123 Instrument Cluster Troubles
 

Unfortunately, I have found that the instrument cluster/gauges is one of those areas better left alone. I have a few problems which I can't figure out:
(car is 83 300cdt)
1. My instrument cluster does not pull out far enough for me to detach the oil line and speedo cable. Why? The Haynes manual doesn't mention any difficulty in getting this clearance.
2. My odometer is broken but my speedo works. Is the speedo cable at fault or is the speedometer itself at fault?
3. My tachometer reads maybe 300 rpms low after having been slightly disrupted while repainting gauges. Does the tach have a mechanical control or electric or is the gauge itself at fault?

The clear front panel of the cluster is also broken off. Finally, my fuel gauge reads erratically despite me having checked the fuel tank sending unit and finding it OK.
Would my best recourse be to just buy a used panel and gauges off ebay with all these troubles? Or if someone has extras, let me know. Thanks.

I have had the instrument cluster out of our 300D a few times.

Although I have never had to do it, apparently the shop procedure says that the speedo cable should first be disconnected at the bottom end.

In my case, there is just enough slack that I can get my hand in and unscrew the speedo cable. Then the rest is easy.

Somwhere in the Diesel Forum, there is/was a very good set of pictures showing how to get at the cluster out in order to upgrade the lighting. Couldn't find it. Did find this:

"Removing the instrument cluster is a piece of cake.
There are no clips holding the cluster inplace, just good fit.
The removal tool is just two lengths of 0.045 inch wire with a small hook at the end.
These are inserted at the top, turned 90 degrees and pull.
I've always used my fingers appling pressure at the top and pulling.
The speedometer cable does not need to be disconnected from the transmission.
You will have to pull some slack to get the cluster out far enough to reach the speedometer cable at the speedometer.
There is an amphenol plug and the econometer hose to be unplugged.
Ease the cluster out and past the steering wheel and that's it.
As for the bulbs, there is a red capped bulb at the lower row of the cluster.
This ain't no bulb but a fuse.
I modified my holder by solderring a twin lead to the sides of the fuse holder and routing the wire back and behind the insulation under the floor mat and soldered a mini-fuse at the end.
Now if the fuse should fail I won't have to remove the instrument cluster to replace it, just lift the floor padding.
Happy Trails Beep Beep from The Spiderman in Houston!!!"


Lots of stuff if you do a search - Guy in Montreal explains how to fix it. - Gears slipping, I think.

Sounds like a used unit would be agood idea! Merceses salvage yards usuyaly have them - Why not post on this site under parts - lots of W123,s being dismantled.

Graham

Thanks for the advice. I actually found the exact cluster I needed on ebay for a very decent price (so far anyways). The speedo cable is attached to the tranny where? Also, when you say gears slipping do you mean the tranny gears?

All of this has been discussed in the forum. Do a search and you will be enlightened.

To remove the instrument panel. First unclip the speedometer cable from the support bracket that is on the firewall about 1/2 way along the entire speedometer cable. This bracket is just below the oil filter, you will see the speedometer cable attached to it. detaching the cable on this bracket will allow you to pull the cluster enough to detach the speedo cable. Get a wire coat hanger. Cut the wire about 12 inches long. On the end of the wire make a sharp 90 turn out of about 1/4 inches of the wire. Leave about 6-7 inches of the wire straight ( from the bent tip ). fold the rest of the wire into a handle of sorts so you can grab the wire to pull it. Or buy these.

http://www.samstagsales.com/SirTool/stm_0060-l.htm

Place the wire between the dash ( hook up) and the instrument panel and push it in about 3 inches. rotate the wire 90 degrees so the hook will grab the rear of the instrument panel and pull it out. Unbolt the speedo cable, Unbolt the oil line, the electrical wires and pull the entire assembly. Now it is out an can be worked on.

CAUTION when connecting a disconnecting the cable from the support bracket be careful not to break any of the vacuum hoses off the main line. the main line is the one going from the vacuum pump to the brake booster. their are 2 small feed lines coming off this big line. theose 2 small lines can easily be broken if you not carefull. it is old and brittle. Don't ask how I know but the new line is $45. I had to buy 2 of them. You cannot reglue them back on.

Odometer. The in the speedometer that drive the odometers are slipping on the shaft and must be re glued.

http://207.210.95.34/~boostd/

Tach. Sounds like you buggered it up. It is a sensitive instrument. either find another or have it repaired.

Clear front panel. super glue it.
or buy a used one.

Fuel gauge. More than likely your sending unit needs to be cleaned.
Use carb cleaner to really clean it after disassembly.

http://207.210.95.34/~boostd/Sender/

Dave

Thanks for the advice. Already cleaned the fuel level sending unit completely. The wires the float rides on and all that were all good to go, though lots of crud in there. Didn't really help.

I've pulled mine and spent innumerable hours completely rebuilding it, resoldered fried leads on the board, replacing fried parts, and etc.

Do yourself a favor and buy a better one from a salvage yard.