High rev when gear shift
 

Hi
I've been having trouble with my M104 auto trans. It seems like when shifting into 3rd and 4th the revs are a bit higher (3000 rpm) and it goes into neutral before shifting up. Any idea on what this could be?

btw car is a 94 e320.

thanks

You are probably noticing it more now that temperatures are lower!

How many miles?

Do you mean it slips when making a 3rd to 4th up shift

The car has run 185000 km. It is due for an oil service though.
yes it does slip going into 3rd and 4th... The shifts are not hard though very softactually.

Read the following article:

http://www.continentalimports.com/ser_ic20242.html

Then, you might try:
1. Do a transmission fluid service.
2. Test transmissson vacuum signal and adjust as necessary.
3. Test transmission shift modulator pressure and adjust as necessary.

With that high mileage I would remove the transmission pan, if it’s clean no metal, change the filter and fluid.

If your model has the mode and B+ switch it complicates the diagnoses, adding the up shift delay actuator to the equation. It can also be valve body related K1 and K 2 accumulators.



If you still have a problem check the vacuum going to the modulator next.


Install a vacuum gauge directly to the modulator vacuum hose, with the engine running on a healthy there should be a steady reading of manifold vacuum present 14” to 22”HG. A quick opening and closing of the throttle should drop the vacuum to below 5” if not fix the vacuum problem first.

Engine vacuum is the load input signal from the engine to the modulator. Under a load condition, normal driving from a stop to wide open throttle, vacuum must drop, if it doesn’t the transmission will have a delayed, chattering, slipping up shifts. The vacuum modulator job is to increases working pressure base on a vacuum signal.
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