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SuperModerator
1986/1990 W126
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17,649 Posts
Discussion Starter · #1 ·
Hello people. I replaced my cluster recently and the economy gauge doesnt work properly. I know its just the gauge cos i have another dial that works fine nice and smooth (the rheostat thing doesnt work on that one though).

Its not the end of the world and i'm happy to ignore it really, but if anyone has any tips on how to get it to work normally? Or even perhaps if its easy to transfer the economy gauge unit from one dial to another?

The connection for it looked a little like it had some sort of white flaky almost corrosion on the brassy material. I've sprayed it a little with silicone in case that works but i have to paint my needles before i replace the cluster..
Thanks :)
 

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SuperModerator
1986/1990 W126
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17,649 Posts
Discussion Starter · #2 ·
Ps what it does is just sit around the middle of its arc, so it doesnt settle to the black side at idle. It moves around a bit apart from that but only in the other directio ie red, so its like its sticky.
 

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'73 450SL, '83 300CD, '01 E320 4matic
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2,449 Posts
You should just switch the working one into the cluster you're trying to use. The four gauges come out as a group.
 

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SuperModerator
1986/1990 W126
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Discussion Starter · #4 ·
Lose the dash lights that way though. Perhaps changing the rheostat would be the answer, but i'm scared of mucking up another cluster..
 

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Premium Member
2012 CL550 4MATIC Coupe - RIP
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10,014 Posts
The Economy gauge is a VACUUM system. First are you sure it's connected properly? Are you sure there are NO KINKS? That is a biggie. Is it square on the nipple? I tapped into mine for my Euro Headlight Height Adjusters and replaced a section of it with softline instead of hardline and it would kink occasionally if I R&R'ed it.

It is fed by a hardline from the engine bay by the Brake booster. There is a mail vacuum line from the engine that goes into that vacuum splitter by the secondary firewall.

Check that.
 

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1986/1990 W126
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17,649 Posts
Discussion Starter · #6 ·
Yup the vacuum seems fine. If i plug in the other one i've got, it works perfectly, so its definitely inside the gauge unit itself.
 

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'73 450SL, '83 300CD, '01 E320 4matic
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2,449 Posts
Lose the dash lights that way though. Perhaps changing the rheostat would be the answer, but i'm scared of mucking up another cluster..
It seems the simple fix would be to either move the working rheostat to the otherwise working cluster, or move the working gauge group (fuel, temp, oil, economy) to the cluster with the working rheostat.

You're going to have to take one apart either way.
 

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Premium Member
2012 CL550 4MATIC Coupe - RIP
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10,014 Posts
Okay, so swap out the 4-way unit. It's very easy.

1. Disconn the temp gauge and the wires connecting.
2. Unscrew the center speedo.
3. Unscrew the left cluster which will be on the right side.
4. Replace and reverse to install...

Easy.. 5 min.
 

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1986/1990 W126
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17,649 Posts
Discussion Starter · #9 ·
Yup changing the dials is easy & i've got 3 different left dials but i havent got one that everything works on, so i'd better just change the rheostat bit over. Or ignore the econ gauge, lol.
 

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1986/1990 W126
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Discussion Starter · #10 ·
Ah the rheostat just pops off! Wish i'd realised that. If only all things were that simple. I thought i needed to mess about with a soldering iron.. :)
 

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2001 ML430, 1983 300SD, 2008 GL450
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909 Posts
There is a note in the FSM about any oil in the line ruining the economy gauge and if I am reading it correctly the part either works or it doesn't. If it doesn't it is implied that it is not repareable. Replacement only.
 
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