722.3 Shifting Issues and Rough Idle in Reverse (W124 500E)

[dinbirb]

I’m looking for some advice regarding my W124 500E. The transmission (722.3) was replaced about 5 years ago. Recently, the shifting quality has significantly deteriorated—it’s no longer as smooth as it used to be.

The Symptoms:

1. Rough Shifting: The gear changes feel "off" (not as crisp or smooth as expected).

2. Reverse Gear Issue: The most concerning part is that when I shift into Reverse (R), the engine starts running very strangely/rough. It feels like the idle drops or the engine is struggling under heavy load.


What has been done so far:

I have already addressed the "usual suspects" to rule them out, but the problem persists:

• New Motor Mounts: Just replaced.
• New Engine Wiring Harness (MKB): Recently replaced.

Since the mounts and the harness are brand new, I’m leaning towards a transmission-related or vacuum issue. Could this be a failing vacuum modulator or perhaps a leak in the vacuum lines? Or is it possible that the B3 piston/clutch pack is causing this specific behavior in Reverse?

Also, what is the community consensus on ATF change intervals for the 500E, considering the high heat soak from the M119 V8?

 

[gsxr]

The rough shifting could be a vacuum issue. Check the vacuum line from back of the intake manifold to the modulator. Test the modulator and verify it holds vacuum without leaking.

The reverse gear issue may be completely unrelated, and could be an engine issue, however it is odd if this ONLY happens in reverse (not D/3/2/B). Need more specific information on this. If the reverse/B3 clutch pack is worn, the typical symptoms are delayed reverse engagement (like, 2-4 seconds), and/or a ticking noise when moving in reverse, that varies with vehicle speed. A 5-year old trans should NOT have worn B3 clutches.

ATF change intervals: About 25k-30kmi if you are using synthetic ATF. Maybe longer with light usage (lots of freeway miles). Cut the interval in half with severe service (racing, or anything that elevates ATF temp regularly), or if using dino ATF.

 

[dinbirb]

The rough shifting could be a vacuum issue. Check the vacuum line from back of the intake manifold to the modulator. Test the modulator and verify it holds vacuum without leaking.

The reverse gear issue may be completely unrelated, and could be an engine issue, however it is odd if this ONLY happens in reverse (not D/3/2/B). Need more specific information on this. If the reverse/B3 clutch pack is worn, the typical symptoms are delayed reverse engagement (like, 2-4 seconds), and/or a ticking noise when moving in reverse, that varies with vehicle speed. A 5-year old trans should NOT have worn B3 clutches.

ATF change intervals: About 25k-30kmi if you are using synthetic ATF. Maybe longer with light usage (lots of freeway miles). Cut the interval in half with severe service (racing, or anything that elevates ATF temp regularly), or if using dino ATF.

Thank you

To answer your question: Yes, there is definitely a delay when shifting into Reverse. It takes about 2 to 3 seconds for the gear to engage after moving the selector to "R".

 

[gsxr]

Thank you

To answer your question: Yes, there is definitely a delay when shifting into Reverse. It takes about 2 to 3 seconds for the gear to engage after moving the selector to "R".

That isn't good. You may have worn B3 clutches. What were the symptoms prior to the rebuild?

Also, who did the rebuild 5 years ago? How many miles since then?

 

[dinbirb]

That isn't good. You may have worn B3 clutches. What were the symptoms prior to the rebuild?

Also, who did the rebuild 5 years ago? How many miles since then?

To answer your questions:


1. Who did the work? The transmission was replaced by an official Mercedes-Benz dealership. Instead of a local rebuild, they installed a factory remanufactured unit (exchange transmission).


2. Miles since then: about 20k


3. Symptoms prior to replacement: The original transmission completely stopped shifting. It just wouldn't engage any gears anymore.


Additional finding:


I’ve also noticed a small ATF leak. It seems to be coming from the torque converter area (bell housing). I suspect that something might have been damaged or not seated correctly during the installation 5 years ago.