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SRT Transfer case:Illustration & Discussion

47K views 67 replies 34 participants last post by  SRT-MANA 
#1 ·
Ok here is our SRT Transfer case.
Many thanks to Resume Speed for helping with links etc. on this thread!
Thanks also to Blown7 for the help on loading all the photos.:)

Below link is a basic parts list for our Transfer case:
http://www.wkjeeps.com/misc/Tcase_2008_Parts.pdf

Below is a write up from my Shop Manual:
The NV146 transfer case provides Full-Time Active Four-Wheel Drive for optimum traction in a wide range of conditions
and is used in the Grand Cherokee SRT8 vehicles. The transfer case center differential distributes torque 48
percent to the front axle and 52 percent to the rear axle along with an electronically controlled clutch pack that is
coupled to the center differential for torque biasing. The NV146 electronics provide an active system because it can
anticipate and prevent slip. The transfer case can redistribute 100 percent of torque to the front or rear axle,
depending on need.
The NV146 single-speed transfer case provides the following benefits:
² No shift lever or driver interaction required.
² Full-time four-wheel drive provides smooth operation and vehicle stability under all conditions because torque
is constantly being transferred.
² Even torque distribution provides traction to maintain forward motion under most conditions.
² The Brake Traction Control System (BTCS) works in tandem with full-time four-wheel drive. BTCS provides
resistance to any wheel that is slipping to allow additional torque transfer to wheels with traction.
² Robust design and improved sealing enhance reliability.
² No maintenance required.

Controls for the NV146 transfer case active clutch (torque biasing device) are located in the Final Drive Control
Module (FDCM) and communicated on the CAN C bus. The FDCM monitors wheel speeds at the front and rear
axles to detect wheel slippage. A complete vehicle dynamics model calculates slip at each tire for given vehicleoperating
conditions. The clutch pack in the transfer case is engaged to minimize the speed difference between the
front and rear axle, resulting in torque transfer to the axle with higher traction. The electronically controlled wet
clutch pack uses an electric motor to actuate a sector plate. The sector plate actuates a clutch lever that applies
normal force to the multi-disc wet clutch pack bridging the differential. The clutch discs are alternately splined to the
front and rear driveshafts. When normal force is applied to this clutch pack, torque is transferred to equalize speed
differences between front and rear axles.

Unfortunately, the shop manual just copied the text and illustrations from a similar transfer case so I was on my own as far as the dismantling and re-assembly of some components.

Basic operation as I see it:
  • The shift motor (which some of us unplug from time to time) rotates the shaft that has a cam attached to it. It appears that it can rotate clockwise and counter clockwise. I can see NO harm in unplugging it for the dyno etc. as the shift arm will not engage the clutch pack for the forward output shaft.
  • The clutch pack is engaged when the cam is rotated...could be partially engaged or fully engaged, therefore increasing the torque to the front wheels. I did note that the clutches in this transfer case which had approximately 6,000 miles (per the junk yard) looked perfect. I did notice a shiny area on the output shaft where the clutches engage though.
  • The chain and gears look substantial...time will tell!
  • The one piece output shaft also looks substantial.
One thing that I was surprised at was with the 1 piece output shaft, the torque may be distributed to the front tires (again through the clutch pack) when the rear tires spin, HOWEVER, the rear wheels will still spin the same. This does not take into account the ABS system that will apply the brakes to the spinning wheel(s).

All in all, a pretty straight forward design.

Enjoy these photos guys!















 
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#4 ·
Somebody sticky this cause this is kick a$$ tech!
Not like those pu$$y a$$ed CAI threads.
Not too shabby for a guy that plays with hammers and saws


J
 
#5 ·
I'm impressed Bill, you should be voted Most Valuable Forum member.

The offroad guys swear by the NP205 "all gear" case, I wonder if a swap is possible if the NV241 craps out. You'd lose the electronic AWD but you'd pick up massive power capability and FT4WD.
 
#8 ·
I'm impressed Bill, you should be voted Most Valuable Forum member.
Blown7 would get my vote for that title.
Think of the time and $$$ Jeff has spent on the electronics alone.:eek:
The offroad guys swear by the NP205 "all gear" case, I wonder if a swap is possible if the NV241 craps out. You'd lose the electronic AWD but you'd pick up massive power capability and FT4WD.
Navy,
Funny you mention that NP 205 transfer case. Western Diff asked if I would be interested in a joint deal with them on a fresh transfer case.
A joint venture, by previous definition, is Builders Bills credit card to be used at will, Western Diff supplying a workable unit. NO THANKS!!!!!

There appear to be much easier ways to prevent breakage of the transfer case.
I would go about it exactly the same way the SRT engineers would.;)
Bill
 
#7 ·
Nice write up Blingster!! Was this just a fact finding inspection of the T-case?

GC
 
#9 ·
Exactly GC....I wanted to be knowledgeable about the transfer case.
I started at the rear of the drivetrain (9" posi Ford) and have worked up through the driveshaft and related issues (harmonics), through the transfer case and transmission. Now where???
In the past 11 months I have learned so much about these JGC's.
I enjoy the learning as obviously you do!
Bill
 
#11 ·
WoW! nice write up. Question Bill, from looking at it,what do you think is the weak link in the "transfer case"? also QUOTE: "One thing that I was surprised at was with the 1 piece output shaft, the torque may be distributed to the front tires (again through the clutch pack) when the rear tires spin, HOWEVER, the rear wheels will still spin the same. This does not take into account the ABS system that will apply the brakes to the spinning wheel(s)." Do you think it would be best to pull the ABS fuse and not just turn off the T/C at the track because with some wheel spin the ABS will be applyed. Thanks again and nice write up.
 
#12 ·
Thanks Viper.
There have only been 2 transfer case failures that I know of so far:
  1. Due to running different size tire heights front vs. rear
  2. We will find out next week when our member has it taken out. My offer still stands as far as buying the junk transfer case to see what happened.
As far as pulling the ABS fuse at the track, I had a terrible experience with doing that.
My proud Jeep hung its head as it did an AWFUL 2 wheel diagonal peel in front of spectators.:mad:

I am looking in the future as ABS and traction control being friendly and useful.;)
Bill
 
#15 ·
Bill, forgive me for prying, but you strike me as the Willy Wonka of cars... in your garadge are dozens of Umpa Lumpas constructing, destroying, testing, developing gear-driven components :D

What in the world do you do for a living!
 
#18 ·
I think Bill saves the destroying for himself. And, hmmm..lets see..what could "Builder" Bill do for a living...hmmmm. AHA! I got it. He is a Chippendales dancer...;) :D
 
#17 ·
Thanks Bill. Very good write up.
 
#23 ·
Good job bill!!!

Looks like a strong TCase. Chain and shaft look good. Does it look like there is any way to control the tq transfer with a switch? Example, I would love to have as much power going to the front at all times while at the dragstrip. Maybe we can rig up a reostat switch to control it???

Thanks for all the hard work.
 
#24 ·
Chris,
Looks like just a 5 volt supply to the DC motor.
I would remove the 4 10mm head bolts from the motor.
The motor pulls out pretty easily. It is keyed with 1 spline removed so it only goes in one way.
A 90 degree rotation (either way) should give the maximum torque to the front wheels.
The computer will probably not like it, but then again, what does it like that we have done???
Let me know if that works!
Bill
 

Attachments

#26 ·
Haaaaa!
1) To see what areas (if any) could use strengthening.
2) Different gearing??;) Actually, you could run different gears in the back than the front by simply removing the chain and disabling the front diff. Unfortunately, you would lose the 4 wd (ok..3 wheel drive) advantage.

A closer guess would be to look at the pointed questions that Blown7 asked the SRT Engineers.
Amazing answers that I NEVER would have thought of.
Bill
 
#27 · (Edited)
A closer guess would be to look at the pointed questions that Blown7 asked the SRT Engineers.
Amazing answers that I NEVER would have thought of.
Where can this be seen?

**nevermind....found it on the charger forum**
 
#32 ·
OK, here is what I have found. I had B&G raise my idle to 700. Ever since I had this done, the jeep will not shift from 1st to 2nd or 3rd until 4 or 5K most of the time. I can cruise at 70 without my foot on the gas petal and the vehicle continues to pull and my transfer case will not engage all the time. I was told the PCM does not affect the Transmission or Transfer case. I disagree.
 
#33 ·
FLsrt8,
Lets hope Jeff jumps in with his knowledge on PCM's.

From my JGC Shop manual:
POWERTRAIN CONTROL MODULE (PCM)
The PCM is a pre-programmed, microprocessor digital computer. It regulates ignition timing, air-fuel ratio, emission
control devices, charging system, certain transmission features, speed control, air conditioning compressor clutch
engagement and idle speed. The PCM can adapt its programming to meet changing operating conditions.
The PCM receives input signals from various switches and sensors. Based on these inputs, the PCM regulates
various engine and vehicle operations through different system components. These components are referred to as
Powertrain Control Module (PCM) Outputs. The sensors and switches that provide inputs to the PCM are considered
Powertrain Control Module (PCM) Inputs.
The PCM adjusts ignition timing based upon inputs it receives from sensors that react to: engine rpm, manifold
absolute pressure, engine coolant temperature, throttle position, transmission gear selection (automatic transmission),
vehicle speed and the brake switch.
The PCM adjusts idle speed based on inputs it receives from sensors that react to: throttle position, vehicle speed,
transmission gear selection, engine coolant temperature and from inputs it receives from the air conditioning clutch
switch and brake switch.
Based on inputs that it receives, the PCM adjusts ignition coil dwell. The PCM also adjusts the generator charge
rate through control of the generator field and provides speed control operation.
Bill
 
#37 ·
Bill from the looks of that chain, the transfer case looks pretty formidable. Any updates on what you're planning or are you going to run the stocker until it breaks?

When I spoke with WD they mentioned something about the ATLAS transfer case possibly being an option.
 
#38 · (Edited)
I had an ATLAS in one of my Wranglers. It it very adaptable but it's primary advantage is it's extreme low gearing. Unless you are doing some rockcrawling it would probably not be worth it. Plus it is not "Street or Strip AWD" friendly.

Mabye a NP249, 247, or 242.... Still have the low range though but both have the option for full time 4wd / Awd. I also know some companies are making very strong hybrids of those cases.
 
#39 ·
Double post...
 
#40 ·
Sorry, I missed your earlier post.

I believe WD is barking up the wrong tree by thinking we can use the Atlas.
They also came up with possibly using a straight axle for our front diffs.:eek:

Until one of us breaks the transfer case at the strip, I am going to keep the stock case and see what happens.
It does look somewhat robust.

If the rears hook well with the drag radials, the transfer case should NOT be transmitting massive amounts of torque to the front diff.

Now the front axles and front driveshaft may be a different story.

Again, the electronics are not going to like an Atlas very well.
Bill
 
#41 ·
#43 ·
Wow some nice pictures of the inside of our NV146 Transfer case there Bill!!!
 
#44 ·
Way to search the archives, Jose.
 
#46 ·
Thanks Chad! Yeah I bumped into this thread via Google while looking for a flange to mate to this NV146 Transfercase for my new Rear driveshaft.
 
#45 ·
wow, zombie alert. Enjoyed the pics. One thing, when one does burns up, it smells like garlic mudbutt and doesn't look nearly as clean as that one. Absolutely awful. Not much to do with these except bake and cool the shaft or try to squeeze more clutches in.
 
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