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Discussion Starter · #1 ·
Over the weekend I installed a 2.5" Rough Country suspension lift. The lift included new coils and shocks. Pretty easy install, (minus the 2 hour delay I had to spend re-tapping the thread for one of the rear shock mounts because I sheared off one of the bolts while trying to remove the old shocks.) But other than that a pretty staright forward install and not too difficult. I am really pleased with this set up and I am replacing the stock tires next weekend for a set ocf 31x10.5x15 BFG A/T's. The only thing I have noticed is a decent amount of vibration accelerating from 2nd to 3rd gear around 2500-3000 rpms. I'm wondering what is causing this, could it be the angle the drive shaft is at after the 2.5" lift? I thought I wouldn't have any problems with a lift under 3". Anyone else ever experience this?
 

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Every Jeep I've ever seen lifted will behave differently. Some you will get no vibes and some you will.
 

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Did you drop the T-case mount at all? That's an easy (and cheap) thing to try.
 

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For a short wheelbase TJ, any lift height over 2", and often even at 2", will generally require that you at least drop the t-case at or at least pretty close to an inch to prevent vibrations. The longer wheelbase Unlimited is the model that gets away with taller lift heights before needing things like t-case drops or SYE/CV driveshafts.
 

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Most mfgs who sell lift kits also have a t-case drop available.

...but yes it's basically spacers.
 

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Any suggestions on how to drop the t-case? Is it just spacers?
Some will only drop it enough to cure the vibration...for a 2-3" lift - usually just installing a few washers as lowering spacers will fix it. Test Drive, if it still vibrates, add more washers.

Stole this pic from the internet to show aftermarket spacers:

 

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If you have a newer TJ, you will probably need longer t-case skid plate bolts to handle the extra distance created by the spacers or washers. Just remove one and take it into your local hardware specialty store and get one with the same size threads but 1" longer. Newer TJs use metric bolts there and they must be hardened, standard bolts aren't strong enough. A metric 10.9 strength is fine. If you have an older TJ that still uses SAE bolts there, they need to be at least Grade 5.
 

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Discussion Starter · #10 ·
Awesome guys, as usually getting lots of useful knowledge here. I will update once I drop the t-case. It was a 2.5" lift so about an inch should be enough? Am i doing a lot of damage by driving it the rest of the week until I can add the spacers saturday or should I not drive until I fix?
 

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Awesome guys, as usually getting lots of useful knowledge here. I will update once I drop the t-case. It was a 2.5" lift so about an inch should be enough? Am i doing a lot of damage by driving it the rest of the week until I can add the spacers saturday or should I not drive until I fix?
You'll be putting stress on your u-joints and/or pinion bearing until it's fixed so there's no way of telling whether you'll damage something. If I had another vehicle or mode of transport I'd definitely play it safe. It takes about 20 minutes to do with washers that can be had at any hardware store. If you only need to drop a fraction of an inch there will be no need for new bolts. I have mine dropped 3/8" with stock bolts and plenty of threads holding it up. Older TJs (97-02) have countersunk style bolts and may not be available at a hardware store.
 

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Here's the kind of bolts I'm talking about. Mine were much better than this set.


Oh, and I can tell you that a u-joint failing at 50+ mph is not a fun thing to happen and can lead to more damage when the shaft digs into the asphalt and beats the daylights out of your tub.
 

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Discussion Starter · #13 ·
Thanks again for all the advice and suggestions for this problem. I went ahead and installed some washers to drop the skid plate/t case about 3/4" and that stopped the vibration completely. This is only a temporary fix and I ultimately plan on installing a SYE and a new driveshaft, but the washers will keep me going for the moment.
 
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