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.
Rob

Okay, 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/viewto...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?15...l=1#post223890

[Bullitt]

Hmm... No, it was not sticking.

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