Transfer case drop

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by Cornfed-90K5, Sep 13, 2000.

  1. Cornfed-90K5

    Cornfed-90K5 Registered Member

    Feb 17, 2000
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    Fresno, California
    I am in the middle of playing around with the height of my t-case. I put the kit I bought on when I had the 4" lift. It wasn't enough for the 6". So I tried putting the factory spacers on top of them. This completely gets rid of my vibration, but when I have the vehicle in reverse and accelerate or it is under a load(backing up hill) it feels and sounds like something is binding. So basically where I sit know is I am trying different combo's till I find one the works. If anyone knows what could be causing that binding sound is I would be very greatful, and please if someone has come out with the magic amount to lower it I can use any help offered.

    1990 K5 Blazer
    1977 Jeep CJ5
  2. Blue85

    Blue85 Troll Premium Member

    Jul 26, 2000
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    Grand Rapids area
    the vibration sounds like axlewrap. How is the rear end lifted 6"? All spring? Spring/block?

    How much lower than stock is your T-case now?

    I don't think that there is a magic amount to lower the T-case. It is going to depend on the pinion angle that your lift kit has given you. It's important to know what U-joint angles you are running. There are some big contraptions that you can buy that let you find the angles, but you can do a fairly good job with tape measure and a yardstick. Assuming that you remember your high school geometry, you just need to park the truck on a flat slab of cement and take a bunch of measurements. Put the yardstick (or some other straight object) as close to exactly in line as possible with each component that you wish to find the angle of: Driveshaft, rear pinion and T-case output shaft. Then make two measurements from the ground to the yardstick, one at each end or wherever is convenient, noting the distance between the two measurements. Then you subtract the two measurements from the ground to find the rise of that driveline component and the distance on the yardstick between the two measurements is the length. It is clear to see what you are doing if you draw a right triangle on paper for each driveline component. The length (yardstick distance) is the hypotenuse (longest leg) of the triangle. The rise (difference between the two tape measure measurements) is the vertical leg of the triangle. Then you use the appropriate inverse sine function on your calculator to find each of the angles. This gives you the angles of each driveline component relative to the ground. Then you subtract and add the those angles to find the angles of the driveline components relative to each other. Namely, you want the angle in both U-joints. They need to be within 1 degree of each other. If they are not, you can go back to the triangles that you drew to figure how far to move whatever parts to get where you need to be. It is good to have a little bit of error on the side of having the pinion a little bit too high. This compensates for axlewrap when you are mashing the gas in first gear.

    Without knowing what angles are in your driveline, all other adjustments are just guesswork.

    It's also a good idea to make sure that your T-case to cross-member mount is in good shape. The rubber in these tends to break up over time and then it allows your transfer case to move around a little under certain loads, changing all of the angles a little.

    '85 JIMMY
    '90 paint/grill/trim 5"susp 33/12.5/16.5
    Fresh 350 B&M '87 TH700
  3. TX Mudder

    TX Mudder 1/2 ton status

    Jul 10, 2000
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    Don't forget that lowering your tcase does not lower the whole unit evenly. You decrease rear driveline angle (good) but for every degree you decrease rear angle, you increase front driveshaft angle (not good.)
    I thought lowering it would help me out, but my problems is front shaft angularity (rear is fine) so lowering my tcase would have worsened my problem.
    -- Mike

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