If you’ve recently installed a small lift (anywhere between 1″ and 3″) and you’re getting drive line vibrations, then this modification may be for you. When you lift your jeep up away from your axles, you are also lifting your motor and transfer case up. This means the angle that your drive shaft travels from the transfer case to your axles is steeper, causing vibrations. There are a few ways to fix this. You can lift your motor by installing a 1″ motor mount lift (MML), you can install a Slip Yoke Eliminator (SYE) in combination with a new Constant Velocity (CV) drive shaft, or you can drop your transfer case. My 1st two suggestions are likely a better solution because you will not lose clearance, but they are not cheap. A MML will cost $60+, and a SYE/CV kit will likely be over $400. A SYE/CV kit is usually required for lifts above 4″. There are kits you can buy to drop your transfer case, but in my opinion they offer no real advantages over a cheap drop such as this, and they are normally at least twice the cost.
Note: The bolt sizes will only work for 2003+ TJs. If you have an older TJ you will need a 1/2″ x 2″ coarse thread bolt.
Tools:
- 13mm socket
- 17mm socket
- 18mm socket
- Ratchet
- Floor jack
- Torque wrench
Parts:
- 6x 12mm x 1.75 x 50mm grade 8.8 or 10.9 bolts
- 6x 12mm flat washers
- 12x or 18x 1/2″ BLT thick flat washers
Time:
- 40 minutes
1: Start with your jeep on a level surface. Loosen but do not remove the four bolts that mount your transmission to your transfer case skid.
2: Place a floor jack underneath the middle of your transfer case skid. Use a piece of wood to distribute the load on the skid. Jack it up a bit past where it touches so you know it is holding the weight of the skid.
3: Loosen all three bolts on the opposite side of the handle on floor jack, but do not remove them.
4: Loosen all three bolts on the same side as the handle on the floor jack. Lower the jack slowly so your transfer case is resting on the 6 bolts.
5: Slowly raise the floor jack again so it is just starts to move the transfer case off the bolts a bit, and remove the three bolts on the side with the jack handle.
6: Your transfer case should now only have three bolts in one side, and a gap on the other to allow you to attach the new hardware. Use a bolt -> flat 12mm washer -> transfer case skid -> 2x or 3x 1/2″ BLT washers -> into your frame. This is where you need to use a bit of judgment. I bought 18x 1/2″ BLT washers myself because I wasn’t sure how many I would need. I started off with only two on each bolt hoping it would be enough to help out with the vibrations, and it was. If you installed only a budget boost, one or two on each bolt may be enough, but if you have a 3″ suspension lift you may want to go right to three washers each bolt, and it may take even more. It’s really up to you and if you’ve got the time and patience, you could start with one, try it, and work your way up from there if you still have vibrations. The image to the right shows the thickness difference between a conventional washer and the BLT type. I chose to go for the BLT type even though they were around $.90 each so I wouldn’t have to buy roughly 30 washers. Insert all three bolts the same way, and bolt them up not quite tight. You still need the other side to be able to hang a bit.
7: Do the same on the opposite side. You should not need to adjust the floor jack but it doesn’t hurt to make sure it’s still snug against the bottom of the skid. Replace all three bolts, and you can go ahead and tighten them up. The service manual says 33 ft. lbs., but they also used locktite. If you are not going to use locktite, torque these bolts to 55 ft. lbs.
8: Move to the other side and tighten them the same, then remove the floor jack.
9: Tighten the 4 transmission mount bolts to 30 ft. lbs.
10: Take your jeep for a quick spin. You will likely notice a difference the 1st time you take off in 1st gear, but a test drive around the block couldn’t hurt. My vibrations were gone completely, but you may need to add more washers.
Hopefully your vibes are gone. Every jeep is different, and this is not a surefire solution. It is a cheap solution though, so it doesn’t hurt too much to try it out. It cost me roughly $20, mostly because I went for the expensive washers. Most after market transfer drop kits are 1″, so it actually might save you a bit of clearance as well.