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8 & 10 cyl Bristol cars Type 407 onwards - restoration, repair, maintenance etc

Neutral gear safety switch

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Old 30-03-24, 02:25 PM
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Default Neutral gear safety switch

Can anyone point me in the right direction please.

I have been checking over my 410 in readiness for a trip to Europe. Quite by chance I have found an issue when starting the car.

The engine will turnover and start when the auto shift lever is in Drive! Thatís in addition to the normal positions of Neutral and Park.

The engine will not turnover/start in any other position (1st, 2nd or reverse).
I donít know how long this has been an issue as I only ever start the car in Park.

I believe the switch on the side of the shift lever only controls the reversing lights. I disconnected that switch anyway but the problem still exists. I donít know if there is another switch or relay located elsewhere on the car.

All thoughts will be very much appreciated.

Brian
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Old 30-03-24, 02:48 PM
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Unhappy

can't over any help, sorry

but

take care. i had the same with my 411. startable in any gear . Unfortunately i started the car in what i thought was park. I got out and about 5 minutes later, the car drove itself forward, hitting another of my cars. To had insult to injury , it then hit a 2nd car (also my own)

expensive mistake

bw

James
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Old 30-03-24, 04:58 PM
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Looking a little further into the wiring. There is a single wire from the bottom half of the transmission box, which I suspect connects to a solenoid. This wire goes directly to the starter relay.
Disconnecting this wire, the car will not start with the shift lever in any position. This may indicate (hopefully) a faulty solenoid.
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Old 30-03-24, 05:19 PM
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Brian,

The Neutral Start Switch sits in the transmission and it sounds like you found it. It is supposed to provide a route to earth/ground for the starter solenoid (when in neutral only, of course).

I have the same problem with mine albeit I have pushbutton transmission selector. Mine will start in Reverse. The experts this side of the pond say my selector cable needs adjusting so that the selector in the valve body (a pivoting plate with lobes on it for each position (PRNDL etc)) is aligned correctly and only closes the Neutral Start Switch when the neutral lobe is aligned with the switch.

I haven't fixed mine yet but hope that helps.

David

Last edited by dwomby; 30-03-24 at 07:12 PM.
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Old 30-03-24, 07:09 PM
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Thanks for your reply David, yes it sounds like I may need to make a slight adjustments on the linkages.

My concern now is, if I try and tweak any of the linkages, I may make matters worse.

As my car is currently running so well, I am inclined to leave everything as is for the time being and look at it again in the not too distant future.

Brian
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Old 30-03-24, 07:11 PM
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Quote:
Originally Posted by DODD View Post
Thanks for your reply David, yes it sounds like I may need to make a slight adjustments on the linkages.

My concern now is, if I try and tweak any of the linkages, I may make matters worse.

As my car is currently running so well, I am inclined to leave everything as is for the time being and look at it again in the not too distant future.

Brian
I had exactly the same concerns and reached the same conclusion and have left it alone for now too!

David
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Old 30-03-24, 08:23 PM
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The neutral and park safety switch provides a path to earth from the starter solenoid. A white and brown cable runs between the starter solenoid and the safety switch. Either the safety switch has become permanently shorted or the solenoid has found another path to earth or the gear selector is not operating the switch as intended. The first course of action would be to remove the white and brown cable from the solenoid and test continuity to earth with a multimeter with the gear lever in all positions. It should only have continuity in neutral and park.
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Old 30-03-24, 08:28 PM
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Quote:
Originally Posted by David C View Post
The neutral and park safety switch provides a path to earth from the starter solenoid. A white and brown cable runs between the starter solenoid and the safety switch. Either the safety switch has become permanently shorted or the solenoid has found another path to earth. The first course of action would be to remove the white and brown cable from the solenoid and test continuity to earth with a multimeter with the gear lever in all positions. It should only have continuity in neutral and park.
David,

If the safety switch was permanently shorted or the solenoid had another path to earth, wouldn't Brian's car start in 1st 2nd and Reverse too?

David
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Old 30-03-24, 08:33 PM
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Sorry - didn't read carefully enough. You are quite right. It looks as though the mechanism is either worn or out of alignment and operating the switch when it shouldn't.
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Old 31-03-24, 08:53 AM
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Hmmmm

I do recommend anybody with a faulty gearbox safety switch to get this fixed ASAP by somebody who knows. Any automatic that is capable of starting when the box is not in neutral or park will, sooner or later, offer you a very exciting, not to say dangerous, experience.

As has been pointed out there is a lead between the solenoid and the gearbox that is supposed to provide an earth to the solenoid only when the gearbox is in Park or Neutral

We were already on our way on a European tour some years ago and just had a load of recycling to drop off. Having dropped it off the 410 declined to start- nothing, not even a click. Loath to leave her in a recycling yard, however well deserved her fate, let alone abandon the trip, I worked out (quite quickly Iím proud to say) that the safety switch on the gearbox had gone open circuit. So I shorted out the offending article by taking a piece of wire from the solenoid to earth and we were quickly on our way again. The plan being to place the beast in park every time we stopped, open the bonnet, disconnect and close the bonnet again. Conversely check that in park, open the bonnet, reconnect, close the bonnet before attempting to start the engine again.

All went well until a certain petrol station in Spain when she was started whilst in gear, seriously startling a number of Spaniards to say nothing of the driver and navigator. Fortunately no harm was done, but that was pure luck - it could very easily have developed into a disastrous situation.

As I understand it the switch sits below the oil level in the gearbox so I think it unlikely that whatever operates it will have worn out, I think more likely that the switch itself is falling apart.
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Old 31-03-24, 10:08 AM
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Thanks everyone for your thoughts.

Just to reiterate, currently my 410 will start in Park, Neutral and unfortunately Drive but not in 1st, 2nd or Reverse.

I donít believe I have any worn parts as my automatic transmission and torque converter were fully overhauled last year by a specialist company and overseen by a Bristol Specialist, the latter whom incidentally, I have the highest regard for.

Yesterday when I was trying to trace the source of my problem, I disconnected the wire between the starter relay and transmission gear box and tried to start the car in each position of the shift lever. On turning the ignition key I heard the clicking sound, as expected in each position.

Currently, I believe the problem lies in the linkages. I will contact the Bristol specialist on Tuesday; I am sure they will have come across this problem before and point me in the right direction.

I agree with all, that itís not an ideal situation and needs to be resolved asap.

Brian
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Old 31-03-24, 10:41 AM
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If I remember rightly although some Chrysler gearboxes had a combined inhibit and reversing light switch on the gearbox, the inhibit switch on the 410 is at the base of the gear selector with a single function reversing light switch mounted on the gearbox. This would make more sense of the car starting in some gears and not others.
With any luck I have managed to attach a picture of the inhibit switch mounted on the gear selector on a 410
http://www.bristolcars.info/forums/a...1&d=1711878008
Attached Images
File Type: jpg IMG_4198.jpg (244.6 KB, 15 views)
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Old 31-03-24, 10:58 AM
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Absolutely correct David, the one on my 410 only controls the reversing lights and is the same as per your photo. My initial thoughts when I saw this switch, that was the most likely cause, until I disconnected it and found there was no change to the problem, except that the reversing lights didnít work.
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Old 31-03-24, 01:46 PM
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My memory is letting me down. As Dodd says the reverse switch is on the shift lever and the neutral inhibit on the gearbox. A bit of research suggests that the culprit in your case is the lever inside the gearbox that operates the switch. This is known as a Rooster Tail due to its shape.
Be aware that there are at least three different types of switch and Rooster Tail. Pre about 1970 - per the 410 - the switch had a single contact and only inhibited the start. After this the switch had 3 wires and dual function to include reversing lights.
It seems it is possible to change the rooster tail with the transmission in the car but I can't immediately tell whether the valve body has to be removed.
You may want to consider a couple of upgrades while you are about it. The simplest is to swap out the pressure regulator valve for Sonnax 22771A-02K and the manual valve for Sonnax 22771-09. This allows the transmission to fill in Park and saves the "clunk" when engaging drive.
The other upgrade is to replace the valve body with a slightly newer unit to allow part throttle kickdown.
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Old 02-04-24, 08:39 PM
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I had the opposite problem on my 410 - it would not start at all on a trip to France. I managed to work out that it was the inhibitor switch that had failed so using some stout logs found at our gÓte as axle stands, I bypassed it so that it would start in any gear. I was very careful to double check it was not in gear when starting for the rest of the trip.
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Old 02-04-24, 09:13 PM
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Quote:
Originally Posted by Sam410 View Post
ÖÖ so using some stout logs found at our gÓte as axle stands, I bypassed it so that it would start in any gear. ÖÖÖ
Sam - that all sounds an immense amount of hard work when all you needed to do was to open the bonnet to connect an earth to the solenoid as per my previous post. But you did do much better than me at not starting the engine whilst in gear!
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Old 02-04-24, 10:15 PM
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I don't remember the precise details now, but whatever it was I did it was easier to reach from underneath the car!

On another French trip the ignition switch packed up and after phoning SLJ for instructions I spent a thousand miles having to hotwire the car at every start. It has just been rewired with a new loom so I hope these travails are behind me now... (Touches wood!)
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Old 15-04-24, 09:20 PM
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It turns out my problem was not what I described to Brian above.

In my case, it was that a previous owner had replaced the starter relay with a non-standard one and mis-wired it so that the relay was permanently grounded - thus the car would start regardless of the gear selector position.

The Neutral Safety Switch had been left out of the circuit. I have fixed it now.

David
Quote:
Originally Posted by dwomby View Post
Brian,

The Neutral Start Switch sits in the transmission and it sounds like you found it. It is supposed to provide a route to earth/ground for the starter solenoid (when in neutral only, of course).

I have the same problem with mine albeit I have pushbutton transmission selector. Mine will start in Reverse. The experts this side of the pond say my selector cable needs adjusting so that the selector in the valve body (a pivoting plate with lobes on it for each position (PRNDL etc)) is aligned correctly and only closes the Neutral Start Switch when the neutral lobe is aligned with the switch.

I haven't fixed mine yet but hope that helps.

David
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