How To: GM Transfer Case Pump Rub Kit

[bigdaddydiesel]

Chevrolet & GMC Light Duty Truck Pump Rub Kit Installation Instructions
(GM Transfer Case Models 136, 146, 246, 261HD, 263HD, 263XHD, 261XHD)

Make sure to provide the year, make and model when ordering.

The issue with the GM transfer cases is that the fluid pump flange as pictured below is so thin that it almost has a type of knife-edge on the tabs that keep it in place. Over time, whether in four wheel drive or two wheel drive the flange will rub a small hole in one corner of one of the tab spaces in the back half of the transfer case. This is an issue mainly because when this happens the fluid will be pumped out the transfer case and can cause permanent damage to the transfer case requiring a rebuild or replacement of the entire transfer case.

This picture shows the knife-edge on the flange that is the issue:



This picture shows the MA upgraded billet flange that is MUCH beefier…



There are a couple of different transfer case pump rub upgrade kits available, but the one I used for this DIY is a kit produced by Merchant Automotive; I purchased mine from Willie Parsons (aka: mrmanners) with Synthetic Motorsports, a Sponsoring Vendor here on DuramaxForum.com. The kit can be purchased here.

To remove the transfer case from the truck, first be sure to remove the drain plug to drain the fluid. The drain plug is shown here and yes, mine was “Buggered” by the previous owner using what looked like maybe pliers to remove it…lol



Then remove the front and rear drive shafts. To do this remove the u-joint mounting tab bolts and tabs, then take a pry bar and pry toward the transfer case, they should move without too much effort and then slide right off of the output shafts in the transfer case. Be careful to have a good hold on them so they don’t fall and hit you in the head…lol



Once the drive shafts are out, remove the wiring harness connectors and pull the harness out of the way and it does pay to go ahead and use a zip tie to hold it over by the brake lines at the frame rail to prevent damage throughout removal and installation.

Once the harness is out of the way, remove the vent tube that goes across the top of the transmission, to do this gently pull it off the “nipple” on the transfer case and place the hose somewhere on top of the transmission to prevent damage. It is located on the top of the driver side of the case as shown here.



If your truck has a manual shifter in the floor you will now want to remove the “actuating rod”. To do this use either a very small pry bar or a small screwdriver and pry the ends off, this is simple and it should pop right off without issue. If you have push button four-wheel drive then you don’t have to do this. The front end of the rod is shown here.



Now you need to remove the nuts from the studs at the transmission adaptor. Once those are off you are ready to drop the transfer case out of the truck. It DOES pay to have a buddy there to help wiggle is out. It is a tight fit, but once you pull it back far enough to be lose from the transmission, tilt it forward and down at the same time and it should drop between the cross member and the transmission adaptor.

Now that you have the transfer case out of the truck, although you CAN do this on the floor, trust me when I say having it on a workbench or table helps. But either way I would put an old piece of cardboard under it to catch excess fluid when it comes out.

That being said set the transfer case flat and remove the rubber grommet shown in this picture.



Once that is out you will need to buy, beg, borrow or steal the right snap ring pliers to remove/release the retainer ring on the bearing inside the case for removal. The rear transfer case housing WILL NOT come off without doing this. That ring holds the bearing and shaft assembly in the proper alignment in the transfer case. The proper snap ring pliers will have flattened ends, they are shown in the next pictures.







Continued in the next post.....

[bigdaddydiesel]

Once that ring has been release go ahead and set the transfer case on end vertically with the rear transfer case housing in the air and begin removing the bolts that hold the two case halves together. Once they are out there are two ways to get them apart, one is to use two 90* pry bars in the prying tabs manufactured into the case sides, but if you do not have them then you can take a metal putty knife and slide it into the seal between the cases and work it through the sealed area breaking the bond between the cases. Once that is done you should be able to pull the rear housing off of the assembly. It is a little tight, but will come off with very little effort.

Once the assembly is apart you will see where the pump flange is on the main shaft assembly shown here. (With the upgraded flange already installed, I failed to get a pick of the old one still on… Sorry about that…



Now, use the same snap ring pliers from earlier, and this can be tricky, but GENTLY pry apart the snap ring that is holding the bearing in place and use a flathead screw driver to move it out of it’s grove above the bearing while you hold the snap ring open. Like I said though, this is tricky as that snap ring is kind of touchy and it may take a try or too to get the pliers to hold while you move it up with the pliers.





Once that is off you can simply slide the rest of the assembly pieces off including the flange you are replacing. That flange however needs to be disassembled and some have Philips head screws and others like mine have a Torx bit style screw, but remove the screws, and install the upgraded flange.



Now, before you throw it back together, make sure to first clean all of the old sealer from the mating surfaces of the two case halves; using brake cleaner to make sure it is good and clean is a good idea IMHO. But it needs to be good and clean.

Once it is clean, remove and inspect the magnet found at the pump filter shown below. You want to make sure that you clean that space out good and also clean the magnet well.

PLEASE NOTE: There is a GM TSB not using too much sealer upon re-assembly of the two halves of the transfer case because when you assemble them, the sealer that squeezes into the transfer case can break off over time clogging the filter to the pump. If this happens it disrupts fluid flow and that can ruin your transfer case. Use ONLY a very small 1/8 inch bead of sealer around the mating half of ONE side of the case halves. But, try to make sure that it is closer to the outside of the housing , but be sure to run it to the inside of the bolt holes.

Once that is done re-install the shaft assembly the way it came apart. Below you will see the result of too much sealer being used as mine was originally assemble with too much from the factory.

Location of that magnet:


Dirty Magnet; Looked like I did mine JUST IN TIME!!!



Clean Magnet



Now, to reassemble the two halves of the transfer case housing, and this can also be tricky, but is not nearly as hard as it may sound. Making sure that you have the alignment of the tabs on the pump flange in line with their spaces in the housing, and that snap ring that holds the bearing/shaft assembly in proper alignment IN THE HOUSING, not on the bearing; carefully wiggle the back half of the housing down onto the front half assembly. Do this while it is still vertical so that you can keep your tab alignment and everything lined up right for the back housing to slide into place. When that is down on the assembly, re-install two of the bolts that hold the two halves of the housing together back into the housing at opposite ends to hold them together, but DO NOT tighten them down very tight, just enough to keep everything together for the next step.

Now lay the case on it’s side the way it came out of the truck, you know, up is up and down is down…lol Once that is done, go back to the hole where you used the snap ring pliers to release that snap ring, using a light you will be able to see the grove in the case housing as well as the grove in the bearing where it belongs. You want to use those snap ring pliers to spread the snap ring into place in the HOUSING GROVE. Again, while tricky this is not that hard. Once you have that held into place, take either a long flat head screw driver or skinny pry bar and stick it into the hole behind the bearing on to the FRONT of the transfer case and pry it toward the back of the case. Watching in there as you do this, you will be able to see and feel when the snap ring gets into the right postion on the bearing and it should pop right into place, but a little playing with it to make sure it is in the grove all the way around the bearing is advisable. Do this by releasing the snap ring in the grove and then move the tabs on the back and forth to seat it. Now, this may take a couple of tries to get right, but it works really well.

Once that is done, put the transfer case back on the front end and begin putting the bolts back into it and torque them to 34 ft-lbs. Reinstall the rubber grommet that came out of the hole at the bearing. Clean the old gasket off of the area on the front of the transfer case where it meets the transmission adaptor. Now re-install into the truck with the new gasket there, exactly as it came out. The rest of the torque specs are below.

Transfer Case Drain Plug 15 lb-ft
Fill Plug 15 lb-ft
shield bolts 15 lb-ft
speed sensor 11 lb-ft
t-case to t-case adaptor nuts/studs 36 lb-ft
t-case to transmission adaptor boltss 36 lb-ft

I may think of things to add, and will add anything anyone feels it needs, but that is it in a nutshell. You now have an upgraded transfer case.

Congratulations!!!

[jbrown1132]

great write up!:rockin

[duramax07tmd]

Nice write up Chris!

[llypower]

great write up!! need to do this to mine yet.

[2006blackmax]

Thanks

[bigdaddydiesel]

Glad I could help.

[mrmanners]

Great writeup Chris.

[DMAXfirefighter]

Nicely done Chris :rockin

[Duraskank]

Great writeup.