R129 SL320 gearbox not upshifting when cold

[JonahTal]

Hi there!

I have a ‘99 r129 sl320 with 88k mileage. It has recently (last 2-3 months) began failing to upshift when in Drive.

This tends to happen when the engine is cold, it seems to struggle to shift up to first gear (and occasionally second) to the point where I can sometimes almost hit the limiter before it changes. When it does change, the shift is very harsh but then seems to smoothen up as time goes on.

I have tried running through the gears a few times before pulling off, just to get things moving, which seems to help somewhat. I also had the transmission fluid changed recently which I hoped would resolve the issue.

I am beginning to worry this is something serious, but hoping someone might be able to shed some light on the issue as I understand gearbox faults aren’t uncommon on these models..

Any help is much appreciated! Thank you!

 

[BTB 500]

Hi & welcome.

If the ATF level and condition are both good the next thing would be to get the fault codes read. The 5-speed box is pretty reliable ... the only common issue is the electrical plate, which isn't particularly costly to fix. That doesn't usually give the symptoms you've described though.

One thought ... as I'm sure you know, the gearbox delays upshifting when cold to warm the engine up faster. I wonder if it could be something as simple as a temp. sensor fault?