bigmalcy Posted March 2 Report Share Posted March 2 Hi folks - Today I finally got some time to poke around the old girl, mainly the cooling side of things (see other post), but I also took the tunnel off and started looking into the overdrive problems. As described in a separate thread, the overdrive had started disengaging when the car got warmed up: it would work perfectly when the car was cold, then disengage once the car was warm. Eventually, though, on a long drive home (500 miles), the overdrive refused to engage, even when cold. So - I have whipped the tunnel off and had a play around: Overdrive works fine when operated manually: engagement is firm and the lever is not too stiff, based on my experience, whether operated on left or right sides. Solenoid appears to be the culprit: when I removed it from the car and applied 12v to it, I found that the plunger was held in when I pushed it in, but the 'pull in' circuit was clearly not working. Now - having gone through one solenoid before, I got very careful about a) setting the solenoid up, and b) keeping an eye on the Ammeter, to make sure that whenever I flicked the switch, the large pull in current was not held for longer than a split second. I am convinced that it was operating fine, in this regard. I also fitted a 10A Fuse that re-sets after tripping, just to add some more protection. Now - in poking around today, I found a previously un-known fault which may well have something to do with the issue: the battery is sitting at 15V with the engine turned off! No doubt, I have an issue with the Alternator, which was fitted 10 years ago and done a couple of thousand miles since then. I have not had a chance to look into this side of things yet. But - I am interested to know if this could be the cause of the overdrive solenoid failing. What I don't understand is why it would engage ok when engine cold, then disengage when hot. I also don't understand why it is just the pull in circuit that has failed, when it was the hold circuit that would have been running at excess Voltage for long periods of time. Aside from the solenoid - would there be any other devices on the car that would not like 15V? It has petronic ignition, but based on the drive today, that doesn't seem to have been affected. Regards Malcolm Quote Link to post Share on other sites
Lebro Posted March 2 Report Share Posted March 2 How confident are you of the 15V reading ? have you got an alternative meter to check. I have never heard of a lead acid battery holding 15V when not on charge. To answer the question, I don't think 15V would harm the soleniod, but to get to 15V the charging voltage would be much higher than that !! Bob. Quote Link to post Share on other sites
ianc Posted March 2 Report Share Posted March 2 Conventional lead-acid battery holds about 2.2 volts per cell when at rest (not being charged), so 13.2 volts across its terminals. I would suspect your multimeter ! The problem with your overdrive could be a loose connection, which vibration whilst driving could cause to come adrift temporarily. Not easy to find - if in the 3A, could be the dash-mounted switch. Ian Cornish Quote Link to post Share on other sites
Ralph Whitaker Posted March 2 Report Share Posted March 2 Most charging systems put out around 14v to charge a 12v battery. A fully charged battery would be at best 13.5v. I don`t think it would be possible to get a 15v reading from a 12v battery, so I too suspect your multimeter is lying. Ralph Quote Link to post Share on other sites
RobH Posted March 2 Report Share Posted March 2 24 minutes ago, Ralph Whitaker said: I too suspect your multimeter is lying. Definitely this if the battery was not on charge. Battery chemistry just does not allow 15v to be developed. Quote Link to post Share on other sites
bigmalcy Posted March 4 Author Report Share Posted March 4 Geez you guys are good... or I'm not good enough I obviously trust digital instruments too much... and don't know enough about 12v car batteries So I checked the voltage with another meter and it was sitting at a nice and healthy 12.5 Volts without the engine on. Can't measure it with the engine running as she is currently 'dry'... but I don't expect any issues. However... I'm still struggling to come up with a viable explanation for the overdrive solenoid failure and symptoms leading up to it. Anyway - I'll fit a new solenoid and see how she goes... Thanks again! Quote Link to post Share on other sites
Lebro Posted March 4 Report Share Posted March 4 Correct adjustment is essential, the solenoid must be able to pull fully in to switch off the "pull in" coil. if it fails to do that the coil will burn out. Bob Quote Link to post Share on other sites
bigmalcy Posted March 5 Author Report Share Posted March 5 22 hours ago, Lebro said: Correct adjustment is essential, the solenoid must be able to pull fully in to switch off the "pull in" coil. if it fails to do that the coil will burn out. Bob Hi Bob - yup, totally aware of that... and having just fitted a new solenoid without touching the clamp position of the actuating arm (i.e. not changed anything other than the solenoid), I can confirm that it is working exactly as it should. Ammeter on the car gives a big flick when the solenoid pulls in, but pretty much stays in it's original position. For some reason, when I put an ammeter in the circuit to measure amps when engaging, there appears to be too many losses in the ammeter because the solenoid didn't have enough 'oomph' to pull in and sat on 7 amps for the split second it took me to read the value. If I gave it a little 'help', it would pull in all the way and the current then drops to less than 1 amp when fully pulled in. In both the engaged and disengaged state, the overdrive lever has some play in it (i.e. the solenoid plunger is not being restricted by the overdrive mechanism reaching its limits of travel. All in all - I still think the adjustment is and was spot on... and I still can't explain why the overdrive would 'play up' only after the car was properly warmed up... then return to normal after cooling down... until of course it 'played up' permanently. Anyway - I'll put it down to a faulty solenoid and keep watching that Ammeter like a hawk for the first 100 engagements or so Quote Link to post Share on other sites
Lebro Posted March 5 Report Share Posted March 5 Great, hope its all sorted now. Bob Quote Link to post Share on other sites
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