1984 300SD - Neutral Safety Switch ?? - PeachParts Mercedes-Benz Forum

Gregory · #1 04-28-2014, 11:17 AM

The road trip was going well, the car running pretty good for retarded IP timing. On the last leg of my road trip yesterday I stopped at a rest area just east of Boise. When I went to re-start the car, no starter. The indicators came on, the plugs glowed, but just one little click at the crank position of the key.

I put it in neutral, the same. Jiggled the shifter several times, nada. Same for the key.

A guy came over and offered to help. He put a long jumper wire from the positive battery terminal to the starter solenoid and it cranked and started right up.

I looked through the forum this morning for the NSS info then went out to test the car. It immediately cranked. After letting the plugs glow, it started right up. I set the parking brake and put it in reverse, got out and checked the reverse lights, they were on.

The body has 225,000 on it.
Could the key switch be worn out?

Do NSS ever intermittently fail? Do they always fail to completely dead?

Any other ideas to what might cause this problem?

I hesitate to drive the car to anywhere and turn it off. I will put a long heavy wire in the trunk just in case, but I need to figure this out and fix this unreliability.

EDIT ::: New shifter bushings installed 2 weeks ago. They were the two bushings under the car, in the tranny tunnel, exposed to the elements.

mach4 · #2 04-28-2014, 11:28 AM

Might just be adjustment. Here's how to check.

Put your foot firmly on the Brake. Put the car in L and turn the key to the start position and Hold it in the start position. Then move move the shifter deliberately forward. When it gets in the neighborhood of N it should start cranking and as you continue to move it forward it should stop cranking and then start cranking again in the vicinity of P. If it does this, then your switch is very likely fine and you just need to adjust the NSS. You might possibly need to replace the linkage bushings as these can cause the problem if they wear or fall out.

Getting the proper adjustment can be tricky. In mine, P always works, but N can be hit or miss depending on the position of the shifter in the detent.

Gregory · #3 04-28-2014, 01:45 PM

Quote:

Originally Posted by mach4

Might just be adjustment. Here's how to check.

Put your foot firmly on the Brake. Put the car in L and turn the key to the start position and Hold it in the start position. Then move move the shifter deliberately forward. When it gets in the neighborhood of N it should start cranking and as you continue to move it forward it should stop cranking and then start cranking again in the vicinity of P. If it does this, then your switch is very likely fine and you just need to adjust the NSS. You might possibly need to replace the linkage bushings as these can cause the problem if they wear or fall out.

Getting the proper adjustment can be tricky. In mine, P always works, but N can be hit or miss depending on the position of the shifter in the detent.

I did this test as you suggested. It cranks as the shifter passes through N and at P.

I drove it around town on errands, it started fine today five times with no trouble.

Next time it fails, I'll be wearing a suit & tie for sure, lol.

mach4 · #4 04-28-2014, 02:06 PM

I think you'll be just fine. The switches are pretty much binary - they either work or they don't. Not unheard of to be flakey, but not typical.