Talkin’ ‘Bout My Gen-eration: ZF 6-Speed Differences in Generation 1 & 2 Valve Bodies

Maura Stafford

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Much like classic rock songs, it seems as though non-electronic and now non-computerized valve bodies are becoming the oldies but goodies. The Turbo 400, C6 or 904 that were gone through without scan tools or meters are like songs we originally heard on vinyl records. Sure, they might have skipped a gear or a beat, but with a slight nudge, they were still functional. And rebuilding an A413 or 200-4R valve body now seems almost as easy as sticking in a cassette tape and tapping along: if one of these units comes into the shop, your hands start rebuilding them instinctively - no reference material required. Yeah, maybe a unit with too many miles rolls in that needs to be replaced, like a cassette with too many listens and the tape started crinkling and pulling out. Still, working on these primarily hydraulic-only units can be fun and almost carefree, like hearing an old favorite play on the classics station and being able to sing along because you know all the words by heart.

Then came the era of '80s and '90s music and transmissions like the AODE, A518 and 4L60-E produced with electronics. Meters and scan tools needed to be purchased, cars started having CD players instead of cassette decks, and even hard-rocking groups like Van Halen started adding synthesized keyboards. Parts catalogs had to include a section entitled "Electronic Components" for these new transmissions. Fast forward to today and we're at the dawning of a new mechatronic age in which valve bodies have computers attached to them and you can store roomfuls of albums on your laptop, iPod® or thumb drive. Is your vehicle having a drivability complaint? Maybe it just needs to have the computer re-flashed. Like that new Springsteen song? Download it from iTunes® right now. And how about the CAN-BUS technology and the ability of all the vehicle's systems to communicate with each other? Or, on second thought, maybe I'll just add that Springsteen song to my cloud so that I can access it from my home computer, TV, smart-phone and Kindle®.

Technology is crazy stuff, and it's already changed dramatically within our generation. And I don't think it's gonna just f-fade away. It's going to keep progressing and we need to as well if we want to stay in business - continuous learning is essential!

Even within these new, cutting-edge transmissions, it seems as though the learning curve on how to improve performance has shifted into high gear - the generation gap within some of these new transmissions is sometimes five years or less - making it a challenge to keep up with changes and properly identify units.


A perfect example of rapid transmission evolution is the ZF 6-speeds. In these units, modifications to the mechatronic (Figure 1) were made in 2006 to increase oil flow, which reduced the duration of the shifts. So ZF6 "Generation 1" ranges from 2000 to 2005 and encompasses the ZF6HP19/26/32 versions, while ZF6 "Generation 2" ranges from 2006 through current production and are referred to as ZF6HP21/28/34 units. These 19, 26, 32 and 21, 28, 34 numbers designate sequentially larger amounts of torque capacity of the transmission.

Figure 1

Much like the differences in societal generations, the Generation 1 versus Generation 2 changes in the ZF6 are subtle, yet non-interchangeable (the Ford 6R60/80 seem unaffected by the generation change and are typical of the ZF6 Generation 1). These ZF mechatronics may look nearly identical externally, but they are programmed differently and do not act the same.

The photos in Figures 2-17 show the differences between the ZF6 Generation 1 and 2 valve body components for both the "M-shift" (manual valve) and "E-shift" (solenoid controlled manual valve) version. There are some obvious differences between the E- and M-shift versions within each generation, which would be expected due to the method in which the manual valve is operated. Upon closer examination, though, there are significant differences between Generation 1 and 2 whether you are looking at the E- or M-shift versions; even many of the end plugs are slightly different in size. Attention to detail is a definite must when rebuilding these valve bodies. (By the way, forget about trying to swap Generation 1 and Generation 2 solenoids - they have different flow rates. In fact, during a rebuild, you should make every effort to put a solenoid back in its original location because the TCM learns their flow rates.)


E-Shift, Lower - PR Valve Side


Figure 2
Gen. 1
Figure 3
Gen. 2





M-Shift, Lower - PR Valve Side

Figure 4
Gen. 1
Figure 5
Gen. 2


E-Shift, Lower - Solenoid Side

Figure 6
Gen. 1
Figure 7
Gen. 2


M-Shift, Lower - Solenoid Side

Figure 8
Gen. 1
Figure 9
Gen. 2


E-Shift, Upper - Notched Side
Figure 10
Gen. 1
Figure 11
Gen. 2


M-Shift, Upper - Notched Side

Figure 12
Gen. 1
Figure 13
Gen. 2


E-Shift, Upper - Straight Side

Figure 14
Gen. 1
Figure 15
Gen. 2


M-Shift, Upper - Straight Side

Figure 16
Gen. 1
Figure 17
Gen. 2


The ZF6 mechatronic can be identified as a Generation 1 or 2 prior to taking apart the valve body by counting the number of orifices on the bosses on the cast side of the upper valve body (Figure 18). A Generation 1 unit has only six orifices, with six accumulator pistons mating in the bores inside the valve body. A Generation 2 has seven orifices and accumulator pistons.

Figure 18

Another way to verify generation is by measuring a ZF6 unit's pressure regulator valve and sleeve (Figure 19). A note of caution, though: there are some BMW 6- and 7-series transmissions which have six accumulators, but completely different-sized pressure regulator valves than either a ZF6 Generation 1 or 2 mechatronic. Due to diameter and length differences in both the valve and sleeve, none of these parts can be interchanged.

Figure 19

The changes to the ZF 6-speed are not an exception or anomaly amongst mechatronics. I'm not trying to cause a big s-s-sensation, but you'll be seeing these types of rapid changes occurring in the 6T40s, 722.9s, etc. That's right - we're talkin' 'bout a new generation.

Maura Stafford is a Sonnax project engineer and a member of the TASC Force® (Technical Automotive Specialties Committee), a group of recognized industry technical specialists, transmission rebuilders and Sonnax Industries, Inc., technicians.

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Subject(s) Included
  • General Diagnostics and Theory

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