As the title said, 2014 e350 4matic 76000 miles. I have an issue when the trans downshifts into 4th gear, it kicks, rmps jump up then drop back down. More pronounced is from 5th to 4th, other than that it's very smooth in all gears. Trans service was done at 70000 miles at dealer. No leaks no codes nothing. One thing I noticed, removed gas pedal assembly to clean underneath, after that took it for a ride, no more kicks all smooth, shut off engine and restarted it, kicks again, could it be a faulty pedal assembly, or something else. Thanks

 

codes?

 

no codes, nothing

 

Had the car diagnosed at the dealership. No codes found software up to date, foreman performed adaptation no better, he suspects b2 valve solenoid or b2 clutch wear. What's the next step

 

Whenever I hear the word "suspects" at any shop, I take it as code for "try parts at customer expense, whether they work or not".

I don't know how much you want to know but here's some info....
I believe that if a shop has MB mfg/STAR software, it should be able to see actual operating parameters to verify electrical/sensor/communication condition. Just because a code is not thrown doesn't mean that a system is perfectly ok. The ECM allows for an operating range - as long as the component doesn't begin to operate outside of the range for a specified period of time, there won't be a code. But the component may be almost at the range limit and affecting vehicle operation. But operating parameters means that a diagnostic unit and tech need to actually drive the car to see them, sometimes that's not done. This way the actual command to the solenoid can be verified at the time of the downshift (or at other up or downshifts). This can look at voltage, pressures, and also verifies that the CANBUS communications to/from the TCU and ECU are ok.

Three things that come to mind as possible considerations.
1. There is a primary wiring harness connector at the transmission. It plugs in directly to the conductor plate. Remove and verify that the pins are clean, not bend and that no transmission fluid has leaked into the connector. This is to ensure that a poor connection is not an issue.

2. I know nothing about your particular transmission maintenance - has the fluid AND filter ever been changed? Sometimes just doing this can solve a shift shudder or issue.

3. Your transmission has 7 or 8 control solenoids attached to a conductor plate, which is in turn attached to the valve body inside the transmission. These solenoids are controlled by the TCU (transmission control unit) which is part of the conductor plate for all practical purposes. As the solenoids receive or drop current, they control fluid flow to spool valves in the valve body, which move and route fluid in/out the various clutch packs engaging and disengaging to control the gearsets (shifts). There's also a number of sensors in there. As you can imagine, the TCU has a lot of inputs to correlate to get the shifts right.

B-series solenoids are brake control solenoids, K-series solenoids are clutch control solenoids. That B2 solenoid is used in combination with additional solenoids on 1-4 upshifts so it seems that if there's an issue it would impact those shifts as well, not just the 5-4 downshift. That 5-4 downshift activates the B2 and three of the K-solenoids (I think K1,K2,K3) to downshift. So if solenoid replacement is seriously considered, might need to include the K-solenoids. However I think I can see why the shop is thinking about the B2 solenoid, the 5-4 downshift is the first time the B2 activates - it then activates on all lower downshifts. B2 activates at 1st gear selection and stays activated to and including 4th gear.

If the transmission fluid/filter is being changed, it's a perfect time to consider any change to the solenoid(s) or conductor plate. A further step would be to remove, dis-assemble, thoroughly clean, and re-assemble/install the valve body to ensure all fluid passages are good. However, this needs to be done correctly, torqued to spec, and all of the many check ***** back in the right place. An easier route may be to remove/clean screens or replace the solenoid(s), leaving the conductor plate and valve body in place, but obviously if there is any debris in the valve body, it stays. I think most shops simply replace the entire conductor plate/solenoids as a unit, that is the limit of their transmission work, other than a torque converter replacement or something.

I think Items 1 and 2 are reasonable steps. Item 3 is strictly up to you and how far you wanted to go. Replacement of the B2 solenoid would not add huge expense but again, it's not known if changing it or other stuff will solve the issue. I wanted to outline general transmission operation so you could get an idea of what's going on.

 

Thank you for this detailed explanation. Transmission was serviced at 69000, at the same dealer. Looking at the vmi there was no warranty repair work, just regular maintenance. As far as shifting goes, 1-2 sometimes jerky but 95% smooth, 2-3 you feel it sometimes 3-4 smooth 4-7 smooth. Downshifting 7-6,7-5, smooth 7-4 you feel it. 6-5 smooth 6-4 you feel it, 5-4 is felt the most. Sometimes you feel the 3-2. I am leaning towards the solenoid rather than clutch wear. What do you think?

 

Chek out this thread same issue as me

2014 E350 W212 Transmission Clicking Noises + Hard Downshift at Higher Speeds - Mercedes-Benz Forum
https://www.benzworld.org/forums/w21...ng-noises.html

 

It sounds like you do have an issue with B2. When the transmission is in 5th gear, it has K1, K2 and K3 engaged. When it downshifts to 4th gear, it will release K3 and engage B2. Did they do a control unit log print out? It would show the adaptation numbers for each clutch pack. I have rebuilt many of these but have never ran into an actual hardware problem with B2....... But you can never say never. One thing I can tell you, those solenoids will never fail electronically. It's either clogged solenoid, valve body passage or the B2 assembly.

 

He performed adaptation of the trans to lower the shift fill times and it lowered the nr, but still has the harsh engagement into 4th, that's what it says in the paper