On a Volvo fitted with overdrive when you downchange the gearbox with the overdrive engaged, the O/D also disengages. When changing up again you have to press the spring loaded g/knob switch again to re engage the O/D.
I have an O/D unit on my MGB that always stays active once it's switched on (except when you're in 2nd or 1st). The problem is if you forget to disengage the O/D and you're in 2nd wanting to change into 3rd, it directly selects O/D 3rd.
I would like to incorporate the Volvo relay system onto the MG but cannot fathom out the Haynes book on the Volvo wiring diagram. Conversely the MG wiring diagram is very simple.
What relays etc do I need from a Volvo to make this idea work, and can anyone supply a fairly straight forward wiring diagram/sketch for me to make a small loom please?
|
Alan,
Do your manuals tell you which types of overdrive are fitted to your MGB and the Volvo, e.g. Laycock de Normanville 'J' type or 'A' type? These have different systems of switching that may require a slightly different circuit to be devised.
By the way, we two have had some interesting discussions on BMWs, Triumphs, etc, by personal e-mail, as a result of your coming across my profile on this forum, and I looked forward to reading your own profile only to find that it is not given. I'm sure a brief introduction to your background and cars would be interesting.
|
Alan, you wrote to me directly with answers to my follow-up and I hope you don't mind if I repeat them here, for the sake of continuity and in the hope that others will be able to help. You said ...
"The MGB has an L de N Type LH and the Volvo has a J, P, or a J/P Hybrid. I didn't really want to confuse the issue with types as I thought that they all seemed to be activated by a simple electromagnetic solenoid.
On the Volvo I assume that the switch simply energises a relay which makes the circuit throw in the solenoid. A gearbox actived switch breaks the circuit (when 3rd 2nd or 1st are selected) and cuts the relay. This can only be reactived again by the gear knob switch. This is what I want on the MG. The Swedish wiring diagram that Haynes copy from Volvo needs a different mind set to understand it.
I was just hoping that I could save some time in asking someone more familiar with the vagaries of the Volvo type set up."
I regret that I am not at all familiar with the Laycock overdrives that you have on your cars. I was hoping that they were 'A' or 'J' types as fitted on various Triumphs. These two types are basically the same but the 'J' type is much stronger and, because its solenoid uses the power of the hydraulic system to switch the O/D in or out, it is wired directly from the gearstick switch (no relay). The older 'A' type uses electrical power for the switching and therefore has a relay between the gearstick switch and the solenoid to handle the greater electrical load.
I'm sure your MGB and Volvo overdrives will be essentially the same as either the 'A' type or 'J' type and all that matters to us here is "does the MGB have a relay in the circuit?". To be honest, the fix that you are after will probably be the same either way but I thought it best to establish the current(!) circuit before we try to come up with a solution.
You are right, it would be far better for someone who knows the Volvo system to explain it to us rather than to try to 'reinvent the wheel'. I would be interested in the mod for my own Triumph which has the 'J' type overdrive, although I have trained myself to automatically push forward the O/D button on the gearstick every time I change into third, to avoid those embarrassing and dangerous jumps straight into O/D 3rd.
|
Alan,
Here is my immediate response,I know the problem well but am not at my workshop at the moment. The floowing will encourage you but I thnk I can dig up an older manual an draw up the diagram for you may be even this evening Regards Peter
Firstly bear in mind that what you require is the latching relay associated with the overdrive form a Volvo. This engages the overdrive with a single push if you are in 4th and disengages overdrive with a further push.
From memory this relay was under the left hand side of the dash above the turret and can be found by following the cable that comes from the gear stick under the carpet. This relay has a de-bounce circuit to avoid the Overdrive from jumping in and out whilst you push the button so it is the best solution.
This latching relay is always reset to be disengaged when powered up with the ignition thus guaranteeing the overdrive only engages when in 4th and the button is pressed.
From memory a fused 12 volt feed from the ignition cct and a ground is fed to the relay, two wires from the button and one wire from the 4th gear switch and output wire to the overdrive solenoid.
|
Peter,
Thank you very much for your response. On the Haynes Volvo 740 diagram there's a reference to several electrical items connected to the O/D. #123 Relay - #77 Overdrive contact - #201 Actuator solenoid - and #54 Overdrive switch.
Would a simple spring loaded flick-switch as fitted to early Mini screen washer systems (if you're old enough to go back that far!!) replace the Volvo gear knob switch? This could replace the Lucas on/off dash switch without changing too much from the original.
I (and I'm sure David) look forward to receiving more news from you.
Alan.
|
|
|
|
David,
The MGB does not have a relay in the O/D system - it's fed by a very simple sub loom from the main harness. I have fitted a small warning light next to the dash board switch to try and remind myself but as you say there are still those occasional moments when the 'box goes from 2nd to 3rd O/D. I suppose that if my switch was on the gearlever (as on the later MGBs) it wouldn't be too much of a problem.
The solenoid in the O/D unit closes a ball valve which forces the internal pump to apply pressure to the drive clutch. I have made a simple rig to bench run the gearbox / O/D unit and to check that the pump runs at around 400psi. Also it's good for checking any leaks before putting it back in the car.
On the old Volvo system I think the switch is simply a spring loaded activator which brings a relay into play until the gearbox switch (ie 4th to 3rd) breaks the circuit.
|
Alan,
I hadn't realised that the older MGBs had the O/D switch on the dashboard. I can see how that makes it even more difficult to remember to switch off.
It sounds from your description as though the overdrive is similar to the 'A' type even though it has no relay. Perhaps the switch was capable of carrying a higher current than that on the later Triumphs.
Reading Peter's response, it looks as though you are in very capable hands. It is very unusual for a query to completely stump this forum and I'm pleased that Peter has maintained our good reputation on that score!
Regards,
David (Dizzy).
p.s. 'Dizzy' is my old school nickname, resurrected for this forum to avoid confusion with the other David W, our resident expert on Peugeot, Citroen, Land Rover and much else.
|
Right I have the information and diagram you require relating to a decent overdrive circuit. You can use the 740 or the 240 series circuit whichever is the most available in your scap yard but the cct is the same email me and I'll send you the circuit no probs Peter@3DAssociates.co.uk
Regards
Peter
|
Further to your question, no the spring loaded washer bottle switch will not do, this will only temporarily engage the overdrive. unless you want to use one instead of the overdrive button in the diagram I can send you when you email me.
Usr a button in a convient place or on a car autin many years ago, yes I do go back that far, I fitted on triggered by a floor mounted dip/main beam switch, no relay required.
Regards
Peter
|
Peter,
I assumed that the Volvo button had two terminals like the 'Mini switch'. I'm getting a bit ahead of myself here! I'll wait for your details. Once again thank you for your help.
Regards,
Alan.
|
|
|
|
Peter,
Thank you very much. I will email you for the circuit. When I've made the loom and fitted the mod., I'll also post the information off to the MG club that I belong to. I'm sure that other B owners will want to do the same.
Regards,
Alan.
|
Hi,
I'm back at the workshop this evening so will send it then.
Regards
Peter
|
|
|
|
|
|
|
![Audi Q6 e-tron 225kW Performance 100kWh S Line 5dr Auto [S+V]](http://images.honestjohn.co.uk/imagecache/url/crop/90x60/https/cdn.uk.prod.group-mobility-trader.com/images/cas/d825933426311e8489e7f76f635a45a1/d2eda1c4c6924101a9be3d2d80c8e923.jpg)
