Driveline vibrations between 20-30 mph

[Jwalk34]

So a few weeks ago I installed a 2.5” lift on my 00 Tj. Complete lot with all 8 adjustable control arms, adjustable front track bar and rear track bar relocation bracket.

I was told that it would not be necessary to do a SYE&cv driveshaft if I went with adjustable control arms since the lift wouldn’t interfere to severely with the geometry.

My mechanic is saying he doesn’t believe adjusting the rear upper control arms will help any and that I need to go with either a Tcase drop or sye/cv drive shaft.

Any information would be helpful, also does anyone have the specs on acceptable driveshaft/pinion angle for the rear. So I can give him a starting base?

Thanks!

 

[tworley]

Can you post some photos?

All jeeps react differently to lifts. You may need to space the tcase skid down with a couple of washers to get by.

 

[Jwalk34]

Can you post some photos?

All jeeps react differently to lifts. You may need to space the tcase skid down with a couple of washers to get by.

At the moment no, jeep is at the shop.

So do you think it’d be worth having him humor me and adjust the rear uppers anyway? Or too difficult to say with out pics?

 

[tworley]

Doubtful. I think spacing the tcase down is going solve the issue. Not an entire 1" drop but with just a couple of spacers under each bolt. Or even adding a motor mount lift.

 

[Alex01]

Has an alignment been done since the lift?

 

[Jwalk34]

Has an alignment been done since the lift?

Yes an alignment was done. Drives straight no pull. Just the vibration between 20-30mph

 

[Alex01]

Yes an alignment was done. Drives straight no pull. Just the vibration between 20-30mph

It would be easier to diagnose with the jeep in your possession but as tworely said dropping the t-case will likely solve the issue.

If it was me I would start by measuring the angle of the output/pinion in the rear to confirm they are the same. (top photo)

If they were then I would remove the front driveshaft and see if the vibs are still present. If not you know it's in the front. If so, then it's likely in the rear. (you could go one step further and replace the front shaft, remove the rear shaft, put it in 4wd and drive around to confirm.)

From experience, jeeps can be picky with pinion angle and something that works for one person likely won't work for the next. It took me a while to dial in my front pinion making .5* adjustments and test driving it.

But, if it doesn't bug you to have a minimal drop keep adding washers under the t-case until the issue goes away.

 

[Jwalk34]

Stopped by the shop on the way to work and snapped these quick.

So the mechanic is saying he’s worried that if he adjusts the control arms it’ll begin to create bind on the shocks and springs.

 

[Alex01]

My eyeball angle finder tells me the rear lowers need to be extended or the uppers shortened. (perhaps a mix of both.) Adjusting the pinion slightly shouldn't cause anything to bind. Since you already have adjustable control arms it seems like a shame not to attempt to use them to fix the issue.

 

[Gollywomper]

To me the pinion looks like it may be too high for that style of drive line. In a perfect world you want your pinion angle to match the t case output angle. with a Non DC style shaft like you have in the rear.

 

[tworley]

Hard to tell exactly with those photos. But I agree, looks a touch high maybe.

Your springs will not be in a bind. Shocks, if their body is hitting the spring perch, can be turned upside down or the spring perch can have a notch cut into it.

 

[Nickgsjeep]

I

Doubtful. I think spacing the tcase down is going solve the issue. Not an entire 1" drop but with just a couple of spacers under each bolt. Or even adding a motor mount lift.

I second this approach, every jeep reacts slightly different to lifts, they just do. Your driveline geometry has been changed so attempting to correct should be relatively easy/cheap. A slight t-case drop or motor mount lift should do the trick until you are ready for a new double cardan drive shaft and sye

 

[Jwalk34]

My eyeball angle finder tells me the rear lowers need to be extended or the uppers shortened. (perhaps a mix of both.) Adjusting the pinion slightly shouldn't cause anything to bind. Since you already have adjustable control arms it seems like a shame not to attempt to use them to fix the issue.

Appreciate the info. Yea I think I’m running into a mechanic that’s not necessarily comfortable with the parts. He told me he’s never used or seen adjustable control arms. And is only going off his common knowledge.

 

[Jwalk34]

I

I second this approach, every jeep reacts slightly different to lifts, they just do. Your driveline geometry has been changed so attempting to correct should be relatively easy/cheap. A slight t-case drop or motor mount lift should do the trick until you are ready for a new double cardan drive shaft and sye

So you don’t think it’s a good idea to try adjusting the control arms first before adding spacers to the Tcase?

 

[bobthetj03]

Did your mechanic adjust the lengths of the arms to be the same length as the stock arms he removed?

 

[tworley]

^^That was going to be my next question. You want the arms adjusted so that at full bump, with coils removed, the bumpstops are centered on each other (upper and lower)

 

[Jwalk34]

Did your mechanic adjust the lengths of the arms to be the same length as the stock arms he removed?

No I preformed the install a few weeks ago and followed the manufacturers recommendation of lengthening the arms to a certain spec longer than the factory ones (that I can’t recall at the moment)

 

[Nickgsjeep]

So you don’t think it’s a good idea to try adjusting the control arms first before adding spacers to the Tcase?

It wouldn’t hurt to try and get the pinion angle and t case angle to match up, that would be ideal. A slight t-case drop fixed my issue until I got a motor mount lift, then when I went an inch higher I did a sye and a double cardan shaft.

 

[bobthetj03]

No I preformed the install a few weeks ago and followed the manufacturers recommendation of lengthening the arms to a certain spec longer than the factory ones (that I can’t recall at the moment)

Well, that will complicate things a bit. Manufacturer's recommendations are really just a starting point. The axles need to be cycled to full bump with the springs removed to make sure the axle is centered and hitting the bumpstops properly. Yeah, it's a lot of extra work, but only until you do that we are just spitballing as to whether adjusting the arms further will be helpful. Adjusting the arms so the yokes are parallel to each other couldn't hurt if you want to try that first.

 

[xxdabroxx]

Pinion needs to drop for sure.