1984 300TD starting issue
 

398K miles, having issue with ignition switch I think, first time last week starter did not engage when key turned, found junction box in front of battery & starter engaged when "jumped", cleaned all terminals & car started normally 1/2 dozen times then needed to be "jumped" again, NSS seems to not be involved as starter not engaging after placing in neutral, switch doesn't feel bad but HVAC engagement has always needed slight backwards turn to engage, should I replace switch?

Not getting the part highlighted in red. The Neutral Safety Switch and or the shifter bushings can cause the no cranking issue.

When the NSS is going bad sometimes putting it in neutral will allow it to start sometimes not.

This thread shows away to bypass the NSS. If your starter always cranks after that bypass you it is reasonable the NSS and or the shifter bushings are the cause.

The Steering Column Lock is in between the Key Tumbler and the Ignition Switch. I had parts inside of my Steering Column Lock break (people have said that the Steering Column Lock is no longer available; hope that changes).

While it was working I found that on the Ignition Switch I had a contact on one side entirely burned off but the arm itself was still making contact so it was still working.

In my case the new Steering Column Lock came with a new Ignition Switch and a new Vacuum Shutoff Valve.

The backup up lights also go through the Neutral Safety Switch.

To remove the NSS electrical connector you need to move back a plastic tab (if memory serves) and the white plastic part can be rotated.

The NSS sounds like the most likely culprit, other than the key switch. Not sure why you conclude "seems OK" just because it won't start in both P or N. Usually the problem is in the shift linkage, not the NSS. I still got a few new NSS I bought clearance years ago and was selling cheap on ebay. Made in India, so maybe not reliable. Also, the long oval connector of later transmissions, not the round type in photo of post #2 which I vaguely recall the 1984 transmissions use. I should have a round one in my box of parts from a stripped 1983 300D, but not tested.

Note there is exterior shift bushings on the exterior and ones inside below the Shifter. I had one of the inside and 2 of the outside shifter bushings fail.

Yeah I recall when my NSS went out it didn’t matter if it was in park or neutral. I think the solenoid current is carried through the switch regardless of the park or neutral position. It gets interrupted in a spot common to both.

I recall measuring the current in the NSS and it was actually pretty high. It goes directly to the solenoid and that has a hefty draw.

I bought a new NSS from some no name cheapo brand and it failed in two months like this.

I have read elsewhere on this forum that if the NSS has failed the starter will still engage in neutral. Is this not correct? The ignition switch has had an issue,after starting,for years, I have to turn the key counterclockwise slightly to engage the HVAC, so the switch is worn in that respect, I don't think shifter bushings are worn. After I jump at the box the starter engages normally a few times which indicates corrosion on an electric connection to me

To clarify if the shifter bushings are good and your NSS is not starting in park it has still failed to work as it is supposed to.

It is just that people have noted that when the NSS is not working/falied in Park it will sometimes still work in Neutral. If it starts in Neutral only you have to decide if the safety part of Neutral Safety Switch apples or not.

Note there is a learning curve. 3 weeks after I got my Mercedes I had the Car Towed because I thought it would not start (and it had to happen at night and in the rain). In fact I left in in Drive; which was why it would not start.

I was used to vehicles that had an ignition switch/steering column lockout that kept you from turning the key when it was in anything but park or neutral.

I was planning on replacing the NSS but today the starter failed too engage even when jumped at the junction box so I assume the problem has been the starter all along, Searching for replacement which I think should be a Bosch reman but any input on other brands?

From what other members have said it is either Bosch reman or if you have a local shop rebuild it and replace any defective parts with Bosch parts.

Mine would not crank. Using a 2x long enough to go down to the starter housing (at the back of the intake manifold) and long enough so that you could give it some good smacks with a hammer got it to work for awhile and then nothing.

That Starter Bolts can be hard to remove and mine were.

When I took the starter apart I found my Brushes were worn down to like 1/4 inch. I ordered new brushes (with the metal tab and holes for screws on them) and a new Bosch Solenoid (it has an update that looks slightly different).

One of the Members said that if the Brushes are worn it can mimic a bad solenoid. I decided to see if that was true or not and re-used the old solenoid and it has been a few years with no issues. All mine needed was some new brushes and the armature sanded down to make it faction normal.

Any advice on removing those bolts? I’ve been underneath & having hard time getting enough leverage on the wrench

People don't like my solution. I gave up on it and removed what is needed for me to take a hole saw and drill holes in the fire wall to get as straight as possible shot at the bolt heads. But, I have kind of a rust bucket.

You have to measuer as best you can and get a small drill bit, drill a hole and stick a wire through it and see where it comes out till you aproximate where you want to use the whole saw. After that if you altercation you use a rotary file (one for use on steel).

Links to how others did it. What I remember from it is some have used a long chain of extensions (1/2") far back enough that a breaker bar can be used and even with a pipe extension. I think I also read mention of at least 1 U-joint.

DIY Links by Parts Category - PeachParts Mercedes-Benz Forum

Post number 15 has a pic and gives an idea where I drilled out the fire wall. Post 23 has something I did to the bolts before installing them.
http://www.peachparts.com/shopforum/diesel-discussion/294461-stripped-hex-om617-starter-bolts-igotit.html

The fire wall holes helped later as I to again pull the starter of to remove the Transmission.

I have always used a 3/8" metric allen socket w/ adapter to 1/2" extensions (2) so I can swing the socket wrench at the aft end of the transmission. One guy posted how he bent an allen wrench so he could swing it in the engine bay. For those who don't know, the allen head is on the aft side, so you can see the bolt head from the engine bay, but no normal tool can reach it from that side. The starter is bolted to the engine (actually the adapter plate), which is nice if you want to turn over an engine outside the car without the transmission.

Before faulting the starter, insure the solenoid is providing 12 V to the motor. If not, I think the solenoid can be removed with the starter mounted to the engine. Don't fault the starter motor unless you measure >10 VDC from its case to the big supply stud while trying to crank. Insure the ground connection is solid, which is from transmission to frame on driver's side (down low) in my 1985 300D. That was bad for me once, as I saw smoke from the speedo cable once while cranking. Sanding and silicone grease fixed that.

Just what happened to me. I had the Starter off and the solenoid screws are Phillip's heads. I used an hand impact and the heads of all of them stripped which had me drill out the screws. Others seem to frequently have the same issue.

I’ve read the write up elsewhere on this sight advising use of 20” 1/2” extension with U joint but I can’t get a straight shot to connect to the cut off section of Allen key, transmission dipstick tube is in the way, I have removed the bolt that holds the tube to head but it’s still blocking the tool