How To Fix A Front Intermediate Shaft Bearing Assembly / Front Axle Disconnect Assembly

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Well here is another part that is very common to fail with a bunch of different names to confuse you and us:

1. Front Differential Axle Disconnect Assembly (Most Normal People Call It This)

2. Intermediate Shaft Bearing Assembly (GM Dealers Call It This)

3. Splined Disconnect or Gear Pods

In lamans terms, this part basically disconnects or disengages the front drive axle when the driver switches from 4WD to RWD or 2-Wheel Drive. Their are 2 different versions of front differentials on these vehicles, One is called S4WD (Selectable 4-Wheel Drive) & A4WD (Automatic 4-Wheel Drive). The S4WD differential contains both an actuator & the axle disconnect. For our article, we will call it the FRONT AXLE DISCONNECT ASSEMBLY for the S4wd models and INTERMEDIATE SHAFT BEARING ASSEMBLY for the A4wd models, more info as you read.

Parts Involved: Image 1 is the Front Axle Disconnect (2 Versions GM Part #:15884292 or 15884291), Image 2 is the Front Differential Actuator (GM Part #: 12471631) which engages the front axles. Purchase both parts together here

front_axle_disconnect_Intermediate_shaft_bearing_housing_assembly

front differential axle actuator

Here is information about the 2 different front drive axle(s), courtesy of General Motors:

S4WD- Selectable Four Wheel Drive Axle Description & Operation:

The image below shows the actuator (top) and how it bolts to the disconnect assembly(bottom)

Exploded view of axle actuator and the axle disconnect

The front drive axle on the S4wd or Selectable 4-Wheel Drive differentials use a disconnect mounted right next to the passenger side CV axle and oil pan. Their is both an actuator that is used to engage the front axles when 4WD is enabled & a disconnect assembly that is used to disengage the front axles when switched back to 2WD or Rear Wheel Drive.

Explode view of transfer case and axle disconnect with 4wd actuator

In the exploded view above,  the yellow box is the components of the 4WD axle disconnect assembly and the green box is the axle actuator. These parts are sold separately and if you are replacing the disconnect assembly, you should also strongly consider replacing the actuator as it must be removed to install the new disconnect assembly. The red box is the front differential.

When the driver switches to 4-Wheel Drive, the TCCM(Transfer Case Control Module or 4WD computer) sends a signal to the electric actuator mounted on the disconnect and it energizes a plunger to extend out and push the clutch fork and clutch fork sleeve out to engage the drive axles. This engages 2 gears inside the differential and makes the front differential act very similar to a non locking rear differential or in other words a semi-floating axle used on RWD cars for years. This is done because a traditional ring & pinion gear set is used to transmit the driving force from the engine and transfer case to the front differential. This type of front differential allows for the turning of the front wheels so each wheel can spin at different speeds during a turn and still use the power generated from the engine. This prevents your tires from being dragged across the pavement during a turn and more importantly prevents the internal gears from being damaged. The front drive axles are also CV axles and allow for turning also and absorbs much of the turning force.

A4WD- Automatic Four Wheel Drive Axle Description & Operation:

This part of the article we will call the front axle disconnect, the proper GM name of Intermediate Shaft Bearing Housing Assembly as this system, the name actually makes sense. This is because the differential intermediate shaft slides through the Intermediate Shaft Bearing Housing and rides on bearings inside the assembly. In fact bearing failure inside the housing is one of the biggest causes of replacement. Once the bearings start to fail, they will make noise and these noises are a symptom of the housing needing replacement. The A4wd front differentials are similar but they do not have an electric actuator and they do not actually use the disconnect assembly to disengage the 4WD. This is also one way for you to determine which system you have. If you look under the vehicle where the inner passenger side CV axle connects to the front differential, you will see the axle disconnect assembly. If a black plastic unit is attached to it, then you have the S4wd (selectable) and if you do not have it, then you have the A4wd(automatic). The image below shows the electronic actuator and the intermediate bearing assembly outlined in red.

actual image of a front axle disconnect with axle actuator for S4wd

The A4WD models uses the same differential carrier assembly, however the Intermediate Axle Bearing Housing Assembly is slightly different. The clutch fork, clutch fork sleeve, and gears have been replaced with a single splined sleeve that connects the right side drive axle to the inner axle shaft directly. This allows the passenger side CV axle to be directly connected to the intermediate axle shaft inside the differential. If the transfer case is activated by the PCM, then the clutch assembly within the transfer case controls the amount of torque applied to the front differential.

Ok, So now we know what these parts are and how they work. Next is the symptoms associated with a failed or failing Front Axle Disconnect/Intermediate Shaft Bearing Housing Assembly

Symptoms:

1. Their is usually NOT a trouble code set set when these fail so a check engine or 4wd light may not even illuminate on the dash

2. The vehicle fails to engage into 2WD, 4WD, or AWD

3. Noise – A rattle in the front end is noticeable at lower speeds and no external components of the suspension or steering have play or damage

4.  Excessive play in the axle shaft connection inside the axle disconnect.

Remove & Replace Instructions:

1. Raise & support the vehicle properly, remove the passenger front wheel, splash shield, & then remove the passenger front CV axle.

2. On S4WD models, remove the electric axle actuator from the axle disconnect assembly by removing the 2 bolts and electrical connector. This part is also very common to fail, If this part has not yet been replaced, then we strongly recommend replacing it now or at a minimum test it. If you think about it, the axle actuator has gone through just as many cycles as the disconnect and if the disconnect failed, well then the axle actuator is probably right behind it.We have seen it over and over in our shop, not this exact part but parts similar to this, Think about the labor you are already doing and if it were my vehicle I would be replacing the actuator at the same time. If you have A4WD, then you can skip this step as you do not have this actuator on your vehicle.

3. Remove the wire harness clip located on the axle disconnect.

4. Remove the 4 bolts attaching the axle disconnect from the front differential. The images below show both systems:

A4WD system showing 4 bolts to remove assembly

S4WD showing removal of actuator and disconnect assembly

4. Remove the old disconnect assembly

5. Remove the new part from the box and remove the protective plastic plugs inside of each seal.

6. The new units are pre-greased internally from the factory, however just like most any seal, it is a good idea to apply a small amount of lube along the lip of each seal with your finger. This prevents the seals form being damaged when the metals shafts slide through them during installation.

7. Install the new unit and make sure it is flush to the oil pan.

8. Tighten the 4 axle disconnect attaching bolts to the differential to 35 foot lbs.
9. On S4wd electric shift models, clean the actuator on the point where actuator meets the internal shift fork of the new disconnect unit. Install the actuator, Tighten the 2 bolts of the electric actuator to the axle disconnect to 53 Inch Pounds

10. Reinstall the remainder of the items in the reverse order.

IMPORTANT NOTES:  Do not nick or cut the inboard oil pan inner shaft seal!!     Also the axle disconnect must fit flush against the oil pan in order for the inner axle shaft to line properly!!

Joel

ASE Certified Auto Technician 16+ Years Of Auto Repair Experience

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18 Responses

  1. leonard says:

    thanks learning about four wheel drive parts. could not help a customer because did not know what parts of four wheel drive were or how to look them up. Now i know that is was the front drive axel parts. Go figure Next time I will know. thanks

  2. Nick says:

    I posted a little walkthrough of this procedure. Hope you find it useful!

  3. Larry Waldron says:

    the mounting bolts are out of the disconnect assy, and the differential on the other side, but neither one will move.
    What is the recommended way to loosen the assy’s, so I can remove them.
    I am trying to remove the oil pan.
    I am working on 2004 gmc envoy, 4wd with 4.2 eng.
    I have pried and beat on it lightly, so as not to break it, but it does not move.
    Any suggestions u may have would be greatly appreciated. thank you.

  4. Larry Waldron says:

    well I managed to break the intermediate shaft bearing assy, inboard housing.
    The collar that fits into the side of the oil pan, is still in the side of the oil pan. Now I have to buy another bearing assy, to replace it. I dont want to break the differential housing the same way. How do i dislodge the collar that fits into the side of the pan? Seems to be the only thing holding it on.
    Just call me stressed. Ready to pull my hair out.

    • Tim 05 trailblazer says:

      hey there larry, i just had the same problem today on mine there is a small c clip that goes around the end of the cv shaft you are suppose to squeeze this together and its suppose to slide right off /apart. but there is also one inside at the bottom of the cv shaft at the bottom of the boot. my housing had actually been chewed up due to a metal ring inside my housing that bolts to the oil pan. so all of my inner seals inside the housing including the metal rings are distroyed… so i will find out tomorrow if i have to buy the whole housing unit or if i can buy just the seal to insert it back in? i kinda dinged my up on the outside edges a tiny bit but i think it can be fixed with a little light file job or a soft flapper wheel on a grinder. my 4wd was messed up for a couple of years lol….NOT SO GOOD. but come to find out one of the metal clips that had came off from inside was preveting the 4wd from engaging cuz it was in the way & thats what caused everything else to get all chewed up. & this is also why my cv axel did not just slid out when i unbolted it. so i had to pry a little with my fork tool… so im hoping that i can just get a seal replacement for it cause i think the whole unit is real expensive like 500 bucks or sumthn. but what i had to do was basically get ahold of the c clip in between the small gap in it and rip it off instead of squeezing it like it says to do for removal because mine was all bound up from it being chewed up. but all that time it had been like that my rearend would still engage and my a4wd still worked just no 4lo or 4hi in the front but the back worked. amd it had been like that for a couple of years and just now started making the rattle noice at slow speeds. the whole time i had thought it was the 4wd actuator…. but the comments above says if you have the A4WD MODEL NOT TO WORRY ABOUT THE ELECTRIC ACTUATOR BUT MINE HAS THIS SO I WOULD LIKE TO KNOW WHAT IS UP WITH MINE MY 4WEEL DRIVE UNTIT HAS: A4WD 4LO & 4HI SO WHATS UP?????? IT IS A 05 4.2 V6 INLINE 6 LS TRAILBLAZER. I THINK THE GUY THAT POSTED THOSE WAS BACKWARDS WHEN EXPLAINING THEM. AND WHAT IS THE S4WD
      ? IS THAT JUST STANDARD 4 WHEEL DRIVE? & ALSO I WOULD LIKE TO KNOW WHAT YOU ENDED UP DOING AND HOW? CUZ I WOULD IMAGINE YOU HAVE THIS FIXED NOW HOPEFULLY? PLEASE REPLY WITH COMMENT AND THE PROFESSIONAL THAT EXPLAINED FROM ABOVED ABOUT THE DIFFRENT SYSTEMS WHY DO I HAVE THE ELECTRIC THING ON MINE AND IT STIL IS THE A4WD MODEL???? JUST DOESNT MAKE SINCE? PLEASE HELP!!!!!!!! so you dislodge the coller from squeezing the c clip together and it slides right off. but remember there is one on the bottom too.

  5. Joel says:

    Thanks for the question Tim,
    Here is an explanation of the 2 systems:

    S4WD – stands for Selectable 4-Wheel Drive and this model will have the actuator bolted to the axle disconnect. This system can be switched by the driver to be in 2WD or 4WD with a switch inside the vehicle. This system essentially allows the driver to switch between 2WD & 4WD when needed such as to save fuel on highways,etc.

    A4WD – stands for Automatic 4WD and the vehicle automatically controls the 4WD system by simply engaging the transfer case only. This system has no actuator and also internally the axle disconnect does not disconnect and they actually call it an intermediate shaft bearing instead. This system uses the front axle & differential to be totally engaged or not totally engaged and will only spin if the transfer case is enabled to do so by the TCCM (Transfer Case Control Module).

    It can be confusing but if you do not have the actuator, then you have the A4D system, if you have the actuator, then you have the S4WD system.

  6. Jimmy says:

    Does anyone know if you have to remove the 4 wheel drive in order to take down the oil pan on a 2005 GMC ENVOY XL ?

  7. Josh says:

    how do i remove actuater switch on transfer case of 2001 dodge diesel

  8. Josh says:

    thanks anyway i got it. it does thread with wrench 1.1/16
    0r 1.1/8″

  9. Bob says:

    So I have a 02 trailblazer with the s4wd and the 4 wheel drive will not engage. All electronicis are fine. When you lift the front off the ground and turn the wheel with 4 wheel engaged it makes a clicking noise. Could this be the shaft bearings or the actuators or the intermediate shaft its self…. help.

  10. how to tighten a 03 trailblazer side mirror?

  11. JeanAgosto says:

    im having an issue where there’s a leak coming from somewhere in this assembly. i have selectable 4wd so i have an actuator. my mechanic (mostly due to me) does not want to take it apart unless he has the pieces that he thinks are failing. in this case, he believes its seals. my question is this…does the actuator have a seal that could fail? does the disconnect have seals that could fail? im trying to just buy whatever seals i need in order to get this done and over with.

    • Joel says:

      Most of the time the internal intermediate shaft bearing fails and starts to overheat which then causes the seals to leak. It is very rare to be able to repair one of these and we have been unable to source the bearing itself. GM dealerships used to sell the parts separately and you may want to check with them. We checked for the bearing and our dealer says it is discontinued. The case of this is sealed with RTV and the shaft seals are available from the dealer. So far we have been unable to find any aftermarket kit or anything to repair this.

  12. Triston says:

    This is what I found on a 2003 trailblazer! 4wd quit working so I checked the electronic side of the 4wd! Everything checked out good! So I took off the front axle disconnect all is pretty simple, then I found the weakest link in the front axle disconnect the actuator fork! And to no surprise the guide pin on the back of the fork broke off! This part is a dealer only part it is $100 plus labor a lot better than $650 and I suspect that is the problem with all the disconnects it cheaper to fix and the dealer nor auto repair stores don’t wanna mess with it cuz ain’t enough money envolved! Part 11 in the schematic

  13. Chad says:

    I’m working on 02 envoy. I have ALL bolts removed on the Front Axle Disconnect it’s in two pieces the problem I’m having is I can’t get the back side of the Disconnect off the oil pan…NEED HELP A.S.A.P email me at c_fuller03@hotmail.com

  14. Crystal says:

    the bearing on needs to be replaced on my front differential were the front drive shaft connects in. is there any way to replace that bearing and seal without having to take the whole front differential apart??

  15. Randy says:

    The front disconnect housing broke of and was in pieces. A gear is left on the intermediate shaft and can’t force it out. Can I drive it out from the carrier side?

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