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#16
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Current Diesels: 1981 240D (73K) 1982 300CD (169k) 1985 190D (169k) 1991 350SD (113k) 1991 350SD (206k) 1991 300D (228k) 1993 300SD (291k) 1993 300D 2.5T (338k) 1996 Dodge Ram CTD (442k) 1996 Dodge Ram CTD (265k) Past Diesels: 1983 300D (228K) 1985 300D (233K) |
#17
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Current Diesels: 1981 240D (73K) 1982 300CD (169k) 1985 190D (169k) 1991 350SD (113k) 1991 350SD (206k) 1991 300D (228k) 1993 300SD (291k) 1993 300D 2.5T (338k) 1996 Dodge Ram CTD (442k) 1996 Dodge Ram CTD (265k) Past Diesels: 1983 300D (228K) 1985 300D (233K) |
#18
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My thought is that the signal to the tach has to have some sort of a gearing to get the voltage to turn into a certain rotation of the tach to give its indication. If the voltage provided frm the sensor/amp to the tach is "miscalibrated", then the tach wont rotate enough per the signal. My other thought is, how do the needles come off the gauges? Is it possible to only install these things one way, or is there some sort of a set screw that friction fits the needle onto the tach shaft going through the gauge face? Perhaps my idle reading of just over 500 now that Ive turned it up is really 400+ higher, and the reality is that the needle location is just misaligned. Thoughts???
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Current Diesels: 1981 240D (73K) 1982 300CD (169k) 1985 190D (169k) 1991 350SD (113k) 1991 350SD (206k) 1991 300D (228k) 1993 300SD (291k) 1993 300D 2.5T (338k) 1996 Dodge Ram CTD (442k) 1996 Dodge Ram CTD (265k) Past Diesels: 1983 300D (228K) 1985 300D (233K) |
#19
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Perhaps you have a tach with an electrolytic capacitor leaking...
I think you can ' gear' a tach if you need to... but you have to understand the clipper circuit and the resistor/capacitor timing circuit feeding it... At a certain level I just made that up... and at another level I did not make it up.... LOL There is probably one of those 7000 series OP Amps and a 555 circuit which can be adapted to do what you need to tweak it... Pay no attention to this... might be making that up also... but if I am not...and you understand the concept ... please post and explain what I said...so I can understand it... LOL
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1980 240d , chain elongation, cam marks reference: http://www.peachparts.com/shopforum/diesel-discussion/10414-help-i-need-check-stretch.html http://www.peachparts.com/shopforum/diesel-discussion/305365-9-degrees-chain-stretch.html evap fin cleaning: http://www.peachparts.com/shopforum/diesel-discussion/156207-photo-step-step-post-showing-w123-evaporator-removal-1983-240d-1982-300td.html?highlight=evaporator A/C thread http://www.peachparts.com/shopforum/diesel-discussion/297462-c-recommendations-mb-vehicles.html |
#20
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at 60mph the load on the TC is lighter than at 70, so the slippage could account for it. I am doubting it's that far off though. weird. I wish some of my tachs worked so I could see what RPM my speeds were at.
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#21
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Have you taken one apart? Do you know how the needle attaches to the shaft that goes through the gauge face? Can that just be on in an incorrect position and thereby have error across the entire range?
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Current Diesels: 1981 240D (73K) 1982 300CD (169k) 1985 190D (169k) 1991 350SD (113k) 1991 350SD (206k) 1991 300D (228k) 1993 300SD (291k) 1993 300D 2.5T (338k) 1996 Dodge Ram CTD (442k) 1996 Dodge Ram CTD (265k) Past Diesels: 1983 300D (228K) 1985 300D (233K) |
#22
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SO I think it must be the alignment of my tach needle. Anyone know how the tach needle attaches to the gauge? Perhaps I can turn it a bit to get it to align right and read correctly...
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Current Diesels: 1981 240D (73K) 1982 300CD (169k) 1985 190D (169k) 1991 350SD (113k) 1991 350SD (206k) 1991 300D (228k) 1993 300SD (291k) 1993 300D 2.5T (338k) 1996 Dodge Ram CTD (442k) 1996 Dodge Ram CTD (265k) Past Diesels: 1983 300D (228K) 1985 300D (233K) |
#23
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The needle is pressed on the shaft similar to the speedometer head. You can pop it off. There have been past threads that talk about how to remove the needle. Folks have used spoons and etc. .
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1983 123.133 California - GreaseCar Veg System |
#24
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Yeah I will drfinitely check once I am in a position to roll under the car.
Can the needle only be installed one way on the shaft, or is it splined with multiple possible installation angles? If so, it may just be off by a few splines from how it came from the factory, and a reinstall and refit would make it fine.
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Current Diesels: 1981 240D (73K) 1982 300CD (169k) 1985 190D (169k) 1991 350SD (113k) 1991 350SD (206k) 1991 300D (228k) 1993 300SD (291k) 1993 300D 2.5T (338k) 1996 Dodge Ram CTD (442k) 1996 Dodge Ram CTD (265k) Past Diesels: 1983 300D (228K) 1985 300D (233K) |
#25
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.
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1983 123.133 California - GreaseCar Veg System |
#26
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your calculations also might be more accurate if you were talking about a manual transmission but how are you going to measure the percent slippage at the torque converter? I would check into what leathermang was saying about the electronics before you take your tach needle off. Also a failsafe method of checking the RPMS is just measure the pitch of the engine - the droning "note" that you hear when you're cruising on the highway. If you can measure that then you have the frequency of your engine. I used that method to measure the RPMs of a small two stroke motor once. ... you might have to account for having more than 1 cylinder though because what you're hearing is the frequency of combustions.
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'82 240D 224K miles manual transmission mods: wooden 4by4 bumper, EGR delete and older EX manifold without EGR port, glass pack muffler (cheapest replacement muffler), rebuilt bosch injectors with Monark nozzles working on: aux electric fuel pump, coolant/fuel heat exchanger/filter head, afterglow, low oil pressure buzzer/LED Last edited by samboyellowsub; 04-30-2010 at 03:48 PM. |
#27
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I verified the PN of my speedometer for a 3.07 geared car with an 85 mph speedometer. So, if I have a 2.47, then we have to make the assumption that a converter or re-gear was done on my speedo. There is going to be some typical range of slippage of the TC, and a quick analysis is going to be within a few percent. Plus, if someone posted their RPMs at 60 and 70 for a car with a known 3.07 diff, I could calculate the slippage and have a really close valuation. The electronics bit was some theory, and we will have to think about it, but there is too much complexity. A "recalibration" of the tack would be a far easier way to go, given that it appears that I am roughly the same number of RPM off at both idle and high-speed. The other option that Ill work through is taking a used tach that is known good and see how it reads. That could shed insight too. The major indicator of something else being wrong, to me, is that when I got the car, the RPMs were reading maybe 450... If I am 400 off relatively consistently, at idle and speed, then that could make sense. Add some error in there for slippage at various torque levels (speeds) and everything could make good sense.
__________________
Current Diesels: 1981 240D (73K) 1982 300CD (169k) 1985 190D (169k) 1991 350SD (113k) 1991 350SD (206k) 1991 300D (228k) 1993 300SD (291k) 1993 300D 2.5T (338k) 1996 Dodge Ram CTD (442k) 1996 Dodge Ram CTD (265k) Past Diesels: 1983 300D (228K) 1985 300D (233K) |
#28
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are you positive that you have the 2.47 in there? i think getting a tach that is known to be good is an excellent idea. that would have essentially the same certainty of measuring the RPMs by measuring the pitch that it makes. Thats the only way you're going to know. Otherwise aren't you also making an assumption that you are exactly 400 RPM off.
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'82 240D 224K miles manual transmission mods: wooden 4by4 bumper, EGR delete and older EX manifold without EGR port, glass pack muffler (cheapest replacement muffler), rebuilt bosch injectors with Monark nozzles working on: aux electric fuel pump, coolant/fuel heat exchanger/filter head, afterglow, low oil pressure buzzer/LED |
#29
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If you do end up with a 2.47 rear and correct speedo I would like to know your setup. I have the 2.47 with a 3.07 geared speedo in my 82 coupe and my speedo is off by 40%. I looked for reducers and couldnt find anything to fit. I was going to pull apart the speedo and switch gears to get closer but never got around to experimenting
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1982 300CD Turbo (Otis, "ups & downs") parts for sale 2003 TJ with Hemi (to go anywhere, quickly) sold 2001 Excursion Powerstroke (to go dependably) 1970 Mustang 428SCJ (to go fast) 1962 Corvette LS1 (to go in style) 2001 Schwinn Grape Krate 10spd (if all else fails) |
#30
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400ish, with a bit of variation across the speeds due to tc slip makes perfect sense because my engine sounds normal at idle compared to my other w123 cars but reads really low - 3-400 rpm off...
__________________
Current Diesels: 1981 240D (73K) 1982 300CD (169k) 1985 190D (169k) 1991 350SD (113k) 1991 350SD (206k) 1991 300D (228k) 1993 300SD (291k) 1993 300D 2.5T (338k) 1996 Dodge Ram CTD (442k) 1996 Dodge Ram CTD (265k) Past Diesels: 1983 300D (228K) 1985 300D (233K) |
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