Gear box big problem slk230 r170

[FREDYFLAME]

R170 - year 2000 230k 72k miles on the clock
a while ago I had an interittent fault of not changing gear and feeling like the hand brake was on.
stop the car turn off it was ok again.

Now every time we have a hot day, around 24degrees when i put it into drive it clunks really badly jolts forward and then stays in first and will not change
It only seems to happens on hot days. I does not happen on cold days when the engine is hot, this has no effect tuning it off now has no effect
Although since it got worse it has been hot every day so I am rather worried its permanant
one thread sugested possible changing the gearbox oil
and magnets on the transmission
Any help would be great as very reluctant to take to main dealer but they seem to be the only ones around Southport UK with latest software (unless anyone knows a good indie near me) Thanks
Have dipped it and it was just up to bottom mark so topped it up still same even in cooler weather now
Realy doeas make a horrible clunk as I move it into reverse or drive
Tony

 

[Cole@MBS]

Have a short test done, i have changed so many RPM sensors on the rear on the 170!

Such a common fault!!!

When i was a merc breakdown tech, i used to carry all 6 sensors, it was that common!!!

 

[FREDYFLAME]

short test?

I am afraid you have lost me there what is a short test and what is the sensor that relates to this problem? Thanks

 

[Cole@MBS]

A short test is what a dealer would do, a rpm sensor is a sensor on each corner of the car!!

 

[television]

These give the speed signal, if the car does not receive a signal the gearbox does not know what to do, and locks up in 1st or 2nd