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Thanks for the additional information, you have either an AW-70 or AW-70L (lockup tranny and torque converter). There seems to be a bit of overlapping data for the 1990 and 1991 years in the brickboard transmission table but I'm leaning towards the Lockup version (I just recently pulled a Lockup tranny out of an '89 740 that still had it's original engine and trans).
Based on the information you posted (you didn't notice any difference in forward power between "D" drive and "1" low-gear positions), then Table Y2 of page 48 in Volvo service manual TP30687 is what we should be reading. I'll transcribe it below:
Check:
1. Transmission fluid level.
2. Kickdown cable setting.
3. Gear selector.
4. Does the vehicle creep in position "1"? If yes, go to 6. If no, go to 5.
5. Check line pressure and stall speed. If correct, go to 6. If not, go to 7.
6. Check the one-way clutches. Remove the propeller shaft and turn the coupling flange by hand (turning the flange with the trans in neutral). It should be harder to turn clockwise than anti-clockwise (as viewed from the rear). If it's the same in both directions, go to 8-1. If it's correct, go to 8-2.
7. Check for particles in oil pan (Don't just drain the fluid. You must remove the pan and inspect for metal particles, and clean the pan and filter while it is removed). If particles are present, go to 8-2. If no particles, replace (or clean and check) the valve body assembly. Also, clean/replace the oil strainer. Check gear selector mechanism operations and check the accumulator piston C1. If no change after this, go to 8-2.
8-1. Replace or rebuild the transmission (probably a fault in one-way clutch #2).
8-2. Replace or rebuild the transmission (probably a fault in clutch #C1).
Needless to say, I would strongly encourage a very careful assessment of steps 1, 2, and 3. Try overfilling the fluid by 0.5 or 1 quart and see if it makes a difference. Look at your throttle body and make sure that your kickdown cable isn't hung up on anything. If you pull the kickdown cable manually, does it feel like it has a decent spring behind it (attempting to pull it back into the cable sheath). Make sure that it retracts as much as it should. And lastly, make sure that the gear selector is all the way in position. You will want to crawl under the car (properly raised) and work the selector by hand. Make sure that nothing is damaged, bent, or out of sync with normal shifting of the selector lever (loose bushings in the linkage, etc).
I would strongly encourage you to do the above checks with a suitable repair book. While Haynes does have some material, the best option would be a Volvo service manual that covers the 700 series AW70/AW71 transmissions (like the TP30687, TP31642, TP30868, etc). Aside from that, a Bentley book for a 240 would be a good manual to have, and then finally the Haynes books for the 240 and 740 (the 740 book only goes up to '88, and the 240 book is laid out a bit better).
Lastly, when was the last time you cleaned the transmission filter? (not a fluid flush, but actually removed the pan and changed the filter) The reason why I'm asking is because it may be clogged. Here's some information from the www.brickboard.com AW70 transmission FAQ that may resolve the problem:
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Quote: "Intermittent Shift Failure: Clogged Filter
[Query:] After starting, everything goes well, the transmission shifts, but in a short while, suddenly, the transmission becomes disconnected, losing traction; moving, I accelerate and the motor increases revolutions but the car behaves as though it were in neutral. I must stop the motor, wait a moment and repeat the operation. While the problem is occurring, if I accelerate in neutral I hear a slight buzzing noise of gears even though the transmission has not engaged. The oil is new. I changed the kickdown cable. [Response: Abe Crombie] The things you list sound like a stopped up filter inside transmission pan. Did the pan get removed and the filter inspected? The filter is a fine metal mesh strainer and can be cleaned in most cases. I didn't read your previous post of a month ago so I do not know how this started but using shop clothes to wipe off things inside transmission or to wipe the pan when it is off, can introduce lint that the transmission filter will catch when it is running. The debris on filter then starves the transmission pump for oil. The transmission pump will whine when operating with excessive vacuum on its inlet due to a plugged filter. When you stop and shut down engine, the lint falls off the filter and it will work again for a period of time until the lint is sucked up onto filter once again."
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A few more posts for you to read, regarding filter/strainer and pan cleaning operations:
http://www.brickboard.com/RWD/?id=645312
http://www.brickboard.com/RWD/index.htm?id=655545&show_all=1
http://www.brickboard.com/RWD/index.htm?id=721635
Checking the transmission fluid for proper level in both warm and cold engines:
http://www.brickboard.com/FAQ/700-900/TransmissionAuto.htm#TransmissionService
God bless,
Fitz Fitzgerald.
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'87 Blue 245, NA 231K
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