Last post on Jul 09, 2013 at 7:15 AM
You are in the Isuzu Trooper
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Isuzu Trooper, SUV
#3265 of 11966 TOD transfer case
Feb 06, 2002 (11:08 am)
I went by my local Isuzu dealership today (Moss Robertson Isuzu; Gainesville, Georgia) and was able to get more exact information on how the TOD transfer case functions. I spoke with a very helpful die-hard Isuzu fan/mechanic for about an hour. The same process takes place as I indicated in my earlier post, but on different mechanical principles.
I'll do my best to explain.
A main shaft runs completely through the transfer case from the input(from the transmission) to the output(rear driveshaft). There is also a second shaft that is connected to the front driveshaft. A transfer case chain connects these two shafts together.(This is no different as compared to other modern transfer cases). However, the connection between this chain and the main shaft is not direct. The chain is attached to a "clutch assembly" gear that rides freely on the main shaft. This "clutch assembly" gear includes approsimately 6 clutch discs. Behind this "clutch assembly" gear, an armature plate is mounted directly to the main shaft through splines on the main shaft (This plate resembles the face of flywheel). Behind the armature plate, the electromagnetic coil is mounted. There are also speed sensors mounted on the transfer case to detect the speeds of the front and rear driveshafts.
When the computer detects different driveshaft speeds, the computer will send electricity to the electromagnetic coil. This coil then creates a magnetic field and attempts to push the armature plate away thereby compressing all the clutch discs in the clutch assembly gear. This action then allows torque to be transmitted to the transfer case chain and then to the front driveshaft.
The mechanic indicated that there is a small amount of preload applied to these clutch discs in their assembly. This would justify the spinning of the front wheels in my low friction experiences.
We also discussed "modifying" the wiring to make an "all the time 50/50" 4wd high transfer case by keeping electricity at this coil at all times. He indicated that this should not cause a problem, but that I should verify that 12 volts are being sent to the coil and not some lower voltage adjusted by the computer. This would allow our transfer cases to function like the non TOD transfer cases for 4wd high applications. I was also concerned about running the coil "hot" all the time. He indicated that this should not be an issue because this is how automatic transmissions are designed and that the Isuzu Vehicross virtually runs the coil "hot" a substantially greater % of the time as compared to the Troopers.
I will investigate this system by measuring the voltage going to the coil under the various conditions. If it is 12 volts, this is good news. At least for my 1999, the TOD computer is mounted directly under the passenger seat. It will be very easy to mount a swith under the seat that is hidden and easy to turn on/off from the driver position.
He also indicated that back in 1999, Isuzu used only one wiring harness. At least, that is what he said. The wiring diagrams he showed me confirmed that.
I wanted to at least better explain what I learned. I do not mean to drag out this TOD discussion.
In regard to torque measurements. Torque to the front driveshaft will never exceed 50% of the available torque, and could potentially be limited by the strength of the clutch pack within the transfer case.
Mike, based on the owner's manual and my personal experience, I believe the front driveshaft may receive up to 15% of the available torque (without TOD indicator lights) due to the preload placed on the "clutch assembly gear" during assembly.
Has anybody added an engine oil cooler?
Feb 06, 2002 (11:24 am)
Great detective work! Could you do me a favor and e-mail me what you wrote above to mikeiace.com so I can put it up in the "FAQ" section of http://isuzu-suvs.com I find it great reading and something that a lot of Isuzu owners would find useful. Also if you figure out a way to make it 50/50 all the time, take pics and do a writeup for the "How-to" section!
Feb 06, 2002 (11:25 am)
My buddy's dad had a '94 Blazer and that thing would grind the ABS and make a huge racket, it was also very sensitive. I find on the '00 Trooper the ABS rarely kicks in and when it does, it's quite smooth.
Feb 06, 2002 (2:06 pm)
I just wonder how much torque the electromagnetic clutch can actually transfer to the front axle, if not all of it. If I had TOD, I wouldn't lock-it into the'50/50' split unless I was off-road That slipping in turns would probably burn the clutch out real easy.
#3269 of 11966 50/50 split
Feb 06, 2002 (2:53 pm)
Yes, you would only use the 50/50 split in off-road situations.
#3270 of 11966 50/50 4hi
Feb 06, 2002 (3:08 pm)
Excellent info cknott...I would love to find out how to "lock in" to 50/50 4hi, such as for deep snow. Keep us updated!
One thought, if you are locked in 50/50, would there be any problem with driving on dry pavement (where normally TOD would be 15/85)? Probably not a problem, but too expensive to risk damaging anything.
Feb 06, 2002 (3:12 pm)
Yes it would be a problem. The same reason why you can't drive with a Part Time system engaged on dry pavement. Something has to give and it will be the diffys or the TOD T-case.
#3272 of 11966 Moss Rodertson Isuzu Dealership- cknott
Feb 06, 2002 (6:34 pm)
I live in the Gwinnett area. I have taken my 2000S Trooper to this dealership for recall work and they seemed pretty knowledgable. I have also been to Lou Sobh in Duluth and it felt like the typical dealership attitude. Do you have any experience with these dealers and what do you think of their service..any private shops you would recommend? Thanks for any info.
#3273 of 11966 TOD/ Dealership
Feb 07, 2002 (6:25 am)
I do not intend to drive on dry or even wet concrete/asphalt with the transfer case locked in 50/50. I would like this feature on snow, dirt roads, and any other loose surface above 20 MPH. However, even with this potential feature engaged on asphalt, I do not believe that it will cause any excessive additional wear to the transfer case and front axle that would cause failure as compared to the conventional TOD system. I do believe that you will definitely wear out your tires sooner. As Mike said, something has to give. For these Troopers, you will only need to worry about bouncing your truck on sandstone in Utah or New Mexico in order to bust gears, shafts, or transfer cases.
I am somewhat anal about people touching my vehicles. My wife is allowed to put gas in the car, carry passengers & cargo, and drive the vehicle. I do everything-else.
I have had only one "warranty" claim with this vehicle. My limited slip rear end did not engage as "tightly" as I wanted it to. In many situations, even with both rear tires on the ground, I was having to engage the parking brake to provoke the limited slip clutches to engage.
I took it to Moss Robertson. One day they looked at the vehicle and ordered the parts. Two weeks later the parts arrived. They took one day to install new clutches in the limited slip case. I was somewhat apprehensive about them working on the rear end because of the necessary alignment that must take place between the ring and pinion, and ring gear backlash. The vehicle came back to me in great condition, no unusual sounds in the rear end and the limited slip reacts much more efficiently. Now I only need to engage the parking brake when one of the rear tires is in the air.
I've noticed that I have long posts....sorry.
#3274 of 11966 re: 99 fogs
Feb 07, 2002 (6:30 am)
The truck is pre-wired for the fog lights. Once you removed one or two empty switch covers, you should see the plug where the oem switch(part#8971355120.. $45) plugs into;it could be foamed wrapped to prevent it from rattling. You will also need a relay(part#8970939101.. $21).The wiring by the bumper slot is easily accessable.