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Dart Overdrive Inhibitor Switch

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rogerharrop
Posts: 116
Joined: Sat Nov 17, 2018 11:54 am
Location: Watlington, Oxon
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Dart Overdrive Inhibitor Switch

Post by rogerharrop »

Hi All,

I believe my overdrive inhibitor switch on the gearbox is playing up. Question - where is it mounted and also I've read on an MGB forum that the position of the switch in relation to the contact pad inside the gearbox is controlled by some fibre washers between the switch and gearbox casing and as wear takes place the number of washers has to be reduced.

Does that make sense for the Dart?

Many thanks

Roger

Ian Hastings
Posts: 163
Joined: Tue Mar 15, 2016 3:00 pm

Re: Dart Overdrive Inhibitor Switch

Post by Ian Hastings »

The switch is located on the top cover of the gearbox, screwed into a boss directly above the 3rd/4th gear selector shaft (and sometimes another switch on the 2nd gear shaft as well).
The switch engages with an indent in the shaft and that is adjusted by thickness washers below the switch. I cannot see wear being a major factor there so regular adjustment should not normally be necessary.

csm1406
Posts: 93
Joined: Sat Feb 13, 2016 6:06 pm
Location: west sussex

Re: Dart Overdrive Inhibitor Switch

Post by csm1406 »

Hi
I have an o/d on my SP250 which jumps out regularly - mainly after a short period of use. The unit has been fitted for less than 10,000 miles - should I fit a new inhibitor switch to see if that helps. I have been told it is unlikely to be wear on the o'rings because of the relative low use. Any hints / tips gratefully received.

Cameron

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RadfordJim
Posts: 140
Joined: Tue Feb 16, 2016 10:19 am
Location: Coventry

Re: Dart Overdrive Inhibitor Switch

Post by RadfordJim »

Silly question but have you checked the gearbox oil level? It should be 1/2" to 3/4" above max (as mentioned previously on the forum). Topping up the oil solved my sluggish/intermittent overdrive operation đź‘Ť
Jim in Coventry - Home of the Daimler

HenryC
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Joined: Mon Feb 15, 2016 8:31 pm
Location: Surrey / East Hampshire

Re: Dart Overdrive Inhibitor Switch

Post by HenryC »

I agree with Jim's suggestion.

On my MGB, when the gearbox oil level drops below a certain level the overdrive drops out intermittently. I then know it's time to top up the leaking gearbox!

I don't know if it's the same electrohydraulic operation on the Dart o/d - but its a thought.
Cheers, Henry Curwen
Registrar for Conquest & Century Saloons (DJ250/1, DJ256/7, DJ260/1)

Conquest (Drop Head) Coupe DJ252

rogerharrop
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Location: Watlington, Oxon
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Re: Dart Overdrive Inhibitor Switch

Post by rogerharrop »

Thanks guys - yes the oil is OK - if anything it worked fine after a recent oil change then this happened

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JohnM
Posts: 206
Joined: Thu Feb 11, 2016 1:31 pm
Location: N W London

Re: Dart Overdrive Inhibitor Switch

Post by JohnM »

Hi Roger,
do you know whether you have a "J" or "A" type overdrive?
The J type solenoid acts directly, so the electrical connection to the solenoid is often the culprit for an intermittent overdrive, but the A type operation is more complicated, and as well as the electrical connection there's a mechanical setup that can also cause problems. Have you also checked your overdrive switch connections? (Mine is on the gearlever and occasionally decides to disconnect itself!)
HTH ,
John
John M in Middlesex, NW London
1962 SP250 "B" Spec
DLOC Herts Region Sec

rogerharrop
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Re: Dart Overdrive Inhibitor Switch

Post by rogerharrop »

Hi John,

It's an A type and, yes, I've actually fitted a new overdrive switch and checked electrics so all that's left, I think, is the inhibitor switch

Best

Roger

rogerharrop
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Location: Watlington, Oxon
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Re: Dart Overdrive Inhibitor Switch

Post by rogerharrop »

Thanks for the advice all.

I ordered a new switch and was reconciled to the hassle of removing the tunnel to get it done but then had a brainwave! Maybe it's located right next to the dipstick and maybe I could get at it through the hole on the tunnel. I found I could - enough to get less than an eighth turn on the existing switch and....it's done the job! Don't know how long for but it was worth the try.

Best

Roger

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JohnM
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Joined: Thu Feb 11, 2016 1:31 pm
Location: N W London

Re: Dart Overdrive Inhibitor Switch

Post by JohnM »

Great stuff, Roger - well done!

John
John M in Middlesex, NW London
1962 SP250 "B" Spec
DLOC Herts Region Sec

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