1994 960 sedan, torque converter or transmission rough transition at 40-50 MPH Topic is solved

[tmcmilli]

Hello,

On my 960 sedan, I have an issue I've been puzzled about for awhile. When driving at around 40-45 MPH maybe up to almost 50 MPH, only at low RPM cruising, the transmission or the torque converter in the transmission will struggle to smoothly transition from either third to fourth gear or perhaps more likely the torque converter locking and unlocking. It shifts or locks/unlocks kind of rough and almost slams back and forth a bit as it's trying to settle in to one state or the other. It was rare that it happened but it's getting a little bit more frequent and more noticeable now so I want to get it fixed.

This often occurs when I'm going on level ground or very slight uphill grade and at this particular speed range. It acts like the car isn't sure which gear it wants to be in because it kind of bounces back and forth between 2 states. You can feel it easily. Immediately I back off the throttle or more often I give it a little more throttle to make it unlock the torque converter or downshift from fourth to third, whichever is happening. Fluid was flushed about 25K miles ago as a routine maintenance item. I've owned the car for a little over a year and almost 30K miles. It's been doing this ever so slightly for a long time but concerned it's getting more noticeable. Under normal or moderate acceleration it always shifts perfectly through all 4 gears. At highway speeds like 60 MPH and up on highways this never happens. I can start up a a bit of a grade in fourth gear and the torque converter will unlock just fine, and depending on the grade it will then kick down to third gear just fine. The transition back to fourth is smooth, again at highway speeds. Current mileage is 183K.

Previously when I first got the car in December 2017 there was a bad vibration when the car was under load, which turned out to be the transmission mount. This was replaced a good 15K miles ago and eliminated the vibration. But that problem existed when I got the car and who knows how long it was run like that by a previous owner. This car had a great body but maintenance was somewhat neglected by previous owner(s).

The car always shifts smoothly all the way to fourth gear under normal to moderate acceleration. I never drive it hard. Downshifts under other conditions are always normal, like pressing the accelerator pedal to kick it down to a lower gear to pass someone or like I said going uphill on the highway or whatever. It's this cruising along at a particular speed when it wants to change states from fourth to third gear or as I say more likely torque converter locking/unlocking, that this slamming back and forth occurs.

Any thoughts on whether this could be the torque converter or a solenoid or the transmission itself? Fluid level is fine and not really dirty.

I used to own a notorious 2002 Volvo V70 XC and after the fluid got fully hot, the transmission started slamming when upshifting from third to fourth gear (5 speed automatic). This isn't that severe but it has gotten to where I am concerned about it and want to fix it. And I can't say that it's only after the fluid is hot. Cooling system is in good shape, I've had cooling system flushed and the radiator is newer i.e. not original to the car. That's all I can tell you at this point. Any thoughts are appreciated.

Thanks,
Tom

[jimmy57]

How does it behave if you accelerate a bit more and the shift to 3rd and 4th with TC lock happens at higher speed and with higher engine output?

Things that have impact on the shifts: 1. fluid condition and type 2. engine performance

The locking TC is one reason fluids have gotten so complicated. Additives that make that action happen smoothly had to be developed. If the wrong fluid is used or if the fluid in there is past its useful life then the TC will shudder or grab on locking. If the engine is not running right then the throttle amount you use will offset the load signal delivered by ECM to TCM and the shifts will be harsher and at the wrong speeds.

[tmcmilli]

It is normal under a bit more moderate acceleration. It could be the fluid. That's a fair point. I'll have another look at it to see the color and level. I know there are 2 sets of marks for cold and hot. It's not that expensive I can have it flushed again. My independent Volvo mechanic disconnects the return line and pumps the transmission fluid into a vessel, like what the VolvoXC guys call the "Gibbons method" of changing the transmission fluid.

The engine itself never sputters it runs as smooth as silk and is not missing or faltering when these events occur. It seems to be clearly in the transmission part of the drive train, if that's what you're asking. It acts to me like the torque converter is unable to decide whether to lock or unlock and is shuddering between the 2 states. And I would say under these stated conditions, it is at that point where the transmission needs to unlock the torque converter or downshift gears. It's at a pretty low RPM in this speed range because of the gearing of the rear axle, 2.73 I think? My mechanic told me they changed the ratio in a bit later model to a higher ratio lower gearing maybe right after mine in 1995.

I'm not a mechanic and I appreciate the inputs of those who know way more than me. Thanks for the reply. Checking the fluid next.