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#1
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Speedometer
I had to drive for a ways on a road with a 10mph speed limit today. It made me look at the speedometer and I realized that it's one of those situations where you can look at something for many years and not really see it. I 'saw' that the distance between 0 and 20 mph is considerably smaller than the distance between 20 and 40 mph. And that the distance between 20 and 25 mph is considerably further than the distance between 60 and 65 mph. As many years as I have been driving 123's I'd been thinking that the speedometer needle progressed in a linear fashion around the numbers. Apparently not.
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1977 300d 70k--sold 08 1985 300TD 185k+ 1984 307d 126k--sold 8/03 1985 409d 65k--sold 06 1984 300SD 315k--daughter's car 1979 300SD 122k--sold 2/11 1999 Fuso FG Expedition Camper 1993 GMC Sierra 6.5 TD 4x4 1982 Bluebird Wanderlodge CAT 3208--Sold 2/13 |
#2
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Kerry, Now that's most interesting. I'd never noticed before, but will surely take note tomorrow morning when I start my car up. I teach at a community/ tech college and am surrounded by all sorts of intelligent folks. This matter will now be on my endless list of questions that need answering. I'll let you know what I learn. This speedo is mechanical, not electrical. Right?
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John Schroader bio burnin' 83 300D, '83 300 SD, '79 240D "I've never met a man who was good at making excuses who was good at anything else" Ben Franklin "You cannot permanently help a man by doing for him what he could and should do for himself" Abraham Lincoln |
#3
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I teach at a community college too. Yes, it is mechanical and something is odd since you gear ratio must be consistent. I'm wondering if what appears to be a round ring of numbers on the speedo is really an elipse, accounting for the inconsistent distances.
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1977 300d 70k--sold 08 1985 300TD 185k+ 1984 307d 126k--sold 8/03 1985 409d 65k--sold 06 1984 300SD 315k--daughter's car 1979 300SD 122k--sold 2/11 1999 Fuso FG Expedition Camper 1993 GMC Sierra 6.5 TD 4x4 1982 Bluebird Wanderlodge CAT 3208--Sold 2/13 |
#4
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I just looked at pics of my gauge clusters and the spacing is the same all the way around. Got any pics of yours?
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1985 300TD Turbo Euro-wagon 1979 280CE 225,200 miles 1985 300D Turbo 264,000 miles 1976 240D 190,000 miles 1979 300TD 220,000 GONE but not forgotten 1976 300D 195,300 miles 1983 300D Turbo 175,000 miles http://i42.photobucket.com/albums/e3...e485-1-2-1.jpg |
#5
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No, I don't have a picture of mine. Weird. Maybe my speedometer is not mechanical.
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1977 300d 70k--sold 08 1985 300TD 185k+ 1984 307d 126k--sold 8/03 1985 409d 65k--sold 06 1984 300SD 315k--daughter's car 1979 300SD 122k--sold 2/11 1999 Fuso FG Expedition Camper 1993 GMC Sierra 6.5 TD 4x4 1982 Bluebird Wanderlodge CAT 3208--Sold 2/13 |
#6
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Just looked at my W116 79 300sd. It is not the same as my 85TD. 0-20 is much smaller than 20-40m just like the TD. But the five mph increments from 20mph upwards all seem to be identical distances whereas on the 85TD they vary. Weird.
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1977 300d 70k--sold 08 1985 300TD 185k+ 1984 307d 126k--sold 8/03 1985 409d 65k--sold 06 1984 300SD 315k--daughter's car 1979 300SD 122k--sold 2/11 1999 Fuso FG Expedition Camper 1993 GMC Sierra 6.5 TD 4x4 1982 Bluebird Wanderlodge CAT 3208--Sold 2/13 |
#7
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I just looked at my (mechanical) W123 speedometers. The increments are all the same, considering that the first line is 10 mph (not 0 mph).
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#8
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Mine is linear except that the rest position is not "0" but rather... I think "5". Or maybe "10". I don't have that car with me at the moment but I know it's one or the other.
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#9
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How can the rest position be 10mph and not 0? Near as I can tell, when my car is sitting still the needle is at rest.
Anyone else have varying 5mph increments?
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1977 300d 70k--sold 08 1985 300TD 185k+ 1984 307d 126k--sold 8/03 1985 409d 65k--sold 06 1984 300SD 315k--daughter's car 1979 300SD 122k--sold 2/11 1999 Fuso FG Expedition Camper 1993 GMC Sierra 6.5 TD 4x4 1982 Bluebird Wanderlodge CAT 3208--Sold 2/13 |
#10
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The speedometer on my w124 starts at 10 mph I think. So I have to guess at my speed if slower that that.
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1993 W124 300D 2.5L Turbo, OM602.962 2000 Chevrolet Cavalier, 2.4L DOHC 2002 Ford Explorer, 4.0L SOHC 2005 Toyota Prius, 1.5L http://www.fuelly.com/sig-us/40601.png |
#11
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Did a quick search. It looks like the consensus is that the 85 TD speedometer is mechanical and not electronic. However, both I and a person with a late 84 TD have noticed that our speedometers read fast. Could it be that we have varying distances written on the speedometer face but the speedometer needle is following the same arc as ones without the varying distance.
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1977 300d 70k--sold 08 1985 300TD 185k+ 1984 307d 126k--sold 8/03 1985 409d 65k--sold 06 1984 300SD 315k--daughter's car 1979 300SD 122k--sold 2/11 1999 Fuso FG Expedition Camper 1993 GMC Sierra 6.5 TD 4x4 1982 Bluebird Wanderlodge CAT 3208--Sold 2/13 |
#12
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Isn't the speedometer portion of these "mechanical" odometer/speedometer instruments a magnetic and spring combination drive? If so it is very likely that the odd arrangement at or near the bottom of the scale is due to drag and non-linearity of the magnet-spring based drive system.
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1961 190Db retired 1968 220D/8 325,000 1983 300D 164,150 |
#13
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I'm not sure how they work. But the scale is definitely different on both sides (10-20 and 110-120) on my 85. Would the drag issue apply at the high end of mph? Why would the 116 and TD be different?
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1977 300d 70k--sold 08 1985 300TD 185k+ 1984 307d 126k--sold 8/03 1985 409d 65k--sold 06 1984 300SD 315k--daughter's car 1979 300SD 122k--sold 2/11 1999 Fuso FG Expedition Camper 1993 GMC Sierra 6.5 TD 4x4 1982 Bluebird Wanderlodge CAT 3208--Sold 2/13 |
#14
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My speedo in my 82 240D starts at 10mph.. if the car is going slower than that, naturally, the needle doesn't move.
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1982 240D 4spd, 327,000mi |
#15
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Yep, same on my 85 and 79 240Ds.
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1985 Euro 240D 5 spd 140K 1979 240D 5 spd, 40K on engine rebuild 1994 Dodge/Cummins, 5 spd, 121K 1964 Allice Chalmers D15 tractor 2014 Kubota L3800 tractor 1964 VW bug "Lifes too short to drive a boring car" |
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