Transmission is automatic. Here's what happens:

Start in 1st gear, get going,
change to 2nd gear, pick up speed,
change to 3rd gear,...
get to 4th gear if lucky.

If 4th gear is reached then everything's okay, at least for a minute. Then the trans fails and falls back to 3rd or 2nd gear.

If 4th gear is not reached the trans slips right away and stays in 3rd gear or falls back to 2nd.

Either way, after a downshift, the gear it was in is usually lost. And after a complete stop all the gears are lost and the car barely moves even with the gas pedal depressed, with severe slippage of the trans and jerking. The car does not move at all while idling in drive and reverse does not work.

Sounds like a mechanical problem, right? Well here's the weird part:

After the car is turned off and back on the transmission operates normally again with a repeat of the above.

I'm thinking of replacing the transmission with another (used) one, but that might not necessary.

Has anyone else had this happen?

What engine does it have, and what market was the car built for?

Inline four cylinder? Inline six cylinder? V6?

If it has the inline six cylinder (as most 960s do), it would have an AW transmission. Not the AW70/71/72 that the four cylinders or the V6 would have gotten... altho I believe some/all/most of the European V6s and turbo 4s got the ZF transmission instead of the AW unit.

When you say the transmission fails, do you mean it merely downshifts into 3rd gear? Or does it slip into neutral?

Assuming you've got the inline six cylinder, the first thing to check would be the trouble codes. Check out the FAQ for instructions on how to pull codes (might as well check both the engine and transmission computers). Since this transmission is electronically controlled, if there were no codes I'd suspect a speed sensor of some sort or whatever solenoid is used to engage 4th gear. Or... if the transmission computer has never been replaced/repaired, perhaps that's bad. You would have a sport/winter/normal mode button near the shifter if this is the transmission you have.

With the AW70/AW71/AW72 units, the overdrive relay would be the first suspect, the overdrive solenoid would be the second. The shifter would have an overdrive button on it if you had this transmission.

The ZF transmission would be indicated if you had a PRND321 shift pattern and were missing an overdrive button and a shift mode button.

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alex

'89 765T, 171,1xx mi

Thanks guys, I really appreciate your replies. I'm gonna look into getting a flush done with a new filter.

By the way, it's a 960. Sorry I forgot to mention that. My mechanic tells me that the transmission is a ZF, as opposed to an AW.

A friend just experienced similar on a Nissan. His Trani filter was clogged. In the morning when all the fluid was allowed to settle, the car would shift OK, get a block from the house and he had shifting and slipping issues. BAsically the filter was so clogged that it was circulating. Any girgly sounds like the Trani pump was running dry?

I never heard of it on a Volvo though.
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'75 Jeep CJ5 345Hp ChevyPwr and two motorcycles: it wasn't Volvos safety , it was Longevity that sold me

Hmmm...I don't recall hearing any girgling noises. I do, however, remember some repeated shh-like noises coming from under the hood somewhere. They started a few days before the failing of the transmission began. Maybe they're related.

What 900 car and which transmission do you have?

Have you tried a transmission drain, full flush, and fill? I use Amsoil synthetic transmission fluid, and similar but less severe problems disappeared after the flush and fill from standard fluid.