A727 Neutral Safety switch oddity...

[GassMann]

Hey all,

I have an odd situation I need more eyes on. I rebuilt the transmission during a full rebuild a few years back. I did not replace the neutral safety switch. Since the overhaul, I have had issues with starting ONLY in park. In neutral, it will start. In park, it has to be in an EXACT position to start and sometimes even that does not work. Down under the car, I can feel the selector compressing the switch, so I know it is making contact.

OK... ohmmeter time. In neutral, ohms are zero... full contact. In park, I get somewhere between 99 and 191 ohms?!? Wiggle the selector JUST right, and I get zero ohms. WTF??? How is that possible? I mean, the switch is just a simple rod connected to a spring connected to the post. Spring compressed... i.e. park or neutral... contact is made. Reverse or drive, switch spring is NOT compressed. I pulled the switch, tested the ohms on the bench through travel. No change so it can't be the switch. If I replace the switch, I fear it will produce the exact same scenario.

Has anyone seen this before??? Any ideas on what the hell is going on with this?

Thanks in advance for any insights you might have.

 

[65CopCar]

What kind of shifter?

Cheetah shifter in my race car. Fought the exact same issue on and off for over 20 years. I finally solved the problem once and for all.

Not for the faint hearted, but I put a limit switch with a cam in the shifter itself. Works great.

 

[Rishi]

In neutral, ohms are zero... full contact. In park, I get somewhere between 99 and 191 ohms?!? Wiggle the selector JUST right, and I get zero ohms. WTF??? How is that possible?

Sometimes, the column/console shift mechanism can be a little sloppy, and cause issues like this.

I would UNHOOK the shift linkage from the transmission lever, and repeat your tests of the neutral safety switch (NSS.) Pulling the lever all the forward (into Park), you should feel and hear an audible click, as the rooster comb and parking pawl engage. Move the lever rearward one notch, and it snaps into Reverse. Continue rearward as it snaps into Neutral. Test the NSS at each of these points.

Repeat as necessary to assess: each time it snaps into Park, is the NSS testing correctly, and accurately? If not, you may need another NSS. If it's not the NSS, then you may be looking at dropping the pan and valve body to inspect and correct.

Now, if the NSS and shift linkage test reliably, your looking at an issue with the shifter linkage. It seems a common topic that some of the plastic bushings break, or there is wear, causing some shift abnormalities.

 

[GassMann]

What kind of shifter?

Cheetah shifter in my race car. Fought the exact same issue on and off for over 20 years. I finally solved the problem once and for all.

Not for the faint hearted, but I put a limit switch with a cam in the shifter itself. Works great.

The transmission is in my 66 Charger with standard shifter. Nothing special. The linkage is aged... as one could imagine. But the linkage is doing what it needs to do... shift from drive to park. The pall is in when in park and locks the rear end, so I know the leaver is set right.

 

[Geoff 2]

Tighten switch 1/8 turn. If no good, get a new switch.