Volvo P1800 J-Type Overdrive selecting in 2nd, 3rd and 4th

[Tint]

Hi folks hope you well.
Just had J-Type OD Overhauled (New 'O' Rings - had hardened with age).
Before overhaul overdrive only engaged in 4th gear, now engages in 2nd, 3rd and 4th, is this correct. If it should only be 4th is there an issue leaving it as is or is this detrimental to the gearbox and OD.
Cheers.
PS Engages beautifully now, instantaneous and smooth.

[Derek UK]

OD should have a lock out switch to stop it working in any other gear but 4th. The switch is mechanical and is only depressed when in top gear. That completes the OD electrical circuit so that OD solenoid is only activated when in top gear. If the two wires to the switch are inadvertently shorted together this safety function won't work. It's essential that you fix this, as damage to the gearbox will happen if you select reverse with the OD engaged.
Switch is situated on top of the gearbox cover plate, the flat part at the front of the remote shifter mechanism. There is sometimes 2 similar switches, one for OD and the other for the reverse lights. If you don't have reverse lights the wiring might be transposed. Not sure if that is possible but put out there for consideration.

[Tint]

Thanks Derek, appreciate your prompt response.

The transmission specialist that did the gearbox did question the switches that you refer to, the overdrive inhibitor switch and also lack of reverse light switch on my gear box. The reverse light has never worked so now I know why. Of course I couldn't enlighten the specialist of their function and assumed they had figured it out.

I have pictures of the gearbox on the bench taken whilst they were working on it (still not figured how to put pics on here) it looks like there was only one switch there, with one black wire going to it. Before they did the work overdrive only engaged in 4th gear as I believe it's supposed to.

So if this switch was not connected is this the likely reason overdrive selects in all gears. Should there be one wire or two wires going to the overdrive inhibitor switch. When on the bench and thus off the car I could only see one wire.

I can see from Brookhouse Volvo Simon has both the overdrive inhibitor switch and reverse switch, and also an overdrive relay, do you know where the overdrive relay switch lives? And what it's function is.

Thank you
Steve

[c1800]

A short explanation of relays and how they work

http://sourceresearch.com/newsletter...orks.cfm?emART

Your relay is under the hood and if the original type will look like the one shown on the Brookhouse site.

https://classicvolvoparts.co.uk/part...LighterSensors

[Volvorama]

In the meantime be very careful not to allow overdrive to try to engage in reverse. This can wreck the unit, apparently. Overdrive inhibitor switch should be the one on the left hand side of the gearbox top (as viewed from the rear).

[Derek UK]

I'm can only partially answer you, If you look at the link below you'll see that the lid shown has 2 switches. The passenger side one is for the OD lock out. The other is for the reverse light. Not always fitted but it replaces the hard to get at one under the lower back end of the gearbox. The latter position fine when there is no OD but it appears that it is just possible to use it when OD is fitted but the connection for the wire may short out on the OD adaptor. https://www.volvoforums.org.uk/showthread.php?t=282906
These two switches are same part number, which makes the possible mistake of transposing the wires even easier.

The lid shown is I believe one from an earlier box. The later ones with J OD have a higher and more beefy extension.

I stand to be corrected but I believe that the later gearbox with J OD dropped the relay. D type OD certainly used one. J type solenoid is different to that on the D type and Laycock may have said that a relay wasn't needed.

Checking the wiring is difficult due to the switch being on top of the box. Engine off with ignition on and in 4th gear you should be able to hear the solenoid clunk in when you us the OD switch, It shouldn't clunk in any other gear. Test in 1,2 and 3 plus reverse ENGINE OFF. Dash light only indicates that the switch alongside the wheel is in the ON position and not that the OD is engaged. Does your car have any small access panels in the sides of the tunnel adjacent to the switches. Some cars have them and some don't.

[Tint]

Cheers C1800, excellent relay overview.

Thanks Mark, unfortunately even though warned I have just selected reverse with OD light on, with the engine running to get car back in garage, there was a nasty clunk, but didn't engage into reverse, all still seems ok, fingers crossed. Cant imagine any clunk is a good sign mind.

Derek,
Again much appreciate prompt response.
Very useful and has me better prepared for when I get in touch with the specialists tomorrow.
Solenoid clunks in each gear carrying out your instructions.
If there has been any damage hopefully specialist will rectify at his cost, only picked it up this morning, had had quite an amount done, gear box bearings front and back, clutch and slave, rear axle checked for wear and new oil. Gearbox now sealed rather than casket, same for OD, and of course OD refurbed with new o rings.

[old fart]

The switch on top left of gearbox isn't an inhibitor switch, rather it is the switch which is operated only in 4th gear to allow the overdrive to work. The wire should run from the solenoid on the side of the gearbox to this switch, and from there to the column switch. It could be that the switch on top of the gearbox is knackered, and is making contact all the time, although normally when they pack up they don't work at all.

[Tint]

UPDATE:
The specialists that did the work (they have done an exemplorary job by the way) have instantly held up their hands, school boy error on their part, booked in to have the Overdrive Inhibitor Switch wired back into the circuit. Thanks Derek your detail allowed me to broach this in an informed way, prior to my question I had no clue.
Toodleloo