OD relay

[hairyapple]

Is there a generic relay that can be used to switch the OD on and off? I am using the cowl (steering wheel) mounted switch. This is a retrofit and so I have nothing to go by. The Volvo part # is 669102 and is available from Brookhouse but I was hoping I could get something state side.

[Ron Kwas]

ha;

Any generic three or four terminal relay will do the job nicely...see article for options on wiring diagrams: http://sw-em.com/OD_Retrofitting.htm#Wiring_of_the_OD

Cheers

[tdz840]

ha;

Any generic three or four terminal relay will do the job nicely...see article for options on wiring diagrams: http://sw-em.com/OD_Retrofitting.htm#Wiring_of_the_OD

Cheers

Ron
Ive book marked your web site several years ago and continually refer back on various items. Very informative - thank you!
Question: On MGBs/Triumphs I have owned in the past the OD could be activated in 3rd and 4th. Useful around town and in the stop start driving we see today.
Is this possible and how should it be done.
I know the issues with linking out the 4th gear switch and selecting reverse.
I dont want it on all 5 gears!!
Cheers
Russ

[Ron Kwas]

Russ;

If you must have OD available in 3rd gear also, you would have to enable it with a switch in the same way it is enabled for 4th gear only (I expect this could essentially be accomplished with another strategically located switch on the gearbox cover)...both switches could be wired in parallel....but I frankly don't think it's needed...with the wide torqueband of our engines, combined with the gearing, it results in good overlap, so I just question how necessary it is to have 3rd/OD available.

Cheers

[hairyapple]

rk
thanks for the info and web page. I did look up that particular question already and either didn't recognize the answer, electrics are my weak spot, or missed it entirely. Will look again.

TDZ840 and RK
My 62 sedan if fitted with an OD already and it doesn't seem to have a lock out incorporated as I seem to be able to shift into any gear while it is on w/o any detriment. I don't usually do this except by accident, because I have been told that it really isn't good for the trans or OD. How is the lock out supposed to work? And is my information correct? If the lockout isn't necessary why is it there and why would it be okay to defeat it?

[Derek UK]

Ultimately the lockout is there to protect the overdrive. It will likely be terminally damaged if you select reverse gear with the overdrive engaged and then let out the clutch. Parts of the OD are designed to rotate in one direction only.

[TomTom]

I can appreciate one attraction of OD on 3rd, for overtaking on A roads. Rather than sitting in 4th and changing down, you would sit in OD 3rd (just bearable at 60-ish) and flick down for overtaking, which is quicker and smoother than a manual change could ever be.

I wouldn't fit this because I don't do a lot of cross-country driving, but I dare say there are some who do.

Tom

[tdz840]

Russ;

If you must have OD available in 3rd gear also, you would have to enable it with a switch in the same way it is enabled for 4th gear only (I expect this could essentially be accomplished with another strategically located switch on the gearbox cover)...both switches could be wired in parallel....but I frankly don't think it's needed...with the wide torqueband of our engines, combined with the gearing, it results in good overlap, so I just question how necessary it is to have 3rd/OD available.

Cheers

Ron
Thanks for the info However as TomTom says driving in the UK is very different to the US. The roads are smaller with lots of traffic and having the addition of 3rd and 4th overdrive would be beneficial. Afterall 6 gears in the UK is now commonplace with cars being fitted with 8 gears!
Thing is trying to find the space for the extra switch on top of the transmision would be challenging. Perhaps the existing switch could be used for 3rd with OD 4th on some form of electrical isolation that is manual and free from the gearbox. Does that make sense or complete cobblers?!
Russ

[hairyapple]

Ultimately the lockout is there to protect the overdrive. It will likely be terminally damaged if you select reverse gear with the overdrive engaged and then let out the clutch. Parts of the OD are designed to rotate in one direction only.

Finally a response that makes sense. I've asked this question a lot and this is the 1st time I've heard this. I had never thought of this scenario. Now it all makes sense. The lock out is specifically meant to protect the overdrive from rotating in the wrong direction. I guess I've just been lucky so far. I'll bet when the conversion to the long shifter was done the lockout was never incorporated. As soon as my right arm is out of this sling, I'll get it onto a lift to see for sure. Thanks

[Derek UK]

The Amazon was never factory fitted with the extension and short shifter so the lock out switch is fitted to the long lever top plate on those cars that left the factory with OD. All the top plates are interchangeable on the M40/41 but the early type 1800 extension makes the shift lever sit very low and far back between the very front of the seats. Some people like that but the later 140 type puts it up in the air a it and a little further forward. It's a more chunky lever and although very solid, sometimes feels a bit stiff. This M41 would normally have a J type OD.
There is a cast in ring on the non OD top plates which gives you the position to drill and tap for the switch if you need to. There is a similar ring in the plastic steering column cowl which lines up with the Volvo switch.

[asneddon]

If it was only reverse that can damage the OD then you could use the reverse light switch to isolate it. I'm pretty sure you can also damage the OD by putting too much torque through it, causing the cones to slip, this wearing it out pretty damn fast

That said, I think Volvo were being a little over cautious as I doubt the 1800cc can burn the cones out without the driver being aware they are slipping. If I didn't have the 4th gear cutout switch then I would just hook up a relay to the reverse switch and use that to ensure you don't engage reverse with OD enabled.

[hairyapple]

The Amazon was never factory fitted with the extension and short shifter so the lock out switch is fitted to the long lever top plate on those cars that left the factory with OD. All the top plates are interchangeable on the M40/41 but the early type 1800 extension makes the shift lever sit very low and far back between the very front of the seats. Some people like that but the later 140 type puts it up in the air a it and a little further forward. It's a more chunky lever and although very solid, sometimes feels a bit stiff. This M41 would normally have a J type OD.
There is a cast in ring on the non OD top plates which gives you the position to drill and tap for the switch if you need to. There is a similar ring in the plastic steering column cowl which lines up with the Volvo switch.

More humble thanks. Got any idea what the thread for that switch is?

I am not sure if the current od is d or J but that will be obvious when the car is in the air. I have recently acquired a j type od that I plan to put into my 67 wagon. This unit is from a 1970 144. The shifter extension came with it along with the lock out switch so I have something to look at when I start this project. Since I am going to use the stock shifter, now would be a good time to correct the rattle I get in the gear lever at certain speeds and in 2nd and 3rd. Anyone have any idea what's going to need looking into? Maybe it's not the lever maybe it's the tranny.

[hairyapple]

If it was only reverse that can damage the OD then you could use the reverse light switch to isolate it. I'm pretty sure you can also damage the OD by putting too much torque through it, causing the cones to slip, this wearing it out pretty damn fast

That said, I think Volvo were being a little over cautious as I doubt the 1800cc can burn the cones out without the driver being aware they are slipping. If I didn't have the 4th gear cutout switch then I would just hook up a relay to the reverse switch and use that to ensure you don't engage reverse with OD enabled.

Could you elaborate, starting at "If I..." I don't believe I understand the difference between "the 4th gear cutout switch" and the "reverse switch"
Would you pinpoint the locations for each, just to clarify and an explanation of their individual ***tions? Thanks

[Derek UK]

Tapping the lid - Some info here http://www.brickboard.com/RWD/volvo/927947/444-544/tapping_tranny_cover_overdrive_lockout_switch.html

Using the reverse light switch, lower rear of GB, would mean OD in all gears. After the OD solenoid is de energised the hydraulic pressure probably wouldn't reduce quickly enough to stop problems when changing quickly from 1+OD to reverse. When used with the original 4.56 back axle OD is a useful 5th gear when used with the best spec engine. OD with a 4.10 axle needs lots of extra power to make it a viable 5th gear but does make it what it's called, an overdrive. Good for quieter cruising when conditions are favourable, flat roads and no strong head winds. Perhaps not quite that extreme but fuel consumption won't improve much, if at all, if you lug it in OD.

[PaulWphoto]

I'm sorry I don't get this. Doesn't 3rd+O/D=(approx)4th? After all the O/D was just an early manifestation of a 5th gear. The gearbox works just fine throughout the range without mods - and I am not a purist at all.. Or you could fit a ford sierra G/B if like me you keep searching for the extra gear that isn't there.

[Mike Arnold]

Thread.

I don't know off hand what thread the screws are that hold the switch on to the o/d but most threads on the 120 are UNC (with some UNF). If you need replacement ones you can try classic bolt stockists such as Namrick. However, UNC/UNF are becoming difficult to find.

[Derek UK]

I'm sorry I don't get this. Doesn't 3rd+O/D=(approx)4th? After all the O/D was just an early manifestation of a 5th gear. The gearbox works just fine throughout the range without mods - and I am not a purist at all.. Or you could fit a ford sierra G/B if like me you keep searching for the extra gear that isn't there.


Looks like you agree with me. Od/M41 works best from about 50mph in A to B driving. Ford box can be fitted but would probably work out more expensive and you'll have to cut the floor a bit. It's a nice box but there's not much wrong with the original if it's in good condition.