Speedometer not accurate

[Bullitt]

Hi!

When I am driving around 80 km/h my speedometer shows 60 km/h...
Ive been told my car won't pass inspection when I am taking it to the DMW in Norway to get license plates because of this.
I have a 85mph speedometer, and bought new dust shield, angle drive, lower and upper speedo cable from DMC California back in 2015.

Is the new parts perhaps calibrated to the 140 mph speedometer?

[DMC5180]

The angle drive is a fixed ratio. The speedometer gets calibrated to the input RPM of the cable. The rule of thumb setting is 1000 RPM wheel rotation equals 60 MPH Or 95.56kph

My understanding is that one of the vendors is selling an angle drive that is not the correct drive ratio, its close, but not too the original spec. I’m not sure who it is though. I have not needed a new AD for several years.


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[Jonathan]

Any chance something is slipping? That could be another possibility to explain why it is reading a speed lower than what you're actually driving. I assume the odometer is counting the total miles at this same lower rate?

[Bullitt]

Any chance something is slipping? That could be another possibility to explain why it is reading a speed lower than what you're actually driving. I assume the odometer is counting the total miles at this same lower rate?Dont know, could be. I have to check the connections. Not sure about odometer either.

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[Jonathan]

The speedo and odo should be in sync because they run off the same input. If you find the odo reading higher than the speedo (and thus what it should be reading) another possibility might be that the speedo needle wasn't reinstalled correctly. I say reinstalled because if you say had it disassembled to replace the trip reset shaft for example, one of the steps to do that job is to remove the needle from the speedo. If it got put back on too low, it might be reading 20 km/hr low at all times. Do you have any other reference speeds? Like when you're driving 50 km/hr or 100 km/hr? That might help figuring it out.

[Bullitt]

The speedo and odo should be in sync because they run off the same input. If you find the odo reading higher than the speedo (and thus what it should be reading) another possibility might be that the speedo needle wasn't reinstalled correctly. I say reinstalled because if you say had it disassembled to replace the trip reset shaft for example, one of the steps to do that job is to remove the needle from the speedo. If it got put back on too low, it might be reading 20 km/hr low at all times. Do you have any other reference speeds? Like when you're driving 50 km/hr or 100 km/hr? That might help figuring it out.Hmm maybe you are into something there. Sombody previosly installed a new sticker over the speedometer showing other figures... Dont know why they did, maybe because of this or because 85mph was to low in their eyes. I guess I had to pull the needle out to get the sticker off... As far as I remember the needle could only fit one way. But this was over 5 years ago....

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[PJ Grady Inc.]

The angle drive is a fixed ratio. The speedometer gets calibrated to the input RPM of the cable. The rule of thumb setting is 1000 RPM wheel rotation equals 60 MPH Or 95.56kph

My understanding is that one of the vendors is selling an angle drive that is not the correct drive ratio, its close, but not too the original spec. I’m not sure who it is though. I have not needed a new AD for several years.


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It's not just one vendor but all that sell the new style angle drives. These are generic 1/1 ratio units that will give a reading that is off by 12% as I recently explained in another speedo thread. Only a genuine Smiths Instruments unit, and earlier DMCH copies, have the correct ratio. The repro unit suffers from poor tolerances though while the originals problem was poor assembly and lubrication. I've rebuilt hundreds of the S.I. units over the years and the failure rate is very low. The newer copies are inferior.
Rob

[Bullitt]

It's not just one vendor but all that sell the new style angle drives. These are generic 1/1 ratio units that will give a reading that is off by 12% as I recently explained in another speedo thread. Only a genuine Smiths Instruments unit, and earlier DMCH copies, have the correct ratio. The repro unit suffers from poor tolerances though while the originals problem was poor assembly and lubrication. I've rebuilt hundreds of the S.I. units over the years and the failure rate is very low. The newer copies are inferior.
RobOkay, Thanks Rob! Im used to them beeing off the other way around, showing more than what you actually drive. And 20 km/h is a lot, so I guess something more must be wrong?

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[MikeWard]

Is it purely indicating the wrong speed, or is it sticking at 60km/h?

The reason I ask is that mine used to stick between 30-40mph, the needle would then ping up and it would work up to 55mph before getting stuck. In the end I sent the speedo head itself off to be serviced and that cured the problem.

Have a look at this thread for further details http://www.deloreaneurotec.uk/viewtopic.php?f=21&t=4160&p=55041#p55040



The repro unit suffers from poor tolerances though while the originals problem was poor assembly and lubrication. The newer copies are inferior.The current repro's are garbage for sure. It's a shame no one can convince Speedograph to manufacture their repro anymore http://www.speedograph-richfield.com/html/rgb2401.html they site 'health and safety' reasons as the excuse - a real shame as they are bullet proof. http://dmctalk.org/showthread.php?1558-Angle-Drive-Martin-Gutkowski-s-unit&p=223890&viewfull=1#post223890

[Bullitt]

Hmm... No, it was not sticking.

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[Bullitt]

Hmm... My dust shiled was loose.. It turned freely... I swear I could remember i had to push it in place... Put a string of butyl around it to "glue" it in place. Ill have a test drive and see. http://cloud.tapatalk.com/s/5ad77cde014b0/received_10156046134620259.mp4

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[PJ Grady Inc.]

Hmm... My dust shiled was loose.. It turned freely... I swear I could remember i had to push it in place... Put a string of butyl around it to "glue" it in place. Ill have a test drive and see. http://cloud.tapatalk.com/s/5ad77cde014b0/received_10156046134620259.mp4

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If someone changed the speedo face to a 140 or 170 MPH chances are they didn't calibrate it properly. A slipping adaptor cup would probably give very inconsistent readings. NOS cups are a looser fit than the repros but they are normally locked in place when you mount the wheel so that shouldn't be a problem.
Rob

[Bullitt]

If someone changed the speedo face to a 140 or 170 MPH chances are they didn't calibrate it properly. A slipping adaptor cup would probably give very inconsistent readings. NOS cups are a looser fit than the repros but they are normally locked in place when you mount the wheel so that shouldn't be a problem.
RobOk, well it did not help "gluing" it back on. It was pulsating a little bit... But that is normal I guess. I found a photo of the sticker that was put over the original speedo(which is the one that is in my car). As far as I can see the speedo would be correct with the sticker on, so I guess they calibrated it then. Is that an easy thing to do? https://uploads.tapatalk-cdn.com/20180418/a6707c8c0997cdd5a94cf42a77c166af.jpg

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[Chris 16409]

Look at both top speeds in Km/h. The original 85MPH speedometer tops out at 140 Km/h. The new decal that was applied goes all the up to 220 Km/h. The means the speedometer itself should have been re-calibrated to match the new top speed. Maybe the new decal was applied with no re-calibration or bad re-calibration. The needle may also have been reinstalled at a slightly different position.

[PJ Grady Inc.]

Look at both top speeds in Km/h. The original 85MPH speedometer tops out at 140 Km/h. The new decal that was applied goes all the up to 220 Km/h. The means the speedometer itself should have been re-calibrated to match the new top speed. Maybe the new decal was applied with no re-calibration or bad re-calibration. The needle may also have been reinstalled at a slightly different position.

Actually mechanical speedo's are traditionally calibrated at 60MPH in the US because the highway speed limit is where the accuracy is most critical.
Rob

[DMC5180]

Bullitt,

Is there a reason you need too have the KPH speedometer? I noticed you have or had quite a few old American cars. I can’t imagine those needed conversions too.


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[David T]

If you think the speedo is inaccurate the first step is to check the odometer against a measured mile. The longer the measured course the more accurate you can get. Here in the US it is convenient to use the mile markers on limited access highways. Once you know the odometer is accurate you check your speedometer. The math is easiest at 60 MPH because it works out to 60 seconds which equals 1 minute exactly. If the odometer is not accurate you probably have the wrong ratio in the angle drive. Got to fix that before you can check the speedometer. Once you have an accurate odometer, if the speedometer is not accurate it must be calibrated separately. One way is just to pull the needle off and stick it back on at 60 MPH while traveling at exactly 60 MPH. At least you will know it is accurate at that speed but can be way off at other speeds. To properly calibrate the speedometer it is removed and calibrated on a testing stand at 1,000 RPM's whcih is 60 MPH and then checked at other speeds. It can be off up to 10% but is supposed to be correct at 60 MPH. If the dust shield was slipping the needle would be bouncing so much you would not be able to read it. If it bounces a little it means one or both of the inner cables is slightly kinked and probably need lubrication. Pull the inner cables and put them on the floor on a clean newspaper. They should lay in a nice large, smooth circle with no kinks. Lube them with speedo lubricant (you can get it at an auto supply) and reinstall if they are not kinked.

[Bullitt]

Bullitt,

Is there a reason you need too have the KPH speedometer? I noticed you have or had quite a few old American cars. I can’t imagine those needed conversions too.


Sent from my iPhone using TapatalkNope I don't need it, That is why I removed the sticker. The Original has both mph and kmph.

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[Bullitt]

If you think the speedo is inaccurate the first step is to check the odometer against a measured mile. The longer the measured course the more accurate you can get. Here in the US it is convenient to use the mile markers on limited access highways. Once you know the odometer is accurate you check your speedometer. The math is easiest at 60 MPH because it works out to 60 seconds which equals 1 minute exactly. If the odometer is not accurate you probably have the wrong ratio in the angle drive. Got to fix that before you can check the speedometer. Once you have an accurate odometer, if the speedometer is not accurate it must be calibrated separately. One way is just to pull the needle off and stick it back on at 60 MPH while traveling at exactly 60 MPH. At least you will know it is accurate at that speed but can be way off at other speeds. To properly calibrate the speedometer it is removed and calibrated on a testing stand at 1,000 RPM's whcih is 60 MPH and then checked at other speeds. It can be off up to 10% but is supposed to be correct at 60 MPH. If the dust shield was slipping the needle would be bouncing so much you would not be able to read it. If it bounces a little it means one or both of the inner cables is slightly kinked and probably need lubrication. Pull the inner cables and put them on the floor on a clean newspaper. They should lay in a nice large, smooth circle with no kinks. Lube them with speedo lubricant (you can get it at an auto supply) and reinstall if they are not kinked.Will do! Next time I have test plates I will check the odometer.

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[Elvis]

After 100.000km driven just by me, my angle drive also failed. To me it seems like
the gears are worn out a bit.

Got a new and more robust one and I can confirm, it is between 10...15% off.

I can recalibrate the speedo, no big deal, but the kilometer-counter will always be off
as it needs different gears. Is that perhaps available ?


If you want to ship your speedo to Germany - I can calibrate yours, too.
PN me if interested.

[Bullitt]

After 100.000km driven jut by me, my angle drive also failed. To me it seems like
the gears are worn out a bit.

Got a new and more robust one and I can confirm, it is between 10...15% off.

I can recalibrate the speedo, no big deal, but the kilometer-counter will always be off
as it needs different gears. Is that perhaps available ?


if you want to ship your speedo to Germany - I can calibrate yours, too.
PN me if interested.Will keep this in mind! Thanks!

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[Bullitt]

I have found a local company that calibrates speedometers, so no problem there.

I have not checked it against a GPS yet, but reset my trip counter and had a drive.
At the end of my trip the counter said 88 miles. (I guess it is in miles, since the speedometer says 85 mph) Measured the driven distance in google maps, and it said 87 kilometers.
That would be way off. The trip counter should have said around 55 miles. On the other hand, I dont mind the speedo measuring in "kilometers" in stead of miles...

[Jakub]

Please observe pictures below,
top line on my phone is speed according to GPS,

62701627006269962698

Daytime pictures are with angle drive from certain European supplier, one form the evening are with angle drive from Smiths Instruments dated November 1985.

Original angle drive has following ratio, wheel/cable 16/18, I came across following other ratios, 7/8 which is almost correct, 1/1 which gives about 12% inaccuracy and most outrages 8/7 which presents very good chance for a big ticket.