2005 4.8is transmission shifting / slipping issue

[o3x5e53]

Just throwing a thought at you. Maybe the vanos is shot? I read a article that when the vanos isn't working properly..it runs really sluggish/poor performance.

[Lee Nedirof]

Sometimes the sounds come from your transmission along with trouble in shifting due to malfunctioning of the torque converter. Also, you should check to see if there is any leak in the transmission fluid.

[X53Jay4.8is]

Originally Posted by desertfire

As an extension to my previous questions, how can I verify that the Torque converter is working correctly ? (i.e. what tests can be done to verify?)

CC

From your earlier description of the transmission behavior I would have thought that your troubles are the torque converter.

[StephenVA]

Any updates?

[desertfire]

Sorry for not having posted in a while, work had me all over the place and then the holidays hit, but, I did not give up on my quest to solve the issue of the erratic transmission behavior.


To handle the issue of the “transmission failsafe” mode kicking in and locking the machine into limp mode in either 3rd or 4th gear I looked into an OBD compliant scanner to clear the codes. While going through the different units out there I figured I would get one that would be able to decipher the BMW proprietary codes as well as potentially give me the ability to view real-time operational data to get some inside view on what is going on. I settled on purchasing a CReader CRP123 scanner as it seemed to fit the requirements although being a little more expensive. It had positive reviews overall and I took the plunge.



I drove the car and had the data stream reading going to get visibility into the shifting sequencing and the overall behavior and noticed that the issue is specifically occurring when shifting from 4th to 5th gear and when the torque converter clutch is either in open or regulated conditions. The more interesting part though is that when manually shifting from 4th to 5th, the 4th gear would sometimes “stick” although the unit would respond that the gearbox was in 5th gear.



Doing this for about a week or so of occasional driving I also observed that the shifting was quite harsh and would sometimes “hammer” into gear when shifting up or down between gears 1,2, and 3, leading me to believe that there was something not working with the pressure handling in the valve body. I poked around online and found a decent amount of documentation on the zf6hp26 transmission and explored the design of the system. It is interesting to note that the documentation I have found from ZF is all marked as zf6hp19/26/32. After looking at the design I eliminated the clutch plates/packs as being a source of the issue because of the erratic behavior. Also, I eliminated the torque converter as a source because the issue is specific to a certain gear set and is varying in behavior. The design of the transmission is very intricate yet the functionality is quite modularized and all of the shifting behavior is controlled by the Mechatronic valve assembly. The Mechatronic valve assembly has a series of dampers in it that are supposed to aid in balancing the transmission pressures during transitions so I am going on the assumption that pressure balancing may be causing a problem in the valve body management / sequencing. A rebuild of the valve assembly is apparently what was needed so I ordered a Sonnax “Zip Kit” (Gen 1) for my X5’s transmission.


The kit arrived and I proceeded to dive into dropping the valve body from the transmission and disassembling. I was successful in doing the rebuild myself, however, I took my time to do it (2 weeks on and off) and ran into several minor setbacks that, knowing what I know now, could have been handled in advance differently. Ultimately, I could write up an entire other thread on the experience of doing the valve rebuild with the Zip kit but it would take some definite effort and time. If there is enough interest as feedback on this thread then I’ll take the time to do a detailed write-up and pictorial of the job as well as provide practical info on the planning for doing it so that you are not hung up. It is a very interesting experience.


One thing I will share up front is that the documentation is lacking of several details which I was able to deduce, and also the diagrams of the exploded parts are not entirely correct and I recommend looking at the other documentation Sonnax has online on the differences between the Gen 1 and 2 of the transmission valve bodies for a correct breakout. Observations of the condition of the valve assembly is that the solenoids were very dirty and 3 out of 4 had their filters clogged with sediment, potentially explaining the pressure issues. Also, the damper pistons on the inside of the assembly were literally crushed and not doing any level work, potentially explaining the “bump” shifting.



I would also like to share that I refilled the transmission with Ford Mercon SP transmission fluid that I picked up at the local Ford dealership for significantly less than the ZF lifeguard or BMW branded fluid. Being that the 6R60 transmission is identical and that there are numerous other posts about the fluids being the same, I took the plunge and am quite happy to confirm that the transmission works perfectly on the Ford Mercon SP fluid.
Once reassembled and returned to operation I can report that the shifting is smoother and does not hammer anymore, which is a relief, however the issue of the behavior of the slip has changed but not gone away.
Now the “slip” is more discernable as if the unit is falling in and out of gear rather than a clutch plate slip. The error returned on the code reader now is specifically a “gear 4-5 ratio monitoring” error, whereas before it was consistently the “clutch E” errors, which is a relief to a certain extent.
Based on the design of the Mechatronic, and after doing some more research on this specific error on the other variants of the 6hpXX series of transmissions, it seems that the issue is now related to the solenoids of the valve body.



I feel that I have reached that “next level” in the game and ordered a set of replacement solenoids as well as the Torx bolts for the mechatronic to body mounting so that I’m sure that the current bolts aren’t used anymore as they have been torqued a number of times and I don’t want to take any risks.

The valves got in this week so this weekend I’ll jump back into the deep end here and see about throwing them in place. Shouldn’t take me more than 3 hours to do it at this point

Updates coming soon.

[SlickGT1]

I'm deff down for a valve body rebuild writeup. I'm sure there are quite a few of us who will benefit.

That being said, if you search for my name and solenoids, you will see a thread from me. I should have a link in it from another member, with a writeup on swapping out the solenoids.

So I never got a failsafe. But mine were gunked up as yours were. My issue was slow reverse, and only after slightly aggressive driving. Basically after it got nice and hot, it wouldn't shift into R right away. Took 3-5 sec to actually kick in. Sometimes very violently.

I also changed the mechatronics sleeve, and the rubber mount for the valve block. Figured while I'm in there, why not.

Have like 20k miles on it since the fix. No problems.

[itscoo2pyopants]

Good info in here, bookmarked for later

[crystalworks]

^What they said. Please do a write-up if you have time. Bookmarked.

[desertfire]

So…. I must admit that it is weird to feel comfortable about draining and disassembling a transmission as a “routine” weekend thing to do… but it has become fun.

I ordered the set of replacement solenoids and the Torx bolts for mounting the Mechatronic valve body to the transmission main body from thectsc .com . The Torx bolts were not listed so I reached out to them via email from their site and got a response from them and they processed the order directly to me via P**pal and the products were delivered promptly. Excellent service I must admit. And, it looks like the product was drop shipped directly to me from a ZF distribution point, which means that surely if there is anything I could POSSIBLY need I could get it from them, which is good.

I pulled the car into the garage and had the transmission drained and valve body out in about 45 minutes. 10 minutes later had the electronic unit removed from the valve assembly and proceeded to replace the solenoids. The original solenoid bodies were colored yellow, green, and one black. The new solenoids are yellow, BLUE, and one black. After comparing them I went on the assumption that the blue ones replaced the green ones and that the yellow ones were a direct replacement. The new solenoid set also came with a foam strip to insulate the connectors.

I replaced the solenoids one at a time, starting from left to right of the valve assembly, making sure to number and place the old unit into an egg crate that I used as a tray and taking a new solenoid from the package. Can never be too safe when doing these things so I made sure to absolutely isolate the old from the new. After replacing the solenoids I then placed the foam strip onto the connector array on the electronic module and mounted the module to the valve body. Immediately following I mounted the valve body to the transmission and closed up the transmission.

Total time was 2 hours, and I took my time. Not sure if this should be disturbing, but it was effortless.

I forgot to mention earlier that the Mercon SP fluid that I drained had about 1000 miles on it, which really isn’t much, but it drained out relatively clean and the viscosity was not changed, adding that the fluid is perfectly compatible.

Before refilling the transmission I took the time to reset the transmission “adaptions” by using the BMW INPA software and a USB cable that connected the vehicle to my laptop. Purchased it on Amazon for about $30 and is VERY MUCH WORTH every penny. Got in and reset the adaption, cleared any errors, and also configured the door auto-lock feature to automatically lock the doors when the car reaches 15 MPH, which was annoying me that it didn’t do it in the first place.

After doing the reconfiguration I pumped the fluid back in and topped it off with an extra half quart that I had lost during the drain/disassembly. I made sure to fill the transmission cold, start the engine and continue filling until it started streaming from the drain plug, and jumped in while it was running to flip through the gears and then went back under to continue filling. I did the gear shift flip three times to make sure that there was nothing left to fill, and then plugged the fill hole.

I drove the car around our subdivision, literally, and it felt like an ENTIRELY DIFFERENT VEHICLE!! Being late in the evening I decided to take it out the next day.
Took it out the next day and… Wait for it…… THE PROBLEM IS SOLVED !!!!!!!!!!! (I think I even cried for a second...)

The car shifted like it is brand new, can’t even feel the gears as they go through. Took it easy though as the ECU needs to re-learn the mechanics, so drove it easy and coming to steady full stops and not gunning at all for about 50 miles or so.. a good weekend’s running of errands and stuff…
The following week I decided that the vehicle needed “pressure testing” so I decided to go “Russian submarine testing” style and see how far I could push it to see at what point I’d start hearing noises so went for a 1400 mile weekend road trip through the southwest… a true pass/fail scenario ;-). Hills, declines, long grades, winding roads…

The vehicle performed flawlessly… winding up through the hills, especially in sport mode, was the most refreshing experience after all the troubles. It appears that the mileage has even gotten better… averaged 25 MPG on the freeways and 19 in town… made the trip on a little over 3 tanks, which was also nice.

I have a few more road trips planned and will post the progress as things move forward, but if there is anything I can recommend to anyone that has a vehicle with a ZF 6hp series transmission with about 100k miles on it since it’s last service is to replace the solenoids, rebuild the valve assembly with the Sonnax kit, replace the bridge seals between the mechatronic and the transmission body. Not sure whether the Ford Mercon SP fluid is any better than the ZF branded one, but I have an absolutely positive experience with the Ford Mercon SP fluid that I can vouch for as a testimonial

The PTSD from having dealt with the transmission issue hasn’t worn away yet and I’m still weary that the issue will come back, but after taking the “girl in a red dress” out for a weekend and clearing the 193k mile mark, I feel that the issue is completely solved.

For those that are out there and are having transmission issues, I truly hope that this “adventure” helps you in solving the problems you are experiencing.

Safe travels!

[Omerta]

Thanks for the follow-up, glad to hear you resolved the problem!