Overdrive Problem...

[mazz2]

Hello,

I have a 1970 P1800e and the overdrive has decided to stop working. I can still use the first 4 gears but when I try to engage the overdrive nothing happens; not even the light comes on. I have looked underneath and cleaned all the electrical contacts (solenoid etc..) traced the wiring back and nothing obvious seems amiss, so now i'm a bit stumped. If someone has any ideas, they would be much appreciated. Also if someone could tell me which relay operates the OD it would be most helpful,
Many thanks.

[mike gilbert]

Have you checked the fuse under the dash? I could be wrong but I don't think the 1800E has an overdrive relay. The 1800S has one but it uses a different type of switch to the E. The E switch is a bigger unit and has 'on' and 'off' positions but the S version is just touch sensitive so uses a relay to act as the on/off switch. I don't think its the solenoid because you would still get power to the light on the dash even if that were the culprit, so it has to be a break in the live feed to the switch or the switch itself has stopped working. With the ignition on you should get a permanent live feed to the switch (it only has two wires) so, presuming the fuse is OK, thats the next thing to check. If you have current to the switch then the switch is your culprit, if not its a wiring problem.
Mike Gilbert.

[mazz2]

Thanks for the suggestions Mike. I have tested the switch and it is fine and all fuses are OK; so the plot thickens. There is actually a relay under the left wing which has 'overdrive' stamped on it, I requested a OD relay replacement from Brookhouse, and they sent me the one that is next to it,arghghgh - I think I need a manual! Any other ideas would be much appreciated,,all good fun,,:)

[mike gilbert]

I've checked the electrical sections in both the handbook and my workshop manual and there is no overdrive relay listed among the electrical components or illustrated in either wiring diagram. Do Brookhouse actually say there is an overdrive relay or are they just sending you one from a description of the unit and location you've given them? If they say there is one then my books are wrong but otherwise its possible someone has been making alterations in the past.
Mike.

[mazz2]

Mike,

I just asked Brookhouse for an OD relay and they have apparently sent me one, so I can only assume this is correct! However with all present relays now actually working the problem still remains. I tested the solenoid with a jump lead and earthing to the gearbox and it didnt seem to do anything; should I be able to hear an audible 'clunk'? Even if the solenoid wasn't working should the light still come on? With the key in the 'start' position there is no live feed to the switch.

Thanks for your help :)

[mike gilbert]

I have no idea if the solenoid makes an audible noise when it operates but I don't think that is at fault anyway. I can tell you that a relay will make a pronounced click, especially when you operate it with the engine not running i.e. background silence. If you are certain the relay you've fitted is actually part of the overdrive wiring, it will make a click when it operates and the light on the dash will come on regardless of whether the solenoid is working or not, so as that is not happening it suggests the fault lies elsewhere. You say there is no juice getting to the switch, so Have you tested whether there is any current going to number 3 fuse? If there is current to both sides of the fuse holder but not the switch then there is a break in the wiring between the fuse and the switch. You have to ascertain if power is getting to all the components - fuse/switch/relay/solenoid - in that order and only when your happy with that look for a faulty component.
Mike.

[Stuart Read]

Hi

Not sure if adding my two pen'orth will help or hinder. . .

It should be relatively straightforward to check if you have power at the solenoid (ie a voltmeter) If you do, then either the solenoid is at fault or the internals of the overdrive unit.

If you don't have power at the solenoid, check the output from the relay. If there's power there, then either a broken wire, connection, or the top-gear sensor on the gearbox is the likely cuplrit.

Hope this helps. . .

Stuart

[mazz2]

Well I have finally figured it out. Simply there is a break, either corrosion or otherwise, in the wire between the fusebox and the switch. I patched a new wire in its place and it works fine. There isn't actually a OD relay on the 1800e, I was confused by the fact one had 'overdrive' stamped on it, maybe it was borrowed from an earlier car and used for something else. Thanks Mike and Stuart for your suggestions, much appreciated. If anyone needs a wiring diagram for the 1800e follow the below link, there are also some other useful documents to download (OD unit, hydraulic servo,owner manual etc..)

http://volvo1800pictures.com/document/72E_wiring.jpg