Help please with my overdrive unit

[simonmetalback]

Any tips or ideas on my overdrive which doesn't work. I bought the car last year knowing it did not work. First I have checked the fuse which had blown, replaced with no luck. Removed switch and tested all ok. I have been told check the solenoid. Also should I have power to the two wires going to the O/D switch.
Also my rev counter is very intermittent any ideas.

Thanks

[404ROD]

One of the commonest causes of the overdrive not working is low gearbox oil. The overdrive uses this oil as well and if it is too low the overdrive looses pressure. This did happened to me once and when I topped the gearbox oil up all was OK.

Rod

[Stagdad]

If the fuse had blown check the 2 wires up to the switch haven't warn through and shorted where they come through the gear stick shaft.May be the fuse blew as the wire shorted and now the wire is severed.Can you hear the solenoid click when you turn on the ignition (don't start the car) with overdrive selected and 3rd or 4th selected, I can hear mine quite obviously with my head under the car.
Cheers Steve

[Colonel Mustard]

As Rod mentioned, the Overdrive is actuated by gearbox oil under extreme pressure (450 psi), so low oil would affect it. The electric solenoid allows the oil under pressure to overcome the springs in the overdrive. An inhibitor switch prevents actuation of the unit unless 3rd or 4th gear is selected. Some basic checks can easily be carried out. Steve's idea about listening for the solenoid is a sensible start. If you have a multimeter or test lamp, you can easily check the circuit. Going backwards from the solenoid, the next component is the inhibitor switch (very close to the gear lever, on the N/S of the gearbox...under the car). Does it get a live feed with the ignition on? If not, then follow the circuit...it's not that complicated. If there is power and the solenoid makes no sound when energised, then it could be a faulty solenoid.
The rev counter on a Stag has the unusual characteristic of being switched by induced current from the coil positive wire. It is susceptible to damage from electronic ignition modifications and a good solution is to have the gauge modified to negative switching.

Hope this helps.

Chris

[jleyton]

As others have said, the feed to the solenoid goes through a fuse, inhibitor switch and the o/d switch and runs a pretty complicated path with quite a few connections.

At the solenoid itself, you simply have the feed and a short earth wire that is earthed next to the solenoid itself.

You could run a direct 12v feed to the solenoid to see if you can hear it click. If it does with the direct feed but not with the normal feed then you can be pretty sure then there's a problem somewhere along the feed line.

Cheers

Julian

[Mike Stevens]

As mentioned, the wire down the gearlever is flexed everytime you change gear and it eventually fractures the copper core inside the plastic. This fairly easy to check by pulling each wire in turn, end to end. If one of them seems to stretch a bit, then that one has probably got a broken core.

Another point, when you replace the gearlever knob, don't screw the inside nut down further than the top of the threads on the gearlever itself. There is not much clearance inside the knob and a shorting of the live feed to earth (and a blown fuse) is likely if the nut is too far down.

Ign on (engine off), O/D switch on, lean out the open door and gently put the gearlever into 3rd or 4th. You should easily hear the solenoid click. If not, you have a wiring issue which is relatively easy to fix!

Cheers,
Mike.

[Stagnant]

I had an O/D fuse that kept blowing, followed by the O/D not working at all. The wires inside the gear lever looked OK but as everything else also looked OK I replaced them - problem solved for a fiver.

Mark

[simonmetalback]

Thanks guys for some very useful tips. I have just fitted my car with a luminition ignition kit, so this would explain the rev counter. I will have play with the over drive at the weekend. Thanks again.

[tractorjames]

Maybe worth cleaning the 2 overdrive filters while your on with the job, i just done mine while the car was in the air and im glad i did with the ammount of metal and sludge in there.

James

[Stagless Steve]

Not sure about the J-type OD but the A-type has a check lever on the opposite side of the OD to the solenoid so that you can check the correct positioning of the actuator arm inside the solenoid bracket. When actuated the check lever should move to a position whereby you can insert a 4.5 mm drill bit shank through the hole in the check lever and into a hole in the side of the overdrive. Give that a check because even if the solenoid is functioning correctly, if that lever isn't moving correctly it means that the solenoid movement isn't being correctly transmitted through the actuator shaft. If that's the case then you may need to tighten the pinch bolt on the actuator arm.

Steve