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Discussion Starter · #1 ·
Trying to help my dad with his S60.

135k miles. Car is in very good condition and runs well. Within the last two months, he told me that the car felt like it was doing something strange and he suspected the transmission. I suggested that he make sure the trans fluid was clean. Apparently he took it to a local shop and had it flushed but the issue is still present.

Today, I took it for a short drive. Basically, it feels like there's a stutter in 2nd gear, kind of like a brief pause during regular acceleration. To be clear, the car shifts into gear fine (no pause), takes off in 1st all right, and I didn't notice any flare between any other gears. It's after the 1-2 shift and then, bump, just a single stutter in acceleration. I drove it a few miles, stopping frequently and then starting again in 1st. Happens every time.

Under harder acceleration, I felt a more abrupt shift from 1 to 2, more like my Polestar.

Thoughts?
 

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There are three levels of control for this automatic transmission. The highest level is the TCM, transmission control module, that uses input signals from sensors to decide when to shift. Those sensors include the throttle position, engine rpm, and transmission output rpm. Located inside the transmission is a set of solenoid valves. These valves are turned on/off by signals from the TCM. They control the flow of transmission fluid which is used, under pressure, to operate hydraulic piston/cylinder devices that do the work of shifting gears, and also operate mechanical clutches that are constantly immersed in transmission fluid(aka wet clutch). So you have electric signals(1) converted to hydraulic signals(2) that operate hydraulic pistons(3) that shift the gears, and work the clutches. Working backward, if a wet clutch was defective, or a hydraulic piston device, then you would be seeing problems in all of the gears, not just 2nd to 3rd. However, there is a specific solenoid valve that controls this shift. These valves are known to become clogged over time with oxidized transmission oil. They may not open all the way, or they may not close all the way. It is possible to open up the transmission, remove the valve body, inspect the solenoids, and replace them as needed. I have never done this, and likely I will not attempt this. A transmission shop will likely road test the car, decide to remove the transmission for rebuild, open it up, and while they are in there replace worn clutch plates, and any worn bearings they find. Since the car is in otherwise good condition, this sort of repair bill may be justified. Or, it may not. Given that the transmission was recently flushed, and now has clean fluid, there is a small chance that the solenoid will begin to work normally, eventually. I doubt that driving the car as is damages the transmission or any other part of the drive train. If you want to pursue this further, there are several videos on u-tube that show automatic transmissions being opened up, diagnosed, and repaired.
 

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Discussion Starter · #3 ·
Thanks for the reply. I wondered if it might be related to the valve body and had already researched replacement options. However, I agree that there's a chance that the new fluid could help if given some time.

Appreciate your help.
 

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Does the issue happen only when the car is good and hot after driving for 20 -30 minutes, or also when the car is cold?


Sent from my iPhone using Tapatalk
 

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I have a correction to the description of the TCM, given above. There is no "throttle position" in a fuel injected engine. I should have said "accelerator foot pedal position" or words to that effect. The TCM has to know if the driver is feathering the pedal, attempting to accelerate slowly, or if the pedal is further depressed in an effort to accelerate as fast as possible.
 
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