Let’s talk about the eight-speed automatic transmission that BMW has been using across their lineup for the past 15 years—the ZF 8HP. First, I’m a huge fan of the manual transmission, despite knowing that many modern automatics can outperform my manual shifting abilities. For most of my driving life, not having a manual-equipped steed in my stable was unthinkable. However, when looking for a “family car” to replace my track-prepped Subaru STI in 2014, I found the ZF8-equipped 328i Sport Wagon to be pretty great. While the F31 3 Series wagon was offered with a manual overseas, we only received the automatic here in the U.S.
There are three generations and many flavors of ZF 8HP, all built to handle different levels of horsepower and torque. It first debuted for BMW underneath the 2008 F01 760Li (with the big V12 engine) and has been fitted in a range of other BMW models over the past decade and a half. It’s not a dual-clutch transmission (DCT), but instead a traditional torque-converter automatic. Thanks to its advanced valve body it provides firm and fast shifts, just like a DCT.
The ZF 8HP can be found in brands beyond BMW, with Jaguars, Land Rovers, and Chryslers all being outfitted with variations tailored to their power outputs. Unlike BMW, which says the ZF 8HP has a “lifetime fill” and doesn’t have a service interval, the other manufacturers and ZF themselves recommend a transmission fluid service every eight years or 50,000 to 75,000 miles.
So, what’s with the “lifetime fill”, BMW? Per Gareth Foley at FCP Euro, “BMW rates these transmissions for a ‘lifetime fill,’ however, through our channels at ZF and speaking with the engineers of those transmissions, we’ve learned that the transmissions are tested to 100,000 miles with an “acceptable rate of failure” on the original fill. 100,000 miles is BMW’s definition of a ‘lifetime fill’ and that’s passed the extended warranty and ‘good-will’ repair limit, meaning a failure after that is no longer BMW’s responsibility.”
Given ZF’s recommended service interval, at nine years of ownership and 60,000 miles on the odometer, it was time to service the ZF 8HP in my 2015 328i Sport Wagon. (Only 60,000 miles in nine years? Yes, I split time between my project cars. Don’t judge me!) In addition to the time and mileage indicating a service was due, there was a faint audible groan at startup and cold shifts had started to hang a bit longer than usual.
After receiving the full ZF service kit from FCP Euro, I took my M Sport wagon over to a local trusted shop, RRT Automotive. The kit consisted of a new pan with integrated filter, pan bolts, and more than enough ZF Lifeguard fluid to complete the service.
RRT technician John Jean allowed the transmission to cool down and began work, removing the under-body paneling to access the transmission pan. The old fluid was drained and the pan was removed. The new ZF pan was put into place and the new bolts were installed and torqued in proper sequence to spec. The transmission was initially filled cold and the fill plug was reinstalled temporarily.
Now the fun bit! The engine was started and transmission fluid was brought up to temperature (between 40 and 50 degrees Celsius) for the second fill, with a scan tool being used to monitor the transmission fluid temperature. The transmission was shifted through all gears (while parked) to ensure fluid was dispersed throughout. Once reaching the desired temperature range, the fill plug was removed a second time and additional fluid was pumped into the transmission, again waiting until it poured out from the fill plug. At that point, everything was buttoned back up and the job was complete.
How’s it feel after the service? Once warmed up, there wasn’t anything “bad” before per se, but I’m happy to report the faint groaning is gone and the first few cold shifts are improved. As we all know, preventive maintenance is what keeps these cars on the road and operating at peak performance. So, if you have a ZF 8HP-equipped car and haven’t done a fluid and filter service, check your time and mileage on the current fluid—it just might be time! —Mike Bevels