that hold on the trim ring. Remove the gauge from the housing by unscrewing two screws in back. (not shown) There are three tabs on the needle center cover. Carefully fold one of them straight. They are aluminum and I just did it with a small screwdriver but you might make a puller tool like a crochet hook. You should be able to finesse the cover off. Remove the two screws holding center cover base. Remove the two screws holding the dial. Quote Link to comment
dp320 Posted April 21, 2014 Author Report Share Posted April 21, 2014 Remove the bar that holds the dial, has a bushing for the needle shaft and which has a hole for the "vertical" gear. There are two screws, already removed in this photo. (Note for later that the brass outer cup has a tab with "extra stuff" on the high number side of the assembly.) Now here's where I made a mess of things during the disassembly. Hopefully this will be clear enough to follow. This photo shows the rotating magnet that drives a cup that the needle shaft sits in. I ruined my spring. But with some patience managed to get it OKI. Quote Link to comment
dp320 Posted April 21, 2014 Author Report Share Posted April 21, 2014 The needle spring needs to go back onto the shaft. The cup on the right fits under and inside the brass holder. Shaft is friction fit into center of cup. Cup with shaft ready to be reattached to assembly. There is a split brass ring that you can gently pry or just push the spring firmly down the shaft until it is the same elevation as the tab that holds the other end of the spring. The "simpler" looking tab on the outer brass cup is actually the zero adjustment for the speedometer. Insert the spring end into the tab. There is a stop tab on the cup that needs to be to the right of the stop tab on the brass housing. Hard to see in this photo. You likely will have to adjust the depth of insertion of the shaft into the cup and then readjust the spring elevation. Quote Link to comment
dp320 Posted April 21, 2014 Author Report Share Posted April 21, 2014 A tapered pin holds the spring to the tab. Inserted. Of course all these steps you would be doing carefully in reverse for disassembly. Put the needle shaft in the center of the top bar. Get the gear shaft in the hole and fasten the bar shown in the earlier photo. Do some testing now. Replace the dial. Replace the needle cover base and the needle cover. Bend the tab back under. Test again to make sure the needle clears. More to follow about zeroing the odometer and putting the glass and trim back on. Quote Link to comment
SS320 Posted April 21, 2014 Report Share Posted April 21, 2014 ^^^Thanks for posting. Great writeup & pics so far. Very handy info. Quote Link to comment
wayno Posted April 21, 2014 Report Share Posted April 21, 2014 This is interesting, if I had the time I might pull one of mine apart, if you cannot get the spring to work properly, contact me, as I have several complete speedo assemblies around here that likely have a good spring, I am sure I can make do with one less. Quote Link to comment
dp320 Posted April 21, 2014 Author Report Share Posted April 21, 2014 It only makes sense to zero your odometer after a complete rebuild. The state is just going to say "beyond mechanical limit" on the registration anyway so restart the clock when it makes sense and is actually a fair and honest thing to do. Besides, mine obviously was wrong. So the first thing to do is to remove this slotted arm that holds an alightment ring for each number dial. This arm is held on by one screw. You can pivot the arm in a small radiused slot. This adjustment lets you align the numbers to fit in the box of the dial. There is a C clip on the odometer axle. (Sidenote: the gauge I'm replacing had yellow tenth mile numbers and the C clip shown here is much more difficult to push off than the one on the gauge I put back.) Once the C clip is off what you do is take the blade of a screwdriver and push each tab ring starting from the tenths. With the tab ring pushed (towards where the C clip was) you can wheel the numbers into position. You'll need to check the first one against the opening in the dial. Then repeat this process to the highest number. Replace the slotted arm. Hopefully you did this so that you have adjustment in both directions (screw in center of radius slot). Quote Link to comment
dp320 Posted April 21, 2014 Author Report Share Posted April 21, 2014 Clean up the glass. Here is the inner glassholding insert. Push carefully but firmly all around on the glass until the gasket begins to pop off and the insert pushes out. Clean the glass and all the pieces. Or send your ring to a plater. Replace the gasket if necessary. Strips of electrical tape if nothing else. My parts donor gauge. Quote Link to comment
dp320 Posted April 21, 2014 Author Report Share Posted April 21, 2014 Wayno, Thanks. I was hoping someone might have some donor gauges. My worm is shot so that would be the key piece. I'd be happy to work with you to turn some questionable gauges into some number (probably fewer) of working gauges. Quote Link to comment
wayno Posted April 21, 2014 Report Share Posted April 21, 2014 I don't actually know how many extra speedo gauges I have, it looks like I have around 4 extra gauges, one the speedo needle shaft looks to be broken, while one with a good shaft, the face is bad(mph numbers), so if they were combined, one would end up with extra parts, and one good looking gauge. I have already gutted one of the other assemblies out for the fuel gauge for another member, so it's not like I am trying to keep everything/all the sets working, they are just here for parts. How soon you need these parts? Quote Link to comment
Gemmer Posted April 22, 2014 Report Share Posted April 22, 2014 The worm gear that drives the odometer on my 64 PU 320 is worn out just as yours was. Do you have an extra? If so, can we work something out? Gemmer Quote Link to comment
Gemmer Posted April 22, 2014 Report Share Posted April 22, 2014 I tried to post yesterday, don't know what happened. My 64 PU 320 needs a worm gear for the odometer also. If you have one available could you contact me? Thank you Gemmer Quote Link to comment
dp320 Posted April 24, 2014 Author Report Share Posted April 24, 2014 Gemmer, No extra (good) worm gear here anymore. I imagine if nothing else could be found that the gear could be plated to rebuild the worm section and then machined, even hand-filed. From this thread on Ratsun it looks like there's a possibility the 520 worm gear is the same as the 320, with just a different face???? http://community.ratsun.net/topic/42668-need-good-521-guage-cluster/ Quote Link to comment
Gemmer Posted April 25, 2014 Report Share Posted April 25, 2014 Sounds like this is a common issue with the older Datsuns. For me right now it's just a PIA. Guess I'll just put up with it. Thanks Quote Link to comment
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