I'm working on my '75 300D which recently stopped starting. It seemed like a battery drain problem, but after a new battery (it was hight time) and a new voltage regulator, I've still got nothing.

When turning the key to the glow position, instead of the normal buzzing noise sounding it is a very high pitched squealing buzz. When I turn the key to hit the starter, I hear clicking from the ignition switch but the engine does not turn at all.

I tried to jump it with another car, and the engine turned once or twice but then stopped doing that.

Now I'm looking at the starter motor and solenoid. I haven't done readings with a voltmeter yet, but if the solenoid is at fault, is it possible to just remove and replace the solenoid, or do I have to get a whole new starter? The same goes for the braided wire from the starter to the solenoid, is this replaceable as well?

__________________
Currently restoring:
1975 300D

There's a bit too much information in this thread

PeachPartsWiki: Starter Motor Rebuild

for your problem but it should show you how most of it goes together.

As you don't have a turbo I'd just remove the whole starter motor and see what's up with it.

(You won't have the trouble as shown here

PeachPartsWiki: Starter Motor Replacement)

__________________
1992 W201 190E 1.8 171,000 km - Daily driver
1981 W123 300D ~ 100,000 miles / 160,000 km - project car stripped to the bone
1965 Land Rover Series 2a Station Wagon CIS recovery therapy!
1961 Volvo PV544 Bare metal rat rod-ish thing

I'm here to chat about cars and to help others - I'm not here "to always be right" like an internet warrior



Don't leave that there - I'll take it to bits!

Before removing the starter, check your voltage at the solenoid and starter.

Also check chassis ground to engine.

Might be high resistance in the cables or a corroded connection or ground.

Jim

__________________
14 E250 BlueTEC black. 45k miles
95 E320 Cabriolet Emerald green 66k miles
94 E320 Cabriolet Emerald green 152k miles
85 300TD 4 spd man, euro bumpers and lights, 15" Pentas dark blue 274k miles

Thanks, I don't know how I missed that, it's exactly what I needed. Time to get to work!

__________________
Currently restoring:
1975 300D

If you understand electrickery don't disregard Jim's advice - see post #3

__________________
1992 W201 190E 1.8 171,000 km - Daily driver
1981 W123 300D ~ 100,000 miles / 160,000 km - project car stripped to the bone
1965 Land Rover Series 2a Station Wagon CIS recovery therapy!
1961 Volvo PV544 Bare metal rat rod-ish thing

I'm here to chat about cars and to help others - I'm not here "to always be right" like an internet warrior



Don't leave that there - I'll take it to bits!

it has a key start? or a knob that you pull out?
Starters on these get a hammering if the glow plugs aren't working .I have seen the filed coils lead melted off inside them because of this.

Because the engine will crank indicates that the remote starter is working but something is wrong. If this is a aftermarket unit, check all in line fuses near the unit wherever they installed it. If possible, get an installation instruction sheet from the manufacture and retrace all connections.

Hope this will help you!!

I looked at the starter and cleaned up the connections to ground and back to the battery. The multimeter shows something between 10.5-11 volts between the posts on the starter. If I short Now I'm thinking about some other things I've noticed since this no-start problem started.

The battery reads 12.4 V between the posts on the multimeter.

The door locks don't work systematically as they did before. Each door must be opened manually; turning the key in the driver's side door does nothing to the other locks.

I recently took the radio out to replace it, so right now there's nothing attached to the connections that would go into the radio.

The instrument panel is also disconnected, but I don't think that should affect anything.

The most striking thing are the noises coming out of the instruments when the key is turned. They are very unstable and high-pitched, but different for each position (I'm going to take a video of this later today).

Based on what I've seen, I think power is getting to the starter/solenoid (hot from the battery), but whatever is supposed to happen by turning the key isn't happening. The connections on the battery are solid (checked those today). What would be the next thing to look at? Ignition switch? Some sort of weird battery drain issue?

Also, just to satisfy my own curiosity, is there something I can do to test if the process that is supposed to happen when the key is in the glow position is functioning? I saw someone test glowplugs with a test light but I'm not exactly sure how that goes?

__________________
Currently restoring:
1975 300D

Here's a video of me showing what's happening at the different key positions. Also, the starter motor and solenoid do nothing at any of these positions.
1975 Mercedes 300D w115 No-Start Issue - YouTube

__________________
Currently restoring:
1975 300D

The starter voltage sounds a bit low.
When you start cranking, I bet it goes waaaay lower.

On a no load condition, you should be seeing battery voltage at the starter.
Do a check at the end of the pos lead at the starter and ground back to battery and also check the voltage using the starter case as the ground.

Jim

__________________
14 E250 BlueTEC black. 45k miles
95 E320 Cabriolet Emerald green 66k miles
94 E320 Cabriolet Emerald green 152k miles
85 300TD 4 spd man, euro bumpers and lights, 15" Pentas dark blue 274k miles

Don't worry about the door locks if they are stock. They are air operated and the vacuum has likely just drained down. They will be OK if you can ever get the engine to start.

Find the flat wire that connects the engine block to the firewall or frame. These will break down internally and cause all kinds of electrical headaches. They are also cheap. I always go for the cheap stuff first.

You might also replace the wire from the started to the (+) side of the battery. Also cheap and can break down internally and drive you nuts.

Also the radio being out has nothing to do with this unless your hot wire is touching a ground. But then all that would take place is a blown fuse, so nothing to worry about there, either.

I replaced both battery cables, put still power isn't getting from the first post on the solenoid (where the positive battery cable connects) to the next post. I found a cheap ignition switch and replaced that but the problem still persists.

Is this enough evidence to just replace the starter motor? I'm not looking forward to taking it out and putting a new one in..

__________________
Currently restoring:
1975 300D