odometer weirdness
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From: Portland, Oregon
odometer weirdness
Something is up with the odometer in my 83S Euro. It seems to only be measuring about 1/3 of the distance the car travels. It doesn't seem jerky when it moves, like it might with some broken teeth, but it is just moving very slowly. For example, my drive to the office is about 8 miles and this morning I reset it and it showed about 3 miles when I got to my destination.
I have had the drive gear break before, but then it did not work at all. Now it sort of works. Speedometer is not affected, but mileage is.
The reset button on the euro is different than on the US Model. I think it is electronic. It will not work if the engine is not running, even if the key is on. The reset button is a small button under the pod, like the high intensity washer button on US models. I don't know if there is anything in that mechanism that could be causing the problem.
Any ideas as to what might be going on?
Thanks in advance
I have had the drive gear break before, but then it did not work at all. Now it sort of works. Speedometer is not affected, but mileage is.
The reset button on the euro is different than on the US Model. I think it is electronic. It will not work if the engine is not running, even if the key is on. The reset button is a small button under the pod, like the high intensity washer button on US models. I don't know if there is anything in that mechanism that could be causing the problem.
Any ideas as to what might be going on?
Thanks in advance
... contrast, on my 911 you pull the speedo out by hand, unplug it, pop it open and there it is.
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From: St. John's, NF, Canada
The speedo and odo are electronic (or, well electrical) in the 928. There are two seperate systems for speed and distance...each receiving impulses from a sensor in the transmission/final drive unit.
You mentioned that the distance is off, but what about the speedo? Does it register roughly correct speed? If so, then I would suspect a problem in the instrument cluster unit. If not, then the problem is likely in the impulse system.
You can have the speedo tested and serviced at any speedo shop or authorized VDO repair depot (VDO used to publish a list on it's US website, but the link is now dead..maybe a call to them would get you a name nearby). But that requires you to pull the pod and cluster, plus do some further dissassembly. And the problem may not be in the instrument at all.
Most people report jerky or non-working speedos/odos...seems you have already experienced the dreaded "disintegrating odo gear" situation, so your speedo "works". Often erratic operation is due to bad connections at the junction point just ahead of the battery box in the spare tire well. There are several connectors located there...cannot recall the exact one for the speedo, but I do remember it has 3 or 4 terminals. The wire diagrams will indicate the correct connector/wire color combo anyway. Check to make sure the connector is clean and tight...often a slight squeeze with a small pair of pliers will do the trick.
You might find other "bad" connections in the wiring for the speedo/odo sensor system. I traced mine down trying to find the cause of a "sticky" speedo...but did not find anything. I have had my speedo/odo check by VDO and it works fine...just jerky for the first few minutes of the first drive of the day early in the summer season. The problem goes away completely after about 1000km following winter layup. Problem is no doubt with the impusle transmitter in the transmisson....and I am OK with it as long as it does not get any worse (and it hasn't).
Hope this helps you troubleshoot your problem. Let us know what you find.
Regards,
SteveCo in St. John's
You mentioned that the distance is off, but what about the speedo? Does it register roughly correct speed? If so, then I would suspect a problem in the instrument cluster unit. If not, then the problem is likely in the impulse system.
You can have the speedo tested and serviced at any speedo shop or authorized VDO repair depot (VDO used to publish a list on it's US website, but the link is now dead..maybe a call to them would get you a name nearby). But that requires you to pull the pod and cluster, plus do some further dissassembly. And the problem may not be in the instrument at all.
Most people report jerky or non-working speedos/odos...seems you have already experienced the dreaded "disintegrating odo gear" situation, so your speedo "works". Often erratic operation is due to bad connections at the junction point just ahead of the battery box in the spare tire well. There are several connectors located there...cannot recall the exact one for the speedo, but I do remember it has 3 or 4 terminals. The wire diagrams will indicate the correct connector/wire color combo anyway. Check to make sure the connector is clean and tight...often a slight squeeze with a small pair of pliers will do the trick.
You might find other "bad" connections in the wiring for the speedo/odo sensor system. I traced mine down trying to find the cause of a "sticky" speedo...but did not find anything. I have had my speedo/odo check by VDO and it works fine...just jerky for the first few minutes of the first drive of the day early in the summer season. The problem goes away completely after about 1000km following winter layup. Problem is no doubt with the impusle transmitter in the transmisson....and I am OK with it as long as it does not get any worse (and it hasn't).
Hope this helps you troubleshoot your problem. Let us know what you find.
Regards,
SteveCo in St. John's
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From: St. John's, NF, Canada
Oh, and the odo reset is electrical...the button actuates a soleniod on the gauge that mechanically resets the odo to zero. I have had mine apart and cannot imagine how it could cause the problem you noted. But stranger things have happened.
Since you mentioned that you had the odo gear replaced, I will note that my VDO repair shop told me that there at least 7 different odo gears used in this model gauge. They had seen 3 or 4 common ones, with the others (mine was one) rarely.
While difficult to imagine, is it possible that your have the wrong gear installed? That would definitely effect the accuracy of the odo, but it is hard to imagine it actually fitting and being that much off. Just a thought.
Regards,
SteveCo in St. John's
Since you mentioned that you had the odo gear replaced, I will note that my VDO repair shop told me that there at least 7 different odo gears used in this model gauge. They had seen 3 or 4 common ones, with the others (mine was one) rarely.
While difficult to imagine, is it possible that your have the wrong gear installed? That would definitely effect the accuracy of the odo, but it is hard to imagine it actually fitting and being that much off. Just a thought.
Regards,
SteveCo in St. John's
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From: Portland, Oregon
Originally Posted by SteveCo
Oh, and the odo reset is electrical...the button actuates a soleniod on the gauge that mechanically resets the odo to zero. I have had mine apart and cannot imagine how it could cause the problem you noted. But stranger things have happened.
Since you mentioned that you had the odo gear replaced, I will note that my VDO repair shop told me that there at least 7 different odo gears used in this model gauge. They had seen 3 or 4 common ones, with the others (mine was one) rarely.
While difficult to imagine, is it possible that your have the wrong gear installed? That would definitely effect the accuracy of the odo, but it is hard to imagine it actually fitting and being that much off. Just a thought.
Regards,
SteveCo in St. John's
Since you mentioned that you had the odo gear replaced, I will note that my VDO repair shop told me that there at least 7 different odo gears used in this model gauge. They had seen 3 or 4 common ones, with the others (mine was one) rarely.
While difficult to imagine, is it possible that your have the wrong gear installed? That would definitely effect the accuracy of the odo, but it is hard to imagine it actually fitting and being that much off. Just a thought.
Regards,
SteveCo in St. John's
The speedometer in my euro is working fine. The speed is correct (or close enough that I would have to measure to detect the difference) the needle moves smoothly and there appear to be no problems with it. The distance on the odometer in the speedo is advancing at the same rate as the trip meter. S L O W L Y... So, do you think I have broken the drive gear or is it some other problem. My experience with broken gears is that when the break, they no longer work at all. This one is still working ..... very slowly, but no pauses just slow and steady advance at about a third of the proper speed. Could there be an electronic or sensor reason for this?:
Thanks for the feedback guys. I hate to pull the pod and take everytning apart just to find the problem is elsewhere.
cheers
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From: Dubai, UAE
I've just replaced my odo gear with one of theose plastic jobs from Rennbay.com. The original gear was broken when got the car.
My spedo is in Km's and Rennbay sent me two gears because they were not sure which one I had. So I've fitted the one that looks correct.
Every time I fill up with petrol I reset the trip meter, and for a full tank of gas it tells me I am getting 250kms of driving. This can't be possible, I think it's under reading but can't figure out why, the speedo works fine. Perhaps it is the wrong gear.
Oh and also, I've discovered why the original gear was made of rubber. Noise. The new gear goes tick, tick, tick, tick, tick as you drive along.
Not a brilliant fix
My spedo is in Km's and Rennbay sent me two gears because they were not sure which one I had. So I've fitted the one that looks correct.
Every time I fill up with petrol I reset the trip meter, and for a full tank of gas it tells me I am getting 250kms of driving. This can't be possible, I think it's under reading but can't figure out why, the speedo works fine. Perhaps it is the wrong gear.
Oh and also, I've discovered why the original gear was made of rubber. Noise. The new gear goes tick, tick, tick, tick, tick as you drive along.
Not a brilliant fix
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From: St. John's, NF, Canada
Joe;
The odometer is a seperate system with the gauge unit...basically a small electric motor that turns a series of gears that rack up the trip and total odometers.
All my experience is with the 84-86 series Euro cars, but I believe all 928s are the same wrt the speedo/odo units. The trip reset button may be in different locations between Euro and USA cars, but their function is the same: an electrical contact switch that operates a solenoid to mechanically reset the trip odometer. Although it may have seemed like it, you cannot press the rest button soft or hard. Your experience is very similar to many others where a trip odo reset resulted in failure of the complete odometer function.
The odo gear in question becomes very brittle over time and eventually breaks, usually on a trip reset when the car is moving. I have attached a comparison shot of my odo gear vs. an after market replacement. In this case, the replacement gear was not quite the right one...the inner gear ring is slightly smaller on the new one that the old. Even this small difference would not operate in the odometer, so it is unlikely you have the wrong gear. It will either mesh in the system or not, in my experience (limited though this may be). I have also attached shot of my dissassembled speedo with the original gear in place. The electric motor mounts on the outer half of the gauge and has a worm gear that turns against the "brown" gear to drive the mechanism.
I think your problem may be elsewhere in the odo mechanism. Possibly the sending unit is missing 2 out of every 3 beats for some reason, or electric motor that turns the odo is simply tuirning too slow. I would probably bet it is the latter, but it is conceivable that the odd tooth is missing from your "brown" odo gear and it is only rotating periodically. Not likely this is the case, but stranger things have happened.
You mentioned your car is a Euro. There are certain combinations of speedos and odo gearing for the various readouts in these cars (ie: MPH vs. KPH) and models of car that the speedo units were fitted to (944, 928, 968, etc). That's why, I'm told, there are so many odo gear combinations available. Maybe your speedo was replaced when the car was federalized and it simply has the "wrong" combination of gearing. Just wondering if that car has always been like this...or did it just start happening recently?
CT928:
While I cannot comment on the quality of the aftermarket gear you have, as long as the gear fits and meshes correctly, it should work fine and without any noise. The clicking noise you have might be from a small size difference in the gear or just some part of the mechanism binding. Might be worth pulling the speedo and testing it on the bench to see where the problem is.
Many people have speculated that the "failed" odo gear was made of a softer compound plastic to act as a sort of "fuse" in the gear system. Over time and with heat, the material deteriorates to the point of becoming a rubber-like consistence. I can attest that a brand new VDO OEM gear is much the same color and feel as the aftermarket gears - not rubbery in any way. Will mine fail again in 15+ years time? I can only hope I will have the car long enough to find out!
I have been lucky enough to find an original Euro 300km/h speedo to retro-fit mine back to the way it was at the factory. It still has the original odo gear in it and it is in decent shape...but I will be replacing it before installing the gauge in the car to be sure. Most likely with an aftermarket gear, too.
Regards,
SteveCo in St. John's
The odometer is a seperate system with the gauge unit...basically a small electric motor that turns a series of gears that rack up the trip and total odometers.
All my experience is with the 84-86 series Euro cars, but I believe all 928s are the same wrt the speedo/odo units. The trip reset button may be in different locations between Euro and USA cars, but their function is the same: an electrical contact switch that operates a solenoid to mechanically reset the trip odometer. Although it may have seemed like it, you cannot press the rest button soft or hard. Your experience is very similar to many others where a trip odo reset resulted in failure of the complete odometer function.
The odo gear in question becomes very brittle over time and eventually breaks, usually on a trip reset when the car is moving. I have attached a comparison shot of my odo gear vs. an after market replacement. In this case, the replacement gear was not quite the right one...the inner gear ring is slightly smaller on the new one that the old. Even this small difference would not operate in the odometer, so it is unlikely you have the wrong gear. It will either mesh in the system or not, in my experience (limited though this may be). I have also attached shot of my dissassembled speedo with the original gear in place. The electric motor mounts on the outer half of the gauge and has a worm gear that turns against the "brown" gear to drive the mechanism.
I think your problem may be elsewhere in the odo mechanism. Possibly the sending unit is missing 2 out of every 3 beats for some reason, or electric motor that turns the odo is simply tuirning too slow. I would probably bet it is the latter, but it is conceivable that the odd tooth is missing from your "brown" odo gear and it is only rotating periodically. Not likely this is the case, but stranger things have happened.
You mentioned your car is a Euro. There are certain combinations of speedos and odo gearing for the various readouts in these cars (ie: MPH vs. KPH) and models of car that the speedo units were fitted to (944, 928, 968, etc). That's why, I'm told, there are so many odo gear combinations available. Maybe your speedo was replaced when the car was federalized and it simply has the "wrong" combination of gearing. Just wondering if that car has always been like this...or did it just start happening recently?
CT928:
While I cannot comment on the quality of the aftermarket gear you have, as long as the gear fits and meshes correctly, it should work fine and without any noise. The clicking noise you have might be from a small size difference in the gear or just some part of the mechanism binding. Might be worth pulling the speedo and testing it on the bench to see where the problem is.
Many people have speculated that the "failed" odo gear was made of a softer compound plastic to act as a sort of "fuse" in the gear system. Over time and with heat, the material deteriorates to the point of becoming a rubber-like consistence. I can attest that a brand new VDO OEM gear is much the same color and feel as the aftermarket gears - not rubbery in any way. Will mine fail again in 15+ years time? I can only hope I will have the car long enough to find out!
I have been lucky enough to find an original Euro 300km/h speedo to retro-fit mine back to the way it was at the factory. It still has the original odo gear in it and it is in decent shape...but I will be replacing it before installing the gauge in the car to be sure. Most likely with an aftermarket gear, too.
Regards,
SteveCo in St. John's
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SteveCo said" I think your problem may be elsewhere in the odo mechanism. Possibly the sending unit is missing 2 out of every 3 beats for some reason, or electric motor that turns the odo is simply tuirning too slow. I would probably bet it is the latter, but it is conceivable that the odd tooth is missing from your "brown" odo gear and it is only rotating periodically. Not likely this is the case, but stranger things have happened."
Based on what you said, is there any way to tell which of the above things is the most likely culprit prior to taking things apart?
SteveCo said "You mentioned your car is a Euro. There are certain combinations of speedos and odo gearing for the various readouts in these cars (ie: MPH vs. KPH) and models of car that the speedo units were fitted to (944, 928, 968, etc). That's why, I'm told, there are so many odo gear combinations available. Maybe your speedo was replaced when the car was federalized and it simply has the "wrong" combination of gearing. Just wondering if that car has always been like this...or did it just start happening recently?"
Steve, I am certain the speedo was replaced when the car was federalized. But it's unlikely the gear combination was wrong since this problem just started in the last week or so. Prior to that time, everything seemed to operate normally and the car has been in this country for many years.
Thank you for taking time to explain everything. I appreciate it.
Based on what you said, is there any way to tell which of the above things is the most likely culprit prior to taking things apart?
SteveCo said "You mentioned your car is a Euro. There are certain combinations of speedos and odo gearing for the various readouts in these cars (ie: MPH vs. KPH) and models of car that the speedo units were fitted to (944, 928, 968, etc). That's why, I'm told, there are so many odo gear combinations available. Maybe your speedo was replaced when the car was federalized and it simply has the "wrong" combination of gearing. Just wondering if that car has always been like this...or did it just start happening recently?"
Steve, I am certain the speedo was replaced when the car was federalized. But it's unlikely the gear combination was wrong since this problem just started in the last week or so. Prior to that time, everything seemed to operate normally and the car has been in this country for many years.
Thank you for taking time to explain everything. I appreciate it.
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From: Helsinki, Finland
Reason why euros do not have same reset button as US cars is rear fog light switch. It takes one spot on instrument pot and odo reset being least used button was easiest to move elsewhere.
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From: St. John's, NF, Canada
Joe;
The speedo unit can be tested, as mentioned before, but requires it to be removed from the car. Not much I can do to help here, I'm afraid.
You can put a multi-meter (set for simply continuity) on the wires from the impluse sensor in the trans/diff and watch the opening and closing of the circuit as the car moves (or rear wheels are turned while the car is raised in the air). Problem is that I don't know how the impulses are sequenced to the gauge. I would assume one circuit "closing" per revolution? But revolution of what? The rear wheels? The input to the differential? Something else? I don't know the answer...maybe someone else on the board does.
You could trace this circuit and measure the pulses at the central electrical panel or at the instrument cluster as well, FWIIW. You will need the electrical wiring diagrams for this, of course. I can help you figure out what's what if you have not got them.
Given that pulling the pod and instrument cluster is pretty simple, I'd suggest this might be just as well to start there. Then either replace the speedo with a known working unit. Or have your unit calibrated at a speedo shop. Either way, you will rule out the head unit...even if you do not fix the problem! It might be worth pulling the pod simply to clean up the electrical contacts on it...this has been known to solve many weird problems in the past...although I have not heard of your specific one being solved this way!
When I get a moment I'll pull out the wiring diagrams and have a look at the '83 versions to see what's what.
Regards,
SteveCo in St. John's
The speedo unit can be tested, as mentioned before, but requires it to be removed from the car. Not much I can do to help here, I'm afraid.
You can put a multi-meter (set for simply continuity) on the wires from the impluse sensor in the trans/diff and watch the opening and closing of the circuit as the car moves (or rear wheels are turned while the car is raised in the air). Problem is that I don't know how the impulses are sequenced to the gauge. I would assume one circuit "closing" per revolution? But revolution of what? The rear wheels? The input to the differential? Something else? I don't know the answer...maybe someone else on the board does.
You could trace this circuit and measure the pulses at the central electrical panel or at the instrument cluster as well, FWIIW. You will need the electrical wiring diagrams for this, of course. I can help you figure out what's what if you have not got them.
Given that pulling the pod and instrument cluster is pretty simple, I'd suggest this might be just as well to start there. Then either replace the speedo with a known working unit. Or have your unit calibrated at a speedo shop. Either way, you will rule out the head unit...even if you do not fix the problem! It might be worth pulling the pod simply to clean up the electrical contacts on it...this has been known to solve many weird problems in the past...although I have not heard of your specific one being solved this way!
When I get a moment I'll pull out the wiring diagrams and have a look at the '83 versions to see what's what.
Regards,
SteveCo in St. John's
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SteveCo said "When I get a moment I'll pull out the wiring diagrams and have a look at the '83 versions to see what's what."
Are you looking in the workshop manuals? Where? What page? I will look too?
Thanks again.
Are you looking in the workshop manuals? Where? What page? I will look too?
Thanks again.
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From: St. John's, NF, Canada
Volume 6 - Wiring diagrams, section 97. I think most of the info you need is on page 97-175.
I am not as familiar with the current flow diagrams as I am with the later wiring diagrams. Sorry, but I will not be much help to you figuring these out in the short term. Study the sample CFD at the beginning of the section. It should help you figure out how to read things. Took me a while to figure out the later diagrams too!
Regards,
SteveCo in St. John's
I am not as familiar with the current flow diagrams as I am with the later wiring diagrams. Sorry, but I will not be much help to you figuring these out in the short term. Study the sample CFD at the beginning of the section. It should help you figure out how to read things. Took me a while to figure out the later diagrams too!
Regards,
SteveCo in St. John's