OK, guys'n gals, time to test your claim to be the genuine Scions of Lucas:
Lucas overdrive operating solenoid - it's that bulge on the side of the overdrive unit that gets hotter and hotter and then tries to burst into flames if it can't achieve its goal of shifting the overdrive oil ball valve.
1) Is it normal behaviour for a solenoid to get too hot when it cannot pull its core completely into the coil winding?
2) Is it possible for it to draw so much current as to melt the supply wires before melting its own internal windings?
3) Is it possible that it has partially destroyed its own internal winding's insulation such that it shorts maybe 1/2 the winding and hence draws twice the current next time it's operated (I=V/R)? It still gives a hearty kick when energised but obviously not enough to operate the valve and stop it burning up. Anyone know what "R" should be on a healthy solenoid?
4) Shouldn't the fuse blow before igniting the whole car, not afterwards? (the wiring seems to be original and pretty heavy gauge).
5) How many 1000 turns of what gauge wire should I rewind the solenoid coil with? (new one is $150 from Moss :-(
I checked the linkage to the valve and all appears to work smoothly so I don't know how it could have burnt out - maybe temporary mechanical obstruction of the exposed "overdrive calibration lever" on the far end of the OD camshaft? This is the later design of OD linkage which protects the solenoid mechanism but still leaves the exposed test lever on the opposite side which is very vulnerable to obstruction from the tranny cover for example (my tranny cover is a flimsy sort of moulded cardboard thing with not much solid in the way of floor panel remaining to screw it down to!).
Andrew Smith
Palo Alto, CA
'60 Healey 3000 Mk.I (with Mk.II gearbox & overdrive units)
1)Many solenoids, including the O/D actuators I've seen, have two windings; a "pull-in" winding which draws a lot of current (and creates enough magnetism to actuate the O/D) and a "hold-in" winding which draws much less current and creates only enough magnetism to keep the thing actuated once it already is.
Current to the pull-in winding is shut off by an internal switch when the solenoid is fully engaged. If it doesn't fully engage, the pull-in winding, which is not designed for continuous use, will eventually melt or kill something else. Lacking specs for this solenoid I can only guess, but pull-in currents of 15 or 20 amps aren't uncommon. Often the supply wiring, which really only expects to have to supply the hold-in current for any length of time, is not quite up to this..
John Wroclawski
jtw@lcs.mit.edu
The solonoid has a switch built in at the top of its internal bore. The resistance is low (about 3 ohms) when the plunger is down (un-energized).
When the plunger is drawn up from energizing it hits the switch at the top of the bore and increases the resistance (to tens of ohms or more -- I can't give you a value but it won't be infinite and will be noticeably higher than the low value), which also cuts down on the current. The reason for all this is that it takes more energy to get the plunger up into the full magnetic field, but little energy to hold it there. If the solonoid is overheating it is because the switch did not activate.
How do you know your solonoid is operaing correctly?
First, remove it from the overdrive by the two screws. Pull the case up and then remove the plunger by unhooking from the operating lever forked end. put the plunger into the case bore and measure the resistance between the wire and the case as you push the plunger up into the bore. At the very end you should see the effect of the internal switch operating. If you don't see a change you'll need to get a new solonoid (about $100 or so).
If all is OK electrically, replace the plunger onto the operating lever and then the body onto the O'dr. Now you need to make the adjustment correct.
The book tells about putting a 3/16" drill through the hole in the operating lever on the passenger side of the O'dr and lining it up with a similar hole in the case. The lever will be moved about 1/4" over to line up. This sets the rod theat pushes up on the ball valve so that this valve just opens. You can observe the action by removing the check falve cap and looking into the bore -- be sure not to lose the spring and plunger that fit under tha cap screw!!!
You should have first loosened the calmping bolt on the operating lever side that the solonoid works. With the 3/16" bit lining up the holes press the plunger up into the solonoid all the way. You can check with an ohm meter that the electrical switch is operating. Now tighten the lever arm clamping bolt.
Remove the 3/16" drill. Go back over to the solonoid and push the plunger (not the actuating arm!!) up all the way. You should find that the actuating arm has a slight bit of free room to move up even further than the plunger pulls it, indicating that it is not restricting the plunger from its full stroke (and thus operatiing the internal switch).
NOW you can reconnect the solonoid wire. Good luck!
Roger Moment
Andrew,
I didn't see many replies to your questions, so here goes.
1) Yes, this would be normal behavior. The solenoid has 2 windings, one to engage and one to hold it engaged. There is an internal switch that shuts of the first winding when it is engagaged. If the solenoid cannot fully engage then it will tend to burn up due to the high current demmands. The windings for engagement are designed for short time operation only.
2) I doubt it. What has probably happened is the internal windings have shorted as you suggest in #3 below.
3) This is most likely the current situation. If you are desperate for the resistance value for a healthy winding let me know I can dig one up and measure it. Moss or TRF can probably also give you this number.
4) NO, Origonal Lucas fuses are expensive to replace and thus are designed to fail long after the part they are supposed to protect fails.
In reality most of our LBC's only have 2-4 fuses rated at 20-30 amps. A very poor design. The solenoid is probably pulling something like 18 amps. Enough to melt the wiring harness over a long period of time but not blow the fuse.
5) Before you spend the $150 for a new solenoid make sure you understand what is preventing your current one from operating correctly. I have found that the most common cause of problems is dirt. You should be able to move the accuating arm manually and it should move easilly and freely through it's total range of movement. You can also disconnect the solenoid from the OD and bench test it. Your service manual should have numbers for the current draw for the solenoid durring engagement and while engaged. Use an amp meter and test it to make sure the internal switch is working.
Kevin Spooner
The Sports Works of Greeley
Specializing in Triumphs and British Sports Cars
britcars@hpfckjs.fc.hp.com