New Owner: 1979 Mercedes Benz 300SD (80k miles) need some help

[alansupra94]

Hello

I have a 1979 Mercedes 300SD with 80k miles. Odometer works and service records from start to now. Only issues are RPM gauge works sporadically and dash lights are off (probably the dimmer)

A few questions:
1. What wheels are those?
2. Where could I find touch up paint or paint in that color?
3. The windows seem a bit "weak". Is there a solution for that?
4. How do the power locks function? With the key in the door?
5. What is the stock speakers and headunit for this car? (It has blankput headunit and speakers. The previous owner paid a shop to install it)
I noticed right away that the car's vacuum system has definitely be re-done and the mercedes benz specialty shop installed several one way vacuum valves (which is smart).
6. Where are common rust spots?

[spock505]

The wheels look to be off a later W210 series, paint code can be found on tab under hood, mine is two letters, three numbers.

Sorry i can't help on the other bits.

[Alec300SD]

Erratic tach - usually poor connection at the tach amplifier under the hood.
Either the female pins on the plug (aka diagnostic port) have spread open too much or there is a cold solder break in the amplifier itself.

The plug can be disassembled and the female pins can be lightly closed.
The circuit board can be re-soldered - but you have to chip away the silicone anti-vibration filler first.
I disassembled my plug and tach amplifier on my 83 300SD and replaced the defective tach amplifier with a good used unit from the local Pick-n-Pull.

Dash lights - check your fuses. Spinning them in place or removing and reinserting can often re-establish a balky circuit.

2). Paint - shoot an email to the classic center with your VIN and request a copy of your build sheet.
They are an invaluable resource and may be able to supply the touch up paint (as well as other parts you made need going forward).

3). Windows weak - regulator arms tend to bend due over time (especially driver's window) due to lack of an auto stop switch when window is closed.
Also may need to lubricate window guides and replace any worn pieces.

4). Door locks - vacuum operated. Master switch is in the driver's door.
Driver's door must be closed - central locking system operated by key in door or by door lock button inside the car.

5) Radio and speakers - Blaupunkt is an original supplier. AKAIK build sheet should list the unit the car came with originally.

6) Rust points - Under battery tray, lower front and rear windshields, rocker panels, wheel arches, hood hinge pockets, lower door seams.

[alansupra94]

Any help is appreciated spock505. I am definitely going to check the paint code.

Thanks Alec300SD. I assume the pictures you attached is the diagnostic port for the rpm. I m going to take a look. It was working intermittently. I will send a email to that link with the vin and see what they find as well.

For the windows, can I unbend the regulator arms? Or once they are bent, they are crap?

Checked rust spots and nothing there. I'm also pretty sure they didn't have CD players in 1979 so this CD player is aftermarket haha. I might replace it with something but not sure yet.

[tyl604]

Yes, you can straighten out the arms on the regulator. I have done that on my 81 300SD; however, it is more likely that you just need to replace the sliding jaw if the window will go up but will not go down. Lots of threads on the forum about how to do it.

[alansupra94]

The window goes down easily. It was going up I had to click the window down and then up, down then up, down then up a few times to get it to the top

[Zacharias]

The wheels could be from a w210 but that style was also sold as knockoffs by the Tire Rack, etc. When you have a wheel off, look on the inside and if it's OE you will likely see either a manufacturer name such as Ronal and/or a Mercedes star stamped into it. If nothing then it's a copy. Only difference is that the copies are usually just a little bit different than the OE, in some way.

I owned a w116 and in my opinion, the very worst rust spot was by the driver's left foot, behind the dead pedal. There is a cavity behind the lower section of of the front fender, blank space between the fender and the body tub, that can fill up with debris and trap water. Your car should have a plastic trim piece covering that, at the rear of the wheel well. If you find only metal there, then your car has been repaired there already. I find that bodyshops inevitably don't bother to reinstall the trim and put a piece of metal over the area instead. If you want to really know what is going on rust wise, pulling that plastic panel (two or three small bolt head screws IIRC) and looking inside will tell. If you are golden there, you should be elsewhere as well.

Also be wary of water intrusion from the windshield seal. This runs down and gets into the factory sound insulation on the floor If it gets bad, or if you have water coming in from another source, it can collect on the rear floor and cause serious rot. Many Mercedes of that vintage rotted as badly from the inside out, as vice versa.

Not to rain on your parade, but a rust-free w116 body car is very, very rare now. Even cars from "dry" states often show some rot. If you are serious, you need to examine the car very carefully.

If it's rot free, you have a real gem there and please treat it accordingly .

[tyl604]

Your window problem sounds more like lack of use problem; ie rust on the pins. Take the up/down switch out and steel wool the pins. That might do it. They are pretty indestructible and can even be easily rebuilt. Same with seat controls on the door card. It is a really great and solid and overengineered vehicle. MB did it right in those days.

[w123fanman]

With the windows, I cannot stress enough that you have to keep the window tracks clean and free of debris and make sure everything is sliding properly. Many people see the regulator is bent and throw in a new one and get pissy when it fails 3 months later. The regulators will warp because of the lack of stop switches but more often it is due to lack of proper lubrication and other parts in the system that have to be cleaned, lubricated, or replaced. My brother has a set of Chinese-made aftermarket regulators in his front doors on his W116 and they have performed flawlessly because he took his time to get the windows moving properly before installing them. That being said I have seen brand new OEM regulators that are already starting to warp when they are still sitting in their packaging.

[alansupra94]

Originally Posted by tyl604

Your window problem sounds more like lack of use problem; ie rust on the pins. Take the up/down switch out and steel wool the pins. That might do it. They are pretty indestructible and can even be easily rebuilt. Same with seat controls on the door card. It is a really great and solid and overengineered vehicle. MB did it right in those days.

I will definitely try that out! Thanks!

[alansupra94]

Originally Posted by w123fanman

With the windows, I cannot stress enough that you have to keep the window tracks clean and free of debris and make sure everything is sliding properly. Many people see the regulator is bent and throw in a new one and get pissy when it fails 3 months later. The regulators will warp because of the lack of stop switches but more often it is due to lack of proper lubrication and other parts in the system that have to be cleaned, lubricated, or replaced. My brother has a set of Chinese-made aftermarket regulators in his front doors on his W116 and they have performed flawlessly because he took his time to get the windows moving properly before installing them. That being said I have seen brand new OEM regulators that are already starting to warp when they are still sitting in their packaging.

I believe that this is the issue. My windows are like this and the sunroof is stuck close at this point. What kind of lube do I use?

[Zacharias]

Originally Posted by alansupra94

I believe that this is the issue. My windows are like this and the sunroof is stuck close at this point. What kind of lube do I use?

The sunroof may not be a lubrication issue. Depends.

Do you hear any attempt at movement when you press the button? If not, you may have a bad switch.

If you hear the mechanism trying to move the roof panel, have someone give the panel a good woof on or two times from the outside as you press the switch. If it hasn't been used for a long time, that might free it up.

Use of the correct sunroof lube is critical on these cars. The roof panel is heavy and runs on nylon 'skis' on a metal runner. Use of any lubricant that attracts dust and dirt will gum it up nicely. If it's very slow (usually more so on closing), that is normally the cause. Or it might just be dry from sitting with no lube at all.