auto to manual hub swap

[tahoe express]

Does anyone have knowledge of a kit or the parts I can use to swap the front auto hubs to manual on a 98 tahoe 4wd.I'm looking to reduce drag and wear on the ever turning parts.Any help or direction will be appreciated.

 

[rhett325i]

I am also curious about this...

 

[aquaholic]

why on earth would you want to do this? the hubs are automatics. they lock when you push the 4wd button and unlock when you push the 2wd button.

 

[bowhunter22]

IFS 4x4s' from GM don't have locking hubs. We have what is called a "central axle disconnect" this is controlled either by the thermal actuator or the vacuum actuator. Now there is a manual cable conversion called "posi-loc" or something like that where a lever is run into the cab to slide your lock ring.

 

[John Redcorn]

IFS 4x4s' from GM don't have locking hubs. We have what is called a "central axle disconnect" this is controlled either by the thermal actuator or the vacuum actuator. Now there is a manual cable conversion called "posi-loc" or something like that where a lever is run into the cab to slide your lock ring.

I don't understand a lot about how the 4wd system works and this'd seem like a good thread to ask.

What all is spinning up front in 2hi? I know the front driveshaft still spins in 2 hi, the cv shafts obviously do, so are they all 3 just spinning but not connected in the diff until you engage?

And if the front driveshaft is spinning in 2hi, is there a difference in the transfer case when you change to 4hi? or would changing to 4hi simply lock in everything up front?


Also, I think I have 2 peg leg diffs. We put it in 4hi on a lift once and just the pass rear and drivers front were spinning. Why'd they do that? why is it hard to turn corners in 4hi if the front is a peg leg?

 

[loulblades]

The transfer case encoder motor should disengage power transfer to the front (via the driveshaft) and the actuator in the front differential should disengage power to the wheels and, in turn, feedback from the wheels.

The front drive shaft shouldn't be turning in 2hi unless the actuator or the encoder motor is not disengaging properly.

 

[bowhunter22]

Ok when in 2wd the left wheel - axle and part of the front diff spins when going forward. In theory the other half of the diff spins backwards along with the intermediate shaft until the central locking collar. Now the right side wheel and the remainder of the right side axle spins forward. Also in theory the front drive shaft should remain still.
Now the front axle as well as the transfer case are filled with lube oil, so you start turning something bathed in oil the pieces near it start to move with it. They are not being driven, they move with the kinetics of everything around them moving.
So the answer to what is moving in the front axle when in 2wd, hopefully everything. It's the sign that all parts are well lubed and free moving and drag is minimal.

Now for 4wd - In the transfer case when 4x4 is engaged a slide ring locks the collar to the shaft that is the front output (drive shaft ) that is driven by the rear output at a 1 to 1 ratio. As the front drive shaft is locked in and up to speed and again in theory the front diff now has power potential everything should be spinning in the same direction the same speed. Once this is achieved the central lock ring is signaled to engage the intermediate axle to the right side axle to complete the front drive mechanicals.

Your front and rear diff are open. As power is applied the truck actually twists and the torque transfer from the drive line believe it or not places a little more weight on the cross corner tires causing the other two to spin. That either ices the surface under the tire or carries a little more water into the mud making that tire easier to turn. As for in the air the front driver is the shorter side to put power through and the rear it's physics 90% of rear drive vehicles (without lockers) will spin the passenger tire.

In 4x4 the front and rear drive shafts turn the same speed. So the front and rear axles turn the same speed. Going straight ahead this is ideal, when turning though the front will start to travel farther than the rear (remember the track circles of a vehicle from auto class) or look at your own tracks in the snow, sand, mud and notice the front circles are larger than the rears. Now remember the front axle and rear axle are trying to travel the same distance. Can't happen drive line gets tight and something has to give, hopefully it's traction. Some times it's u-joints, axles, central axle engagement ring, or a chain jump in the transfercase.


This is very rough explanation, any questions please ask.

 

[TahoeGoBoom]

Ok when in 2wd the left wheel - axle and part of the front diff spins when going forward. In theory the other half of the diff spins backwards along with the intermediate shaft until the central locking collar. Now the right side wheel and the remainder of the right side axle spins forward. Also in theory the front drive shaft should remain still.
Now the front axle as well as the transfer case are filled with lube oil, so you start turning something bathed in oil the pieces near it start to move with it. They are not being driven, they move with the kinetics of everything around them moving.
So the answer to what is moving in the front axle when in 2wd, hopefully everything. It's the sign that all parts are well lubed and free moving and drag is minimal.

Now for 4wd - In the transfer case when 4x4 is engaged a slide ring locks the collar to the shaft that is the front output (drive shaft ) that is driven by the rear output at a 1 to 1 ratio. As the front drive shaft is locked in and up to speed and again in theory the front diff now has power potential everything should be spinning in the same direction the same speed. Once this is achieved the central lock ring is signaled to engage the intermediate axle to the right side axle to complete the front drive mechanicals.

This is very rough explanation, any questions please ask.

so basically, the front driveshaft does turn in 2 high? cuz i can tell you right now mine does. and i would assume my mechanic would have told me this was a problem if it was wrong...

 

[bowhunter22]

Yes it's fine that it moves, I'd be conserned if it didn't.

 

[TahoeGoBoom]

ok, that what i thought. lol
this:

The front drive shaft shouldn't be turning in 2hi unless the actuator or the encoder motor is not disengaging properly.

had me worried for a second.

 

[John Redcorn]

cool thanks for the explanations guys. didn't mean to hijack the other dudes thread.

I remember seeing a tsb, I don't remember what for but it was talking about an np8 pushbutton transfer case and having a tech 2 hooked up to read the front and rear driveshaft rpms in 2hi and said they should be within 5% of each other or something like that.

 

[tahoe express]

So, I guess the only way to acheive zero drag and prevent part wear on open roads is to drop the 2 front drive axles.

 

[loulblades]

Yes the front drive shaft may move but not in the same way (same speed) that a connected (mechanically) system would.

 

[TahoeGoBoom]

Yes the front drive shaft may move but not in the same way (same speed) that a connected (mechanically) system would.

how not? you drive train moves at the same speed that the front wheels would be turning.. the shaft may not see power, but it would still be moving at the same speed.. hence why you can shift into 4 hi under like 45 of w/e it is. if it wasnt going the same speed you would break something..
im just guessing here. but my theory sounds good..

 

[loulblades]

I agree with the bowhunter that the front driveshaft could turn even though the transfer case and differential are not mechanically engaged (i.e. in 2wd). However they are "fluid" (oil in the case and diff) engaged and due to losses in the system (physics involved in turning the driveshaft for instance) it would be highly unlikely that the front driveshaft would ever be able to reach the same speed as if it were mechanically engaged.

 

[John Redcorn]

I found the TSB that says the front and rear driveshafts should be going the same speed in 2hi. this is in regards to NP8 pushbutton autotrak transfer cases

tsb # 02-04-21-005A Slips in 4-Wheel Drive, Noise, Vibration, Leaks, Hot Odor (Diagnose and Repair Front Differential and/or Transfer Case)

I'd post a link but I don't know where you can view them for free.

It says:

Select 2 HI with the transfer case selector switch.

6. Apply the service brake and move the transmission selector lever in any forward gear.

7. Release the service brake.

8. Observe the front and rear propeller shaft speeds displayed on the Tech 2(R). The front and rear driveshafts should be rotating at approximately the same speed (the front driveshaft display on the Tech 2(R) may be slightly higher but never less than the rear). If they are not, skip to the Correction section below. If the driveshaft speeds are approximately the same, diagnose for other conditions that may be causing the concern. If the vehicle is stationary, the front propeller shaft should not rotate freely. It may take up to 54 N.m (40 lb ft) of torque to turn the front output shaft of the transfer case. If the front axle for any reason does not allow the front propeller shaft to spin while in the 2WD setting, the clutch pack in the transfer case will overheat because of the speed difference (slip) across the clutch pack between the stationary front driveshaft and the rotating rear driveshaft.

 

[loulblades]

Thanks for that info.

I have played with the 4wd on my truck for some time and never observed this. I have manually put the transaxle in a neutral position for the rear driveshaft (when my TCCM went bad I used a switch to control the encoder motor). I guess I was under the assumption that the front drive shaft also had a neutral position.

 

[loulblades]

I just looked at the TSB closer and I see it is for an autotrac system. I could see where you would want to keep parts moving in that situation, I would have to do more research to see if this applies to a non auto system.