Interesting facts about the 9 speed gearbox - Jeep Garage - Jeep Forum

Go Back   Jeep Garage - Jeep Forum > Jeep Platform Discussion > 2014+ Cherokee-KL

Join Jeep Garage Today
Thread Tools Display Modes
Old 02-27-2014, 07:06 PM
MartinC's Avatar
My Jeep: 2014 3.2L KL
Join Date: Jan 2014
Location: Champaign County IL
Posts: 57
Thanks: 0
Thanked 6 Times in 6 Posts
Rep Power: 1236
MartinC is on a distinguished road
Interesting facts about the 9 speed gearbox

I came across a very interesting article in another forum which goes into great detail regarding the design of the 9 spd ZF gearbox. I do not wish to flout this forum's rules by providing a link but I will identify the article which is titled "ZF's 9-Speed 9HP Transmission Puts Dog Clutches On The Leash" by Alex Dykes. It can be found by visiting TheTruthAboutCarsdotcom. The article explains the difference between the conventional friction clutch used in most of the gear shifts and the dog clutches. Let me extract a small piece to give you an idea of what's involved:

" To save space and increase efficiency, the 9HP uses two multi-plate clutch elements, two friction brakes and two electronically synchronized dog clutches. ....The way the gearsets are arranged inside the case, shifts from 1-2, 2-3, and 3-4 involve only the traditional friction brake and clutch elements. As you would expect, aside from 1st being fairly low and somewhat distant from 2nd, these shifts feel perfectly “normal.” Under hard acceleration there is a momentary reduction in engine torque (courtesy of the computer to reduce clutch wear) and the shift occurs quickly and smoothly. The shift from 4-5 however is different. The transmission has to disengage dog clutch “A” in addition to engaging a friction clutch. This shift takes slightly longer than the 3-4 shift and the car’s computer makes a drastic reduction in torque to prevent wear of the dog teeth. Shifts 5-6 and 6-7 again happen with the only the friction elements at which point we need to disconnect the final dog clutch for gears 8 and 9 so we get the same kind of torque reduction in those shifts. The result is a transmission that has two distinct “feels” to its shifts, one that has only a slight torque reduction (1-2, 2-3, 3-4, 5-6, 6-7, 8-9) and one that has a more “manual transmission” feel where torque is cut severely (4-5 and 7-8)."

It goes on to say "Downshifts are where the 9HP truly feels different. Because of the design, if you’re in 8th gear and want to pass, the transmission will often need to drop 4 or 5 gears to get to a suitable ratio. (Remember that 4th gear is the first ratio going back down the scale that is lower than 1:1.) To do this the transmission has to accomplish the harder task of engaging two dog clutches. To do this the transmission doesn’t use cone synchros like a manual (too bulky) it uses software. Engaging dog clutches requires a longer and yet more severe reduction in torque than the disengagement because the transmission has to align the clutch and then engage it. In most automatics when you floor the car you get an instant feeling of acceleration that improves as the transmission downshifts. Although there would be moments of power reduction (depending on the programming) during this time, the engine is always providing some force forward. The 9HP’s software on the other hand responds by cutting power initially, then diving as far down the gear-ladder as it can, engaging the dog clutches and then reinstating your throttle command. The result is a somewhat odd delay between the pedal on the floor and the car taking off like a bat out of hell."

There is a lot more in the article that bears reading.

In the same forum, Alex has also posted a very comprehensive and fair review of the Cherokee (including a 30min video) which makes interesting reading.

I commend these references to you all.


Reply With Quote
The Following User Says Thank You to MartinC For This Useful Post:
Sponsored Links
Old 02-27-2014, 10:54 PM
ChadRizor's Avatar
My Jeep: 2014
Join Date: Dec 2013
Location: Arkansas
Posts: 50
Thanks: 0
Thanked 5 Times in 3 Posts
Rep Power: 1246
ChadRizor is on a distinguished road
👍👏. Great information that you've provided. It has answered some of the question I've been pondering over. IMO this is a very efficient design. My father (who is a process engineer), was extremely impressed with the transmission for the jeep Cherokee. He has design many transmission,rear ends, and other parts for well known semi trucks & auto companies before retiring from Dana corporation. So for him to take notice and spend time researching the web tells me this is no slouch jeep. Thanks again for the write up provided.
Reply With Quote
Old 03-03-2014, 06:12 AM
WK2 Rover's Avatar
Premium Member
My Jeep: 2011 5.7L WK2
Join Date: Sep 2010
Location: San Francisco Bay Area
Posts: 290
Thanks: 2
Thanked 13 Times in 11 Posts
Rep Power: 2669
WK2 Rover is on a distinguished road
Re: Interesting facts about the 9 speed gearbox

The 9-speed complexity times 2WD and two 4WD options times two engines times different driving modes (Auto, Sport, etc.) is why the vehicle was delayed. Fortunately firmware updates can continue to improve shift smoothness, performance, and gas mileage.
JEEP 3: 2011 Grand Cherokee Overland 4x4, Hemi V-8 with MDS, Multi-speed Automatic with ERS, Quadra-Drive II with Rear ELSD, Off-Road Adventure Group II, Selec-Terrain, Quadra-Lift, Towing Group IV, Advanced Warning & Adaptive Cruise Control, Bright Silver Exterior with Beige Leather Interior
MODS: BFG All-Terrain T/A KO2 LT-rated tires, Passenger-side "Trail Rated" Badge, "5.7L" and "Hemi" Badges, "70th Anniversary" Badge, Mopar Cold Air Intake, Custom Engine Cover, Chrome Fog Light Bezels, Bright Pedals, Illuminated Door Sills, WeatherTech in front / back / cargo / license plate frame, Mopar Roof Rack, Thule Ski Rack, Thule MOAB Cargo Basket
JEEP 4: 2014 Cherokee Trailhawk 4x4, 3.2 liter V-6, 9-speed Automatic with ERS, Active-Drive II with Rear ELSD, Technology Group, Comfort Group, Cold Weather Group, Granite Exterior with Brown Interior
Reply With Quote
Old 03-04-2014, 11:12 PM
Mr_Taz's Avatar
Premium Member
My Jeep: 2014 3.2L KL
Join Date: Feb 2014
Location: Gatineau, Quebec
Posts: 64
Thanks: 10
Thanked 1 Time in 1 Post
Rep Power: 1211
Mr_Taz is on a distinguished road
Re: Interesting facts about the 9 speed gearbox

Thanks for the information within the article by Alex Dykes and the video on the Jeep Cherokee Limited also has loads of useful facts and evaluation!

Can't wait to get my hands on my Limited
Ordered a Cherokee Limited 2014 -
3.2 Pentastar, NAV, BLACK with Vesuvio Interior, Tow package, Luxury Group, ACTII drive, Automatic 4WD, Off Road Suspension. Delivered : 16/APR/2014

Prev: OLDS Cutlass Salon '77. Camaro Berlinetta '78, Camaro Z28 '79, Nissan SX-200 '81, Nissan KC 4x4 '84, Nissan Pathfinder 4x4 '86, Jeep Grand Limited 4x4 '96, Pilot 4x4 2005.

Happy to be Back in the Jeep Family.
Reply With Quote

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off

Similar Threads
Thread Thread Starter Forum Replies Last Post
Shift Console Illumination Facts des24412 Troubleshooting/Problems 6 03-17-2017 09:53 AM
**JEEPGARAGE EXCLUSIVE! Launch Control tips & Facts! Raise and lower RPM's Scottina06 Grand Cherokee SRT - WK2 72 10-03-2014 03:38 AM
New member new 8 speed gearbox Overlander poppyduc New Members - Welcome! 4 03-20-2013 11:02 AM
Need facts on installing nav edmcfall Audio/Visual/Navigation 13 02-14-2013 09:24 PM

Powered by vBadvanced CMPS v3.2.3

All times are GMT -5. The time now is 09:51 PM.

Powered by vBulletin® Version 3.8.8
Copyright ©2000 - 2017, vBulletin Solutions, Inc.
Copyright 2012 - JeepGarage.Org
The Jeep Grand Cherokee Owners Community is in no way associated with or endorsed by FCA US LLC. Chrysler, Dodge, Jeep, Ram, Mopar and SRT are registered trademarks of FCA US LLC.