No Start in Park: neutral safety, bushings + confusion - PeachParts Mercedes-Benz Forum

blankenship · #1 03-01-2008, 04:05 PM

So, my '82 euro 250 won't start in Park, but will start in neutral. Will also start in park if the shifter is 'jiggled.'

I've been reading up on various forum posts about Neutral Safety switches, shifter bushings, etc, and still can't quite seem to get a handle on my situation.

Which is:

The (2) yellowy-plastic shifter rod bushings appear fine, and there doesn't
seem to be much slack in them. I put the shifter in N and the tranny in N, and adjusted the 'rod adjuster nut,' a bit, to no effect.

My Reverse lights DO come on upon shifting into R.

I've tried to figure out adjusting the NSS, but I don't have an 'adjuster screw' on my trasmission lever that's shown/mentioned in the manuals. I've got the little spot where you're supposed to put a 4mm rod through, and it actually seems to line up when I'm in neutral, but am confused about how you'd adjust it without said screw.

Ideas about solvin' my problemos?

Arthur Dalton · #2 03-01-2008, 04:36 PM

If everything lines up and you have N start and back lamps in R , then your NSS is going bad. The contacts are about had it.
If the shifter bushings are gone, then the rod will not be able to push the NSS all the way to P position b/c the shifter hits the stop gate before NSS engagement, but that is not your problem as the bushings do not have any slop.
Change it before you loose both N and P contact........

Johnhef · #3 03-01-2008, 04:46 PM

Even if you have no shifter bushings, your NSS should still work. I agree, it's going bad, replace it.

Arthur Dalton · #4 03-01-2008, 06:20 PM

<>

It is very common for bad shifter bushings to prevent the NSS from moving into the Park position b/c the shifter hits the Gate trim cover in the car , stopping it from moving any further..so, a bad set of bushings changes the LENGTH of the throw of the rod and it will not have enough throw to put the NSS into Park...You will have no problem in N w/bad bushings b/c there is throw on either side of the gate, but that is not the case in Park. Park posistion is the end of the throw on the gate cover.
The common complaint on worn shifter bushing diagnosis is OK start in N , but no start in P.
..but either could be a bad NSS.

blankenship · #5 03-01-2008, 08:39 PM

so, theoretically i could change the 'throw' of the rod, and get her to start in Park? but since i can push a little allen wrench through the adjustment/pin thingy, i shouldn't even mess w/ that? just get a NSS? is that the theory?

like i said, i have no little 'adjuster screw' on my mechanism. does that mean that all the adjustment is done with the 'locknut' that's on the rod (which acts to maintain the length of the rod/tranny lever/shifter?

Arthur Dalton · #6 03-02-2008, 12:01 AM

Basically, yes...if the adjustment pin is in alignment and the bushings are tight , then the lever/fulcrum geometrics enable the NSS to be in the proper start position when the shifter is indicating Park. It is that simple.
The relationship between the two is in the designers dimensions . But those dimensions can change if one had bad bushing or a bent shift rod , poor adjustment, etc.
However, where one has back-up lamps in R and starter engagement in N and both seem in alignment with the shift indicator gate , then the linkage is verified as OK and the diagnosis would be NSS. This seems to be your situation.
The ONLY reason we make the added notation of checking shifter bushings before condemning a NSS is b/c worn bushings are an often over-looked cause for a No Start in P complaint..specially when the complaint is coupled with an OK start in N. If you look in the Archieves , you will see many post that have remedied a no start in P complaint by replacement of worn out bushings w/o changing the NSS. [ But I do agree that the larger percentage would be a worn out NSS]
It is the mechanically linked relationship of the shifter rod/NSS/shifter indicator that determines if the gear selector and NSS are on the same page.....
If one were to disconnect the linkage to NSS and then click/set the NSS by hand to it's P position and have a starter circuit activation, you know that the sw is OK... that sw verification would indicate that the sw was not mechanically being turned to it's proper position...why??? ......linkage problem....... NOT NSS.
A bad NSS would have worn/pitted elecritical contacts, causing no circuit completion even though the sw was in it's proper position. So you can see , one is an electical failure and the other is a linkage failure...either causing the SAME complaint, but with different diagnosis.
If one can move the shifter and see that the NSS arm is not moving in accordance, then the bush are worn and you can then see that it will take more throw of the shifter to get the NSS into it's P position to start the car..Soooo, if the bushing slop is extreme enough, the NSS can not get to that position b/c the shifter has run out of movement/throw b/c it is hitting the shifter indicator gate and can't go any futher..it is at it's end of TRAVEL b/c the gate is stopping any further movement.
I do not have exact info on your Euro shifter linkage , but the basics should be the same as most shifter set-ups
Worn bushes can be felt by slop in the shifter in any gear , so it is not a hard thing to diagnosis.
So, bottom line..If the NSS is in it's correct gear position, then you have a bad NSS [ electrical sw. problem].. if the sw is not in the correct position, you have a mechanical/linkage problem...