400E transmission vs. 500E Transmission

[alabbasi]

Understanding that the 400E transmission has a 1st gear start valve body. Is there any other difference between the two transmission? I have an E420 parts car and a 500SEL Engine. I'm wondering if there's any other issue with fitting the E420 Transmission with the 500SEL engine before installing it in my 500E.

Thanks

 

[gsxr]

Should be 100% plug+play using the 034 transmission in the 036. AFAIK, everything else is 100% identical besides the valve body, and you want the FGS valvebody anyway.

 

[AndyK]

Should be 100% plug+play using the 034 transmission in the 036. AFAIK, everything else is 100% identical besides the valve body, and you want the FGS valvebody anyway.

Hey. I am still dealing with the transmission switching after Engine swap (4.2 to 5.0 from SL500).

The second gear won’t engage while normal driving (without full throttle), goes from 1st to 3rd gear, pretty smooth though, no hard push

We have:
- Rebuild transmission (the reverse gear was burned on the SL500). This is actually a second transmission because original 4.2 transmission has been used with the SL 500 valve body and after 6 miles the torque converter bearing was torn.

- Rebuild valve body. I used original one from 4.2.
I replaced all necessary springs and piston rings. Shift technologies kit and genuine rings have been used.

What I tested alredy:
- I have played with the vacuum modulator on the driver side. Adding and removing pressure doesn’t provide with any improvement.
- if remove vacuum line from this modulator, the transmission won’t switch even into the third gear before 4500 RPM and shift hard
- I have played with bowden cable, if I make it too loose, it switched to the third gear anyway, and almost no kick down. If make it tight, transmission won’t switch until 5000 RPM and anyway goes into the third gear.
- I replaced kickdown switch under the acceleration pedal, no changes
- I disconnected the vacuum line from the passenger side transmission. No changes.
- I replaced the vacuum valve for this vacuum line for the passenger side, no changes

Finally, I removed single wire from the valve at the back side of the passenger side transmission, I believe this thing related to the kick-down, like kick-down solenoid AND I GOT FIRST CHANGES!!!
The transmission started shifting normally under 2000 RPM from 1st to 2nd gear, but shiftings are were. 1-2-3-4 - R - All gears are available BUT under full throttle the first gear switches to the second gear at 4000 RPM however second gear goes as it supposed to be till 6000 RPM
The first gear was available only once when you switch from Parking to drive you start driving on the first gear then switchs to the second gear and then all next stop and go goes using second gear only, which normal I guess?

I replaced that electrical solenoid and mechanical valve, I used old one from original transmission, And the issue came back, no second gear.

In my opinion, something constantly send power to that solenoid on the back side of the transmission. Any thoughts?

 

[AndyK]

I checked the power on that wire and it always under the power. If I turn on the ignition, there is no power however, once I start the engine, there is 13+ volt.

I have removed kick down switch and that wire still shows 13+ volt

 

[AndyK]

Another update:


I found a transmission wiring harness diagram for the W126. It shows that there’s another module or valve that receives a positive signal from the kick-down switch. In my opinion, this device doesn’t just act as a pickup — it functions as a signal generator that keeps the kick-down solenoid constantly engaged.

So at this point, I need to find a more detailed diagram related specifically to the kick-down system to identify what else receives that signal and what could be causing the issue.

The problem is that this device likely communicates with the ECM or EZL module to temporarily reduce engine torque for smoother downshifting.

That means I’m probably losing some engine power as well.

At the meantime I have the A/C compressor issue as well, based on the information I found when the kick down switch is pressed down the system should disconnect the AC compressor as well

 

[doolar]

Is the B-switch by the gear selector properly connected and in the correct position?

 

[gsxr]

Is the B-switch by the gear selector properly connected and in the correct position?

Yup - this is most likely the cause. The B-switch may be stuck in the "on" position, without the shift lever in the B position (1st gear).

You need to get the electrical kickdown signal working properly, then the transmission shifting should be correct.

 

[gsxr]

I found a transmission wiring harness diagram for the W126. It shows that there’s another module or valve that receives a positive signal from the kick-down switch. In my opinion, this device doesn’t just act as a pickup — it functions as a signal generator that keeps the kick-down solenoid constantly engaged.

So at this point, I need to find a more detailed diagram related specifically to the kick-down system to identify what else receives that signal and what could be causing the issue.

See photo attached below showing the wiring diagram / circuit function of the 400E kickdown circuit. You should have removed relay K29/1 already so ignore that part, but the rest of it is still valid. Full schematic is here. The BM/GM module N16/1 is what provides the voltage, and interrupts the voltage to allow a redline upshift at 6000rpm.

The problem is that this device likely communicates with the ECM or EZL module to temporarily reduce engine torque for smoother downshifting.

Nope. The ECM/EZL has no connection to the kickdown circuit. Only the overload protection switch on the driver side (next to the vacuum modulator) has any connection to the engine management (fuel / ignition / throttle controls). This switch tells the EZL when a shift is in progress, and the EZL briefly retards ignition timing to reduce stress on the transmission frictions. This is all explained in the FSM if you read the relevant sections.

That means I’m probably losing some engine power as well.

Nope, no power loss, other than incorrect shift timing.

At the meantime I have the A/C compressor issue as well, based on the information I found when the kick down switch is pressed down the system should disconnect the AC compressor as well

Nope. The AC compressor does NOT shut off at full throttle on the M119. That functionality exists on all older diesels, but not on any M119 powered vehicle. You cannot use the 126 service manual for anything related to M119 vehicles, it will give you misleading or inaccurate information.

 

[AndyK]

Is the B-switch by the gear selector properly connected and in the correct position?

I never touched that switch (if this switch is inside of the vehicle). How to get access?

 

[AndyK]

See photo attached below showing the wiring diagram / circuit function of the 400E kickdown circuit. You should have removed relay K29/1 already so ignore that part, but the rest of it is still valid. Full schematic is here. The BM/GM module N16/1 is what provides the voltage, and interrupts the voltage to allow a redline upshift at 6000rpm.




Nope. The ECM/EZL has no connection to the kickdown circuit. Only the overload protection switch on the driver side (next to the vacuum modulator) has any connection to the engine management (fuel / ignition / throttle controls). This switch tells the EZL when a shift is in progress, and the EZL briefly retards ignition timing to reduce stress on the transmission frictions. This is all explained in the FSM if you read the relevant sections.




Nope, no power loss, other than incorrect shift timing.




Nope. The AC compressor does NOT shut off at full throttle on the M119. That functionality exists on all older diesels, but not on any M119 powered vehicle. You cannot use the 126 service manual for anything related to M119 vehicles, it will give you misleading or inaccurate information.


View attachment 226353

well, I would like to have the first gear….it’s fan to drive, so I haven’t removed that relay, it’s still in the position

I also didn’t touch the B switch, I have no idea how it look and where it is located

Regarding the overload protection switch,
The connector on the transmission is destroyed and is there any difference how to connect these wirea?. Does it have positive or negative?
I tried to switch the wires, but it didn’t really provide it with any visible results

 

[gsxr]

B switch is located in the shifter assembly. You need to remove the wood console trim to access this. If the switch was moved out of place it could be stuck in the on position. The switch should turn on/off as the shifter is moved in/out of B position.

 

[AndyK]

B switch is located in the shifter assembly. You need to remove the wood console trim to access this. If the switch was moved out of place it could be stuck in the on position. The switch should turn on/off as the shifter is moved in/out of B position.

I have disconnected that connector from the shifter and nothing, same issue

 

[gsxr]

I have disconnected that connector from the shifter and nothing, same issue

In that case you have more homework to do. Also make sure the kickdown switch behind the gas pedal is not stuck on. When you press it with your foot, you should feel AND hear it click as it engages and releases. If stuck on, you'll have the same problem as if the B-switch was stuck on.

 

[AndyK]

In that case you have more homework to do. Also make sure the kickdown switch behind the gas pedal is not stuck on. When you press it with your foot, you should feel AND hear it click as it engages and releases. If stuck on, you'll have the same problem as if the B-switch was stuck on.

While test operations the kick down switch under the acceleration pedal has been removed. I had spare one and replaced it as well, didn’t work

 

[AndyK]

I removed relay K29/1, and the constant power issue is gone.


However, another thing came up — in first gear, even at full throttle, it shifts at around 4,000 RPM, but in second gear it revs all the way up to about 6,500 RPM, hits fuel cut-off, and only then shifts into third.

 

[gsxr]

I removed relay K29/1, and the constant power issue is gone.

Uh - yeah - you should have already removed K29/1 as mentioned back in post #8.

However, another thing came up — in first gear, even at full throttle, it shifts at around 4,000 RPM

Your kickdown switch behind the gas pedal must be installed and working, otherwise it will upshift from 1-2 at 4000rpm. The wire at the kickdown solenoid at the transmission must also be plugged in.

but in second gear it revs all the way up to about 6,500 RPM, hits fuel cut-off

If this still happens with the kickdown solenoid wire disconncted, a valvebody adjustment is needed (click here).

and only then shifts into third.

Does it ever shift into 4th? At light throttle, etc?

 

[AndyK]

The kickdown switch installed
The kickdown solenoid plugged in

It started happening after K29/1 has been removed

Yes it’s always shifts to 4th