boxofbits Posted August 29, 2022 Report Share Posted August 29, 2022 (edited) Good afternoon everyone I’ve had an intermittent problem, always the most difficult to solve especially when the potentially offending part takes some stripping out of the interior to get too! In my experience generally speaking, solenoids either work or they don’t. When operating the overdrive switch in 2/3/4th I can hear the newish relay operating and I get 12 volts at the wire to the solenoid. The solenoid is dated 5/66 which is a bit puzzling as the car was built 23/3/67. I usually allow Lucas parts 1 or 2 months lag behind a build date which seems pretty accurate on average. I did find the original plunger had been cut down. I checked this against a new one from OD Services and they confirmed the new one was the correct length. So I’m sceptical that this solenoid is original and that someone in the past has not encountered a problem before for the plunger to have been shortened. Question is, can these solenoids work intermittently? There is a burning smell from the nylon cap area, but on the other hand they can get hot so unsure if this reflects a fault. Anyone else experienced an intermittent faulty solenoid? Edited August 29, 2022 by boxofbits Quote Link to post Share on other sites
ianc Posted August 29, 2022 Report Share Posted August 29, 2022 (edited) There are two windings inside the solenoid. The beefier one is to pull-in (operate), the thinner one is to hold-in. Both are soldered to one of the terminals on the top (beneath the cover). The thinner wire can fracture and make intermittent contact, or no contact at all. If this happens, the solenoid action oscillates and the device gets very hot as it is taking the full pull-in current (about 12 amps) almost continuously. I have repaired such breaks, but it is not easy as the hold-in wire is both very thin and coated, so removing the coating without breaking the wire is tricky. I wrote about this in Newsletter 13 (Spring 1973), and it was in Section F4 of the Technicalities Booklet (with Neil's super diagrams), so will be in the on-line version in the Register's website. Ian Cornish Edited August 29, 2022 by ianc Quote Link to post Share on other sites
boxofbits Posted August 29, 2022 Author Report Share Posted August 29, 2022 16 minutes ago, ianc said: There are two windings inside the solenoid. The beefier one is to pull-in (operate), the thinner one is to hold-in. Both are soldered to one of the terminals on the top (beneath the cover). The thinner wire can fracture and make intermittent contact, or no contact at all. If this happens, the solenoid action oscillates and the device gets very hot as it is taking the full pull-in current (about 12 amps) almost continuously. I have repaired such breaks, but it is not easy as the hold-in wire is both very thin and coated, so removing the coating without breaking the wire is tricky. I wrote about this in Newsletter 13 (Spring 1973), and it was in Section F4 of the Technicalities Booklet (with Neil's super diagrams), so will be in the on-line version in the Register's website. Ian Cornish Thanks Ian I suspect you might be on the right track there, as I noticed the solenoid was, as you say, very hot, when I was adjusting the lever/plunger a couple of weeks ago. The linkage without solenoid actuation can be moved easily and is free, overdrive can be engaged manually when driving, and when the solenoid works, the overdrive works. I tested it for several miles after the adjustment without a hitch, put it all back together, no overdrive. But it does smell like the solenoid has got very hot. Sometimes it’s a definitive clunk, other times it sounds like a half-hearted partial movement. I’ll have look under the cover to see if anything is evident or perhaps replace the solenoid. Kevin Quote Link to post Share on other sites
ianc Posted August 30, 2022 Report Share Posted August 30, 2022 Kevin, unless you have easy access to the solenoid (e.g. a split gearbox cover), my inclination would be to replace the solenoid. When I repaired the solenoid on my TR2 (much easier access), the repair did not last for ever, and I had to repair again, then gave up and fitted a new solenoid. It's difficult to clean the coating from the fine wire in order to be able to tin it prior to soldering - one risks damaging the wire. Ian Cornish Quote Link to post Share on other sites
Andy Moltu Posted August 30, 2022 Report Share Posted August 30, 2022 Even with a 2 part gearbox cover it is still a pain in the rump to access the solenoid so I would suggest you replace it. Carefully adjust the setting to make sure it only draws the high current when pulling the overdive on before dipping to the low holding current once engaged. Quote Link to post Share on other sites
boxofbits Posted August 30, 2022 Author Report Share Posted August 30, 2022 Hi Ian I had a look under the cover last night, and couldn’t see any break in the wiring, although by the colour and smell of everything it was all consistent with getting very hot. I wondered when a previous owner or repairer cut down the length of the plunger, it was not locking in but was being held in by the primary coil? I would think the primary coil being on permanently is the only component to cause excessive heat perhaps? The shortened plunger is the only tangible modification off standard I can see. The linkage seems fine and it will drop by its own weight when lifted. There is also a set of contacts in the head I notice, but not sure how exactly it sequences from primary to secondary in conjunction with the relay. Luckily I have a split cover!…so was able to remove it relatively easily. I have ordered another unit. As you say it is going to be the easier option, as it might not work reliably in the longer term. Regards Kevin Quote Link to post Share on other sites
boxofbits Posted August 30, 2022 Author Report Share Posted August 30, 2022 16 minutes ago, Andy Moltu said: Even with a 2 part gearbox cover it is still a pain in the rump to access the solenoid so I would suggest you replace it. Carefully adjust the setting to make sure it only draws the high current when pulling the overdive on before dipping to the low holding current once engaged. You are so right Andy..with a split cover I can just manage to get a 5/16” socket with a UJ on the forward-most screw, with the rear cover off, but mandatorily, it has to be dropped and lost in the grit first before retrieval with a magnetic rod and outstretched arm! I think I’ll need to check with an ohm meter this time for correct switching before reassembly. Thanks for your advice. Kevin Quote Link to post Share on other sites
ianc Posted August 30, 2022 Report Share Posted August 30, 2022 (edited) When activated, both coils are energised, but as the plunger rises it lifts the contact at the top, thereby disconnecting the feed to the pull-in coil, leaving just the hold-in coil energised. My article explains all this in detail ! I have modified my split cover to permit easier access to the solenoid, and have fitted a plate to cover the hole. Ian Cornish Edited August 30, 2022 by ianc Additional info Quote Link to post Share on other sites
boxofbits Posted September 17, 2022 Author Report Share Posted September 17, 2022 Just to update this thread, I fitted a new solenoid from ORS and all is well. Conclusion is that the old solenoid had possibly overheated at some stage in its life, especially with a shortened plunger which I wasn’t aware of. I guess 50+ years anything is prone to failure ! Kevin Quote Link to post Share on other sites
ianc Posted September 17, 2022 Report Share Posted September 17, 2022 You should claim under Joe Lucas's guarantee. Glad problem resolved. Ian Cornish Quote Link to post Share on other sites
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