2009 R230 SL350 Kickdown Gear Change Thud

[ATJ]

My second post in 9 months on here, so hello again. Also, probably confirms that the 50k miles, 2009 SL350 I bought has been “SuperLicht" on issues Just a rotted-out fuel pipe and small C pillar leak both fixed very cheaply. However, there has to be a “However” or I wouldn't be writing this, I noticed yesterday for the first time an issue with the transmission on kickdown.

In normal use, the gearchages both up and down are very smooth. Even pressing it hard, the progression through the gears is fine. Perhaps the odd, light clunky downshift when it’s warn. Use kickdown though and it thumps/thuds through the gear changes. From standstill, P and D engage without a murmur or hesitation and there are no random changes or gear holds on a normal drive.

Has anyone come across this before? I’ve searched the threads and not found anything similar. It hasn’t had an ATF change and wonder if it’s just that the oil is losing its viscosity when warm, which is why it is getting the odd clunky downshift when warm.

Any pointers to the potential cause or anyone experienced a similar issue?

Thanks,

Alan.

 

[Petrol Pete]

50K miles and 15 years without a transmission service ?

It's waaaay overdue a service .

 

[MrGreedy]

And engine mounts and the transmission mounts will be also way past their best/due replacement.

 

[ATJ]

50K miles and 15 years without a transmission service ?

It's waaaay overdue a service .

Thanks. I suspect it's degraded fluid too but worth checking in case there's something else going on. That it doesn't do it at all when it's cold might point to it losing viscosity when the ATF is hot.

It has a full MB history with the Digital SR showing the transmission was serviced at 37000, so maybe just waay rather than waaaaay overdue

Cheers.

 

[ATJ]

And engine mounts and the transmission mounts will be also way past their best/due replacement.

I'll have them checked as I wasn't aware they could be an issue. Hasn't been on any of my other oldie "Sunday" cars so didn't spring to mind.

Would it explain the "only when warm/hot" behaviour?

Thanks for the suggestion.

 

[W1ghty]

Thanks. I suspect it's degraded fluid too but worth checking in case there's something else going on. That it doesn't do it at all when it's cold might point to it losing viscosity when the ATF is hot.

It has a full MB history with the Digital SR showing the transmission was serviced at 37000, so maybe just waay rather than waaaaay overdue

Cheers.

If the gearbox was serviced at 37k , the ATF fluid should still be in really good condition . 50k is low mileage to have gearbox problems .
I would be looking to go to an MB specialist for this one to have the fault codes read first .
Where in London are you ?

 

[ATJ]

If the gearbox was serviced at 37k , the ATF fluid should still be in really good condition . 50k is low mileage to have gearbox problems .
I would be looking to go to an MB specialist for this one to have the fault codes read first .
Where in London are you ?

That change was in 2016 and I don't know enough about ATF to know how much it degrades over time. I'm near Ascot, so west of London. I guess Star Services Reading is my nearest specialist unless you have a recommendation?

Thanks.

 

[W1ghty]

That change was in 2016 and I don't know enough about ATF to know how much it degrades over time. I'm near Ascot, so west of London. I guess Star Services Reading is my nearest specialist unless you have a recommendation?

Thanks.

Yep , Star is a good call .
My thinking is that you don’t want to waste money on a gearbox ATF change without a specialist seeing if there are additional faults that need fixing during the examination.
If you were going to do an DIY ATF change yourself for £100 , or buying an icarsoft code reader for £100 that would help in the future with the car then these are options for you ?

 

[Bellow]

Thanks. I suspect it's degraded fluid too but worth checking in case there's something else going on. That it doesn't do it at all when it's cold might point to it losing viscosity when the ATF is hot.

Oil analysis replaces guesses with facts.

Also, shift quality is dependent on line pressure (a variable controlled by the ECU) so possibly a control problem (though I'd expect line pressure to be at its highest in the scenario you describe).

 

[ATJ]

Yep , Star is a good call .
My thinking is that you don’t want to waste money on a gearbox ATF change without a specialist seeing if there are additional faults that need fixing during the examination.
If you were going to do an DIY ATF change yourself for £100 , or buying an icarsoft code reader for £100 that would help in the future with the car then these are options for you ?

A very good point. I have an Autophix 7910 reader that is very detailed for BMW but only OBD2 more generically. The SL isn't showing any codes but it may not be able to interrogate the system in enough detail.

I think this and Bellow's input point me to taking it to Star rather than just to my trusted local garage for a fluid change.

 

[W1ghty]

A very good point. I have an Autophix 7910 reader that is very detailed for BMW but only OBD2 more generically. The SL isn't showing any codes but it may not be able to interrogate the system in enough detail.

I think this and Bellow's input point me to taking it to Star rather than just to my trusted local garage for a fluid change.

Absolutely take it only to an MB specialist for this one buddy .