Pictorial - Easy Tachometer Fix - PeachParts Mercedes-Benz Forum

micklongley · #1 08-02-2007, 09:39 PM

So I am going through each little problem on our new 1980 Mercedes 300SD and I came across some helpful information from this board regarding a quick fix for the tachometer. Mine was not working so I thought I would attempt to fix it. Thankfully it was easier than I thought, but like most things automotive, pictures are worth a lot more than descriptions.

- Locate the tachometer sender (???) on the drivers side fenderwell.

- Unscrew the module from the base unit, make sure your electrical contacts are shiny and in good shape.

- Pull the module from the plastic cap to expose the white silicone material. Find an old flat cigarette butt on the ground and put it between the sender module and the black plastic cap. Reassemble and screw the module back onto the base unit.

- Much to my amazement, this simple fix worked brilliantly, and I hope this pictorial will help someone fix their tach next time there is an idle 5 minutes.

Obviously this will only work in the cases where you need a little more spring in your sender. Your gauge, cabling, etc. need to be good so if this doesn't work for you then you have a more serious problem than I did.

Good luck!
Mick

JimmyL · #2 08-02-2007, 10:06 PM

I've never owned a Mercedes with a working tach. Unfortunately, the NA 300TD, the NA 300D and the two 240's never had one.
The wagon tach is inop, but alas, it is an '85 model, with all their weirdness....

pawoSD · #3 08-02-2007, 10:23 PM

Our 300D, and my '82 300SD have never had working ones....I have a known good amp I may try in the 300D, but on mine I think the problem is the crankshaft sensor....since I have replaced the amp and gauge pod with 0 results (except my clock works now)

My dad's has had a perfectly working tach since the beginning. Oh well.

Biodiesel300TD · #4 08-03-2007, 12:07 AM

Mine works most of the time. It gets a little finakey once in a while. Another thing to try is to pinch the female plugs in the base of the sensor just a little so they squeeze tighter on the pins.

I like the look of that tach better than the 123 tach!

toomany MBZ · #5 08-03-2007, 06:03 AM

That fix worked on my '82 for a while. Replaced the amp in the SD, so far so good. The CD does not have the amp, been working since I've owned it.

NC Benz · #6 08-03-2007, 10:55 AM

Quote:

Originally Posted by micklongley

So I am going through each little problem on our new 1980 Mercedes 300SD and I came across some helpful information from this board regarding a quick fix for the tachometer. Mine was not working so I thought I would attempt to fix it. Thankfully it was easier than I thought, but like most things automotive, pictures are worth a lot more than descriptions.

- Locate the tachometer sender (???) on the drivers side fenderwell.

- Unscrew the module from the base unit, make sure your electrical contacts are shiny and in good shape.

- Pull the module from the plastic cap to expose the white silicone material. Find an old flat cigarette butt on the ground and put it between the sender module and the black plastic cap. Reassemble and screw the module back onto the base unit.

- Much to my amazement, this simple fix worked brilliantly, and I hope this pictorial will help someone fix their tach next time there is an idle 5 minutes.

Obviously this will only work in the cases where you need a little more spring in your sender. Your gauge, cabling, etc. need to be good so if this doesn't work for you then you have a more serious problem than I did.

Good luck!
Mick

Whats the 3 where the ZERO is supposed to be??

Shawn D. · #7 08-03-2007, 10:57 AM

Quote:

Originally Posted by NC Benz

Whats the 3 where the ZERO is supposed to be??

That means the tachometer doesn't start to register until 300 RPM. There are also speedometers that have the starting mark at 5 MPH.

winmutt · #8 08-03-2007, 01:44 PM

Of course this doesnt work for us 85ers

Lonesome · #9 08-03-2007, 02:31 PM

Hey, Now I have a working tach! Thanks.

seabrighter · #10 08-15-2007, 12:54 AM

I just bought an '83 300D and I plan on combing through this forum to get lots of advice! But on this subject...

Both my tachometer and my fuel gauge are finicky. The tachometer sometimes dies while driving, then picks back up again when it feels like it. The fuel gauge tends to bounce around a lot and sometimes goes flat as well. Think I need to replace the gauges themselves?

Douglas.Sherida · #11 08-15-2007, 06:13 AM

Its unlikely to be the gauges themselves.

Is the temperature gauge effected at the same time as fuel? They run on the same ground.

seabrighter · #12 08-15-2007, 04:02 PM

No, temp gauge reads fine as far as I've seen. Just the fuel and tach gauges are kooky. I'm going to look into that tach amp fix, but I have no ideas on the fuel gauge. That's the one I'm most concerned about

#13 08-15-2007, 04:24 PM

Quote:

Originally Posted by seabrighter

No, temp gauge reads fine as far as I've seen. Just the fuel and tach gauges are kooky. I'm going to look into that tach amp fix, but I have no ideas on the fuel gauge. That's the one I'm most concerned about

The fuel gauge issue is more likely to be the sending unit in the fuel tank, you can (carefully) disassemble it and clean it. If you search, you will find some detailed posts. You can access it by removing the first aid box on the rear deck.