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Discussion Starter #1
I'm new here and have been for info. Not finding much I thought I would share my experience replacing a front output shaft seal on the transfer case. Started on Monday, after acquiring the parts. First the diagnosis: front output shaft seal was leaking and getting worse each day. Hey, its a seal should be easy right?!

I contacted a friend who owned a shop and that i have used in the past for company and personal vehicles in the past. A 2005 Tahoe 4x4 LS with then push button 4 Hi, 4Lo and Auto 4x4. System has always worked great with the exception of having to replace the autoshift solenoid a few time. Tahoe has 230k on odometer, owned since new. I sold that to my son, fingers crossed he hasn't destroyed it...yet.

I now have a 2007 2500HD, Duramax 4x4 Classic, W/T, Ext cab. Pretty much a bare bones truck with PW/PD. Manual 4x4 shift 6 speed Allison. I bought the truck with 208k on odometer and now have about 244k. Just in the past week or so the front output shaft seal on the transfer case started to leak. Easy enough I think to replace offending seal, so the U joints while I'm there. Buddy with said shop says "use the Chevy seal from the stealership as aftermarket may have problems". OK, Napa has seal for $55. Stealership sells for $97 out the door. Buy dealership seal made in Mexico. Now need seal install tool. All sorts of prices out there ranging from $200 to $39 from Merchant Automotive. Order MA part and am currently awaiting delivery of said install tool. Drain Plug on transfer case threads --case, not plug, are boogered up. I knew this when I bought the truck and did fluid change on everything. So I am looking for a tap to clean up threads. I have found NO HELP on determining size of tap I will need to clean up threads. Verify with dealership the correct drain plug used for this case and go to industrial hardware store with proper drain plug to get a corresponding tap to clean threads in housing. 17mmx1.5. Not a tapered pipe thread which I thought would be apporopriate. Called and visited several trans shops and case rebuild places to determine proper tap size for this case, NP 261 as it turns out. No luck in finding correct info. Dealership can't give me info either. So now I am looking for a proper tap to clean up threads on case for the drain plug to fit right. Current plug has been modified a bit by me and a lot of teflon tape to seal from the last time I removed it.

Am waiting for the seal install tool to seat the seal and have successfully replaced the U Joints on front drive shaft. I will post some pics once I get back under to document the progress.

If anyone has some insight, please comment. I should have the seal install tool Thursday and will complete the project Friday.
 

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Might be worth taking the drain plug to Fastenal or a similar place and comparing the plug to the taps they have on hand to see if you can find a match.
 

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Discussion Starter #3
so the proper tap would be a M17-1.5

Good luck finding that. Not available in most places, a 16 or 18 would be common but not a 17. Mc Master-Carr has a few, for $100 +. Found one on Amazon, from some place in China for $14 + $25 shipping, might be deliverd by the first of May what a let down. I did just finish this seal job. Tool from Merchant and a 3 pound hammer intstalled that seal right quick. Greased the splines on the shaft and that went in almost without a hitch, the ear on the drive shaft got caught up on a bracket. Put the dust boot back on and attached with a zip tie at each end. A quick turn on the shaft and it slid right in. Fastened the front of the driveshaft to the front diff and torqued to 20 ft lbs. be sure to put the retaining clips on the u-joint caps before putting the straps on. It helps to have an extra set of hands during this. Replaced the trans support bracket. Filled the transfer case with 2.5 qts of Dexron VI and took her for a short spin. Double checked everything, noticed small drip from drain plug, tightened it a hair more, test drive again to freeway speeds 75mph. Shifted into and out of 4 HI. All good, no leaks, no vibration. Cleaned up the driveway with a little simple green and a hose and called it a day.

Now I need to find a proper tap to clean out those threads for both drain and fill plug before the next service....

I will add some pics shortly
 
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