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Vibration after new springs

980 views 17 replies 4 participants last post by  bluejunior 
#1 ·
So feel kinda stupid but i could use some help..
I order procomp rear leafs springs online and it didn't mention they were like 2.5" lift or something till they emailed me a reciept. i was expecting stock replacement basically but not what i got. but yea i installed them and obviously the back is now sitting higher than the front and now i got pretty decent vibration when driving. The leafs had shims so clearly thats to adjust the dif. Angle for when you lift the whole thing right? So basically im wondering what options i have to fix it right now.

Would a leveling kit for front end help me out or do i need to lift the front..? Or anything else i could do to correct it...
Thanks.
 
#2 ·
So feel kinda stupid but i could use some help..
I order procomp rear leafs springs online and it didn't mention they were like 2.5" lift or something till they emailed me a reciept. i was expecting stock replacement basically but not what i got. but yea i installed them and obviously the back is now sitting higher than the front and now i got pretty decent vibration when driving. The leafs had shims so clearly thats to adjust the dif. Angle for when you lift the whole thing right? So basically im wondering what options i have to fix it right now.

Would a leveling kit for front end help me out or do i need to lift the front..? Or anything else i could do to correct it...
Thanks.
Shims will actually make things WORSE in most cases unless you have a special aftermarket piece called a slip yoke eliminator. Depends somewhat on the installation and angle of the shim l, but generally not what you need.

What you want is for the output of the transfer case and the input of the axle to be parallel when driving. Due to axle wrap typically that means the axle should be a couple of degrees shallow of truly parallel.

Take the shims out and see how it does. If it still vibes under certain situations, then likely you need a little TC drop. .5-.75 inches probably.

You can put some 2" poly spacers on the front springs for about $30 that should get it a lot closer to level without requiring some of the extra modifications that come into play at 3".

If you want to know how much lift these procomp springs got you, measure from the center of the wheel to the bottom of the fender flare. Stock that is 17".

Have you called to see if you can return these springs? If you didn't want a lift you may be opening a bigger can of worms than you realize. For example if nothing else I'd definitely suggest new shocks and an extended rear brake line if you got a true 2.5-3" out of these springs plus fixing your driveline angle issues.
 
#5 ·
no i did it myself. And ok. I figured the shims were causing the problem cuz they are for compensating the drive line angle when the whole thing is lifted right? im guessin i just gotta take ubolts off clamp leafs together take off shock, lower axle and remove shim?
 
#6 ·
Pretty much, but you really don't want to re-use u bolts. I'd get new ones.

I'm fairly certain that taking out that shim will improve and maybe even eliminate the angle.probelms. if it gets better but doesn't go completely away you just need a light TC drop.

I'd call and ask about a return first, though. If you can swing it the medium duty crown or Dorman leaves are direct factory replacements so you don't have to mess around with the lift if you didn't want it.
 
#14 ·
Shims are available in different angles. Google should be able to find several sources. The most accurate and likely most effective solution is to get an angle indicator which can be had cheap from places like Harbor Freight and measure the angles of the TC output shaft and differential input shaft from horizontal. Then figure the angle shim needed to get them parallel.

In the meantime, which direction did you install the shims? If they are needed at all, it would usually be thick end forward. But as bluejunior said, you may try removing the ones you have and see if that cures the problem. The forward "rake" of the whole Jeep doesn't affect the rear driveline angle between TC and differential. (However it can make the steering twitchy by effectively reducing steering castor). If the new lift springs just happen to set the axle at the same relative angle to the TC output, then removing the shims may fix it.

IIRC there are some good Youtube videos that illustrate how and why those vibrations are created. Helps understand the cause and the cure.
 
#18 ·
The coil spacers were just a suggestion to bring the jeep closer to level so it doesn't look so face down *** up. The TC drop is the part that will fix the driveline angles.

Should cost about $20 worth of stuff at a hardware store.4 new bolts ~half an inch longer than factory and some stuff to space it. Remove the tranny crossmember, pull out the studs using the double nut method or some big vice grips, then put 1/2-3/4" worth of spacers between the cross member and the frame when you reinstall. At 3.75ish rear lift I needed 3/4" of drop. I used a couple of 3/4" stainless nuts sandwiched between washers about an 8th thick to get there. Better hardware stores would have 1/2" inner diameter stainless steel spacers in various sizes. I suggest you start at half an inch but measure the resulting angles before fully torquing. Add another 1/4" in washers if needed.

You want your axle pinion to be angled down 1-2* compared to the output of the transfer case to account for axle wrap during acceleration where the pinion will kick up toward the floor of the jeep.
 
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