Speedometer problem

[chunstone]

The challenges never end!
I have an original speedometer with the trip odometer. Worked fine before, Are these speedometers something that can be serviced? Must be gummed up. I rolled the trip to 0000 hoping that the speedometer would drop to the correct speed and in doing so I pulled down on the trip mechanism and the speedometer dropped, so the more I pulled on the odometer trip mechanism the more it would go down to zero, but then as you drive, it slowly goes up to 60 or 80 mph or ?? while cruising around the back streets at about 25 mph.
Thanks for any help.

[datzenmike]

The trip odometer is mechanically connected to the car odometer and can be zeroed.

The transmission drive cable is not directly coupled to the needle. The cable spins a magnet inside a cup with the needle attached. (somewhat like rear brake shoes inside the brake drum) The cup has a return to zero coil spring. Magnetism 'drags' the needle around from induced currents.

Sounds like tugging on the adjustment stem is distorting the internal mechanics. Maybe the magnet is rubbing the cup or moved closer causing it to read higher and higher. Maybe the return spring is broken.

[Byron510]

This used to be a serviceable item. Go back 40 years when all gauges were mechanical, there were shops in every city dealing with these for the taxi industry. Today I'll bet those guys are hard to find!

The speedo can be serviced and calibrated, but you'll have to find a guy that still does it. It'll likely be an old guy with a shop in his back yard in this day in age. I know that when I was rallying with mechanical speedos and odo's, I had a local shop make me the drive T and drive cables required. But even in the 90's that guy said his business was coming to an end due to all cars having electric speedos OEM.

Byron

[bertvorgon]

http://www.westcoastmeter.ca/about/

These fellows used to slalom with me and did a calibration of my GTS speedo back in the day.

They might still be able to help you.

Keith

[RMS]

sounds like the speedo cable has been pulled on, loosening the drive end of the speedo head. the drive head is pressure fit on the the housing. if you remove the speedo you will likely find the box with the drive is loose. if this is pulled out or cocked over it will drag on the needle. the tolerances are very tight and it is a big pain to get lined back up... if fully removed. with the speedo removed try seating the box on the drive end with your thumbs. make sure the speedo cable is not pulling on the head when reinstalled.

[chunstone]

Thanks for all the help, I'll check it out and get back to you all.