rodofcv Posted June 16, 2021 Report Share Posted June 16, 2021 Folks, my overdrive had been working perfectly well. On a recent short trip I switched overdrive on and nothing happened. The ammeter had shot to 30+, and I switched off. A couple of days later I absentmindedly switched overdrive on again. The same thing happened. Going out the next day I again switched the o'verdrive on (I was under considerable stress elsewhere at this time!). This time the ammeter didn't register. You may just say that I'm stupid but at my age I couldn't care less. It may be relevant that both fuses are intact. Being completely ignorant of overdrive mechanics and electrics (and many other things), I'm dependant on you learned gents as to where I should start looking? I tried the search facility on here but that leaves rather a lot to be desired. I look forward to your assistance Rod Quote Link to post Share on other sites
Ralph Whitaker Posted June 16, 2021 Report Share Posted June 16, 2021 (edited) Hi Rod, having recently had overdrive trouble myself ,though different problem to yours, I sympathise. It seems as though the solenoid may have stuck, it takes quite a hefty current to initially operate the solenoid as it activates the pull in coil, but when the solenoid is fully in it is supposed to trip a switch onto a holding coil which draws a much smaller amperage. For whatever reason it would seem yours has not pulled in far enough to operate the second holding coil. Depending on how long it was attempting to pull in, it may have burnt out the o/d solenoid, or there may be a seperate in line fuse to the o/d relay which could have blown. Assuming it is not a short in the switch, or the wiring to the overdrive which should be checked first, you need to determine what is causing the solenoid not to pull in and operate the o/d, it could be road debris that has jammed the operating lever, or the rubber boot on the solenoid may have perished allowing damp in that has corroded the solenoid internally. I think you are going to have to take off the gearbox tunnel from inside the car to investigate the cause. Ralph. PS, if you look a little lower down the page you will see my thread entitled More Overdrive Woes, and there is a link on there to a very informative article, but heavy reading if you are not familiar with the overdrive . Edited June 16, 2021 by Ralph Whitaker Quote Link to post Share on other sites
RobH Posted June 16, 2021 Report Share Posted June 16, 2021 (edited) Well firstly Rod, the ammeter should only be registering current flowing in to and out of the battery. The ammeter reading may show that something is wired wrongly - perhaps the overdrive feed is taken from the wrong side of the ammeter. Did you used to see a brief kick on the meter when OD was selected? The circuit isn't fused so it is no wonder neither fuse blew, however the fact the fault has 'gone away' but the OD no longer works suggests to me that you had a short to earth in the OD wiring, and that the wire - or maybe the relay - may now have burnt out. As others have said here it could be a solenoid fault where the high current winding has remained energised. I suggest investigation of the power side of the overdrive wiring. Edited June 16, 2021 by RobH Quote Link to post Share on other sites
NCS_TR3A Posted June 16, 2021 Report Share Posted June 16, 2021 Hi Rod, It's normal for the ammeter to shoot up for a second but it should then drop. The Soleniod has two coils, both are activated initially (this is when the amps go high) to pull the shaft up and engage the overdrive. Once the shaft is fully up one of the coils disengage and amps drop. Sounds like you have a solenoid issue. Might be stuck but I'm guess you will be needing a new one at the very least. Neil Quote Link to post Share on other sites
NCS_TR3A Posted June 16, 2021 Report Share Posted June 16, 2021 Wow, when I started replying there was no other reply to this :). You guys type fast Neil Quote Link to post Share on other sites
Ralph Whitaker Posted June 16, 2021 Report Share Posted June 16, 2021 10 minutes ago, RobH said: The circuit isn't fused so it is no wonder neither fuse blew, however the fact the fault has 'gone away' but the OD no longer works suggests to me that you had a short to earth in the OD wiring, and that the wire - or maybe the relay - may now have burnt out. I suggest investigation of the power side of the overdrive wiring. I was surprised by this statement, so had to get the wiring diagram out for a look, and you are quite right, the solenoid side of the O/D relay is not fused, however the relay operating side should be connected to Fuse A3 according to my diagram, but as neither fuse has blown that discounts my suggestion to check the switch and wiring to the relay. If the fault was in the wiring from the relay to the solenoid, say a short to earth, would that burn out the relay in lieu of a fuse? Ralph Quote Link to post Share on other sites
RobH Posted June 16, 2021 Report Share Posted June 16, 2021 33 minutes ago, Ralph Whitaker said: If the fault was in the wiring from the relay to the solenoid, say a short to earth, would that burn out the relay in lieu of a fuse? Quite possibly Ralph. There's only so much current the contacts can take. Quote Link to post Share on other sites
John McCormack Posted June 17, 2021 Report Share Posted June 17, 2021 I suspect a short in the wiring, usually where the wires go through the tunnel to the gearbox. It could also be the solenoid as suggested above. My daily driver TR2 had this exact problem a few months ago, I couldn't find a short so replaced the solenoid (the wires to the solenoid were so stiff with age they broke off when I touched them) Problem fixed with the new solenoid. Check the wiring first, then if that is ok buy a new solenoid. They are quite cheap. Quote Link to post Share on other sites
rodofcv Posted June 20, 2021 Author Report Share Posted June 20, 2021 Thank you gentlemen, I will work through the suggestions. This will keep me busy for a little while. I feel sure the problem will be resolved. Rod Quote Link to post Share on other sites
ianc Posted June 20, 2021 Report Share Posted June 20, 2021 If your ammeter showed 30 amps discharge, it's almost certainly not a solenoid problem - see below. OVERDRIVE SOLENOID 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 and 13.4 volts. Ian Cornish Quote Link to post Share on other sites
Teher Posted July 14, 2021 Report Share Posted July 14, 2021 My overdrive was working very well then started to work every other time then not at all ... Tested, the relay seemed to work correctly, but in the end, by changing it, we realized that it was he who was faulty ... Result: a simple £ 30 relay on the firewall changed in 10 minutes and everything works again! Quote Link to post Share on other sites
Hamish Posted July 14, 2021 Report Share Posted July 14, 2021 It’s always satisfying to find a fault and easily fixed. well done. Quote Link to post Share on other sites
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