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#1
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Tach compatabillity
Hello,
I have aquired a tach from a '72 300sel 6.3. I would like to make it work in my '71 280se, which I am converting from the old inline 6 gas to turbodiesel I removed from a wrecked 1985 300d. What can I do to make it work with the diesel engine? Any advice is greatly appreciated. |
#2
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That depends on what type of tach setup it has. The diesels (up to 1984) used an AC coil sensor at the crank, fed to a tach amplifier on the fender, and then to the gauge. What do the cars you have use?
__________________
-diesel is not just a fuel, its a way of life- '15 GLK250 Bluetec 118k - mine - (OC-123,800) '17 Metris(VITO!) - 37k - wifes (OC-41k) '09 Sprinter 3500 Winnebago View - 62k (OC - 67k) '13 ML350 Bluetec - 95k - dad's (OC-98k) '01 SL500 - 103k(km) - dad's (OC-110,000km) '16 E400 4matic Sedan - 148k - Brothers (OC-155k) |
#3
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The 300d was a '85 and I believe it read off of the flywheel, I also have parts from a '83 300d so whichever setup is the easier I will more than likely go that route.
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#4
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The '83 setup will be easier. The 84 and 85 models get the tach feed through a computer box.
__________________
-diesel is not just a fuel, its a way of life- '15 GLK250 Bluetec 118k - mine - (OC-123,800) '17 Metris(VITO!) - 37k - wifes (OC-41k) '09 Sprinter 3500 Winnebago View - 62k (OC - 67k) '13 ML350 Bluetec - 95k - dad's (OC-98k) '01 SL500 - 103k(km) - dad's (OC-110,000km) '16 E400 4matic Sedan - 148k - Brothers (OC-155k) |
#5
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Will the tach gauge from the 1972 300SEL 6.3 V8 gas be compatible with the tach amp and related parts for the 1983 300D?
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#6
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If they have the same type of connector, then I'd assume it'd work. The '83's have a two-pin (or three, one is an extra ground) connector.
__________________
-diesel is not just a fuel, its a way of life- '15 GLK250 Bluetec 118k - mine - (OC-123,800) '17 Metris(VITO!) - 37k - wifes (OC-41k) '09 Sprinter 3500 Winnebago View - 62k (OC - 67k) '13 ML350 Bluetec - 95k - dad's (OC-98k) '01 SL500 - 103k(km) - dad's (OC-110,000km) '16 E400 4matic Sedan - 148k - Brothers (OC-155k) |
#7
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The 6.3 tach has two wires; a red and green. I think the metal casing is a ground.
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#8
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And where is the rest of the 300sel?
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#9
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I wish I knew; I purchased the gauge cluster from ebay.
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#10
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I doubt it would be compatible. The tachometer for the gasser reads ignition pulses - 3 or 4 per rev depending on how many cylinders you have. The diesel tachometer gets one pulse per rev. You'll want to find a tach from a diesel and transplant it.
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1984 300TD |
#11
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Quote:
Also I was wondering how the late model diesel tach works; I know those read off of the flywheel instead of the crank but I am not sure how it reads 100+ teeth and converts it to a pulse for the tach. |
#12
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techguy512 has produced a tach amp replacement that uses a small microcontroller (computer) to do what the old analog part did. It may be that he can adapt that to convert the signals. The issue is that the tachometer expects a steady stream of pulses, and not bursts - so his algorithm would have to be somewhat complex. It would have to behave like a Phase Locked Loop.
It will be much, much, much easier (not to mention cheaper) to retrofit a diesel tachometer. It looks to be a straight conversion with no extra holes. Some rewiring is required, of course.
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1984 300TD |
#13
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Maybe not so much. First thoughts would be to go to the next controller in the series. 2k of code space, and two independent timer/counters. One to measure input pulse rate and one to create output pulses.
We would need to know with a great deal of certainty lots of details about the gasser tach (input pulse rate, input signal levels, etc, etc).
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Bob '82 300D Petrol B-G Metallic |
#14
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Did the w115/w114 diesels have tachs? I was under the impression that a tach was never offered as an option for that body style which uses a similar gauge cluster as the w108/w109s
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12V / 24000 Imp. 230 / 29 / 3 8Zyl. / 4Tkt There is a blue stamp on the unit that reads: 225 10.68 This particular tach unit was used on the m100 engine. Hope that helps; I greatly appreciate everyones help so far, thanks. |
#15
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Steve Brotherton has/had a VDO service shop. He should know how to make it work.
Or ask the folks at www.paspeedo.com The Rube Goldberg in me says to have a machine shop fit as many crank triggers on the crank damper/pulley as needed to have a proper reading. Sixto 87 300D |
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