Overdrive problem

[Davemate]

I am trying to get my overdrive working,it's a "j type".When cold the overdrive engages for a split second but then it disengages, so it is trying.Once I have driven for a 5 min nothing happens,but the main thing is it's engaging when the switch is in the off position !
On the way home from work tonight I double checked it by removing the gearstick switch and holding the wires together,when I do nothing happens when I let the part I get the revs drop as the overdrive engages for a split second again once I have done a mile or so then nothing
Am I right in thinking that the live should activate the solenoid and engage the overdrive
which would mean my solenoid is knackered as it's working back to front !

[neilnaz]

Dave I may have misunderstood you here. You first mention that the O/D engages at first then gives up. Then when you were testing later you suggest that it is operating/working/in when disengage/off selected and not operating/out when engage/on is selected.

Can you confirm that the overdrive is actually working despite it being back to front? What I mean is, if it is working then the solenoid is not knackered it is just being drivwn incorrectly suggesting that the wiring is incorrect. The solenoid pulls in or releases the O/D. It is just being instructed to do so in a back to front manner.

If it is definitely working I would trace the wiring and try and understand how it has been wired and remedy. If I have misinterpreted what you have said and the overdrive is just not operating at all or is trying and failing then follow the advice about cleaning filters/checking oil and other advice that should be prevalent on the forum.

It may well be that the switch is wired incorrectly and that re-wiring it you will get correct function back again. If it is just operating but in reverse you could always apply Tipex to the legend on the switch and enjoy........  :)

[Davemate]

  When cold the overdrive only engages for a split second then disengages,after I have driven a couple of miles it does not engage at all.

To do the above I have to touch the wires together then pull them apart
When the wires touch there is a small spark but nothing happens until I pull them apart

With then engine not running(nice and quite so i can hear it) if I touch the wires together you can here the solenoid faintly clicking when the wire touch,which it right ! Which contradicts what's happening when the car is being driven.

I have live fused feed going to the gearbox inhibitor,which then goes to the gearstick switch and then down to the soleiod and then to earth.I have split the feed at the gearbox inhibator to go off to reversing switch for the reversing lights.

Is possible that the solenoid is working back to front and is fact clicking the wrong way when energised

[thescrapman]

1344 wrote:

  Is possible that the solenoid is working back to front and is fact clicking the wrong way when energised

Not really.

Whith the cover off, can you feel a clonk if you put 12v straight from the battery onto the solenoid (upper connection, lower should hav eteh earth on it)

If not, it sounds like the solenoid is playing up.

Cheers

[G.in_Lux]

Nicked from Dave Pearson's site:

"If an overdrive fails to operate the first thing to check is the electrical circuit, most cars do not have a relay fitted (it isn't necessary with the low power consumption of the solenoid) but as a lot of solenoids make very little noise when engaging a circuit test is often required. (Note that Sprint/2000/2500/Stag have a separate switch on the gearchange for overdrive 3rd and overdrive 4th, all other cars have one cut-off switch). The units themselves are fairly reliable (the filtration system is excellent) and it is the solenoid which causes most of the problems. If there is power to the solenoid and the overdrive either won't engage, engages cold and not hot, or won't disengage then the solenoid is very likely the culprit. To remove and replace this a 1 inch spanner is required but it must be no more than 3 mm thick.

The original solenoids have the outer metal case held in position with four small roll pins, if the case is very loose (which can cause incorrect operation) then it is possible to tighten it up with care and it may work again. The only other DIY option is to remove a tiny internal circlip and withdraw the operating piston, there are then two external and two internal O rings to replace if you can get hold of them - if you don't fancy doing all this (and there is about a 30% chance of it working properly again after fiddling with) then replacement is the only option. New solenoids are around £75, but the outer case is swaged on and does not come loose. All J type solenoids are interchangeable. Later Dolomite and Spitfire overdrives (after 1978) have a badly made centre to the one way bearing and from around 30000 miles can give the impression of clutch slip, quick getaways from the lights can lead to an embarrassing lack of forward motion. This problem and in reality all other faults mean the unit has to be removed from the car. Although it just about possible to remove the sump and gain access to the fine filter (RHS), pump ball bearing (centre) and relief valve (LHS) it is very unlikely that anything can be gained by doing so. (Very occasionally the relief valve may stick which means the unit can't work). The whole assembly is not too bad to work on and as long as all bits are put back in the right order and the right way round (without too many left over) then it should work again. The one way bearing is awkward to refit, a piston ring compressor can be used if all else fails."

[Davemate]

Looks like a dodgy solenoid then !!!!

[GT6 M]

or no oil in it !!!!!

[Davemate]

Oil is good I only fitted the engine and box three months or so ago and I changed the gearbox oil then.The old stuff was not to bad but it got a new lot anyway