There have been many posts here on failure of the 240 A70/71 automatic transmission overdrive electrical circuit, some of them quite bitter and competitive - check the archives. I'm going to try to help some poor souls by writing to this board again, although I know the snipers lie in wait to abuse me again on this subject. By the way, if you doubt my mechanical bona fides, I'm a retired nuclear submariner and this little overdrive circuit issue is small crackers. I am not offering the Volvo mechanic's "by the book" answer to problems with this circuit, nor am I going to tell you how to "keep it original," or how to perform microsurgery on sealed relays. Instead, I am going to tell you how to fix your car, for good. I eliminated the mis-named "overdrive" electrical circuit on my car, completely, by altering the overdrive solenoid so that it ALWAYS allows operating fluid pressure to the 4th gear circuit in the transmission. My car is now a permanent 4-speed, all day, and it does not depend on the operation of an electrical circuit to give me 4 forward gears.


People write "help" messages here and on other boards reporting that their 240 tranny dropped from 4th gear into 3rd gear and will not shift into 4th gear anymore, or does so erratically, in and out of 4th. this is almost always a failure of the "overdrive" electrical circuit, which enables 4th gear. The "concept" behind this arrangement is butt-backwards of what you would normally expect. If you grew up with Laycock de Normanville overdrives on manual transmissions - on your TRs, your Austin Healeys, and your old Volvos, you think that "overdrive" means an upshift to a higher gear, like from 4th gear to overdrive 4th so you can cruise the interstate - your concept is that you energize a circuit by flipping a switch, which causes a solenoid to retract electro-mechanically, which operates by a lever a hydraulic valve in the overdrive unit, which engages by hydraulic pressure the epicyclic/planetary gears, which changes your final drive output from 1:1 to .7:1 - engine RPMs drop, car goes faster. Right? That's not how it works on a 240 A70/71 transmission. On the A70/71 when you flip the "overdrive" switch you force the transmission out of 4th gear back into 3rd gear and your engine whines, wound out, obviously needing another gear to sustain 65-70 mph or better. This is not "overdrive" - it is more like a second method of shifting into "passing gear" - like for hills, or for a sudden burst to pass a slow truck. I'm not sure why this was needed, because the kickdown function on my 240 transmissions (I have had 5 240s) has always worked perfectly well if I wanted to drop down to 3rd gear from 4th gear. Let's assume that Volvo knew what they were doing and had a good reason for doing this - even so, they could have set it up so that the transmission normally operated in 4-speed mode with the "overdrive" circuit de-energized, then the driver could energize an electrical circuit that would run from a switch through a relay to a solenoid and would cut out fluid to the 4th gear operating circuit inside the tranny and cause a shift back to 3rd. This way, failure of the electrical circuit would give you a default 4-speed transmission. But no, they set it up so that the existence of 4th gear depends on the "overdrive" circuit being energized, all the time, and you force-downshift to third by de-energizing that circuit. This way a failure of the "overdrive" electrical circuit gives you a default 3-speed transmission. No one wants that because everyone operates their A70 in 4-speed mode day-in / day-out, and that is why there are so many messages here about this circuit. It cripples your car for high-speed highway use when it fails. More rpms means more wear on everything turning in the engine.


Now, let's add that this butt-backwards electrical circuit includes a unique relay that sells for anywhere from $30.00 to $50.00, a switch at the top of the gearshift lever with wires that get stressed and frayed, and a solenoid that lists for over $200.00, and is hard to get at with the transmission still in the car, in a very filthy location (grit and hydraulics do not mix well - so you have to spend a lot of time cleaning before you remove the o/d solenoid). And lets add that this electrical circuit is energized all the time you are using your car - no wonder it wears out and parts of it fail!


As you will read elsewhere in here, many times the problem is the relay. You can get to it by removing the glovebox and looking to the left just behind the dash there. It is white. There are plenty of posts on these boards about fixing or replacing (or jumpering out) this relay. If you want to get real nit-picky, you can try opening the relay case and doing solder-surgery on this plastic relay. I had no idea about this when I first engaged this problem - the relay looked sealed to me, and the relay-solderer's guild condemned me as a buffoon. (This is a rough crowd here). One relay surgeon's post on this board even went so far as to include a gallery of close-up relay pictures, in different stages of disassembly and repair - like electrical porn. If you have a relay problem and want to keep this bogus electrical circuit alive, there is already plenty of advice on "doing" the relay. Another main cause of failure seems to be the wires from the o/d switch where they come out of the shift lever column - they can get frayed due to physical stress due to shifting motion. There are posts on this too. The problem could be a shorted or broken wire anywhere in the circuit. You know how to hunt for that. Finally, the problem could be the expensive overdrive solenoid - it could be failed open, shorted, or clogged with crap.


The solenoid mounts to a machined, flat, horizontal surface on the driver's side of the tranny with two 12mm bolts and it has one white wire. The case is the ground. There are two small holes in the machined flat surface, and transmission fluid under pressure passes from one hole to the other, or not, depending on the position of the solenoid. The at-rest, de-energized position of the solenoid prevents fluid from "communicating" between these two holes, disrupting the hydraulic circuit that "enables" 4th gear. Keep in mind that this hydraulic circuit does not CAUSE a shift to 4th gear when complete - all it does is ENABLE 4th gear - the transmission will shift into and out of 4th gear at appropriate speeds/conditions by other means. When the solenoid is energized, it creates an electro-magnet that sucks up the core "slug" against gravity and spring pressure - when this core slug is lifted it opens a channel that allows fluid to pass from one hole to the other - completing the hydraulic circuit, enabling 4th gear. When the solenoid is de-energized (slug in the down position), this hydraulic circuit through the lower part of the solenoid is closed, fluid flow is disrupted and 4th gear is disabled.


If your solenoid fails, or if you are just tired of chasing this backwards circuit, here is the permanent fix. Remove the solenoid. There are good posts on how to do this - get everything really clean first. I had to heat red-hot and bend a cheap 12mm wrench to get the right down-curve offset to remove the two 12mm bolts, without having to get better access by dropping the back end of the tranny a little by removing the center support. Take the solenoid to the workbench. Cut the white wire off, all the way flush with the solenoid top, as an expression of your vengeful frustration with this circuit. Remove the two o-rings (they will either be in the o-ring seal-tracks in the bottom of the solenoid, or stuck to the machined flat surface on the tranny - either way, get rid of them). You will see on the bottom, or "business end" of the solenoid a hole in the very center and a hole near the outer periphery. You want fluid to be able to pass from one of these to the other, so take a Dremel moto-tool with a very fine metal-cutting burr-style bit and route/cut a channel between the two holes. Try to keep this new fluid channel neat and not much larger than the diameter of the largest of the two holes. When finished, blow it off with compressed air, flush it with brake cleaner, etc. - clean all the crap off, metal, dirt, all of it. Put a new o-ring in the outer o-ring channel. I "tack" it in place with a little aviation permatex dotted into the channel in a few spots on a toothpick just to hold the o-ring. There are two ways to go with the inner o-ring - I have done both and both work: (1) leave it out altogether, or (2) slice a small section out of a new center o-ring, for the fluid channel you routed out with the Dremel tool, and tack the resulting "C"-ring (ha ha) in place with aviation permatex, making sure that the open section in the sliced o-ring lines up with your fluid channel. Let the permatex have a few minutes to set so the o-rings won't fall out when you turn the solenoid upside down to mount it. Lay your jimmied solenoid onto the machined surface on the transmission carefully and bolt it down. Now your brick has a 4-speed transmission again, all the time, and the whole o/d electrical circuit is irrelevant - no more soldering of relays. If you want passing gear, kick it down and it will give you third without having to flip a switch on the shift head. I have two cars with this fix on them now, and I have two more 240s (family, with kids) that will get it as soon as their o/d circuits act up.


I hope this helps some regular Joe fix his car and get rid of a headache permanently. Meanwhile, I am ready now for the army of hecklers who haunt this board to start attacking me for every conceivable reason. I think there must be some secret code that I do not know that lets you post here without being savaged by "the regulars." Bring it on, gentlemen.


RDS