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Discussion Starter #1
I've got an odd one here that I can't seem to figure out. I'm driving a 1990 900S and I've noticed that my speedometer tends to stick at zero until I've gotten up to about 15 mph. When I get there, it pops off the stop and works normally and is at least accurate at 60 mph (I've timed it between mile markers). I've pulled the gauge out and found that the needle is free to move through the entire range and doesn't seem to stick at the bottom at all. It's been doing this for about a month now. Can't say it's a problem, but I'd really like to know why it might be doing that. Anyone else ever hear of something like this?
 

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Its probably the speedo cable itself getting 'sticky' due to wear inside the sheath and perhaps also rust inside the ends.

If you can, check the attachment of the cable to the drive gear on the transmission, and you could spray some lube (not sure what sort - anyone have suggestion?) into the speedo gauge end to try and make it rotate more freely inside the sheath.

You can get new speedo cables at least for LHD cars - I haven't found new ones for my RHD ones.

Craig.
 

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Does sound an odd one, but I can't see it being the cable. It does sound like a small amount of friction inside the speedo mechanism, whatever you say.
 

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There isn't much to go wrong inside the actual speedometer that can cause anything audible. Odometer, sure... but not speedo. The cable can absolutely cause noise that one would think is coming from the speedo.
 

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Discussion Starter #5
I'll pull the speedometer out again today and run it with a drill and an old piece of speedometer cable to see if I can find out who the culprit is. Maybe the needle is sticky at the bottom of the range and I just couldn't feel it by bumping it with my finger. If I don't get the sluggishness with the drill, I'll take a look at the cable in the car. Still, I can't imagine the cable binding until the car reaches 15 mph. Wouldn't that break the cable?
 

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It's probably the gears inside the speedometer gauge that are failing. There's some kind of worm gear on a shaft that comes loose and gives you the symptoms you're experiencing. On my 93 900S, it was temperature dependent for a while - on cold mornings, the speedo worked fine. After warm-up, no speed reading.

Based on internet lore, on older speedometers, you could disassemble the gauge and repair the gear. On these, it's much harder from what I've read. IIRC, someone was able to slip a little locktite or crazyglue in through the existing gaps behind the gauge but that's not a group-reported fix. Getting the metal needle off the shaft for complete disassembly is herculean at best.

At first, I thought it was the speedometer gear at the tranny end of the cable so I bought one. I have it new if you want to buy it from me at cost, but it would be a waste of money for you too.

Eventually, the whole thing will fail - you'll lose speed, mileage, and your shift light will stop working. During the period of intermittancy, you'll have to deal with a bouncing needle and flashing 'shift' indicator.

My GPS is now my speedometer and odometer.
 

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The speedometer itself doesn't use any gears. The gear issue you are speaking of causes the ODOMETER to not work.

The cable from the final drive enters the speedometer, then does two things. First, it is solidly connected to a permanent magnet, which is shaped like a small disc. When assembled, this permanent magnet sits just inside what's known as a speedcup--it's just big enough to envelop the magnet which is a little bit smaller than it in all dimensions. The speedcup is attached by a shaft to the speedo needle. When the permanent magnet (which is attached to the final drive by the cable) spins, it creates magnetic drag which pulls on the speedcup, which is attached to the needle. There is a spring also attached to the needle which resists the magnetic forces at work, and this fine balance is how your speedometer indicates the correct speed.

The OTHER, COMPLETELY UNRELATED thing that happens with the cable from the final drive is it drives a gear, which drives another gear, which drives another gear, and that gear is hooked up to the odometer shaft. The input gear on this shaft is plastic, generally white. It tends to break by cracking where the shaft goes through it, causing it to slip. Then there's a black gear which drives another gear which drives the trip meter shaft. (actually when looking at the back of the odo, I think the black trip drive gear is on the end, then the white odo drive gear, but as far as the mechanical power is concerned, the white odo drive gear is first in the "circuit", so to speak.

Staying on the odo shaft, the next gear is the "pot metal" gear, which other than the white drive gear cracking is the other common failure mode of these VDO odometers. The pot metal gear has notches on it which, after the right amount of distance has passed, come in contact with another set of gears on the odo advance shaft, which then contact fingers on the number gears themselves at the appropriate times.

Internet lore would have you believe that separating the odometer assembly from the speedometer assembly requires removal of the needle, therefore killing the calibration, and often breaking the needle. Not so. Three flat head screws hold the two assemblies together. By disengaging the trip reset button from its shaft (very easy once you see how it attaches when you have the odo/speedo assembly out of its black plastic bucket, which is done by removing four, not all five, flat head screws from the back of the bucket), and then undoing the two small black screws which hold the gauge face to the assembly, you can then rotate the gauge face around and access the three flat head screws through the trip reset hole in the gauge face. You need to be extremely careful with the small black screws as it's easy to gouge them and make them not look black anymore, which will bug you every time you look at your speedometer. The white plastic drive gear can be disengaged from the shaft very easily, and then repaired using krazy glue or whatever. If the pot metal gear is slipping on its shaft, which is how all the ones I have repaired have died, then the repair is a little more involved, You need to then disengage the trip meter drive gear as well as the odo drive gear, then put a piece of tape across all the number gears (but NOT the pot metal gear) so they don't get out of line. Then you can yank on the brass retainer on the other end of the odo shaft, which will withdraw the shaft from the assembly. You can then withdraw the pot metal gear, and use a pair of reasonably big pliers to carefully misshape the hole in the center of the gear, by using the pliers on the small raised circle around the hole. Trial and error to get the right amount of misshappenness is key here. Once you think you've got it, you can slide the pot metal gear back into place, then slide the odo shaft back into the assembly, then remove the tape from the number gears, then spin the shaft to test it out. If the pot metal gear now spins with the shaft and doesn't get stuck, you're done! If you can't force the shaft through the pot metal gear, you made it too tight. Pull it back out and work at it.

I would suggest ignoring any "internet lore" perpetuated by those who have not actually had things apart and successfully repaired things, thereby endowing themselves with actual knowledge, rather than just spewing heresy.

Now that you understand how the speedometer and odometer work, you will see that problems with the odometer do not affect speedometer operation.

As for the shift light, in CIS (all 8-valve) and LH2.2 cars (16-valve turbo '85-'88, 16-valve non-turbo '85 and '86), it has absolutely NOTHING to do with the final drive gear, speedo cable, speedometer itself, or odometer in any way whatsoever--the shift-up-light system in these cars is a COMPLETELY isolated system which takes input only from a vacuum sensor (black can with vacuum hose and electrical connection mounted to inside of driver's (LHD) fender well near where APC or EZK box is), and a completely separate engine temperature sensor mounted between the #1 and #2 (closest to firewall) intake runners, and then there's also a "5th gear" switch (mounted on the gearbox itself, look down from the distributor...) which breaks the 12v signal path to the light when you're in 5th gear.

In LH2.4/up cars, I suppose I can see how the ECU might depend on the speed signal sent from the sensor in the back of the speedo as part of the shift light calculation, but I'm not sure on that one.
 

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Now that you understand how the speedometer and odometer work, you will see that problems with the odometer do not affect speedometer operation.
Then that would make your entire post 'lore' and, by your standards worthless - the loose gears in my gauge took out both.

The speedo cable is doing it's best rotating not-so-quietly behind the gauge so the problem is inside the gauge.
 

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I can't imagine how that's possible and would love to have the failure explained. Perhaps I have forgotten about a gear that's between the input from the cable and the permanent magnet?
 

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Discussion Starter #10
Thus far it appears that I have fixed the problem. After pulling the cluster out of the dash and, subsequently, the speedometer from the cluster, I was able to recreate the sluggishness with a drill and a bit of old speedometer cable. I was unable to tell just by moving the needle with my finger if there was a tight region at the bottom of the scale, but I was able to drip a very small amount of LPS lubricant down into the front needle bushing.

After working the needle back and forth with my finger a number of times, I ran it again with the drill and saw none of the hesitation which was present before. I had to be very careful with applying the lubricant as I did not want to allow the coil spring to slip on the needle shaft, and I'll be watching the calibration very carefully. Thus far, I've driven the car two or three times and have had no trouble with the speedometer.

I rebuilt the whole gear system for the odometer a few years back. That system only drives the odometer and not the speedometer which is driven by the magnet-in-shroud mechanism described above. I'll let you know if the sluggishness comes back, but for now at least, it works great.
 

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Great work!

I think Rob's incident was a fluke of repairing the odo and the speedo magically coming back to life--they really don't interact...
 

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What is LPS lubricant? Is that a type of lithium grease? I'm going to try spraying some of that down inside the sheath on the speedo head end of the speedo cable in my 81 turbo sedan to see how that goes before I pull the dash apart to get the instruments out. I might also apply some carefully to the back of the 'socket' that the cable goes into on the speedo head to give that some more freedom of movement.

The speedo head currently in my car is an extremely rare (I've only ever found one!) W 0,6175 ratio head. I got that when I first fitted indiglo gauge faces in my 83 900S because those kits are made to fit the US W 1,008 speedo heads which have a stop pin location for the speedo needle in a different place to the W 0,64 heads used in Australia classic 900's. The W 0,6175 head has the stop pin in the same place as a W 1,008 head but has a gear ratio close enough to the W 0,64's to not really be an issue reading-wise.

I haven't been able to locate a supplier of RHD speedo cables as yet either - Might just have to find a late-year C900 being scrapped and get the speedo cable from it.

Oddly enough new W 1,008 heads do show up now and then on Ebay.

Craig.
 

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What is LPS lubricant? Is that a type of lithium grease? I'm going to try spraying some of that down inside the sheath on the speedo head end of the speedo cable in my 81 turbo sedan to see how that goes before I pull the dash apart to get the instruments out. I might also apply some carefully to the back of the 'socket' that the cable goes into on the speedo head to give that some more freedom of movement.

The speedo head currently in my car is an extremely rare (I've only ever found one!) W 0,6175 ratio head. I got that when I first fitted indiglo gauge faces in my 83 900S because those kits are made to fit the US W 1,008 speedo heads which have a stop pin location for the speedo needle in a different place to the W 0,64 heads used in Australia classic 900's. The W 0,6175 head has the stop pin in the same place as a W 1,008 head but has a gear ratio close enough to the W 0,64's to not really be an issue reading-wise.

I haven't been able to locate a supplier of RHD speedo cables as yet either - Might just have to find a late-year C900 being scrapped and get the speedo cable from it.

Oddly enough new W 1,008 heads do show up now and then on Ebay.

Craig.
 

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Don't you have Google on your steam powered PCs down under Craig. http://www.lpslabs.com/product_pg/lubricants_pg/LPS_Lubricant.html
:cheesy::cheesy: Paul
That would be wind powered ...

WE leave the steam to some other parts that shall rename Nameless ;ol;
Ever tried using google on a 286 ? Easier to ask ;ol;

CraIg ... I am amazed you cannot find a RHD speedo cable , have you looked on the shelf at The local hardware , I could bet it will on the same shelf as the Left handed screwdrivers and the striped paint .
 

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Don't you have Google on your steam powered PCs down under Craig. http://www.lpslabs.com/product_pg/lubricants_pg/LPS_Lubricant.html
:cheesy::cheesy: Paul
I guess I musn't - using 'classic google' here where it's done by post. :roll: Poor panasonic toughbook is overworked and underpaid. lol (yeah I'm at work doing this - sitting on loaded coal train waiting to empty it sometime later today).

What I was more getting at was whether LPS was some sort of brand or the name of an actual product. Going to the link you gave lists a lot of products, two of which are actually called LPS, so the question still isn't really answered. ;-)

I have graphite powder around somewhere though it might not be too good as it's electrically conductive. I suppose if the cable is properly secured to the speedo head nothing should really 'leak' out onto any of the flexible circuit around the speedo head.

And to my other question - that of spraying lithium grease into the cable. Is that likely to be a good thing or a bad thing?

Craig.
 

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Discussion Starter #18
The lubricant I used is officially called "LPS 1 Premium Lubricant". It is dry, greaseless, non-conductive, and penetrates quite well. I am a pilot and I use it all the time on the control linkages and mechanisms of the airplane. Because it is geaseless, it won't attract dirt and dust to the bearing it is lubricating, but also tends not to last for more than a year before you have to re-apply it. Anyway, it has worked well for me and I still haven't had any more hesitation from the speedometer.
 

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The lubricant I used is officially called "LPS 1 Premium Lubricant". It is dry, greaseless, non-conductive, and penetrates quite well. I am a pilot and I use it all the time on the control linkages and mechanisms of the airplane. Because it is geaseless, it won't attract dirt and dust to the bearing it is lubricating, but also tends not to last for more than a year before you have to re-apply it. Anyway, it has worked well for me and I still haven't had any more hesitation from the speedometer.
Ah that sounds like a really good product! Being non-conductive and greaseless are two really useful properties. I wonder if I can find anything like it for sale in auto-parts shops - might be something only aircraft supply outlets carry.

Craig.
 

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Discussion Starter #20
It can be elusive to find, but sometimes hardware stores will carry it. Try a small, local shop and sometimes they will have it or will be willing to order it for you. Also, Grainger carries it so you can order it online or go to a store if you happen to have one nearby.
 
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