So I have my 1985 300D, CA emissions. The engine has been replaced with that from a 1983 300SD and the tranny has been replaced with that from a 1983 300D. No longer CA emissions. Tachometer does not work.

As I understand, the tach in this circumstance ran off of a computer, possibly getting signal from the transmission (?). The computer was in the passenger side kick area.

I'd like to cut the Gordian knot. The car has the conventional pickup from the front of the engine, leading to a diagnostic port on the left front wheel well. That is intact and connected. I have a tach amplifier for that port, and a wire extends from the diagnostic port to a mess of bundled wires on the way to the dash.

Can I do something to wire up the tach to function properly using the conventional set-up (not the set up that goes via the computer in the passenger wheel well?). What would I have to do to make my tach work?

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Der Panzermann und Fraulein Fahrvergnuegen

1991 420SEL 201K "The Big Blue One"
1985 300DT 205K chassis/285K engine nee California emissions "Goldbug"
1983 300TDT 255K "The Womble"
1983 300 DT 214K "Sea Sprite"-Rear-ended a truck
1983 300SD 285K "The Donor" Gave his life so that others can live
1980 500SL Euro 105K "Der Panzer"

Not to hijack, but I would also like to know what the common issues with the stock '85 setup are.

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1979 240D- 316K miles - VGT Turbo, Intercooler, Stick Shift, Many Other Mods - Daily Driver

1982 300SD - 232K miles - Wife's Daily Driver

1986 560SL - Wife's red speed machine

Engine and tranny being from an '83, earlier design, you may need an amp for the tach, with corresponding socket to get signal from balancer pin. If the tach goes on my '84, don't know how to fix.

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83 SD

84 CD

The 1984-85 engines use a FLYWHEEL crank sensor to generate that signal.

You need that signal on the 1985 engines so that the EGR computer can process the A/C wave signal..A/C also needs that signal, klima relay.

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How can you test the "brain box"

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1979 240D- 316K miles - VGT Turbo, Intercooler, Stick Shift, Many Other Mods - Daily Driver

1982 300SD - 232K miles - Wife's Daily Driver

1986 560SL - Wife's red speed machine

I have a functioning tach amplifier to fit into the diagnostic plug with input from the front of the crankshaft (not the flywheel at the rear). But with the transmission from the 1983 300D, is there a way to even attach a flywheel sensor and would that even be desirable? I don't have the data coming in from the EGR system and the turbo anymore. The way I figured getting around this was to "convert" the system to a 1983 set up, simpler. So how would I connect the tach amplifier from the diagnostic plug up so that it feeds input to the tachometer on the dash and what modifications, if any, to the climate control system are needed?

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Der Panzermann und Fraulein Fahrvergnuegen

1991 420SEL 201K "The Big Blue One"
1985 300DT 205K chassis/285K engine nee California emissions "Goldbug"
1983 300TDT 255K "The Womble"
1983 300 DT 214K "Sea Sprite"-Rear-ended a truck
1983 300SD 285K "The Donor" Gave his life so that others can live
1980 500SL Euro 105K "Der Panzer"

At the time of replacing the engine, you could of transfered the '85s flywheel and bellhousing plate to the '83 motor. That would of been the easiest method and you could of kept the same tach and A/C setup. But to do it now with the motor in, I believe it is impossible because I think you need the '85 flywheel.


You will need a 2 prong tachometer from an '83 or older SD. If you look on the diagnostic port on your wheel well, you notice holes with numbers associated with them. #2 is gound and #6 is switched power and leads to the firewall. You will need to add in a wire for #3. Get the wire and plug for the back of the tachometer (instrument cluster) from the donor vehicle. The green-black wire from the tachometer plug goes to the #3 prong on the tach amp and the red-black one goes to switched power that you will need to find. Then hope it works!

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1983 123.133 California
- GreaseCar Veg System

It will work if you wire it properly!
To prove it, I have an '85 turbo engine in my '79 300TD with a working tach (my clock/tach portion of the instruments came out of an '83 donor car) I ran all the wires thru the firewall using some scrap wires I bought somewhere. The pick up coil that senses the pulses at the crank balancer has to be a MB shielded cable, get it off a wrecked car because a new one is buck$

The only problem I ran into was finding 12 volts to power the tach. I got it off a lead that goes hot when the ign switch is "on" - thru a 2 amp fuse to be safe.
I believe all the engines use the rotating magnetic pin on the crank balancer, if you don't have that on your balancer then you will have to find a suitable balancer and swap it (not impossible but a nasty big job compared to the rest of the task!)

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'95 E320 Wagon my favorite road car. '99 E300D wolf in sheeps body, '87 300D Sportline suspension, '79 300TD w/ 617.952 engine at 367,750 and counting!

His stock pickup should be good to go. As far as finding switched power, I would take power from Sun Roof at the fuse block. You tap into it from the fuse area or go underneath the dash and tap into it from below the block. Although there is limited room underneath, there are several lead wires connected to the block by philips screws. The sun roof power lead is located on the left corner nearest the wheel well.

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1983 123.133 California
- GreaseCar Veg System

thanks for the valuable input. I'll let you know how it goes!

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Der Panzermann und Fraulein Fahrvergnuegen

1991 420SEL 201K "The Big Blue One"
1985 300DT 205K chassis/285K engine nee California emissions "Goldbug"
1983 300TDT 255K "The Womble"
1983 300 DT 214K "Sea Sprite"-Rear-ended a truck
1983 300SD 285K "The Donor" Gave his life so that others can live
1980 500SL Euro 105K "Der Panzer"

I recently (days ago) purchased a 1984 300D with a non-working tachometer (and dash lights , but a new rheostat is on the way). I have read numerous threads in the forum and am getting mixed info about whether or not my '84 uses a tach amp or not. The car was originally purchased in Hawaii, and has no tach amp in the plug, so I'm assuming it is not a CA model.

How can I determine how my tach works? Also, is there an online resource for determining your cars features with the VIN?

Thanks!

While I'm here, I am also having trouble getting the instrument cluster out. I took some advice and made my own hooks. These worked great in getting the cluster to move, but I met some resistence on the right side when the cluster was about 3" out. This gave me just enough space to remove some plugs on the left side of the cluster, but no chance for getting at the right side. I couldn't even see what was back there. Rather than tugging away, I just put the thing back in.

I don't think it was the speedo cable since this still had some slack and the resistence was coming from the right side of the cluster. (I didn't remove the speedo cable though.) Also, I couldn't get my hand to the right side with the kick panel removed. I could barely get my hand into the left side from below.

Anyone else had this problem?

Also, when I finally do get the cluster out, should I take any precautions with the oil pressure line? I have read that you should make sure the line is tight when you reinstall the cluster, but is there any chance of oil leakage when the line is disconnected?

Thanks!

If you're in Seattle and having trouble with your dash (or anything else on your car) you need to visit Abe at MBWM parts at 81st and Aurora. He's great and will help you with whatever you need. I know he's out of town now and I believe he gets back the first of May, so if you don't get it out by then I'd visit him, I'm sure he can help you with the dash and tach.

What you describe is that you have a model that does not use a tach amp instead it goes through a computer. Not sure how to trouble shoot it. As far as getting your cluster out, you hope and pray along with tugging a little bit on the cluster to get more room behind there. I've taken out a few clusters that were tight and I just tugged a little more. But when I do, I am always afraid that I might break something and it never happens. But this doesn't mean it might not happen to you. So be careful.

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1983 123.133 California
- GreaseCar Veg System

Very interesing...

I have an 85 non CA car, and the tach does not work on it...

I looked under the hood for the amplifier, thinking I could just take the one from my car and use it... simple repair, right??!?

Well, my 85 has a low-profile cap on the ports where the tall garbage can looking amp would normally sit, like it did on my 85. The holes for the old faashioned type of amp are still there under the cap. Yet, I don't recall if there is even any wires coming or going from it.

Phil's site shows an item for my car (VIN after -A-007353) as an inductive lead from a bellhousing. It looks like this:


the old one looks like this:


The question becomes how does one start troubleshooting the later, newer style of tachometer leads... and does the instrument cluster input change as compared to the older style ones... as if it does, and I find it to be a circuit board or cluster issue, then I can't use my old one from my 83 as a swap-in...

Thanks!

JMH

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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)