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weird downshift problem - beginning of end for transmission? 900 1992

I know the AW71 transmissions are very tough, and mine still shifts great through all the gears. But the last couple of days, it's developed a weird problem - when cruising at highway speeds, even if I nudge the gas pedal, it will downshift immediately out of overdrive and I have to take my foot completely off the gas for it to go into OD again. Needless to say, this means a lot of downshifting to maintain highway speeds. Here's what I know:

-flushed last year with Mobil 1, currently full of nice healthy pink fluid.
-OD relay appears to be working normally: I can engage and disengage OD at will, using the shifter button.
-Shifts through all the gears normally and smoothly during regular acceleration. Even fairly smooth during rapid accel/aggressive driving (which I don't do often!)
-throttle cable, cruise control and kickdown cables show no signs of binding, all operate smoothly, they are in exactly the same alignment as they were before this started happening.

So I'm wondering if this is the beginning of the end for this tranny? Or should I try experimenting with the cable adjustment?

Thanks in advance for any ideas.









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weird downshift problem - beginning of end for transmission? 900 1992

Aside from checking the basic adjustment of the kickdown cable, you should check to see if the plastic sheath is still fixed to the ferrule at the end of the cable. If the plastic sheath is free to move in and out of the ferrule, it has the same effect as changing the adjustment. I believe that when the plastic is out of the ferrule, it has the same effect as shortening the cable and makes the kickdown much more sensitive.








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weird downshift problem - beginning of end for transmission? 900 1992

Thanks, as always, for everyone's input. Over the last couple of days, I have made one important observation, which I think might help a lot: This only happens when the car is warmed up. If I take it on the highway right away in the morning, or after the car has been sitting for a couple of hours, it will shift perfectly into overdrive, and the transmission responds as it always has. After a few more minutes, though, it will start downshifting too eagerly, and then will lose overdrive completely UNTIL it cools down again, at which point I'm again good for about 5 minutes.

I have swapped the OD relay with a known good one, so that's not the problem. Loosened the kickdown cable - no difference.

What's left - OD solenoid/new transmission? Is the OD solenoid known to fail this way, only when the car is hot?

Any suggestions most welcome, since this car will soon need a new timing belt, water pump, ball joints, and tires. The trans going may break the camel's back on this one; I will do all the above maintenance myself to save $, but not for a car with a potentially bad transmission....








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Solenoid, flush etc... 900 1992

Because the gear dropping is happening when the tranny is warm I would suspect it is something internal which may be simply gunk built up inside. AutoRx or synthetic ATF might cure the problem since they will clean the internal parts and conventional ATF will not.

A few thoughts:

I doubt it is the wiring, but did you check the wiring from the OD relay to the shifter and from the shifter to the solenoid? I'd start there as it is the cheapest and easiest fix. Look for cracked and/or corroded wiring. Focus on the wiring to the solenoid connection. Remove, clean well and reattach. Also check where the wiring comes out of the shifter hole and goes under the car. That's where the wiring went on my 240. You could also try removing the solenoid and cleaning it. Others have had success with that. New solenoids are fairly expensive.

If it were my car and the above didn't work, the second thing I'd try is doing a thorough flush using at least 12-14 quarts of the cheapest ATF you can find. I'd also seriously consider adding some AutoRx after the flush, run it for the required miles, then replace the fluid again with either synthetic or at least a high quality conventional ATF. Larue (from the earlier thread I posted) fixed a similar problem with his AW-70 doing a flush with the AutoRx treatment.

www.autorx.com

Good luck!

JW








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Solenoid, flush etc... 900 1992

Thanks, JWalker - I will try solenoid wiring and then a flush, in that order. I've had good experiences with AutoRX in the past for engines, thanks for reminding me about it! Trans has Mobil 1 ATF in it now, which I put in about 1.5 years ago - but this was a neglected car when I got it, so it seems like another flush with the cheap stuff would be the least I could do before possibly letting the car go. Will post back with my results.








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Solenoid, flush etc. (SOLVED?) 900 1992

Well, I went out this morning expecting to do more detective work, but decided to start with the basics, and check the trans fluid level one more time. I had checked it before with a hot car, level surface, cycling through gears, etc. - and it was pretty much at the max mark on the hot end of the dipstick. This morning, I figured I would check it cold, just to see if it was anywhere near the dipstick notch mentioned in the FAQ. Since it was nowhere near, and I had an extra quart of ATF in the back, I figured "why not, what harm can it do?" and put it in.

Well, this seems to have fixed the problem (at least for now): car will shift easily into OD, and kick down with moderate pedal pressure, but gradual pressure allows me to cruise and maintain speed in top gear, just as it always did before. I also noticed it was a little sluggish going into Drive from Park before, and now it will go right in.

Hm, I'm wondering if my dipstick is off? In any case, I'll let everyone know if this ends up just being a temporary fix...








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Solenoid, flush etc. (SOLVED?) 900 1992

Sounds promising!

You might want to jack your car (safely) and check the tranny for leaks. Do the tranny cooling lines crack and leak on 940's as they do 240's?










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weird downshift problem - beginning of end for transmission? 900 1992

The other posts are probably correct: not an internal tranny problem. Yes they are supposed to be unlikely to fail. However I had one fail awhile ago with completely different symptoms and I put in a $300 used on from the junk yard and it worked fine for years!
--
1993 240 Classic; 1993 945 Turbo; 1992 944 Turbo; 1997 850 GLT








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weird downshift problem - beginning of end for transmission? 900 1992

You might want to check out this recent thread. Problem was similar to yours. His tranny was dropping out of OD too. It is a 240 with an AW70 tranny so not much difference in transmissions. FYI - There is more than one thread to follow.

http://www.brickboard.com/RWD/volvo/1515433/220/240/260/280/2401990_transmission_problems.html

Bottom line: A couple of thorough flushes and an AutoRx treatment and all is well with his tranny.

This is a wild guess from someone with no specialized tranny knowledge but it could be a buildup of gunk in the clutch packs. Or maybe the solenoid needs a good cleaning. Is the wiring from the shifter to the solenoid intact and not corroded?









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weird downshift problem - beginning of end for transmission? 900 1992

Thanks, Spook and JWalker, for the suggestions. This isn't cruise-control related - I rarely use cruise control, and when I do it seems to be just fine. And the car isn't really dropping out of OD - it just seems incredibly sensitive to the kickdown function of the gas pedal when I don't want it to be. I think I might try disconnecting the kickdown cable temporarily, as mentioned in the post you sent, to see if the problem persists. If it doesn't, perhaps the cable is binding in the 'business end' of the transmission? I'll investigate further....








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weird downshift problem - beginning of end for transmission? 900 1992

Dear Benfingland,

Hope you're well. Glad to know isn't a cruise control problem. I recall a post, wherein it was mentioned that the kick-down cable can bind within its sheath. A few drops of light-weight oil (transmission fluid) might ease the problem. If I recall correctly, the cable needs to be disengaged from the throttle spool. The end of the cable is held pointing straight up, and the lubricant is introduced by dripping it along the steel cable. The fluid follows the cable into the sheath and eventually works its way to the bottom (presuming you pay your gravity bill).

Your description of how the tranny shifts suggests the problem is not internal. So far as you know, has there every been an incident where the in-radiator automatic transmission fluid (ATF) failed, allowing coolant to mix with the ATF? Absent this - or running for quite a while with low and/or very dirty fluid - it seems unlikely that the tranny is failing.

Hope this helps.

Yours faithfully,

Spook








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weird downshift problem - beginning of end for transmission? 900 1992

Thanks, Spook - this sounds encouraging. I squirted some penetrating oil in the general area last night, and today the shifting seemed a bit more predictable. I'll follow through with the full treatment as you suggest. Will post back with my results. Thanks!








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weird downshift problem - beginning of end for transmission? 900 1992

Dear Benfingland,

Hope you're well. Does this down-shift occur while on cruise control? If so, the problem may be related to the cruise control, more specifically, to the speedometer's signal to the cruise control system.

The problem began when the cruise control would not hold: I'd set it, and then it would suddenly release. I checked for leaks in the the servo (black rubber item mounted to the rear of the throttle assembly) and the vacuum line to the servo. Both were (and are) in fine shape. I also checked the vacuum pump (mounted on the side of the driver's side strut tower). That, too, was in fine order.

I decided next to check the speedometer itself, as that's relatively easy to access. There was obvious damage on one corner of the speedometer's circuit board. By then, the speedo was obviously failing: the needle would bounce around wildly, and sometimes drop to "0", when I was doing 30 mph.

I didn't see a need to check the cruise control module (mounted underneath the dashboard, on the left side of the driver's footwell [as you face the windshield]). Ultimately, I replaced the speedometer with a salvage yard unit (re-set to proper reading) and the cruise control has worked perfectly.

Another possibility is that the over-drive solenoid, or its wiring, is failing. If so, you'll likely find that the shifter's overdrive button ceases to be useful.

Hope this helps.

Yours faithfully,

Spook









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