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I have a vibration that starts at around 40mph. I checked the pinion angel and it's definitely not pointing at the Tcase. It's between flat and pointing at the Tcase. So I'm planning on throwing some degree shims in. My problem is when I had my XJ at the Jeep shop it was parked next to the another XJ. I run 33's. The XJ next to me runs a 5" lift and 35's. So obviously his XJ sat a little higher then mine. I asked him what he thought my lift was. He said his guess was a 4"-4.5". Last night I checked. Top of my D30 to bottom of frame, ya ya I know unibody. I got 13.5" on the front and on the rear 13". Is 4.5" lift right? I have a 2" block on the rear so I'm not sure I want to stack an degree shim onto of a block. So I might end up buying springs.
13.5" from the top of you front axle tube to the bottom of the unibody rail indicates 6.75" of lift in the front, and 13" for the same measurement in the rear shows 7" of lift. Stock height measurements are 6.75" front and 6.0" rear. Might want to double check you measurements, but your jeep does look like it sits pretty tall.
Do you have a slip yoke eliminator in your transfer case (top image shown below)? That will change the style of driveshaft you have from OEM, and will determine how you need your pinion angle to be setup. 7" of lift with a standard slip-yoke driveshaft is not a good setup (bottom image shown below).
Last edited by XJlimitedx99; Feb 13, 2024 at 12:42 PM.
13.5" from the top of you front axle tube to the bottom of the unibody rail indicates 6.75" of lift in the front, and 13" for the same measurement in the rear shows 7" of lift. Stock height measurements are 6.75" front and 6.0" rear. Might want to double check you measurements, but your jeep does look like it sits pretty tall.
Do you have a slip yoke eliminator in your transfer case (top image shown below)? That will change the style of driveshaft you have from OEM, and will determine how you need your pinion angle to be setup. 7" of lift with a standard slip-yoke driveshaft is not a good setup (bottom image shown below).
Thanks for the diagram.Yes It has a sye. And yes it has a double cardan ujoint. I am aware of pinion angels. That's why I said I needed to add degree shims. I have an angel finder. I just need to go figure it out and buy the shims. But my issue is I have a 2inch block in the rear and don't know if I want to add a degree shim to the 2 inch block. So I'm contemplating buying new springs and adding just the shim. But I don't know what size lift I have. I'll go out now and re measure.
Have you considered just pulling the blocks out and lowering the front to match? Would probably be cheaper.
It really does well off road because of how high it is. I feel like I might be defeating some of it's capabilities if I lower it. I guess if I removed the block that would put the lift at a 5" spring lift. So I would have to find 7" springs if I tried to stay where im at. Wow that wasn't where I was thinking this would be going. I guess I could temporarily fix this and eventually get 35" tires instead of the 33" I have now. And lose the 2 inch block. I'm running 4.88 gears anyway so if I did 35's it would go down the hiway better. I have some options to think about tonight.
It really does well off road because of how high it is.
How do you figure? Most people I see try to do everything they can to keep their rig low. There's a thread in the stickies for low center of gravity suspension tips. I could see the height being helpful for a mud truck, but even then your axles are still in the same place. Everything about driveability/stability works better with less lift. Less body roll, less brake dive, better ride quality, steering angles are more manageable, will get less axle wrap from removing the blocks, front end will climb better will less control arm angle, etc.
I've adopted the mentality that its better to have high clearance armor than it is to lift everything out of the way. Currently reworking my rig for 37's on 4" of lift with 14" shocks. It will use the full travel of the shocks and the tires will not rub at full bump/flex and full steering angle. Pair that with high clearance bumpers, sliders, and belly, and you get a very capable and stable rig. Granted, this is a lot more work and you can't be scared to cut sheet metal.
With big tires and low lift, bump stops are your friend. You really only need ~4" of up travel for street driving to stay off the bump stops. I see your profile shows San Diego, so you would probably want more if you're blasting around the desert for those surprise bumps that sneak up on you at 60 mph.
Last edited by XJlimitedx99; Feb 14, 2024 at 06:51 AM.
How do you figure? Most people I see try to do everything they can to keep their rig low. There's a thread in the stickies for low center of gravity suspension tips. I could see the height being helpful for a mud truck, but even then your axles are still in the same place. Everything about driveability/stability works better with less lift. Less body roll, less brake dive, better ride quality, steering angles are more manageable, will get less axle wrap from removing the blocks, front end will climb better will less control arm angle, etc.
I've adopted the mentality that its better to have high clearance armor than it is to lift everything out of the way. Currently reworking my rig for 37's on 4" of lift with 14" shocks. It will use the full travel of the shocks and the tires will not rub at full bump/flex and full steering angle. Pair that with high clearance bumpers, sliders, and belly, and you get a very capable and stable rig. Granted, this is a lot more work and you can't be scared to cut sheet metal.
With big tires and low lift, bump stops are your friend. You really only need ~4" of up travel for street driving to stay off the bump stops. I see your profile shows San Diego, so you would probably want more if you're blasting around the desert for those surprise bumps that sneak up on you at 60 mph.
I completely agree with your center of gravity concern. Thats always the objective to keep everything as low as possible. Where we differ is tire size. As I said before if I change to 35" I would have no problem losing the blocks. But being on 33" tires it effects what I can go over. I'm not referring to the distance from the axle to the ground. But more about brake over angle. We will see what happens. I was really shocked when I realized how big my lift was. It doesn't seem that big standing next to it. I had a TJ on one ton's with a 6" lift and it seemed higher. I'd really like to see your project. It sounds awesome.
Engine: 4.3L with headers and full 3" exhaust system
Getting back to your driveline vibs. I would suggest you try to wiggle the driveline at the slip joint. The reasoning is that when you add blocks, then it extends the driveline since the rear axle is no longer cycling in the factory arc. It may be your splines are loose. As far as lift goes, if your flairs are not factory, then measure to the seam in the body above and subtract 22" front and 22.5" rear. As far as LCOG goes, that is fine but not always wise everywhere. Where I live and wheel, that is a good way to trash the unibody on rocks doing normal wheeling even with rock sliders.
Getting back to your driveline vibs. I would suggest you try to wiggle the driveline at the slip joint. The reasoning is that when you add blocks, then it extends the driveline since the rear axle is no longer cycling in the factory arc. It may be your splines are loose. As far as lift goes, if your flairs are not factory, then measure to the seam in the body above and subtract 22" front and 22.5" rear. As far as LCOG goes, that is fine but not always wise everywhere. Where I live and wheel, that is a good way to trash the unibody on rocks doing normal wheeling even with rock sliders.
I have come to a conclusion. I'm having the spring purches cut and turned. It looks like I need 10 degrees in additional pinion angel. This will alow me to buy spring at a later time and get rid of the blocks all together. It cost much more to go this route but It will be a better end product. That should get rid of my vibration as long as the vibration didn't knock out the carbon joint for being out of phase (fingers crossed).
I went to 4wheel parts and discussed my lift. They said from what they can tell it was a 4.5" spring, 2" block and 1" shackles. So it's 7.5" lift with sag out, 7". So my mystery has been solved. And in the prosse I've decided to get rid of the hack and tap and got a Tom Woods SYE. I would have had the SYE installed today but I found metal the size of ground black pepper in my tcase filter and on the magnet. So I'm in search of a low mileage NP242J near me for sale.
Suspension question
