tachometer frustration - PeachParts Mercedes-Benz Forum

Ya Mar · #1 05-05-2011, 02:22 PM

Hello All,

I was going to take the tachometer from my w123 300TD wagon and install it in my w123 300D non Turbo euro import sedan.

The sedan doesn't have any of the hardware for the tach but it's okay because I was going to switch everything from the wagon.

The first thing I tried to do was remove the sensor from the front of the wagon's engine and this is as far as I got. I can't figure out how the bracket is held onto the engine.

There are some large 24mm? bolts that may be holding the bracket in place? But there is at least 1 small maybe 6mm hole that looks like it's maybe for an hex key but it looks like it has threads so I'm not sure.

But before I go any further, does anyone know if the tach's from turbos are compatible with non-turbos?

Any ideas will be greatly appreciated!!

Thanks,

Stretch · #2 05-05-2011, 02:34 PM

I haven't actually finished the job yet but here's the information I've gathered so far:-

http://www.peachparts.com/shopforum/showthread.php?t=285719

For a mistake purchase and then the correct one and some bits I got from funola...

For the larger bracket which is also the pointer for the timing marks see this before you take it off!

http://www.peachparts.com/shopforum/showthread.php?t=272321

Just remove the sensor from the larger bracket (see first thread link).

It should work providing that you've got a little pin sticking out of the crankshaft balancer and you've got some power running to the tach amp (I'll probably get mine from the supply to the glow plug control box)

Ya Mar · #3 05-05-2011, 02:46 PM

Hey Army,

Thanks for the input, I was reading over your first thread this morning before I got started.

So my w123 sedan doesn't have the bracket. Does that mean I will need to order a bracket to install the tach?

Seems like a better option than trying to remove the bracket from the wagon....

Stretch · #4 05-06-2011, 04:54 AM

Quote:

Originally Posted by Ya Mar

Hey Army,

Thanks for the input, I was reading over your first thread this morning before I got started.

So my w123 sedan doesn't have the bracket. Does that mean I will need to order a bracket to install the tach?

Seems like a better option than trying to remove the bracket from the wagon....

I ended up getting my bracket from funola - If you're going to junk the wagon then I'd swipe the (tach amp) bracket too.

Over here most 300Ds don't have a tachometer so finding those parts is difficult. I tried the dealer - no dice. I tried several specialists - no dice. If you have one already I guess that'll be the fastest way... just don't mess about with the timing bracket on the front of the engine just in case (for some strange reason) the pointer for TDC isn't correct. You'll probably need that in the future!

If you check the FSM there is also a position where you are meant to set up the holder for the sensor - I can't remember the specs though... let me know if you need me to look that up.

Ya Mar · #5 05-06-2011, 11:57 AM

Army,

I can remove the tach amplifier bracket from the wagon, that's no problem. I'm also going to take the tachometer and the wiring from the wagon and install the clock from the 300D in it's place. I won't connect the clock but it will be a good space filler.

But regarding the tach sensor bracket attached the engine...I don't think there is enough clearance to get a wrench in there to loosen those 24mm bolts...and if I did, would coolant pour out? Why is that bracket important for the wagon? Is it doing more than just holding the tach sensor?

Can you send me some more info about where to find the bracket for my 300D non turbo? Since it's a euro import it doesn't have the bracket.

Thanks!

Stretch · #6 05-06-2011, 01:23 PM

Quote:

Originally Posted by Ya Mar

Army,

I can remove the tach amplifier bracket from the wagon, that's no problem. I'm also going to take the tachometer and the wiring from the wagon and install the clock from the 300D in it's place. I won't connect the clock but it will be a good space filler.

But regarding the tach sensor bracket attached the engine...I don't think there is enough clearance to get a wrench in there to loosen those 24mm bolts...and if I did, would coolant pour out? Why is that bracket important for the wagon? Is it doing more than just holding the tach sensor?

Can you send me some more info about where to find the bracket for my 300D non turbo? Since it's a euro import it doesn't have the bracket.

Thanks!

Ahhhh - you are still using the wagon then? It isn't going to be relegated to "parts wagon" then?

OK then the bracket on the engine is this one on my car:-

The only thread / bolt that you can see in this picture is the bit that holds the sensor.

In this picture you can see that the hole which this bolt threads through is oval:-

This oval slot is the adjustment for the sensor so that it detects the pulse at the right point. (I haven't worked out why this is important just yet - but it is in the FSM so I'm blindly following instructions at the moment)

Right back to the bracket. It does 2 things:-

1) It is a pointer for the position of the crankshaft - on the crankshaft balancer you'll see timing marks. The second link that I posted explains how to check that the pointer is in the correct position. (There is no adjustment on the bracket - so I don't quite see what you are meant to do if it doesn't line up properly)

2) It holds the tachometer sensor on that separate bit (the bolt etc in the first picture above)

If you undo the bolts that hold this bracket in place it is possible that you'll get engine oil coming out.

Do you not have a bracket on your normally aspirated OM617?

EDIT:-

If you are using both cars you are going to need a timing pointer on both vehicles - you can't check chain elongation without a pointer for starters...

Ya Mar · #7 05-07-2011, 02:30 PM

Hey Army,

I'm going to take a closer look on my non turbo 617, maybe the bracket is in a different location than on the wagon.

I'll keep you posted!

Thanks,

Ya Mar · #8 05-08-2011, 09:38 PM

Hey Army,

So I found the bracket on my non turbo 617!

I'm going to remove the tach sensor from the wagon, the amplifier and its bracket, and wiring harnesses.

How do I remove the wagons sensor from its bracket? Is it held in by a screw or just a rubber flange?

thanks

Stretch · #9 05-09-2011, 03:05 AM

Quote:

Originally Posted by Ya Mar

...
How do I remove the wagons sensor from its bracket? Is it held in by a screw or just a rubber flange?

thanks

Don't know! Stick your head down there I'm sure it will be apparent - it can't be that complicated. Here's a picture of the sensor I've gotten my hands on:-

Ya Mar · #10 05-10-2011, 12:01 AM

Hey Army,

Been working on the tachometer today and I have a couple questions you might have answers to.

1) The wires coming out of the back of the actual tachometer that goes in the dash cluster are black/green striped and black/red striped. However, out of the back of the Tach Amplifier the two wires are Brown and Black. Can I connect black/red striped wire to the black wire and the Black/Green striped wire to the brown wire or is there somewhere under the dash that they connect before going up to the tach...? I don't want to take all the wires apart under the dash if I don't need to.

2) When i removed the clock from and replaced it with the tach, I plugged the red power wire that was in the clock into the tach and now the clock in the tach works. So I know I have power to the clock at least...

3) I couldn't for the life of me remove the sensor, it seems there is a bolt holding it in place. The picture you attached shows the hole for a bolt, but I'm not sure what mm it is. Maybe 6, or 7? Not quite sure. Do you know? It's really hard to get in there due to clearances. And I broke the wire off the back of the sensor....woops. I'm hoping I can repair it if I can remove it from the wagon but I'm really not sure if I'll be able to.

4) Any idea where I could order a tach sensor? Maybe fastlane parts. If I can't get the wagons off then I'll probably have to order a new one.

Thanks for all your help! I really appreciate it.

Stretch · #11 05-10-2011, 03:15 AM

OK I'll do my best to give some answers - but remember I've not actually got mine fitted yet - the engine is still out for starters (and I can't put that in until I've finished my gearbox rebuild...)

Anyway question 1.

Don't get too worried about the colours of the wires just yet. Take a look inside the tach amp and you'll see that there are several pins that aren't connected to anything. I don't think it is rocket science - be careful - but I'm sure you can figure it out. If I remember correctly you've only got to make 3 or 4 connections. There's something like power in, signal out, signal in and may be a ground?

As far as I can make out on my W123.130 chassis you'll need to run at least one new wire from the tach amp to the tachometer in the dash.

Question 2

Yep the power for the clock seems to be a wire that is common to all W123 wiring looms. If you put the clock back into your wagon then you should be able to get it to work there too.

Question 3 and 4

I've never removed the crankshaft sensor. I bought mine off ebay - someone else removed it for me. I'm surprised to hear you're having trouble though. You could get more access my removing the radiator fan shroud (2 clips at the top).

Like I said I bought my sensor off ebay. I guess the dealer stocks new ones. Try Fastlane? Otherwise in the great US of A I'd be off to one of those pick and pulls everyone talks about. (Although if you have to remove it yourself you could be back to square one again).

toomany MBZ · #12 05-10-2011, 03:22 AM

If this is for your 85's, the cars that have tachs use a different pick up point.

However, if you use an 83 or earlier tach, the set up you refer to will work.

How many prongs on the back of the tach? One with two prongs is what you need for the early tach wiring.

I would think you can get the sensor from Fastlane.

Stretch · #13 05-10-2011, 03:34 AM

Phew I'm glad a voice of experience has joined in - thanks toomany!

toomany MBZ · #14 05-10-2011, 04:16 AM

lol, You're welcome.

MB changed things in 1984, my CD does not have a tach amp at the other end of that sensor wire, (my SD does) but it does have the sensor wire. It's a diagnostic port for the mechanics. At times they need to know the rpm when working under hood.

The signal comes from the transmission, no amplification necessary. The 85's were even a bit different, I think, but those two years had a tach with three prongs on the back of the cluster.

As to the wiring, brown is ground, that's all I understand about that part.

Stretch · #15 05-10-2011, 04:23 AM

Quote:

Originally Posted by toomany MBZ

lol, You're welcome.

MB changed things in 1984, my CD does not have a tach amp at the other end of that sensor wire, (my SD does) but it does have the sensor wire. It's a diagnostic port for the mechanics. At times they need to know the rpm when working under hood.

The signal comes from the transmission, no amplification necessary. The 85's were even a bit different, I think, but those two years had a tach with three prongs on the back of the cluster.

As to the wiring, brown is ground, that's all I understand about that part.

Oh right - thanks for that information - My non turbo OM617 uses a mechanical linkage and I assume a mechanical external tachometer from the oil pump shaft that runs down from the intermediate shaft (running between the timing device and the injector pump). I've never really considered what you'd do with an OM617 turbo until now. (It doesn't have that shaft as the oil pump is driven via chain on the crank as I'm sure you know)