What’s wrong with my transmission?

Hi Baraza,

I drive a Subaru Impreza 2005 model, 1500cc, AWD, automatic transmission. The car is having a “thud feeling” while shifting from drive to reverse/parking and/or when switching off (the same feel that you get when you release the clutch abruptly on a manual transmission car while on drive).

There is also a feeling of the rear wheels locking when turning — while reversing or moving forward but at a slow speed. What would be the problem and do you know someone or entity who can help fix this problem? The car has done less than a 1,000km in Kenya and the ATF and differential oil have been changed “just the other day”.

I look forward to hearing your advice soon. I am in Nairobi.

Kind regards,

Mike

This is sounding like a transmission in the throes of death. There is a step-by-step programme that you can follow to determine how close your gearbox is to complete failure. These steps apply to an automatic transmission — the diagnostic for a manual one slightly different:

1. Lock-up control: Park next to a pavement with the wheels touching the kerb. In Drive, throttle up slowly. Your transmission should allow the car to go up the kerb without the engine revs dropping.

2. Clutch test: First ensure you have working brakes. Engage Drive, hold the brake pedal and press the accelerator all the way down. The engine revs should not dissipate; if they do, then your clutch is not working properly.

3. Smooth shifting: Your car has already failed the static version of this test. From your description, it has passed the dynamic version. The short answer to this is “gearbox malfunction”. Get an error code from the TCM (transmission control module) for a more specific pointer.

4. Vibration test: Check for vibrations. Driving at about 70km/h, switch to Neutral. There should not be any lateral vibrations. If there are, this is either due to a warping of the drive-shaft or suspension damage. Basically, drive-shaft warping is perceived as a vibration in both vertical and horizontal directions, whereas a suspension damage is felt as a vibration in only one direction (either horizontally or vertically).

5. Steering test: When trying to enter a corner at approximately 30km/h, there should not be any discernible under-steer (where the car plows on in a straight line instead of turning). The presence of this may be due to a differential failure, especially in FWD cars. DO NOT try to test your differentials by trying to induce under/over-steer if you are a novice driver.

From those five tests you can try and narrow down the faulty part of your driveline. If it was up to me I would start with number three because it is the most straightforward. The reason I came up with that whole list is because I have no access to your car, so I try and cover all possible bases. Hope it helps.

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