Suburban/Tahoe/Yukon Tcase
- Thread starter protosy
- Start date
C'mon guys... Nobody has any thoughts? Hartman you around? I am pretty sure this thing wouldn't shift out of all wheel if there was a load or slippage. I am also know that the front diff would still be engaged. but it would be cool to have just 2wd for the highway or burnouts :smile:
chad
chad
protosy,
I am planning to use a 2000 model Olds Bravada auto 4WD transfer case in my V-8 powered 4x4 S10 pickup. It has an ECU that allows the transfer case to run only in 2WD mode until rear wheel slipage is detected by the speed sensors in the T-case. It also has a mode that pulls in the front drive when the throttle goes wide open below 5 mph in order to prevent wheel spin in the rear. The transfer case is only a 4WD hi range case and weighs only 2 pounds more than the Borg Warner T-case used in the Sy/Ty. The front drive shaft for this case is smaller in diameter but stonger than the Sy/Ty's shaft since it has eliminated the double cardin joint, and it is 2 pounds lighter. It appears to be more suited to a Sy/Ty swap than the NP8 option Yukon transfer case that you are looking at!
I am planning to use a 2000 model Olds Bravada auto 4WD transfer case in my V-8 powered 4x4 S10 pickup. It has an ECU that allows the transfer case to run only in 2WD mode until rear wheel slipage is detected by the speed sensors in the T-case. It also has a mode that pulls in the front drive when the throttle goes wide open below 5 mph in order to prevent wheel spin in the rear. The transfer case is only a 4WD hi range case and weighs only 2 pounds more than the Borg Warner T-case used in the Sy/Ty. The front drive shaft for this case is smaller in diameter but stonger than the Sy/Ty's shaft since it has eliminated the double cardin joint, and it is 2 pounds lighter. It appears to be more suited to a Sy/Ty swap than the NP8 option Yukon transfer case that you are looking at!
I picked up a 2000 model OLDS Bravada transfer case with ECU brain & wiring harness for $500 down in my home town of Houston, Tx. It only had 8,000 mi on it, and was wrecked due to the floods we had down here in Houston last year (although the vehicle itself was not flooded so all the components were still good!). I also had previously acquired a '94 Bravada transfer case for my swap, but when I discovered the capabilities of the newer generation Smartrac that the '98 up Bravada had I decided it was way more advanced with its 2WD mode, and so I had to get one (thats why I know the weight of the components in comparison).
One thing that I must point out though, in order to use this system you will have to use the vehicles main ECU as well because it downloads vehicle identification data to the transfer case module upon start-up (gear ratio, tire diameter, vehicle type...SUV, 4x4 truck, etc.). It also gives a trigger signal to the transfer case module (via a single multiplex wire connection) when the vehicle is below 5 mph and when the throttle position sensor pushed wide open, in order to instruct the transfer case module to pull in the front drive output to prevent wheelspin on initial acceleration from a dead stop (something that would be very benificial for our purposes I believe!). It is really very simple to wire up. The transfer case module only has 11 wires to attach up (7 wires go to the transfer case itself thru the special wiring harness that comes with the transfer case, the others are power, ground, and the communication multiplex connection). The main vehicle ECU can be reduced to only 8 to 9 wires itself for the functions required (3 wires to the TPS, 2 VSS input wires, 2 power wires, 1 ground, & the multiplex communication wire). I believe that the TPS connections might be able to be reduced to one using only the output voltage from the existing Sy/Ty's TPS, since the same TPS sensor is used on both the Sy/Ty and the '98 up Bravada's. I'm not sure yet if that will mess up the existing input for the Sy/Ty's ECU since current will be flowing to both ECU's, but if all the ECU is looking for is a certain voltage input & not a particular current flow, then it should work.
Anyway, that is where I stand right now on my conversion issues with this type of transfer case!!
<font size=-1>[ This Message was edited by: tloof on 2002-02-19 10:24 ]</font>
One thing that I must point out though, in order to use this system you will have to use the vehicles main ECU as well because it downloads vehicle identification data to the transfer case module upon start-up (gear ratio, tire diameter, vehicle type...SUV, 4x4 truck, etc.). It also gives a trigger signal to the transfer case module (via a single multiplex wire connection) when the vehicle is below 5 mph and when the throttle position sensor pushed wide open, in order to instruct the transfer case module to pull in the front drive output to prevent wheelspin on initial acceleration from a dead stop (something that would be very benificial for our purposes I believe!). It is really very simple to wire up. The transfer case module only has 11 wires to attach up (7 wires go to the transfer case itself thru the special wiring harness that comes with the transfer case, the others are power, ground, and the communication multiplex connection). The main vehicle ECU can be reduced to only 8 to 9 wires itself for the functions required (3 wires to the TPS, 2 VSS input wires, 2 power wires, 1 ground, & the multiplex communication wire). I believe that the TPS connections might be able to be reduced to one using only the output voltage from the existing Sy/Ty's TPS, since the same TPS sensor is used on both the Sy/Ty and the '98 up Bravada's. I'm not sure yet if that will mess up the existing input for the Sy/Ty's ECU since current will be flowing to both ECU's, but if all the ECU is looking for is a certain voltage input & not a particular current flow, then it should work.
Anyway, that is where I stand right now on my conversion issues with this type of transfer case!!
<font size=-1>[ This Message was edited by: tloof on 2002-02-19 10:24 ]</font>
InvisiBill
Active member
Didn't it come up last time that this transfer case uses the same type of system as an automatic tranny, and might not hold up in a SyTy? Weren't the full-size trucks having a lot of problems or something? Though nobody seemed to say anything about the S-trucks...
InvisiBill,
Go back and read part 2 of the AWD vs. RWD vs. FWD post, as TurboTony addressed the issue of where & how often failures were seen. Also, I gave further information on the construction of the later NV-136 (NP4 option)& NV-236 (NP8 option) auto 4WD transfer cases.
As a side note, I have since acquired the auto 4WD full range Hi/Lo NV-236 (NP8 option)transfer case from a '99 Jimmy. This will enable me to still use my V-8 powered '93 extended cab 4x4 S10 truck as a true 4WD truck when desired since it has the 4WD Lo range gearing in it. The single speed NV-136 (NP4 option) case as used in the '98 up Bravada is still the better unit to use in a Sy/Ty, and it is much easier to wire up to the transfer case control module as well! (7 wires instead of 23 wires compared to the NP8 type transfer case).
Go back and read part 2 of the AWD vs. RWD vs. FWD post, as TurboTony addressed the issue of where & how often failures were seen. Also, I gave further information on the construction of the later NV-136 (NP4 option)& NV-236 (NP8 option) auto 4WD transfer cases.
As a side note, I have since acquired the auto 4WD full range Hi/Lo NV-236 (NP8 option)transfer case from a '99 Jimmy. This will enable me to still use my V-8 powered '93 extended cab 4x4 S10 truck as a true 4WD truck when desired since it has the 4WD Lo range gearing in it. The single speed NV-136 (NP4 option) case as used in the '98 up Bravada is still the better unit to use in a Sy/Ty, and it is much easier to wire up to the transfer case control module as well! (7 wires instead of 23 wires compared to the NP8 type transfer case).
TurboTony
Active member
Okay guys, I did a little more digging on the failures that I have been seeing, this is the official explanation right from GM
When the vehicle is driven extensively in low temperatures (-12°C (10°F) or below), slipping may occur when the vehicle is in the 2 HI mode. This occurs because the transfer case clutch pack does not have enough torque capacity to overcome the viscosity of the front axle lubricant. The friction generated by the slipping clutch discs may cause premature wear of the clutch pack assembly
So judging by that the power that is transmitted through the clutchpack doesn't seem to be causing the failure.
On a side note, there is another difference between the K and T series cases
The NV236 transfer case (T Models) uses 8 friction and 7 steel plates. The NV246 transfer case (K Models) uses 10 friction and 9 steel plates.
HTH
TurboTony
When the vehicle is driven extensively in low temperatures (-12°C (10°F) or below), slipping may occur when the vehicle is in the 2 HI mode. This occurs because the transfer case clutch pack does not have enough torque capacity to overcome the viscosity of the front axle lubricant. The friction generated by the slipping clutch discs may cause premature wear of the clutch pack assembly
So judging by that the power that is transmitted through the clutchpack doesn't seem to be causing the failure.
On a side note, there is another difference between the K and T series cases
The NV236 transfer case (T Models) uses 8 friction and 7 steel plates. The NV246 transfer case (K Models) uses 10 friction and 9 steel plates.
HTH
TurboTony
TurboTony,
Can the NV-236 transfer case be upgraded with the NV-246's clutch drum & 10 friction disk pack assembly (or if the drum is the same just adding additional friction discs & steel plates) for added torque capacity? If I am not mistaken the internals and case of the two are basically the same (except for output shaft size & spine count). If so, I should probably do this mod on my NV-236 before I install it in my V-8 powered '93 extended cab 4x4 S10 truck!
By the way, the NV-236/246 transfer cases (NP8 option) have the 2WD Hi lock-in mode that disengages the front differential and at the same time locks the transfer case in 2WD output mode only; whereas the NV-136 transfer case (NP4 option), as used in the '98 up Bravada, has a front differential that is permanently engaged (just like the Sy/Ty's have) and the transfer case is always in a stand-by 2WD mode (the same mode as the auto 4WD mode of the NP8 type case) as long as no wheel slipage is detected by the transfer case speed sensors. Because of this, it would appear to me that in 2WD Hi mode the NP8 type unit doesn't have the front driveshaft rotating while the vehicle is moving (just like any regular 4x4 S10); whereas, the NP4 type Bravada case does see the front driveshaft rotating while the vehicle is moving. This means that the clutch disk pack in the NP8 transfer case will be subjected to drag when the front differential oil is very viscous such as in winter (below 10°F) because the front differential is not rotating the front driveshaft at the same RPM as the rear output shaft of the transfer case. Vehicles with a permanently locked front differential (such as in the Bravada and the Sy/Ty's...or any S10 with a PowerTrax front locker unit) would be causing the front driveshaft to be rotating at the same RPM as the rear output shaft of the transfer case, and thus would not be experiencing the drag on the clutch disk pack of the transfer case when in the auto 4WD mode (of any NV-136/236/246 type cases) or the 2WD Hi lock-in mode (of the NV-236/246 cases).
Using any of these later model transfer cases in a Sy/Ty should not be a problem, since such a potential for drag in the clutch disk pack is eliminated due to the permanently engaged front differential that is used in the Sy/Ty's!! Does that sound plausible to you?
tloof
Can the NV-236 transfer case be upgraded with the NV-246's clutch drum & 10 friction disk pack assembly (or if the drum is the same just adding additional friction discs & steel plates) for added torque capacity? If I am not mistaken the internals and case of the two are basically the same (except for output shaft size & spine count). If so, I should probably do this mod on my NV-236 before I install it in my V-8 powered '93 extended cab 4x4 S10 truck!
By the way, the NV-236/246 transfer cases (NP8 option) have the 2WD Hi lock-in mode that disengages the front differential and at the same time locks the transfer case in 2WD output mode only; whereas the NV-136 transfer case (NP4 option), as used in the '98 up Bravada, has a front differential that is permanently engaged (just like the Sy/Ty's have) and the transfer case is always in a stand-by 2WD mode (the same mode as the auto 4WD mode of the NP8 type case) as long as no wheel slipage is detected by the transfer case speed sensors. Because of this, it would appear to me that in 2WD Hi mode the NP8 type unit doesn't have the front driveshaft rotating while the vehicle is moving (just like any regular 4x4 S10); whereas, the NP4 type Bravada case does see the front driveshaft rotating while the vehicle is moving. This means that the clutch disk pack in the NP8 transfer case will be subjected to drag when the front differential oil is very viscous such as in winter (below 10°F) because the front differential is not rotating the front driveshaft at the same RPM as the rear output shaft of the transfer case. Vehicles with a permanently locked front differential (such as in the Bravada and the Sy/Ty's...or any S10 with a PowerTrax front locker unit) would be causing the front driveshaft to be rotating at the same RPM as the rear output shaft of the transfer case, and thus would not be experiencing the drag on the clutch disk pack of the transfer case when in the auto 4WD mode (of any NV-136/236/246 type cases) or the 2WD Hi lock-in mode (of the NV-236/246 cases).
Using any of these later model transfer cases in a Sy/Ty should not be a problem, since such a potential for drag in the clutch disk pack is eliminated due to the permanently engaged front differential that is used in the Sy/Ty's!! Does that sound plausible to you?
tloof
TurboTony
Active member
Yup, I would agree with your above statements.
I just wanted to make you aware of the cause for the faiures that I have seen. At first it seemed like a cust abuse sort of thing, but with GM's statment of the cause it all seems okay now.
I don't think there would be any problem using these cases in a syty with a fulltime front diff. Especially since no one drives them in extreme cold. Or at least they shouldn't :grin:
I'm looking forward to your install. Keep us updated on your progress.
About your question on upgrading the clutches, I can't answer that one. Just one of those things that you will have to try and see I guess.
HTH
TurboTony
I just wanted to make you aware of the cause for the faiures that I have seen. At first it seemed like a cust abuse sort of thing, but with GM's statment of the cause it all seems okay now.
I don't think there would be any problem using these cases in a syty with a fulltime front diff. Especially since no one drives them in extreme cold. Or at least they shouldn't :grin:
I'm looking forward to your install. Keep us updated on your progress.
About your question on upgrading the clutches, I can't answer that one. Just one of those things that you will have to try and see I guess.
HTH
TurboTony
TurboTony and any other interested parties,
I checked with GM and the clutch drum and inner drive hub are the same part # for all of the NV-136/236/246 transfer case series. The only difference in these units are the friction discs & the final stack plate. The NV-136/236 units have 8 of the friction discs, and the NV-246 has 10 of the friction discs, the discs themselves being different due to thickness. Any NV-136/236 transfer case clutch drum pack can be upgraded with the 10 friction disc/ 9 steel plate pack as used in the full size truck's NV-246 transfer case for added torque load & power carrying capacity. Something to consider for use of the '98 up Bravada NV-136 auto 4WD transfer case in a highly modified Sy/Ty!!!
tloof
I checked with GM and the clutch drum and inner drive hub are the same part # for all of the NV-136/236/246 transfer case series. The only difference in these units are the friction discs & the final stack plate. The NV-136/236 units have 8 of the friction discs, and the NV-246 has 10 of the friction discs, the discs themselves being different due to thickness. Any NV-136/236 transfer case clutch drum pack can be upgraded with the 10 friction disc/ 9 steel plate pack as used in the full size truck's NV-246 transfer case for added torque load & power carrying capacity. Something to consider for use of the '98 up Bravada NV-136 auto 4WD transfer case in a highly modified Sy/Ty!!!
tloof