Amazon: Gearbox w/od

[hairyapple]

my 62 122s 2 door came to me with an overdrive already installed, that was very nice I thought. I was under the impression that the od could only be engaged after making it into 4th gear and always disengaged before any attempt to downshift to something below 4th. Here's the rub-I don't seem to be restricted in this way, I can engage any gear w/o first disengaging the o/d. I sometimes forget to follow the rules as I have a wagon w/o o/d and I get confused. So I assume the 4th gear lock out is either broken or non existent. Do you think this occasional mis-step is going to eventually do great harm? If so, what kind of harm? By the way, this car is fitted with the stock long shifter and I always use the clutch when engaging or dis-engaging the o/d.

[Derek UK]

The stock set up for OD uses a lock out switch on the top plate of the box. This only allows the OD to be energised when the lever is in 4th. If you change down to 3rd it cuts out the OD but will go back to OD 4th when you change up again if you haven't flicked the lever out. If you're getting OD in all gears it will put it under a lot of srain especially if you change down at high revs. The OD oil pump won't be happy. Much more dangerous, and expensive, is trying to change into reverse with the OD still engaged. There are parts that aren't designed to be reversed and have ratchet pawls (my description, which may not be technically correct) to allow reverse to be engaged. These get damaged if OD is still active. If your OD clicks in and out OK it still might take a second or three to completely disengage if you switch it out in 1st. At least wait a bit before trying reverse.
Do you know if you have the lock out switch? I see you have a B20 so things aren't original under there.

[Ron Kwas]

ha;

Your understanding is correct...OD should only be able to be engage in fourth gear, so it sounds like your LO switch is non-existent (or shorted, which is possible I suppose).

The intent of the LO switch is to prevent OD activation in all but fourth gear...in order to spare OD the higher torque of the lower gears, and certain death guaranteed of reverse. Performance-wise, there's no real reason to need first or second plus OD. Some British cars had a third/OD option, but this was never used in the Volvos.

Bottom line is, be gentle and you'll be OK. NEVER, EVER engage OD while in reverse, and to be safe, install (or repair) fourth LO switch, and consider adding OD control (PN1259750) relay from a later 240 to prevent "unwanted reactivation" condition. See: http://www.sw-em.com/OD_Retrofitting.htm

Cheers

[TomTom]

My reading of this is that HA is describing the first situation that Derek mentions above, namely the shift down into another gear without disengaging OD; a completely normal state of affairs, bearing in mind tht you should remember to disengage if possible!

But granted, if he can 'engage' in other gears, then that is a different kettle of fish.

Tom

[hairyapple]

Have I got this rite? if I down shift with the od still engaged ie the lever on the cowl is down, it might automatically be switching out of od w/o my even knowing it. OR I may just have a bad switch or a short. Is there a difinitive way to tell? I will check out Ron's site as well to get an education in this matter. Thanks all.

[Derek UK]

If you have the GB switch and it's working correctly, it should drop out of overdrive when you change down to 3rd. If the lever is still down and the system is working correctly it will go to OD 4th when you change up again.
Best to check with another person, but with the engine off and ignition on you should be able to hear/feel the OD solenoid working when you engage OD with the box in 4th and hear/feel it click out when you change down to 3rd. If the system is correct, using the OD lever with the 3 lower gears, shouldn't energise the solenoid.