Overdrive issues

[Rze30]

Folks - open to ideas here. My J-type overdrive refuses to engage. I have taken the following actions.
Changed gearknob switch for new switch - all working.
Changed relay - all working
Changed overdrive oil and pressure is fine
Changed solenoid (twice) for refurbed units and everytime I fit solenoid - 35A fuse blows.
Tearing my hair out (whats left of it to start with). I get power all the way to solenoid with no issue - tested it with a lamp on circuit and it lights every time. Minute I attach solenoid and flick switch it blows the fuse.

Any ideas???

[jleyton]

Sounds like you've tried most things.

First thing I'd suggest is to either remove the solenoid (sounds like you're used to that by now !)- or use a spare one, and operate it via the normal wiring, but without it screwed into the o/d - you can feel it click if it's working.

If that works ok then at least you've pinned it down to something inside the overdrive. If it still blows your fuse then it's somewhere in the wiring - usully in the lead up the gear lever.

Good luck.

Cheers

Julian

[bunny]

Hi
Not much can go wrong with the overdrive, 99% of the time its wire probs, sounds like the wires in the stick are shorting out
vince

[StagnJag]

Like Vince says, the one thing you haven't mentioned is the wire in the gear stick. It can chafe through the insulation where it comes out of the bottom of the gear stick. Also, as you have replaced the switch, double check that the terminals on the back of the switch are not shorting against the gear knob.

Rgds

Dave

[404ROD]

Have you earthed it correctly?

Rod

[Rze30]

Thanks for all the feedback. To be honest I hadn't thought about wires at bottom of gearstick or the terminals on the switch shorting. Will have a go and take a good look at them and see if it fixes it.
Thanks Folks!

[ampotter]

Careful with the fuse rating (35 amp)! According to the manual the fuse rating for the overdrive is 10 amps.

[Bandit1200]

In support of the above, make sure that you position the gear knob on the shaft, sounds pornographic doesn't it, to avoid the contacts shorting within the head of the gear knob.
If you fail to get the above right you will blow the O/D fuse in the fusebox
Steve

[davidf]

Just want to clarify one thing - when you say "I get power all the way to solenoid with no issue - tested it with a lamp on circuit and it lights every time" - do you mean that you connected a 12v lamp to the solenoid feed wire (and to earth), and switched on the overdrive (ignition on, 3rd or 4th gear, engage switch on gear knob) - then the lamp came on and no fuse blew. If that is the case, it is not a problem with the wiring, it is a problem with the solenoid.
Also, you mention changing a relay - as far as I can remember there is no relay in the overdrive switching circuit.

[Rze30]

Just want to clarify one thing - when you say "I get power all the way to solenoid with no issue - tested it with a lamp on circuit and it lights every time" - do you mean that you connected a 12v lamp to the solenoid feed wire (and to earth), and switched on the overdrive (ignition on, 3rd or 4th gear, engage switch on gear knob) - then the lamp came on and no fuse blew. If that is the case, it is not a problem with the wiring, it is a problem with the solenoid.
Also, you mention changing a relay - as far as I can remember there is no relay in the overdrive switching circuit.

That is exactly what I did David. There is a relay which connects the Solenoid switches to rear window heater. I disconnected the rear window and changed the relay. My wiring is as documented in Haynes guide and there is a relay.

[davidf]

Ok, seem to have a bit of confusion over the relay. The ignition controlled relays are simply energised by the ignition switch circuit, and provide power direct from the battery to high current functions. This avoids switching high currents through the ignition switch contacts - it would burn out the inside of the ignition switch. There are 2 of these relays. One feeds the heater blower and heated rear screen; the other feeds the window motors and the overdrive. In both cases, the fuses are after the relay; the heater and rear screen share one fuse off one relay; the overdrive has a fuse, and the window lift has a circuit breaker.
If the fuse is blowing, the fault is down-stream of the fuse, so it is in the chain - fuse to gear stick, gear stick to gearbox inhibitor switch, inhibitor switch to solenoid.
If you can use this circuit to power a light bulb, then the circuit is OK.
Maybe some-one knows what the resistance of the solenoid should be - I don't have that figure, but it must be over 1.2 ohms to take less than 10 amps. If yours is blowing a 35 amp fuse, it suggests it is less than 0.3 ohms. Have you a meter to measure such low resistances?

[DJT]

That is exactly what I did David. There is a relay which connects the Solenoid switches to rear window heater. I disconnected the rear window and changed the relay. My wiring is as documented in Haynes guide and there is a relay.

Aren't there 2 ignition controlled relays? One of them (93) supplies the HRW (94, 95, 96) and Heater (97, 98, 99), the other (84) supplies the o/drive (85, 86, 87) and the power window circuit breaker (88). Both relays are connected by the same ignition controlled white wire.

Wiring Diagram.jpg

[davidf]

DJT - correct - the item numbers you have given are for Mk1 - different numbers but same principle for Mk2, except that both relays have the same number on the Mk2 diagram.

Mk2:-
One of them (94 right) supplies the HRW (92, 93, 94) and Heater (100, 101, 102), the other (also 94, on the left) supplies the o/drive (88,89,90) and the power window circuit breaker (95)

[bunny]

Hi
Rze said he has changed the solenoid twice so that cant be the prob, unless very unlucky lol.
Before trying the relay maze just check the wiring first, thats usually the prob.

[Firept]

I assume that the J and A type use a similar solenoid switching. If with the solenoid disconnected and then operating the o/d switch the fuse still blows its a wiring or inhibitor switch problem.
If the fuse does not blow its a solenoid problem.
There is a switch contact on the top of the solenoid as the solenoid has 2 windings one is the main pull in coil and the other is the hold coil as you need a large amount of power to get the solenoid to pull in but once it is in it requires very little current to stay there.
As the solenoid pulls in it operates the switch on the end of the solenoid (under the black cover) and disconnects the main coil just leaving the hold on coil powered. this could be where your problem is.
if you look at my album there is some photos of the solenoid with the guts removed.

Paul.