I had my scuttle off today as my speedo was stuck at 30MPH. When the bezel was off, the needle fell back to zero. On reassembly and test, there was no speed reading, but the odometer and tripmeter worked fine.
I'll investegate further, but thought I'd share this tip:
Repairing Jaeger & Smiths Speedometers
By: Anthony Rhodes
Pop it into google and you can download the .pdf - hopefully I'll find the solution in there!
http://www.szott.com/lotusinfo/Smith-ja ... repair.pdf
Other links google threw up:
http://www.magnetic-speedometer-repair.com/
http://www.magnetic-speedometer-repair. ... eedometer/
http://www.magnetic-speedometer-repair.com/cleaning/
And an interseting rig in this clip:
http://www.youtube.com/watch?v=EoTkZGleYbM
HTH
Jon
Speedo Probs?
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Westfield 129
- Posts: 867
- Joined: Sat Jun 04, 2011 4:20 am
Re: Speedo Probs?
An excellent reference. Already printed out.
The service information and the calibration information is pretty good. I was inspired to take apart one of my old speedos, until I realized that I sold all of them a couple of years ago when cleaning out the old BMC parts shelves. But I still have one that doesn't work in my LHD car... I think that I will do this as soon as I get the right angle speedo gearbox for my Datsun 'box in my LHD car. 'Looks like fun!
One thing that I found interesting was the author's pessimism regarding having the speedo head re calibrated by APT Instruments (Smiths dealer here in the US). I have had this done by APT (a new speedo delivered to my calibration specs) and several others rebuilt by Morris Mintz at West Valley Electronics (better than new). Yes, the head can be recalibrated quite accurately.
In both cases, I gave the technician the rotation count from the speedo cable when the car was rolled 52' '9" (1/100th of 1 mile). Pretty easy to do. The result, when the speedo was returned to me, was a perfectly reading speedo and odo. This was with a variety of vehicles, rear end ratios, transmission swaps (rib case~T9~ Datsun 210, Renault R30) and tires from 185/70/13 to 5.00X15, and 285/40/15.
The calibration information the author gives in the manual are very useful, in any case. 'Makes it feel as though the Smiths speedo is almost owner serviceable.
The service information and the calibration information is pretty good. I was inspired to take apart one of my old speedos, until I realized that I sold all of them a couple of years ago when cleaning out the old BMC parts shelves. But I still have one that doesn't work in my LHD car... I think that I will do this as soon as I get the right angle speedo gearbox for my Datsun 'box in my LHD car. 'Looks like fun!
One thing that I found interesting was the author's pessimism regarding having the speedo head re calibrated by APT Instruments (Smiths dealer here in the US). I have had this done by APT (a new speedo delivered to my calibration specs) and several others rebuilt by Morris Mintz at West Valley Electronics (better than new). Yes, the head can be recalibrated quite accurately.
In both cases, I gave the technician the rotation count from the speedo cable when the car was rolled 52' '9" (1/100th of 1 mile). Pretty easy to do. The result, when the speedo was returned to me, was a perfectly reading speedo and odo. This was with a variety of vehicles, rear end ratios, transmission swaps (rib case~T9~ Datsun 210, Renault R30) and tires from 185/70/13 to 5.00X15, and 285/40/15.
The calibration information the author gives in the manual are very useful, in any case. 'Makes it feel as though the Smiths speedo is almost owner serviceable.
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jonclancy
- Posts: 943
- Joined: Tue Nov 01, 2011 9:30 pm
Re: Speedo Probs?
Current state of play:
I have just connected my new speedo cable to the speedo adn ran a corless drill CCW. Seems to work perfectly. I did notice that the shroud on the old cable was worn/melted through to the spiral metal sleeve - that's what prompted the purchase of the new one. Vintage Restorations are no longer able to service these speedos as John Marks has semi-retired. Speedy Cables can undertake this work, though. As all cash is being divirted into the engine rebuilt fund, I'm hoping that the new cable will do the job. Logic dictates that the cable wasn't the cause of a stuck needle and that the needle bearing on the drag cup is a little sticky - but, it's a (pretty much) non-lube item. We'll see when it's all been reassembled and running. I think I will reroute the speedo cable to ensure it's away from any heatsource or abrasion.
From Rhodes:
The spindle may not move freely due to the disk binding against an obstruction. In this case the pointer is stuck in one place or will not rise above a certain level. The spindle pivot may lack lubrication and this will cause the needle to jump from one speed to the next rather than move smoothly. Lack of lubrication between the spindle needle tip and the bearing in the center of the magnet wheel may cause chatter at certain speeds.
I have just connected my new speedo cable to the speedo adn ran a corless drill CCW. Seems to work perfectly. I did notice that the shroud on the old cable was worn/melted through to the spiral metal sleeve - that's what prompted the purchase of the new one. Vintage Restorations are no longer able to service these speedos as John Marks has semi-retired. Speedy Cables can undertake this work, though. As all cash is being divirted into the engine rebuilt fund, I'm hoping that the new cable will do the job. Logic dictates that the cable wasn't the cause of a stuck needle and that the needle bearing on the drag cup is a little sticky - but, it's a (pretty much) non-lube item. We'll see when it's all been reassembled and running. I think I will reroute the speedo cable to ensure it's away from any heatsource or abrasion.
From Rhodes:
The spindle may not move freely due to the disk binding against an obstruction. In this case the pointer is stuck in one place or will not rise above a certain level. The spindle pivot may lack lubrication and this will cause the needle to jump from one speed to the next rather than move smoothly. Lack of lubrication between the spindle needle tip and the bearing in the center of the magnet wheel may cause chatter at certain speeds.
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Westfield 129
- Posts: 867
- Joined: Sat Jun 04, 2011 4:20 am
Re: Speedo Probs?
Overhaul cost here for any Smiths speedo is about $200. Just about the cost of a new Smith's speedo from the distributor (APT instruments). This cost (rebuilt or new) includes calibration if you give the speedo techs the number of speedo cable turns over 52'9" roll. (for MPH reading speedos). I imagine that if you give them the number of turns for 1/100th KM, you can also get an accurate calibration.
While I have been rebuilding the instruments (speedo and tach), the cost of outright replacement is actually a better deal.
As I am replacing my instrument panel (tach in front of driver with a dual gauge, speedo on the passenger side, period ignition/light switch), I am thinking about a new speedo unit, along with a right angle drive for my Datsun gearbox.
While I have been rebuilding the instruments (speedo and tach), the cost of outright replacement is actually a better deal.
As I am replacing my instrument panel (tach in front of driver with a dual gauge, speedo on the passenger side, period ignition/light switch), I am thinking about a new speedo unit, along with a right angle drive for my Datsun gearbox.
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Splat
- Posts: 461
- Joined: Thu Jun 02, 2011 5:12 am
Re: Speedo Probs?
I had my MGC speedo (peanuts on ebay) rebuilt, restored and recalibrated by Speedy Cables. Top job and spot-on readings. They also modified my modern Smiths electronic tacho to match (bezel and needle).