[MJAB]

There are two interesting videos about how the 948TE / ZF 9HP transaxles works. Videos were made by Weber State University (WSU) - Automotive Technology Department - Transmission Lab.

It is split in two parts, the first shows the two dog clutches and how are activated, the second part shows all its main components and shows how it works.

Dog Clutch Demo - ZF 9HP 9-Speed Transaxle Operation - Part 1 of 2

Power Flow - ZF 9HP 9-Speed Transaxle Operation - Part 2 of 2

 

[lohchief]

Now that was cool as heck.Thanks for posting those videos.

 

[Charged021]

Oh so there is a 9th gear. My van will never go into 9th if I have it on cruise control. I actually find this transmission to downshift very slow compared to some of other ZF's. I even think the automated manual Smart For Two transmission downshifts faster. Its know for its extremely slow shifts.

 

[Brian P]

Downshifting from 8th to any lower gear, and downshifting from 5th to any lower gear, is awkward for this transmission to do, because it has to manipulate the engine speed (effectively in neutral) until the corresponding dog clutch is somewhere near matching revs before it can engage it. A big downshift from 8th to 4th is doubly awkward because it has to synchronize and engage both dog clutches in sequence.

I watched the first video but the second one will have to wait until later ...

 

[Charged021]

Its actually one of my biggest pet peeves with this vehicle. Downshift and feeling the increase in speed while coasting downhill in neutral effectively while the transmission makes its mind up what gear to find, not the most safe feeling.
On a side note:
While in manual mode holding the shifter in the "-" position while driving will downshift to the lowest gear possible according to the computer, usually around 5-6k rpm. This also works the other way around in the "+" position for upshifts but its not really useful that way.

 

[Joe Bo]

I tried playing with gears 8 & 9 in manual mode on my 27 mile HWY drive home today. What I discovered was that, in D mode, my PMC will stay in 8th gear @ 70mph @ 2200. Shift to manual, upshifted to 9th and the tach dropped to 1600.

After a minute in 9th, I downshifted to 8th and the tach bumped up to 2100. When I upshifted to 9th again after half a minute in 8th, the tach never drops and the transmission won't shift up again, even though the display says I'm in 9th gear.

Driving conditions are flat on a 3 lane HWY @ 70mph.

I also activated cruise control in 9th, it immediately bumps the tach up and cruises in 8th, though the display says 9.

RAM should update the display to more accurately coincide with the actual gear selected by the transmission, instead of the manual shifter selection.

I'm thinking the PMC rarely, if ever, gets into 9th gear in most driving circumstances, which is a shame. We want that economy gear...sometimes... don't we?

 

[seapro]

I have owned 2 Sprinters with 5-speed trannies and now a gas PM with a 6-speed. When driving in mountains and attempting to down shift I have sometimes not been sure as to which gear I was actually in. I wish all of them had a display to show the actual gear not just the selected gear.

 

[bobojay]

You sure that wasn't the torque converter locking & unlocking vs the gear actually changing? If it is, it won't show a gear change

 

[Joe Bo]

You sure that wasn't the torque converter locking & unlocking vs the gear actually changing? If it is, it won't show a gear change

I'm sure the load didn't change cause tach didn't change. If you read my post, I note that tach changes are indication of gear change, outside of sense and feel of the vehicle.

Try to replicate my test and report your results here. Thats what we're here for.

 

[Joe Bo]

Even in manual shift operation with 9th gear showing operational on the trip display, 9th gear is in fact inactive,

 

[Chance]

I tried playing with gears 8 & 9 in manual mode on my 27 mile HWY drive home today. What I discovered was that, in D mode, my PMC will stay in 8th gear @ 70mph @ 2200. Shift to manual, upshifted to 9th and the tach dropped to 1600.

....cut....

The change between 1600 and 2200 RPM is much higher than the gear ratios between 8th and 9th alone would suggest.

Since you've observed that manual 9th may not actually be 9th, is it possible that 8th wasn't 8th? For example, could it have shifted from 7th to 9th, or some other combination?

 

[Joe Bo]

Tach RPMs are just approx, probably closer to 1900 actually. I shifted 1 thru 9 getting on the HWY. It went into 9th once.

 

[marvin02]

From the owner's manual:

Electronic Range Select (ERS) Operation

The Electronic Range Select (ERS) shift control allows the
driver to limit the highest available gear. For example, if
you set the transmission gear limit to 5 (fifth gear), the
transmission will not shift above fifth gear, but will shift
through the lower gears normally.

You can switch between DRIVE and ERS mode at any
vehicle speed. When the shift lever is in the DRIVE
position, the transmission will operate automatically,
shifting between all available gears.

Moving the shift lever to the ERS position (beside
DRIVE) will activate ERS mode, display the current gear
in the instrument cluster, and set that gear as the top
available gear. Once in ERS mode, moving the shift lever
forward (-) or rearward (+) will change the top available
gear and it will be displayed in the instrument cluster.
To exit ERS mode, simply return the shift lever to the
DRIVE position.

So this isn't a true manual mode.

 

[Charged021]

Choose what gear your van "might" go into, what a deal!
Its manual downshift, not manual upshift. It also might be programmed differently in the many other car manufacturers that also use it.

 

[Chance]

....cut....

I'm thinking the PMC rarely, if ever, gets into 9th gear in most driving circumstances, which is a shame. We want that economy gear...sometimes... don't we?

Great question.

As transmissions get more and more gears, maybe the top one is too tall to yield the best combination of fuel economy and driveability under typical cruising conditions.

What if 8th is optimum for flat no-wind cruising, while 9th is more useful for when there is tail wind or slight downhill? Maybe 7th may yield best fuel economy into headwinds and/or slight up hills, etc...

In the past we always expected the top gear to be most economical, but as gearing is made taller and taller it comes a point where it's too tall to be optimum. These 9-speed transmissions seem to be geared very tall in 9th to replicate some of the fuel economy benefits of CVTs. If so, you can't have 9th geared to be optimum both into headwind and tailwind, or up 1% grade versus down same grade.

Obviously there would be a downside to chasing every bit of fuel economy in this manner -- mainly a lot more transmission shifts.

 

[Brian P]

I'm hearing that the 2016 9HP transmission has a different part number and supposedly both the ZF and Chrysler versions of this transmission have a fix of some sort for the shifting complaints. Wonder what they did? Anyone have a 2016 and can comment? Pay particular attention to the 8th-to-7th downshift and the 5th-to-4th downshift, since those are the ones that are awkward for this transmission to do.

I've had a Chrysler 200 rental car (pre-2016) with this transmission and I thought it was fine.

 

[Charged021]

Great question.

As transmissions get more and more gears, maybe the top one is too tall to yield the best combination of fuel economy and driveability under typical cruising conditions.

What if 8th is optimum for flat no-wind cruising, while 9th is more useful for when there is tail wind or slight downhill? Maybe 7th may yield best fuel economy into headwinds and/or slight up hills, etc...

In the past we always expected the top gear to be most economical, but as gearing is made taller and taller it comes a point where it's too tall to be optimum. These 9-speed transmissions seem to be geared very tall in 9th to replicate some of the fuel economy benefits of CVTs. If so, you can't have 9th geared to be optimum both into headwind and tailwind, or up 1% grade versus down same grade.

Obviously there would be a downside to chasing every bit of fuel economy in this manner -- mainly a lot more transmission shifts.

So what you are getting at is, 9 speeds are too many?
Im always looking at instant fuel economy readout and when my van does eventually go into 9th gear, consumption drops. Its not a lot, but it never increases in 9th.

 

[Chance]

So what you are getting at is, 9 speeds are too many?
Im always looking at instant fuel economy readout and when my van does eventually go into 9th gear, consumption drops. Its not a lot, but it never increases in 9th.

Shouldn't we expect that? I would hope that if engineers programmed it correctly, it wouldn't shift into 9th unless there was going to be an advantage, like lower fuel consumption.

However, when it doesn't shift into 9th by remaining in 8th, is it not possible that it would consume the same or more if it did shift into 9th? Or that the difference would be so minor that it's programmed not to shift early to avoid gear hunting?


I wouldn't necessarily say 9 is too many but we are close -- much depends on many factors. I saw an interview with a ZF executive who stated that going beyond 8 or 9 gears was driven more by marketing than technical needs. That was in response to whether ZF would develop an 11- or 12-speed to surpass the new 10-speeds coming soon.

 

[RDinNHandAZ]

My first car and one of the best I ever owned was a used three speed-on-the floor 1960 Plymouth Valiant 225 cu in slant 6. Running that car up the revs and jamming it into the next gear was a joy I will never forget. No amount of gears will ever replace the memories of that little 6 pulling 5K and the surge as third pulled you forward. Any automatic, or number of ratios pale in driving enjoyment. Sorry for the nostalgia and hijack, I am clearly out of control.

 

[Brian P]

Three on the floor was sporty and fancy compared to three on the tree! And I think the 225 was the "upgrade" back then. The standard one was 170.