Half-way procedure to treat trip meter malfunction (Birkin 1993)

[drhasegawa]

After mileage exceeds 110,000 km, the trip meter of my old Birkin 1993 stops occasionally, and after several 10 kms, it recovers, again, and again.

 

https://drhasegawa.com/prisoner6birkin/birkin-geo.htm#201115

 

Recently, I notice the meter stops after mild backward movement in the parking stop for toilet. So when I notice the trouble, I stop the car at the road side or on the wide open space, and set backward gear, and a bit violently go in reverse 1~2 meters back (kick ass mode). Maybe, twice. Voila, the meter recovers instantly !!.

 

After that, the meter proceeds smoothly for next circa 200 kms.  This can work over several times recently.

 

I am not car engineer and actually amateur Seven fan.  Does anyone explain this phenomenon with mechanical engineering knowledge ? 

 

-- 
Akio Hasegawa, M.D., PhD
Pathologist
Koiwa, Tokyo, Japan

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Edited July 26, 2022 by drhasegawa

[MV8]

Beautiful scenery!

The gears that engage the worms are worn. I expect that soon it will not work at all. Worm gear engagement is adjustable with the screw on the side, over the slotted worm bracket in your picture. I'd look for a replacement of the same model, new or used, then swap the gears or simply note the replacement in the log book. It may not be allowed in Japan for anyone to calibrate the indicated mileage on a replacement speedometer.  

The clutch cable reliability could be improved by allowing the cable eye to rotate freely without the hardware being loose on the pedal. One way is to replace the socket head screw by modifying the pedal. A stepped diameter steel pin can be pressed into the pedal and spot welded on the side opposite the cable eye. A washer would be on each side of the eye followed by the cotter pin.

Another way is to use a larger cable eye to fit a shoulder bolt or sleeve over the original socket head bolt and add washers.

Another way would be custom made stud/pin with threads for the pedal side, a thin flange, with a unthreaded pin/shank on the cable side with a cotter pin hole.

 

Disregard clutch cable mods. No need to modify the pedal at all. The nuts should be jambed together against the pedal and not tightened against the cable eye. It would be better to have an unthreaded shank bolt and washers on each side of the eye.

 

 

Edited July 26, 2022 by MV8

[drhasegawa]

to MV8.  Thanx for your advice.  My chief mechanic also advises me to obtain secondhand VDO meter on the net for worm gear replacement, domestic and international, though, it is very rare, or outrageously expensive in spite of  aging. I hope the meter survives till at least 130,000 km mileage.

 

Re: clutch cable - Mine too once broke and replaced. Then I mastered driving without clutch (Non-synchronous transmission driving). I always carry substitute accelerator cables when driving Seven, which broke twice in the past.  Boys always take a difficult way !

[MV8]

I like your hat!

Standard calibration of cable driven speedometers is usually 1000rpm at 60mph/100kph and adjusted by the tooth count at the transmission end of the cable. I expect any similar specification vdo speedometer from that time would have the same worm drive trip indication gears but a different face numbering. I think all you need are the bronze gears.

The gears you have could be cast in plaster or a flexible mold, a copy of the worn gear made from wax and then built up as a pattern for casting in red bronze or silicon bronze by a jewelry maker with a kiln and centrifugal casting spinner. The new gears could be tested off the car with a drill to turn the cable.

Another option is to take the old gears to a machinist for a production run to cut from bronze rod.

It is a lot more trouble and expense than installing a modern gps speedometer with no cable.

If the throttle breaks again, consider using bicycle brake cable, teflon lined or sleeved that is cut to fit. Should be a 1.5mm cable with 5-6mm housing.

Do you like hoshigaki? I've not made any yet. I usually just dehydrate. I grow many fruiting trees and vines including a few types of asian persimmons; Giombo, Tanenashi, Hachiya, Fuyu, Saijo, "coffee cake", and "Honan Red". All grafted to cold-hardy root stocks.

[Anker]

I had the odometer on my 1987 VDO not work intermittently. I decided to send it to erics@southernelectronics.com refurbish it completely for just under $400. A good value and worth it because there probably are other parts that need replacement.

 

Anker