My 1990 Volvo 740 Turbo with AW71 automatic transmission keeps taking itself out of fourth gear. I have traced the problem to a faulty overdrive solenoid. After nearly suffing a heart attack when I discovered how much the local Volvo wants to replace the soleniod, I began looking for other options.
Is there a way to bypass the overdrive solenoid so that the car will remain in fourth gear on the highway? If so, will doing this cause any damage to the transmission itelf? I do mostly highway driving and I don't tow anything, therefore I have no need to ever take the car out of overdrive gear.
Have you checked the relay if so & it is good you can do the following action Remove the overdrive solenoid from the transmission clean solenoid of any atf & grease Purchase the larger of the 2 O-Rings very carefully make a small grove between the inner flange Reinstall you should now have overdrive I have never personally tried this repair so I do not know if this works It was posted here in this group a couple of months ago I wish I could give credit to the original poster but I am unable to find the post now Glenn
Does the groove in the new O-ring mentioned above actually bypass the solenoid valve, or repair it? It looks to me like the larger O-ring contains the hyraulic pressure being fed to the valve and stops fluid from leaking all over the floor under the car.
The only reason I ask is that from my experience of messing with the overdrive on a manual volvo gearbox (the auto is probably different), strange results happen when overdrive is engaged in any gear but the one it's intended for, such as horrible crunching or screaming noises when in reverse, and having overdrive 1st, 2nd, 3rd; instead of 1st, 2nd, 3rd, overdrive 3rd (4th).
Sorry if I've misunderstood something here, but good transmissions cost a lot more than a bit of TLC on what amounts to a simple electromagnetic plunger valve.
A question for the original poster; have you tried activating the solenoid by directly applying voltage (12v) to it's wire? The coil in the solenoid should have a resistance of about 13 ohms if checked with a multimeter connected between its body and the supply wire. Does it click solidly when energised? If yes, then the valve is working, the only things that could then give problems are, is the valve clogged up and restricting the fluid flow (they are usually cleanable with care), or is the fluid pressure actually high enough to activate the overdrive unit. As an experiment, you could rig up the direct power feed to the solenoid, drive the car, then have a passenger connect the wires to activate the solenoid when you're in top gear, if it works and stays in fourth, then the solenoid and fluid pressure is ok, the wiring or control system is not.
Good luck, Ken
Does the groove in the new O-ring mentioned above actually bypass the solenoid valve, or repair it? It looks to me like the larger O-ring contains the hyraulic pressure being fed to the valve and stops fluid from leaking all over the floor under the car.
The only reason I ask is that from my experience of messing with the overdrive on a manual volvo gearbox (the auto is probably different), strange results happen when overdrive is engaged in any gear but the one it's intended for, such as horrible crunching or screaming noises when in reverse, and having overdrive 1st, 2nd, 3rd; instead of 1st, 2nd, 3rd, overdrive 3rd (4th).
Sorry if I've misunderstood something here, but good transmissions cost a lot more than a bit of TLC on what amounts to a simple electromagnetic plunger valve.
A question for the original poster; have you tried activating the solenoid by directly applying voltage (12v) to it's wire? The coil in the solenoid should have a resistance of about 13 ohms if checked with a multimeter connected between its body and the supply wire. Does it click solidly when energised? If yes, then the valve is working, the only things that could then give problems are, is the valve clogged up and restricting the fluid flow (they are usually cleanable with care), or is the fluid pressure actually high enough to activate the overdrive unit. As an experiment, you could rig up the direct power feed to the solenoid, drive the car, then have a passenger connect the wires to activate the solenoid when you're in top gear, if it works and stays in fourth, then the solenoid and fluid pressure is ok, the wiring or control system is not.
The groove opens up a new passage through the solenoid, bypasses the passage that the solenoid is supposed to open. This just means that the overdrive gear is enabled (not engaged) as it would be during normal driving, i.e. it allows the control system to engage the overdrive gear as necessary.
This is completely different than the way the overdrive on a manual works. On the manual, energizing the solenoid engages overdrive gear, assuming there's hydraulic pressure. Since the pump is turned by the shaft going through the unit, there's no pressure at a stop. If the overdrive is switched on, it will engage as the pressure rises with speed. Also manual transmission overdrive is not designed for use in reverse.
Cheers, thanks for the info, it is obviously very different, and much more similar to the setup on my current 740, which has a 4 speed auto box (retrofitted by myself, was a 5 speed manual car), no overdrive, but does automatically lock the torque convertor into direct drive (like having a normal clutch again) at 58mph, am I correct in assuming that the AW71 selects overdrive based on gear selected and road speed/torque when enabled by the solenoid? I'd often wondered where all the external wires and switches that I'd expected were!
Yes, your assumption is correct. It seems stupid (and more expensive) to have an electric method of disabling top gear instead of having a "3" position on the gear selector. The hydraulic control is there already. Since the 4 speed AW70/71 are a modification of the 3 speed AW55, the only reason I can think of is that it would have required a major redesign to stick that extra position in there.
I have jumpped the relay on every automatic volvo I ever owned (except one with a ZF 4HP 22 tranny). It doesn't hurt anything. My '84 242ti has been hard wired for fourth gear for about 4 years. The relay was fine. I took it out and sold it to a fella who was having trouble with his and didn't want it jumpped. I got $50 from him.
Mike aka Terrible Ted
Jeffrey M C> My 1990 Volvo 740 Turbo with AW71 automatic transmission keeps taking itself
I have a 1990 240DL wagon, had issue with the 4th gear overdrive and made the modifications to the soleniod as follows:
Removed 2 bolts holding item on, with 12mm wrench, drivers side of tranny just under the shifting linkage. Remove the wires, if not already cut or smashed by the linkage. DO not cut wires if they are intact, you may want to replace solenoid someday in the future and if you cut the wire, you have another project to work on.
Removed both large O ring and small O ring around center of solenoid, making sure that no dirt got into the area that the soleniod was removed from. Clean areaa with rag and spray with wd-40 to removed any dirt that gets lodged into hole. I used a mirror to view the area, and bent the spray tube to get the spray to area to make sure it was clean.
Instead of making changes to the tranny, i used a rotozip and hogged out (in a straight line) from the center of the soleniod to the hole outside of the small O ring. Do not go as far as the large 0 ring. Do not replace small o ring as it will prevent the fluid from passing in the groove you just made. It is imperative to be sure you flush the soleniod with cleaner such as wd-40 to make sure that no metal frags get into the tranny. once mod is made, replace the solenoid.
Car will have to heat up and it will shift into all gears as required. If you are in 4th and need to pass, just step on the pedal and it will do it automatically. You may notice a harder downshift when coming to a stop, but this will have no effect on the tranny life.
works like a charm..good luck
Jeffrey M C> My 1990 Volvo 740 Turbo with AW71 automatic transmission keeps taking itself
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