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Discussion Starter #1
I'm starting this thread as an off-shoot of thread #2902 "How to fix your slow-reading speedometer-tachometer 91-94 spiders". That thread did an excellent job covering the electronic speedos and tachs of those year models with the monopod instrument cluster, but left me wondering if there was an "easy" way to adjust my apparently mechanical speedo.

One of the replies in that thread mentioned that Willie R. had covered mechanical speedos in earlier, roundtail models so I went to his website. His pictures were too small to make out any detail, but they did promise some kind of adjusting screw should be hiding in the innards of my '85 speedo.

My speedo's particular problem was that it was reading 10mph high across the board, from 20 mph to 70 mph, as compared to my handheld GPS. Had it been a couple of mph off at one end and increased as the speed increased, the error would have been the "m" or slope term in the linear equation y=mx + b, which an adjusting pot or screw would seem appropriate for. My speedo's problem was a baseline shift, so like the "b" or y-intercept term, but I was still hopeful I could crack the thing open and find something to fix.

At this point in the process I have taken the speedo apart and documented what the various hidden pieces look like, but have yet to get it reassembled to know if I've done any good. The fix appears to be simply taking the indicator needle off its shaft and pushing it back on again to where it is slightly pushing against the stop pin, but in juggling the camera and positioning the pieces I managed to snap the indicator needle off and am having to wait until I can epoxy it back on before proceeding.

If nothing else, though, the pictures should be of use to someone else with mechanical speedo problems who will be able to at least see what pieces there are and how they fit together without (or perhaps before) ripping it out of the dashboard.

Pictures follow:
 

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Discussion Starter #2
Well...they'll follow as soon as I can figure out how to post them. I thought I could upload them directly from my laptop. One moment, please....
 

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Discussion Starter #3
OK, getting closer. Went to the "site usage" forum and now I see how to upload them from my laptop, but now have a bit of a size issue with the pics. As they say in Jamaica, "soon come...."
 

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We have a rule around here- no pics, no help. Quoting Eric, "they can even be of your Alfa".:D
 

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Discussion Starter #5 (Edited)
If all the picture-tweaking that I've done works, this will be an easily-viewable shot of a typical early-to-mid-'80's twin-binnacle instrument cluster. Tach on the left, speedo on the right.

-Post edit: I guess I could have gotten them a bit larger, but oh, well.... Anyway, you can probably see that I have the fairly common "sitting still and doing 10mph (or 9mph in my case)" blues. The needle stop is actually at about 4mph...so there's 5mph of my problem right there.
 

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Discussion Starter #6 (Edited)
From reading the monopod thread, the I first thing I did (unnecessarily as it turns out) was remove the steering column shroud upper and lower halves (four screws from the bottom), then the single bolt at the bottom of the speedo binnacle. If you use an open- or box-end wrench it's not necessary to remove the shroud pieces.

With the binnacle (black) cover removed you are presented with two screws holding the speedo in, one at 3 o'clock and one at 9. The one at 3 o'clock also captures a grounding wire. With those screws removed, you will have to free the tripmeter-reset knob as its cable is hard-connected to the back of the odometer housing. On mine there was a thin nut which kept the reset knob from backing through a hole in a bracket, and removing the nut allowed the knob to pass through the hole.

Pushing up on the reset button/cable and tugging on the face of the speedo will allow you to get the speedo and its entrails out far enough to where the speedo can be disconnected.

These two pictures are of the speedo and its entrails (four wires - one each to a back-lighting bulb and one to illuminate the fan indicator light, the speedo cable, and the tripmeter reset cable).
 

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Discussion Starter #7 (Edited)
Rear view. The yellow wire on the far left of the photo (most inboard wire) is to the fan indicator light. Cable in center is the speedometer cable (goes through the firewall) and the cable on the right is the tripmeter reset cable.
 

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Discussion Starter #8 (Edited)
This is with the speedo completely out and freed from all wires and all cables except for the tripmeter reset cable.

(Note: before removing the yellow wire that goes to the fan indicator light, you will probably want to tag it. I didn't, but will have to remember to turn the ignition on and the fan on to identify which wire is which when time comes to reassemble everything).
 

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Discussion Starter #9 (Edited)
These two photos are of the back of the speedo housing, showing the four bulbholders, the mount for the speedo cable, and the attached tripmeter reset cable (coming back towards the camera and blurred). Second photo is a close-up of a tag giving a scale of "1609 REVS = 1 Mile" which I assume is for the odometer and tripmeter.
 

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Discussion Starter #11
The hammer part has a certain appeal. In the oilfield (my background) that is always the solution first resorted to. Of course no one I know would confess to owning a "little" hammer and a 5-lb sledge would no doubt make the fix permanent, one way or the other. Buying a spare goes a bit against the grain. Following that logic I might as well buy a complete parts car!

Sorry the pictures are coming so slowly...I keep having to fit a little work in and it's becoming quite a nuisance. I would shut the office door, but then people might think I'm up to something! :D
 

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Discussion Starter #12 (Edited)
To go any further into the speedo you need to remove the housing (back) that is secured by two bolts in the back AND whose mouth is secured by the black rim piece (bezel?) that hold the glass face. Start with the rim piece before removing the two bolts.

The rim piece is bent over the flared mouth opening so it has to be carefully pried up all around. It is best to do this a little at a time with a large flat-bladed screw driver so that the rim isn't torn or doesn't look like you used your teeth to get it off. I made about three complete circuits before I could finally pull it apart. Make sure you are standing on a carpeted area or have some kind of cushion underneath because, if you're pulling hard enough, there is a chance the glass face may get away from you when everything turns loose.

If all goes well you will have four pieces in one hand consisting of the black rim, the glass face, a flat rubber gasket, and a stepped piece that might actually be more deserving of the name bezel than the rim piece would be. The other hand will be holding the main body of the speedo.
 

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Discussion Starter #13 (Edited)
Now the two bolts can be removed and the housing taken off. At this point you will have an assembly the front of which consists of the speedo face with the needle, and the back being the inner workings of the odometer/tripmeter and the speedo mechanism.

I've spun the back around to give you all four sides. The dark-colored stem sticking up out of the plastic frame is the key that the tripmeter reset cable turns. I had hoped by this time to have found an adjusting screw such as Willie R. had described on earlier models, but if it's there it's not readily apparent.
 

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Discussion Starter #15
As there was nothing obvious for me to adjust here, I took the bit between my teeth and kept going. There are two more bolts holding the metal piece (most prominent of which is the mount the speedo cable is threaded onto) to the plastic body that houses the gearing.
 

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Discussion Starter #16 (Edited)
Removing the bolts and separating the metal part from the plastic part reveals the gear-turned magnet attached to the metal part and the cup the magnet normally sits in that is attached to the plastic part (and ultimately, via a shaft, to a watch spring and the speedo needle.)

In Willie R.'s article on his website, the adjusting screw he shows serves to move the cup up (relative to the magnet) or down on its shaft. The closer to the magnet, the stronger the attraction of the magnet (field lines, eddy currents, and all that other stuff you learn in electrical engineering but usually forget the semester after) and the more the cup works to overcome the spring and so the needle turns more to indicate a faster speed. Oppositely, the further the cup is moved away from the magnet, the less effect the magnet has on the cup and the less the cup can overcome the force of the spring and so the needle registers a lower speed with regards to the turning of the speedo cable.

As I played with the pieces (taking more photos and eventually breaking the plastic needle in the process:eek:) I found that the cup does seem to have some play in its up and down travel, but I still (or at least, yet) have not found any mechanical adjustment.

To clarify the photo, first of all the face of the part on the left (showing the twin lobes of the magnet) flips over and mounts to the top of the part on the right (showing the open cup). On the far left of the part on the left you see the key for the odometer, and it fits into the gear on the far right of the piece on the right. The shaft of that gear turns the odometer gearing to make the odometer and tripmeter dials increment, but the gear's teeth engage a worm gear (mostly hidden in the piece on the left). The worm gear is itself engaged in and driven by the speedometer cable key. The speedometer cable key's shaft is also common to the shaft of the magnet. (Okay, maybe "clarify" was too strong a word, but I tried.)
 

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Discussion Starter #17
For those of you who might have spent most of the day checking every time I made a new post eager to see how to "fix" your mechanical speedometer, sorry to disappoint. At least for now. I'll have more time to spend prying and poking on mine this weekend and maybe I can find an elusive adjusting screw, now that I sorta know what it does and how this type of mechanical speedo works.

If so, I'll be sure and update this thread and tell all. Once I get my needle epoxied back together (did I mention that the super glue I tried didn't even begin to work?) I'll update on whether pulling the needle off its post and repositioning it from its 9mph position to one slightly pressing against the needle stop pin fixed my particular problem. By the way, I already have pulled the needle off its post and, although I was fearful I'd hear the noise a joy-buzzer makes (the handshaking prank that many of us ordered out of back of comic books when we were kids), absolutely nothing happened. The spring was totally relaxed in that position - which was, after all, the problem.

Anyway, hopefully, if nothing else anyone that was interested in archane Alfa workings was entertained for a bit!
 

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Before you started. did you run it in a drill at max speed to have a reference number?
that way you can tell what the changes are. a 2 speed drill is even better as you can get a low and fast speed reference.

as a rule all you have to do is move the spring. at lest on other meters. the spring spirals out and is fastened to a stop of some sort. most of the stops move. if not they might need to be bent some. and I have seen a few where it just pinches the spring and you just open the pinch and slide the spring until it is right and smash the crimp.

if you have a drill and took a reference and you know how much off it is just move the spring until reading changes n MPH. n being how much off it was when driving.

If possible try to do close 65MPH as that is the only number you need dead on with ;)
but the speed will depend on the drill. You need it to be repeatable so max speed. a 2 speed drill is best as you get 2 repeatable speeds.
 

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Discussion Starter #19
Honestly it never occured to me. It would have made it a lot easier to calibrate the speedo on the bench instead of using my and Obama's plan. We were going to remount the speedo back into the car but leave the glass face off, then make any adjustments necessary to get needle to agree with the GPS. At taxpayer's expense. The last part was Obama's contribution to the plan. But since the only two-stage drill I have is battery-powered I don't know that I'd altogether trust it for very many tries.

I don't think my speedo's symptoms suggest a "tired" spring (a changed k-constant) so much as they do a shift of the needle's position relative to its shaft. With the way the speedo appears to work, it makes me wonder if driving either too long or too fast in reverse might not force the needle hard enough against the needle stop to make it slip clockwise on its shaft.

In re-reading my posts I realize that I made the mistake of writing "odometer" when in most cases I should have put "tripmeter". I will go back and do some editing to make it right.
 

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It sounds like the spring slipped or the spring mount moved. as it is no longer hitting the stop. I do not think it moved on the shaft if it was so tight that it busted when you tried to move it. but ether way moving the spring mount will only change the offset across the board. it will not change the gain.
 
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