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Thread: HOW-TO: replace all tranfercase seals (np233c)

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    Apr 2008
    Fort collins, Colorado
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    HOW-TO: replace all tranfercase seals (np233c)

    this how to was preformed on my 97 zr2 4.3l blazer, with the new process 233c transfer case. all information in this how-to comes from my experience with my truck, yours may not be the same, but i have made every effort to give you all the information i can.

    Identifying the transfer case:

    my blazer has the new process 233c transfer case. with the 3 button electronic switch in the dash "2 hi" "4 hi" and "4 low" (probably the easiest way to identify it.) the best and most certain way is to look at the back of the t case. there is a tag that has the model number on it.

    here is a pic of the rear of my t case. you can see the tag in the upper middle (it has read writing on it).

    pic #1

    What you need:

    assorted sockets and wrenches
    rubber/ soft faced mallet or shop press (or other means of pressing in the new seals)
    screwdrivers/ pry bars
    torque wrench
    gasket (transfer case to transmission)(will update with part # and price)
    rtv sealant (black)
    fluid pump (for gear oil or tranny fluid)
    t case fluid (mine uses dex/mec atf fluid, the exact same stuff that goes in my tranny)

    PN: S-4333N Transfer case rear output shaft seal (may also be called Transmission tail shaft seal) manufactured by motor city(federal mogul) purchased at advance auto (pic #1)
    PN: 15665313 Transfer case output shaft bushing (may also be called Transmission tail shaft bushing) ac/delco and gm manufactured by ac/delco purchased at local gm dealer (pic #1, just inside of seal, not visiable from out side.)
    PN: 710928 Transfer case input shaft seal (this was the "double lipped" seal) manufactured by Federal mogul purchased at advance auto (pic # 3 on the left)
    PN: 4813V Transfer case front output shaft seal manufactured by federal mogul purchased at advance auto (pic # 3 on the right or pic # 5 close up)

    *NOTE: i have a zr2 and i often found that the seals that were listed in the system at the auto parts stores were too small for my vehicle. this was especially true with the rear output shaft seal and bushing. make sure that you have all of the seals before you start, and double check that they are the correct diameter before you remove the old ones! (will update with all part #s and prices)

    Removing the Transfer case:

    1. remove any and all skid plates covering the t case.
    2. remove the front & rear drive shaft (11mm bolts)

    the method that works the best for me is to remove the u bolts(using a screwdriver or something else to keep the shaft from spinning). once those are out you can slide the drive shaft forward. the only way for me to get it out is to put the front of it up into the engine bay as i move it forward. this gives enough room to get it off of the output shaft before you take it down and out of the vehicle. (rear drive shaft is cake)

    here's a pic to show what i mean.

    pic #2

    the front of the shaft goes forward and up until the rear can come off of the t case output shaft. then the whole thing goes down and out (to the rear)

    in this pic the drive shaft is already loose from the t case. also you can see where it normally bolts to the front diff right above the exhaust cross-over.

    3. drain all of the fluid from the t case. (if you have a fluid pump, which you should, it was on the list i gave you! try to pump out all that you can)

    *note: you will spill fluid during this project so put something down to absorb it. like a piece of cardboard.

    4. un-plug and remove the t case shift motor. also remove all of the vacuum lines and all other electrical connections (ie tail shaft speed sensor ect.)

    here is a pic of the vacuum connectors (3 in a triangle shape) as well as the vent tube(above and to the left). also the right hand side shows where the shift motor was removed.(pictured from front of vehicle looking toward rear.)

    pic #3

    5. un-bolt the tranny cross member. the way it was designed (at least on my car) you can completely remove all of the bolts and the tranny will still be supported. even so, place a jack stand underneath it for safety.

    6. jack the transmission up as far as you can and then support it with the jack stand.

    * note: the transmission must always be supported from here on, until the cross member is bolted back in.

    7. remove the transmission cross member.

    pic #4

    8. now un-bolt the transmission to transfer case bolts. there are 5 bolts. pic #3 above shows where they are located and how it separates.(the ones around the outside that are missing in the pic). it is a good idea to support the transfer case during this process.

    9. slide the t case toward the rear of the vehicle until it slides free of the transmission output shaft. (as you can see in pic #3 the coupling extends several inches into the transmission housing. so you will have to slide it that far to the rear to remove it)

    *note: the transfer case is fairly heavy. (i have read 80lbs on other sites) it didn't seem that heavy to me.

    if you have a transmission jack it may be useful during this process. me and a buddy just pulled it out ourselves. i don't think it will be possible to lower the t case after it is separated from the transmission while it is on a jack. i had to angle it down at the front and slide it down and forward to remove it. the reason is that the t case output shaft extends over the frame cross member, which is welded in. so i think it is better to do by hand. buy some beer and invite some buddies over.

    *note: i did re-install the t case by my self, by simply lifting it in place. it was heavy and awkward to do alone but i think most people can do it. be very careful. i dropped it 3 times doing this, i was able to catch it all 3 times (more like it landed on me while i held on) but it was not fun, and the first time i almost lost a nut!

    10. ITS OUT! YAY! see pic #3. (if yours doesn't look like this i don't know how you made it this far.)

    Replacing the seals:

    we will start with the front output shaft seal as it is the easiest.

    there are several ways to remove the seals. the best and technically correct way is to use a shop press. i don't have one of these because they are expensive. also in some cases it is not practical. for example you would have to completely disassemble the t case in order to "press" the seal out from the inside. way too much work.

    another way is by the use of a seal removal tool. i don't own one and have never used one but they seem ok.

    my method uses screwdrivers or pry bars to get the seal out. some people do not like this method, but if you are careful and do it properly there is nothing wrong with it.

    here is a pic of the seal in question.

    pic #5

    what i do is slip a very small flat head screwdriver under the lip of the seal, around the outer edge. between the seal and the t case. i use it to "raise" the lip a little bit. i work my way around the outer edge a little at a time "raising" the seal. i usually tap softly on the screwdriver with a rubber mallet. not much force is required. all you need if for the seal to "lift off" of the surface and for there to be a little space between them.

    next i get a much larger screwdriver and place it in the gap that was just created. now you use the screwdriver, angled AWAY from the transfer case, strike it with the mallet. the goal is to force the seal forward and out of the t case. start slowly and then as the gap opens up you can use more force. simply work your way around pushing it a little farther out as you go.

    some times it helps to hammer perpendicular (straight in) toward the center. this can create a little bend or notch for the screw driver to seat in and really give you something to work on.

    **NOTE: the seal is already trash(im assuming or why would you be replacing it). so it does not matter how badly damaged it gets. HOWEVER it is EXTREMELY IMPORTANT that you do NOT damage the t case mating surface or the output shaft in ANY WAY!!!

    the seal is almost always destroyed using this process so make sure you have the new one already and that it is THE RIGHT ONE!!! (learned the hard way!)

    once its removed clean up the t case and the output shaft. also visually inspect them for damage, as well as the output shaft bearings (which are located directly behind the seals) if any of them are damaged, now would be the time to replace them. i will not go into detail because it is beyond the scope of this how to; but there are several books that give great detail and instruction on the process.

    Last edited by Zygoat; 12-02-08 at 09:06 PM.
    1988 GMC Jimmy s-15 Sierra Classic 4.3L auto (sold)
    1994 Camaro Z28 5.7L v8 4l60e (sold)
    97 Chevy Blazer ZR2 4.3L v6 4l60e
    flex-a-lite black magic III e fan, Flowmaster 50 series suv custom cat back (dual out), Edelbrock 2114 custom intake setup, Turbonetics custom turbo setup DONE!
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