The Amazing 1/2 speed speedometer!

[Normy]

Now...here's a perplexing problem:

Recently, while traveling at slightly extra-legal speeds [] on the open highway, my speedometer suddenly dropped to zero. Everything else worked fine- just now I had no speedometer. And I had the distinct odor of frying electrical wires for a few moments. I pulled over, checked the fuse panel and the fuse for the speedometer itself, and found nothing. When I got home, I pulled the instrument cluster out of the pod and lifted out the speedometer; there was a resistor on the circuit board at the back which was charred and the board itself was slightly burned. Ok, the car is 22 years old; it happens.

New [used] speedometer from 928 International, a reputable supplier, $150. Installed yesterday...and though it works, it displays HALF speed! That's right: 1400 rpm in 5th gear = 40 mph, but my gauge reads about 20 mph. The car is an '85, and the speedometer is for an '85-'86 car.

Hmm. Any ideas? The speedometer works by counting the number of times the rear axle shafts rotate per minute, via an electrical impulse that is triggered from a wheel attached to the differential. My car is a gray market car from Austria known as an S2, whereas the gauge was obviously from an American-spec car due to the metric inner speedometer. The American cars have a different, higher rear-end ratio, but that makes no difference. Their rear wheels rotate the same number of times per mile as my car's does.

[Red Baron]

Sounds like you may have a short in the gage board. Being that the car stays in a salt water enviroment, it could be as simple as corrosion on the copper contacts on the board. You might consider removing the pod to clean all the contactss and while in there you may also consider upgrading your pod lights and gage bezels at the same time. A buddy of mine recently did this with his Euro because of gage gremlins and has had no problems since. The upgrade to the gages is a really nice touch. He went with the kit from Jager.

[Normy]

Originally Posted by Red Baron

Sounds like you may have a short in the gage board. Being that the car stays in a salt water enviroment, it could be as simple as corrosion on the copper contacts on the board. You might consider removing the pod to clean all the contactss and while in there you may also consider upgrading your pod lights and gage bezels at the same time. A buddy of mine recently did this with his Euro because of gage gremlins and has had no problems since. The upgrade to the gages is a really nice touch. He went with the kit from Jager.

Yes, I had some sort of short in the board. I had smoke in the cockpit to prove it

What perplexes me is that when I pulled the speedo and replaced it with a known good instrument...it read HALF. Not full, not twice, not nothing at all.... half. Hmm... a 340 mph speedometer? Maybe in the 727 that I fly for Fedex [NOT; a bit slow...] or a land speed car. But it doesn't work for me!

Now; How does the speedometer work?

[Danglerb]

Maybe it was other "bad" part that toasted your old speedo and not a direct failure of the speedo itself?

[Normy]

Originally Posted by jimmyt123

Are you sure you don't have something in there like is pictured below? Most, if not all of you are too young to remember this kind of gadget, but it's from the way-back JC Whitney days when they sold unbelievably cheesy stuff. This is from the days when speedos were run by cable from the trans. This item was advertised to save wear and tear on your speedometer, by reducing the amount of work it had to do. Matter of fact, reduced it by exactly half. If it showed 20, you were going 40, at 30, you were going 60, etc. All you had to do was get under the car, unscrew the retainer which held the squared speedo cable end in the plastic receiver gear in the trans, pull it out, install the end of the reducer with the squared drive end in the trans, then install your original speedo cable end into the receiver portion of the reducer. Presto! Such a great gadget, all to save wear on your speedo.

But, can you believe that some people who bought these, did not install them to lessen the wear on their speedo, but did so to with criminal intent be able to sell a car with 80K miles showing only 40K? This upset JC Whitney so greatly that they soon stopped selling them. See how a few people screw up the works for the rest of us good, decent, honest folk?

You da MAN! Now, tell me...does JC Whitney have a component I can add on the cheap that makes my 45k timing belt last 90 k?

::slides a Stella Artois to Jimmy::

N!

[surfdog4]

do you still have the remains of the resistor that burned up on the old speedometer? Long shot but it's possible that if it's in a part of the circuit that does the "counting" then the new resistor could be a different value, and resistors are common in 1/2 increments..1k, 2k, etc. Just a thought...

Also, perhaps a newbie stupid answer here, but my '81 has an 85mph speedo, but there is also a 140mph version..i don't know how long those two options continued, but perhaps you could have 85 mph speedo guts with 140mph face?