I have a 1981 300TD with an odd problem. The speedometer registers slower than I'm actually travelling. I figured this out by calling my wife who was driving behind me in our 2000 Jetta TDI as we were on an open stretch of road. My speedometer read 62, hers read 70.

That's not the odd part, tho'. The trip meter and odometer are both registering MORE miles than I've actually travelled. Last night, I travelled roughly 70 miles (according to Google Maps) in two hours of actual driving time. When I got home, the trip meter and odometer read roughly 240 miles higher.

I am beginning to think that my brand-new 25-year-old car has a lot fewer than the 210,000 showing on the clock, which makes me happy, but I'd like to have an accurate reading. I've found links for the speedometer fix, but I didn't know if the two problems could be related in some way. Any thoughts?

I cannot belive your odo is off THAT far. maybe you meant 24 miles off? or 2.4 miles off? and I guess you were doing lots of low speed driving to only go 70 miles in 2 hours?
John

Someone swapped a cluster out of a non-diesel W123....they are calibrated to certain rear rends and not universally interchangible for that reason..yeah they fit but you would have the issue that you describe.

__________________
Proud owner of ....
1971 280SE W108
1979 300SD W116
1983 300D W123
1975 Ironhead Sportster chopper
1987 GMC 3/4 ton 4X4 Diesel
1989 Honda Civic (Heavily modified)
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Section 609 MVAC Certified
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"He who fights with monsters might take care lest he thereby become a monster. And if you gaze for long into an abyss, the abyss gazes also into you." - Friedrich Nietzsche

It's a little strange that the speedo reads low, they usually seem to read high for some reason. I actually was successful doing a half-ass re-calibration on my speedo about a year ago, and it still seems to be accurate. I carefully lifted the needle past the stop peg and marked the location where it stopped, then removed the needle (which you have to do to get to the odometer anyway) by gently prying it up with a couple of tea spoons. When I replaced the needle, I adjusted the location by the amount of error (say 8 mph) and pressed it back on. It actually took two tries to get it "close enough" (within about 1-2 mph at highway speed) based on using the mile markers and a stop watch for about 5 miles. This method is "less than elegant" but it seemed to work, and it was free, YMMV. Also, I would not assume that the speedo on the Jetta is exact either. I would verify the speed with a GPS, or mile marks before doing anything.

Regarding the odometer error, has you paid attention to how it rolls over? I had another problem (with the same speedo) a few months ago. While driving, the "10" digit seemed to be sticking to the "1" digit and rolling over too soon, so the odometer might record 20 or 30 miles after only 10 miles. I more or less followed the "speedometer fix" link and used some parts from another unit to get it working smoothly again. Working on the odometer isn't that hard, just a PITA. If you break it, it probably needed replacing anyway.

That may explain the speedo error, but not the odometer being off by 240%.

someone put Kph euro guts into a Miles US spec speedo from a gasser model?

__________________
Proud owner of ....
1971 280SE W108
1979 300SD W116
1983 300D W123
1975 Ironhead Sportster chopper
1987 GMC 3/4 ton 4X4 Diesel
1989 Honda Civic (Heavily modified)
---------------------
Section 609 MVAC Certified
---------------------
"He who fights with monsters might take care lest he thereby become a monster. And if you gaze for long into an abyss, the abyss gazes also into you." - Friedrich Nietzsche

Possible, did the 81 originally come with a 85 mph speedo (like my 82)? Maybe someone did "upgrade" it with the incorrect speedo. What it needs is the 125 mph unit from either a 83 or 84, not an 85, with 3.07 gears. I still wouldn't be surprised if the odometer wheels are sticking and flipping over early.

I'm thinking the speedo is actually a mix of a bunch of junk someone happened to have laying around since neither part is accurate and by different magnitudes (speedo vs odometer). I'm sure if you looked at it cloesly you will see signs of it having been tampered with...EG odometer changes as somepoint different than the odoincrimenting...numbers not lining up...mismatched dirt on numbers...scratches or other marks...

__________________
Proud owner of ....
1971 280SE W108
1979 300SD W116
1983 300D W123
1975 Ironhead Sportster chopper
1987 GMC 3/4 ton 4X4 Diesel
1989 Honda Civic (Heavily modified)
---------------------
Section 609 MVAC Certified
---------------------
"He who fights with monsters might take care lest he thereby become a monster. And if you gaze for long into an abyss, the abyss gazes also into you." - Friedrich Nietzsche

The problem with this method is that you can only get it to read right at a single speed.

I once calibrated one the other way, which involves adjusting the spring which returns the needle to zero. It wasn't extremely hard, and worked great,

True, I got mine pretty close at about 75 or 80, but it seems to be within a couple of mph at lower speeds, based on those roadside signs in 35 mph zones. Actually, I'm a little surprised it worked at all. Someday I'm sure I'll have to have it calibrated correctly, or just replace it.

Thanks everyone for the replies.

Yes, It has an 85 mph speedo. The tenths wheels are actually turning too fast by themelves. Nothing seems to be sticking, but the tenths just fly by at at unusually low speeds. In fact, that was what made me notice the problem in the first place

I first noticed the problem driving the beltway around DC last weekend. The signs would indicate X miles to such and such exit, and I would compare the distance to my trip meter. In 1/4 mile, the trip meter clicked over 6/10.

A few minutes later, when we had gotten off the beltway, I asked my wife to tell me when one minute had gone by and I checked the trip meter. I would guess we were going about 45 (if everyone was ignoring the speed limit as usual) and the trip meter ticked off 1.4 miles.

I know that neither of these is an accurate scale to determine precisely how far off the odometer is, but it definitley shows me that something is wrong.

What made me notice the speedometer was not entirely scientific, but sort of sociological. Again, driving on the beltway where the speed suggestion is 55, I was driving with the needle stuck on 55 ad I was right in flow with the traffic, passing some, geting passed by others. If you are not familiar with driving on the beltway, when traffic moves the average car is going 65.

So, I need a new and proper instrument cluster?

A repair may be possible, but its probably more hassle than its worth, and may not be successful if the guts are just plain wrong. I'd replace it with a similar and proper instrument cluster. When you replace the cluster, you can go in and set the odo to the mileage your current odo is showing, or leave it alone and make a note with a sticker on the A pillar of the actual mileage.

There are a few cars being parted out now in the Parts forum, so go over there, shoot out a few emails, and you'll probably be able to find a whole cluster at a good price.

peace,
sam

__________________
"That f***in' biodiesel is makin' me hungry."

1982 300TD Astral Silver w/ 250k (BIO BNZ)
2001 Aprilia SR50 Corsa Red w/ 5.5k (>100 MPG)

Do a test with better control. Those 1/4 mile signs aren't very accurate, but highway mile markers are pretty close. I bet you're reading about 1.6 on the gauge for each mile you travel.