Vibration after transfer case replacement-new

Discussion in 'GM Powertrain' started by Family Force 6, Jul 19, 2012.

  1. Family Force 6

    Family Force 6 Rockstar 100 Posts

    I replaced the transfer case this weekend (NP246) on my 99 suburban with a unit I found on craigslist, supposedly a factory rebuild unit. When I dropped my rear driveshaft I noticed the ujoints probably needed to be replaced. I took in to a machine shop and had them press in new joints. When I got it back and installed everything it had a "body" vibration at 50. Inspected the driveshaft and they had installed the rear u-joint incorrectly (it was VERY hard to move the joint, like it was binding). I took it back and they replaced both u-joints. Reinstalled last night and the vibration is better, but it still does it at 60-65. I took the front driveshaft out to verify that the front u-joints weren't bad and that was not the problem.

    Question: Could the transfer case be bad and causing the high speed vibration?

    Is it possible that the driveshaft could now be out of balance? I'm not sure what would cause that.

    Do the brass c-clips need to be installed at the rear diff cups that are strapped in? I didn't think they were installed when I took it out.

    Thanks for the help!
  2. tbplus10

    tbplus10 Epic Member Staff Member 5+ Years 5000 Posts Platinum Contributor

    The only two issues I could imagine here are your new T case has a bad tailshaft bearing or when assembling the driveshaft they didnt get the correct position in relation to the yoke and the driveshaft.
    I'd check driveshaft balance first, although I'd be surprised if that was the problem.
  3. Family Force 6

    Family Force 6 Rockstar 100 Posts

    I took it in to a local drive shaft shop and they said it was unbalanced. Hopefully that fixes it.

    I'll update this tonight if that was the problem.

    Just curious, would there be any other symptoms of a bad tailshaft bearing? Would it be making noise if it was bad enough to cause vibration? Would it be leaking TC fluid?

    I'm frustrated with the machine shop I took it to originally. They must of re-installed the yoke in the wrong position! I used them since they are open on the weekend, but I had to take it back 1 time already and it still wasn't right!
  4. dpeter

    dpeter Epic Member 5+ Years 500 Posts

    Is it a one piece drive shaft? I believe the clips need to be on to insure that they are centered, if not then the drive shaft could be off center and act exactly like an out of ballance one.
  5. RayVoy

    RayVoy Epic Member 5+ Years 5000 Posts

    I'd be looking for a new shop reaaaaaaaal soon
  6. Family Force 6

    Family Force 6 Rockstar 100 Posts

    It is a one piece. I'll install the clips. The shop said that 2 grams is tolerable, but that it was off 5 grams +.
    They also said that just installing new u-joints could throw it off balance and it was a good idea to test it whenever new u-joints are installed. Has anyone else heard that before?
  7. tbplus10

    tbplus10 Epic Member Staff Member 5+ Years 5000 Posts Platinum Contributor

    Yea, it happens, not every time but it isnt unheard of.
    5 grams of spinning mass doesnt sound like much but depending on how far off a center line it is it could cause a serious vibration.
    If the tailshaft bearings were out you might not have any noise indications but you'll normally get a fluid leak.
  8. Family Force 6

    Family Force 6 Rockstar 100 Posts

    OK, got the drive shaft back from the shop and installed and the vibration is GONE! Success! New transfer case installed and transmission filter changed with new AMS Oil synthetic tranny fluid.
    My 14 year old son helped with the project (we ended up manually lifting the new transfer case in to place after the transmission jack I rented proved completely worthless). He had a great time and it was great father-son bonding time.
    Next up- two upper ball joints and 1 lower ball joint, new A/C hose and receiver drier. Then.... it's camping time!

    I found it interesting that the drive shaft got out of balance after the new u-joints were installed. The driveline shop that balanced it says it's not uncommon and that whenever you install u-joints you should check the balance of the shaft. Interesting, I've never heard that before.
  9. tbplus10

    tbplus10 Epic Member Staff Member 5+ Years 5000 Posts Platinum Contributor

    Thats cool your son got to help, great bonding time and he gets to learn a little about auto mechanics.
  10. dpeter

    dpeter Epic Member 5+ Years 500 Posts

    I had never expected a u-joint could be that far out of ballance. So what would be the equivelant to 2grams and as tbplus10 has pointed out, how far off center could it be and still be OK?

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