The transmission has never been great since I got the car. It was really the biggest thing letting down the enjoyment of hooning around on boost.
The previous owner put the average/lazy shifting down to how you drive it and “catching it out” when it’s shifting. In reality, the transmission was just in a sorry state.
When pootling around town in D mode, it would surge and flare between gears, making D mode pretty gross but bearable. On the open road when it was already in gear, it was lovely, but the changes were bad otherwise. Sport mode was worse, as with the xHP Stage 3 transmission flash, the shifts were hard as anything. Slamming into gear, and lurching like crazy on down shifts.
Manual mode was the worst though. With little to no load, up shifts were OK. With load (and on boost), it was like the engine cut power between shifts and it would lurch hard. Downshifting was unbearable. The xHP flash adds rev matching to the downshifting, and because the trans wasn’t playing nicely, every time the car blipped the throttle to rev match, the car would surge forward. I grew tired of it pretty quick.
BMW claims these transmission are “Lifetime Filled” and never need to be serviced. Strangely, ZF, who make the transmission for BMW, actually have a service interval (60-80,000miles, 95-130,000km) and have all the service parts and guides available.
My car, having just ticked over 160,000km, was clearly overdue for a service. On top of that, running more power than stock, and having the transmission tuned, it puts a lot more stress on the transmission than it would normally have.
The first step to seeing if I could fix the issues without a replacement low KM transmission, was to service it. I had a plan, first I would do a simple drain and fill of the fluid, run the car for a few hundred KM and then drop the pan (with integrated filter), drop the valve body, replace the seals and then refill with new fluid.
A couple of weeks ago I ordered all the parts I needed (a new oil pan with filter and gasket, a new bridge seal and the four tube seals) and took the car into work for the drain and fill. On the LH side rear of the transmission is a plug with an internal 8MM hex, this is the fill plug. On the back of the pan is a large drain plug with a 10mm hex.
Now, there is LOTS of discussion online about which fluid to use. Most people (and ZF) recommend the genuine ZF Lifeguard 6 fluid, but that is hard to get in NZ, and very expensive. I decided to use the fluid that Caltex recommended for my car, which was the Havoline Synthetic Multi-Vehicle. It’s a Dexron VI/6 spec fluid, and meets various standards that are used in the same ZF transmission I have. Others have also used Dex VI fluid with great results, so I felt fairly confident it was OK to use. Use Lifeguard 6 if you can get it, otherwise do your research and use the fluid recommended for you.
I filled the transmission back up, ran it through the gears and added fluid with the engine running, in park, at 30-40c until the fluid starts to come out. When it drains down to just a few drips coming out, that’s when you refit the fill plug.
I chose not to reset adaptations for the transmission software yet, but already the improvement was noticeable. The shifts were smoother, a lot of the flaring was gone, and best of all, the horrible lurching when downshifting in Manual mode was almost gone.
Over the next 300 odd KM the shifting got better and better. It would have its good and bad days, and when it was good it shifted like a new one. The bad days were still better than previously, but not perfect.
So over that period the parts I ordered arrived, and once we had more Dex 6 in at work, it was time to get the car back up and pull the transmission to bits. This time I chose to work on the car at home, as it gives me a bit more freedom around timing, and hell, I have all the tools I need at home.
We close early on Saturdays at work, so after work I came home, and up went the wagon on my QuickJacks. They fit perfectly under the car, and I was able to lift it using the factory jacking points on the sills.
I knew what I was in for as I took a good look around when doing the drain and fill. The under tray above needs to come off, along with the two brackets it mounts to next to the exhaust. You also need to remove the exhaust bracket that mounts to the rear of the transmission. This uses an E-Torx bit, but I found an 8mm spanner or socket fit and worked OK.
There was no hint at all that I had added 1/3 the total capacity of fluid as a bright red, just a couple of weeks ago. It was all dark brown.
The pan is secured by about 24 T40 Torx bits. I cracked them all loose, but did not remove them immediately, and then one by one, starting at the rear by the drain hole (with the plug still removed), I removed the screws to let the back of the pan lower. The pan still has a huge amount of fluid in it that doesn’t drain normally, so by slowly lowering the back of the pan more fluid drained out the hole in a contained manner (rather than removing the pan full of fluid and pouring it on myself).
With the pan off, I needed to remove the valve body from the transmission. This is held to the transmission with about 14 T40 Torx screws. There are a lot more screws than just those ones, but they are smaller than T40. DO NOT REMOVE THEM, only the T40. Once the screws are all cracked and loose, more fluid will drain out of the valve body. The valve body is pretty heavy, and fragile, so take care when removing and refitting it.
I removed them with a pair of needle nose pliers, and carefully twisted them back and forth to free them up. The old seals were completely flush, and the new ones sat proud. The old ones were also hard and crumbled when pulled out.
I reinstalled the valve body, and fit the new oil pan. I filled the transmission up with fluid until it started to run out (about 3L), and then started the car and kept filling. The final fill when at temp, was about 7.5L of fluid. That’s a lot more than a standard drain and fill can remove.
Using INPA I reset the transmission adaptations so that it would forget what it learned with the old fluid and start to learn how the new fluid and seals work.
I haven’t driven much yet, but a quick drive yesterday showed a huge improvement in shifting. In D the shifts are silky smooth, and shifting under load is hugely improved, to the point it chirps/spins the wheels on a change to second gear where previously it would either slur the shift or feel like it cut power.
Obviously as the trans “learns” back in again, and the new fluid clears out the old stuff, it should get better, so i look forward to driving it more and seeing how it goes.
If anyone wants to take this job on, and I highly recommend they do, here are a couple of YouTube videos that helped me out a lot
It’s not a hard job, just messy and time consuming. These cars are getting old now, so even if it has low miles, it would likely still benefit from the seals being changed. At the least, draining the fluid, dropping the pan and replacing the pan (which has the filter integrated into it) is a good start and can be done on jack stands in a garage with minimal tools.