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Overdrive not working after the winter lay off


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This happens after no use over winter but on first run after OD works after a few miles but not this time. I can hear the relay operate  and have been underneath and when in any OD gear the solenoid does not operate. So guess it is an electrical problem.

Now this is what I do not get. The relay has 4 terminals and I know how these should work but mine only has 3 connections the middle one C2 is not connected.  C1 goes to the regulator and has 12V even without ignition on. W1 goes to the OD stalk and has 10V with ign on and on operating the OD stalk goes to 0V. W2 goes to the brake light switch and beyond and 10V with ign. on and on operating the OD stalk.

All this happens with the gear lever in neutral.

Cannot work out how the OD ever worked

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In case it is a A-OD, get yourself a dedicated relay, ideally a modern one costing about 3 £.

W1 = 86 = 12V control current, from OD lever-switch via OD switch on the GB.

W2 = 85 = Ground

C1 = 87 = output, towards solenoid

C2 = 30 = input 12V

In case of J-OD, a relay is not necessary.

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If the wiring is standard, the relay can only operate when the gearbox interlock switch is closed. If you can hear it click with the box in neutral, something is definitely awry. Perhaps the wiring has been altered at some time? The connections you describe do sound odd, are you sure there isn't a loose wire which has come disconnected from C2?

The 10v you are measuring is due to the resistance of the relay coil and is not significant. 

(Unfortunately Jochems' information. above is not the standard wiring scheme, though it will work. Usually 12V ignition-switched supply goes to W1 and W2  is connected to earth when the OD switch is on and the interlock is closed. ) 

 

od.jpg.4305543e61b086ed03b99cda5c37dfaf.jpg

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As Rob's diagram shows, if there's no wire connected to C2 on the relay, the solenoid will not be energised.  That wire has fallen or been pulled off, so you ought to be able to locate it somewhere near the relay, and re-connect it.

If you are uncertain whether you have found the correct loose wire, use a multimeter to check the resistance between the wire and earth (chassis/bodywork) - should measure about 0.8 ohms.  Here's some info from measurements which I made years ago:

Today (25/05/09), I made some measurements on a brand new, spare, overdrive solenoid which I bought from Moss some time ago. I think it is fair to assume that it was built to the same specification as the original Lucas item.

Pull-in (Pull-in and Hold-in coils in parallel) 0.8 ohms, drawing about 15-17 amps.

Hold-in (pull-in circuit disconnected by plunger operating the switch within the top of the solenoid) 12.5 ohms, drawing about 1 amp.

For the technically-minded, this means that the Pull-in coil has a resistance of about 0.85 ohms, and takes about 14-16 amps.

The current drawn will depend upon the state of charge of the battery, which is usually between 12-13.4 volts.

Ian Cornish

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The relay is mounted on the bulkhead below the brake master cylinder. Wiring has never been touched nothing in the vicinity fallen or pulled off.  The wiring looks modified, at least the one going to the column switch from W1 starts black then YG. May be other bodges and sounds like the interlock switches have been bypassed. But as said worked up until now.

What do I need to remove to get at the interlock switches and solenoid

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10 hours ago, eng622 said:

The relay is mounted on the bulkhead below the brake master cylinder. Wiring has never been touched nothing in the vicinity fallen or pulled off.  The wiring looks modified, at least the one going to the column switch from W1 starts black then YG. May be other bodges and sounds like the interlock switches have been bypassed. But as said worked up until now.

What do I need to remove to get at the interlock switches and solenoid

Probably just as well the o/d is not working if the interlock switches have been by passed. If you accidentaly engaged reverse with the o/d on it`s goodbye overdrive.

Don`t waste money on a new original looking relay, mine did not last a year, and when I took it to bits it was nothing more than a very small relay fitted in an ally can to look original. Replaced mine with a modern relay from the local car shop for £6 and it works perfectly.

Ralph

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Unfortunately, for access to the switches the transmission tunnel has to come out.  

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Hi Eng622,

             have you got a name. I am Roger, greetings.

Where about's are you

 

The wiring is simple once you  have access (as above).

Sort out the wiring first - correct colour codes etc (it really does help).

Then, you can investigate the problem.  As mentioned above any decent On/Off relay will do the job  THIS WORKS WELL

Have you got a wiring diagram (RobH's diagram is what you need)  Look Here

Have you got a test meter or light bulb on fly leads - these can save a lot of time and swear words.

Is the OD an 'A' or J' type???

With the correct gear selected does its inhibit switch give continuity across its connector tags this is a must.

Using the wiring diagram apply power and trace where the 12V goes to (or doesn't)

Roger

 

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  • 2 weeks later...

All now working have od on 2nd,3rd and 4th not 1st so assume wiring is all good. Because the relay is in the engine compartment the wire to the solenoid had become detached from the relay and fallen out of sight touching the exhaust but as double insulated only damaged the outer one.  

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On 7/3/2022 at 11:09 PM, eng622 said:

All now working have od on 2nd,3rd and 4th not 1st so assume wiring is all good. Because the relay is in the engine compartment the wire to the solenoid had become detached from the relay and fallen out of sight touching the exhaust but as double insulated only damaged the outer one.  

That was a simple fix then. Good to hear you found the fault.

Ralph

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