Neutral safety start switches

[richard5933]

Our 4108 has two neutral start safety switches. They are wired in series. Both test good (switched closed on both when in neutral).

Problem is that I have to use the neutral over-ride switch to start the engine. When I picked up the bus from the seller in the fall he told me that there was an intermittent problem. It's no longer intermittent.

I'm assuming that this has something to do with why the rear start switch doesn't work.

My only thought is to do what I can to follow the wiring diagram and double check all the connections/terminals associated with the neutral safety system

Anyone have suggestions of other things I might be missing?

[thomasinnv]

Neutral safety relay? I would expect the neutral safety switches to activate a relay, possibly the relay has failed?

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[richard5933]

I'm suspecting that either the rear start switch or the connections to/from it are the cause. My head is spinning from reading the wiring diagrams trying to understand this, but it looks to me like there is a connection from the front start switch through terminal #19 in the engine panel to the rear start switch. I don't see any relays in the area between them in the diagram. I'm looking at diagram 11286 if anyone is following along. Both start switches are located in the upper portion of the diagram.

Since the override switch works just fine, at least I know that there is nothing going on with the starting system.

Not sure, but it looks like there is some connection between the two start switches and the auto shut-down relay. So, I'm wondering if all my problems could be related to a bad switch or connection.

This will take more digging. Not this weekend though, as it seems as though winter isn't done with us - cold, wet, and blustery outside with snow accumulation tonight. Fun. Guess I have time to study up some more.

[richard5933]

Best $30 I've spent recently...

Using the endoscope I got from Amazon it was possible to see inside the hole where the neutral safety switch mounts. Apparently there is a notch that is intended to line up with the ball on the bottom of the switch when in neutral. Mine was ever so slightly off center and caused the switch to open. I was able to move the linkage slightly and get things to work - maybe 1/32" to 1/16" was enough. Doesn't seem to be an electrical problem at all.

The guy I bought the bus from was only the second owner and had it a few years. From what he was telling me, he had intermittent problems with the neutral safety switch. I don't know how far back it goes or if the original owner had the problem, but the guy I bought from has occasionally had to use the over ride switch so I know the problem is not totally new. Other than this, the transmission shifts smoothly and the linkages all seem to be working properly. The grease fittings were all serviced in the fall.

I spent time reading the manual and then double checked the linkage adjustment. According to the manual, the linkage is correct when both clevis pins can be moved freely when the transmission is in neutral. That's what I've got. Perhaps the shaft that has the notch is just sticking a bit? I've got proper oil pressure in the tranny, and the fluid/filter have both been changed recently. Any chance that the shaft hasn't gotten enough lubrication due to the low mileage over 40+ years and has gotten gummed up? Or perhaps this is a sign of something larger?

Any tips on remedies would be welcome. The manual doesn't really say much about this portion of the transmission, and I have zero experience with the inner workings of a Spicer 4-speed.