NastyNinjaBEar

I did some searching but couldnt find any posts where the vibes only occurred during braking.

Some back story about the journey first.

Bought the jeep and the previous owner said he did a 2 inch lift. What he meant was, he added longer leaf shackles and that's it. The shackles are adjustable with 2 different settings.

So I installed the Rough Country 4.5 inch kit, but had to use the lifted shackles on the tallest option. When I first drove the jeep after the lift, it accelerated smoothly but any time I let off the gas, it would vibrate as I slowed.

I changed to the next lower option on the shackles. Now it wouldn't vibrate when I slowed but any time I used the brake it would. So It got rid of about 80% of the vibration.

I then ordered stock shackles and installed last night. This got rid of MOST of the vibration, even when I brake to about a medium pressure. But If I brake too hard it vibrates still.

I found 2 degree shims at the local auto parts store, would this be the next thing to try?

I'm new to all this stuff so I'm learning as I go.

MonacaYankee

You need a Slip yoke eliminator

NastyNinjaBEar

Thats just the end of it? Why does everyone discuss pinion angle and its relevance to vibration. If i needed a SYE why does it only vibrate when i brake and not all the time? Any further insight as to why thats the solution would be awesome!

cruiser54

He/she likes to just throw crappy info out with total disregard for people's issues.

I apologize for that. Most everyone here prides themselves on giving good advice. Some....not so much.

Perhaps you can isolate the vibration front to rear to give you a starting point. What if you test brake using only the park brake?

NastyNinjaBEar

I dont think it has anything to do with the actual brakes as much as just fast deceleration of the vehicle. Since it originally vibrated just when I let off the gas and slowed down with no brakes.
Also to clear that up further. I have completely replaced the entire braking system. It vibrated before and after.

I definitely believe its drive shaft.

cruiser54

Any lift blocks in the rear?

Motor/trans mounts worn?

Exhaust pipe hitting here?

NastyNinjaBEar

I will definitely take a look and shoot a pic.

I should mention too, that the rate of the vibration does change with the speed of the vehicle too.

LACK

Sounds like drive line vibes. Although it could be something as simple as an out of balance tire.

NastyNinjaBEar

I've run the tires on my old cherokee an the new one. No vibration on the old one and no vibration before the lift, so I think the tires are narrowed out.

LACK

Chances are youre getting drive line vibrations then. Acceleration vs deceleration puts a different load on the rear axle/drive shaft.

Are you running a transfer case drop?

NastyNinjaBEar

Yes, the lift kit came with a 2 inch tcase drop which is currently installed.

Should I add a couple washers to the drop and drop it more?

LACK

Transfer case drops are kind of a band-aid, just trying to go through the process of elimination and rule out some things.

I wouldn't drop it any further, puts a lot of extra stress on your motor mounts as is.

The proper fix would be adding a slip yolk eliminator or lowering the lift. The pinion angle on the rear axle should be parallel to the output on the transfer case with a stock style driveshaft. You dont want to point the rear axle up at the transfer case unless you are running a SYE and double cardan shaft.

Stock configuration.


SYE configuration

NastyNinjaBEar

Awesome. So thats where I figure things would go. The next question is, how do I measure the angles accurately. I can shim the axle. I can't imagine its very far out...if its only vibrating part time and less so when I lowered the lift.
My understanding is that 4.5 shouldnt need SLE but is on the edge.

How can I accurately tell what angle to shim?

LACK

Get a little magnetic based angle finder. Measure the angle of the output on the transfer case, then match that to the angle of the pinion of your rear axle.

Just be forewarned that mat not solve your vibration issues, which could be caused by the extreme angles of the u-joints on the stock driveshaft.

NastyNinjaBEar

Do I have to remove the drive shaft to measure the angle?