Failed Rear End: Getting Home?

I'm thinking one of the prime candidates for my next failure (98 'burb, 180+k) is the rear end.
The story I get is that they don't give much warning: maybe a
little tire chirping on the turns and then "bam!"....
I'm thinking that, as long as there aren't parts laying on the pavement, I should be able to put the vehicle in 4wd "Auto" and limp home on the front diff without damaging any other systems.
Or am I just wishing?
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PeteCresswell

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I've only had one rear end fail and it gave plenty of warning. It whined for at least a year before it started howling. I guess it depends on which component fails first.
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(PeteCresswell) wrote:

Pete, sounds like you may have heard about the Grenade 80 (G80) optional locking rear end?
They don't give much warning when they fail BUT depending on how they fail you may not be able to move the vehicle without some work. I have seen them break at the weight pivot and lock up tight. Pull the cover (try to save the oil) then remove the broken parts so it can move. Then toss it in 4X4 and drive home.
I have done this a few times. Best one was when a multi-piece drive shaft under my BILs Subaru Justy failed outside Syracuse. Drove up there and looked it over. Finally decided to beat a can over the output shaft housing and drive it. He made it to my shop and went part hunting. Found out that all the parts cost more than the car was worth! He wanted to drive it so I did a few modifications. Took the front yoke and cut it in the lathe so it was smooth all the way back. Drove it into the trans with a rubber mallet to get it as tight as possible. Then made up a cover for the housing just in case it slipped back. Locked the transfer case into 4X4 and disconnected the interior lever. He drove that car for 4 more years as a front wheel drive!
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Steve W.
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Per Steve W.:

This is something that I've just come to realize: that the stress on a locked-up 4wd system on pavement is from the difference in rotation between front and rear wheels. I had always thought it was between the two front wheels.
I'm guessing, then, that the "4wd Auto" setting has something to do with de-coupling the front and rear systems.
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PeteCresswell

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(PeteCresswell) wrote:

Most of the torque wrap is due to the difference in rotational speeds during turns. The reason is because all 4 tires need to turn at different speeds. With an open differential on each end and in 2wd this isn't a problem. The diff. allows the tires to rotate as needed. When you toss it into 4wd the transfer case gets a LOT of stress if your on surfaces with good traction. I have seen them break apart, drive shafts torn up, failed U-Joints.
4wd Auto is a PIA system. In the non-auto system the front axle has a simple collar which slided across a set of splines to lock the right hand axle together. This takes the place of the locking hubs used on other makes and earlier GM products. The parts that usually fail are all outside that axle. The actuator (vacuum, electric solenoid, wax pellet) or the cable are the usual culprits.
On the 4wd Autos the front axle is a LOT more complex. What they did is install an electric clutch pack on the input shaft as well as the interlock. When you select the auto position it uses signals from the ABS and speed sensors to engage/disengage the clutch pack as the ECM thinks it needs 4wd. The problem is people leave them in auto 4wd through most of the winter thinking it's better. However every time a tire slips the clutches cycle and causes shocks in the system. I have rebuilt a LOT of the front axles.
Other than the clutches the systems are a lot alike.
Now if you look at a Bravada you will find the same type system, EXCEPT the interlock is missing on the right axle, and there is a viscous coupling in the transfer case that allows the front and rear drives to rotate and drive but still slip to prevent torque wrap. They also are full time 4X4 so no selector switches or actuator to mess with. BUT you do see increased tire wear normally.
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Steve W.
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