Pinion angle help (read: lotsa vibration)

I bought a '99 XJ about two months ago, and have been working to get it ready for Moab. It has a 6.5" Rock Krawler 3-link front suspension on the Dana 30 HP and 2" Teraflex spring pucks. The rear is a Teraflex "Grand-up" coil spring conversion, 8.5" lift on the 8.25" unit. ARB's front and rear, 35"x13.5" Toyo's, SYE on the rear with a new driveshaft and double-cardan yoke, 4.56:1 gearing. The thing does great out at 5-Mile Pass here in Utah. But getting there is a real treat...enough vibration to shake the fillings out of your teeth.
On the highway, it feels okay up to about 50 MPH, then the vibes become noticeable. At 70+, there's a deafening low-freq vibration. Today I pulled the front driveshaft out, and the low-freq went away, but there is still a vibration under throttle load coming from the rear. When I back off of the throttle, it goes away. I originally thought it might be a bent axle, but now I don't think so. I'm thinking pinion angle or caster is contributing to the front vibe.
I had the alignment done a couple weeks ago at Empire Tire in SLC, and the caster up front is 5.1* and 5.3* left and right. The measurements I just took on the rear: Driveshaft is at 21*, rear pinion is at 12*, so a difference of 9*. I know that you want the angle to be close to 0* or 1* as possible. Would 9 degrees difference make the vibration under acceleration occur at higher speeds?
Also, when slowing down to a stop, I can hear a lot of gear noise from the front end. I thought it was the unit bearings with a flat spot, so I replaced them. Now it almost sounds like a spider gear, but I'm leaning toward improper pinion depth/backlash. The axle seals were recently done at a local shop, and since then I can really hear that gear clicking sound.
Any help or advice on what to do nect would be greatly appreciated.

9*???? you should get that addressed pronto! are you sure that is the correct measurements? that seams like a lot of difference. improper gear setup in the front can give quite a bit of noise, i would also presume that your front pinion angle is not right either at 8.5" of lift and 5* castor. the only real fix for that is rotating the knuckles or axle tubes.

probably not something that you would want to do, but lowering the rig a bit could reduce your angles and help with road friendliness... 5.5-6" will fit 35's if setup properly.

btw, nice looking rig!

dgrigorenko said:

9*???? you should get that addressed pronto! are you sure that is the correct measurements? that seams like a lot of difference. improper gear setup in the front can give quite a bit of noise, i would also presume that your front pinion angle is not right either at 8.5" of lift and 5* castor. the only real fix for that is rotating the knuckles or axle tubes.

probably not something that you would want to do, but lowering the rig a bit could reduce your angles and help with road friendliness... 5.5-6" will fit 35's if setup properly.

btw, nice looking rig!

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That and what T-case do you have and what type of SYE kit?

Sorry...taken with a cell phone.

The t-case is stock, NP242. No shims or drop kits. The slip yoke eliminator on the rear: I don't really know. I bought the driveshaft and SYE from Teraflex. Installed, $350. That kinda hurt. I think I could have done it myself for cheaper getting a Tom Woods unit.

dgrigorenko said:

9*???? you should get that addressed pronto! are you sure that is the correct measurements? that seams like a lot of difference. improper gear setup in the front can give quite a bit of noise, i would also presume that your front pinion angle is not right either at 8.5" of lift and 5* castor. the only real fix for that is rotating the knuckles or axle tubes.

probably not something that you would want to do, but lowering the rig a bit could reduce your angles and help with road friendliness... 5.5-6" will fit 35's if setup properly.

btw, nice looking rig!

Click to expand...

When I took the measurements on flat fround, I measured first on the slip yoke at the pinion end...21* was the reading. The flat spots on the housing next to the diff cover gave me 78*, subtracted from 90 gave me 12, which I got the differenct of 9 degrees.
Ben Hanks Racing is a local shop, who fabricated a new upper control arm for me for the three-link. I told them about my "minimally adjustable" rear setup. The rear LCA's are adjustable, but the tops ar not. The lowers are adjusted all the way in, as short as possible, and the tops are fixed. My best option that I see is to take it to Ben Hanks and have them fabricates some new uppers to account for that difference in angle. They have treated me right in the past, and I trust them...they definitely know what they're doing.
I am trying to avoid lowering it, though it would be easy to pull the pucks up front. Then, I guess I would just cut the coils in the back?

On your front, if they only replaced the axle tube seals they would not have had to mess with the pinion. The shims for the carrier are supposed to be held on by the pressed on bearings so the backlash should not have changed any despite that the carrier had to be removed and reinstalled. Is this a disconnect axle? It may simply be that the carrier/pinion bearings are worn out and need to be replaced.

Osmosisfrank said:

I had the alignment done a couple weeks ago at Empire Tire in SLC, and the caster up front is 5.1* and 5.3* left and right. The measurements I just took on the rear: Driveshaft is at 21*, rear pinion is at 12*, so a difference of 9*. I know that you want the angle to be close to 0* or 1* as possible. Would 9 degrees difference make the vibration under acceleration occur at higher speeds?

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9 degrees of pinion angle on a SYE will cause the symptoms you describe. You want less than 3 degrees. With the lack of axle wrap the slinky conversion provides I would try for 0-1 degree.

Most likely on the front you are going to need to get down around 2-3 degrees of caster to eliminate the drive line vibes. With the amount of lift you have. As someone else said you may want to consider getting the knuckles rotated.

I've been told that with too much caster, it'll steer like a grocery cart, and too little, like a land-barge Cadillac. True?
Thanks again for your input on this. Gonna get the rear pinion angle taken care of this week.

Osmosisfrank said:

I've been told that with too much caster, it'll steer like a grocery cart, and too little, like a land-barge Cadillac. True?
Thanks again for your input on this. Gonna get the rear pinion angle taken care of this week.

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With too little caster your wheel will not want to stay centered and you will wander. When you make turns you will have to manually return the wheel to center. But to put it in perspective my old J10 only had 4 degrees of caster per factory specs.

Another option to consider is to use offset ball joints to pick up 2 more degrees of caster. That way you can get a reasonable compromise between pinion angle and caster; however, the offset joints don't hold up as well and cost more.

Yeah, seems like the place that set my alignment quoted me $320 for offset ball joints. I THINK that was per pair installed, but not sure. And that was to get my camber back to 0 degrees. I'm about -1.1 deg. right now.

Osmosisfrank said:

Sorry...taken with a cell phone.

The t-case is stock, NP242. No shims or drop kits. The slip yoke eliminator on the rear: I don't really know. I bought the driveshaft and SYE from Teraflex. Installed, $350. That kinda hurt. I think I could have done it myself for cheaper getting a Tom Woods unit.

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You need degree shims, your pinion is pointed way to low. -B

Osmosisfrank said:

Yeah, seems like the place that set my alignment quoted me $320 for offset ball joints. I THINK that was per pair installed, but not sure. And that was to get my camber back to 0 degrees. I'm about -1.1 deg. right now.

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It has been a few years since I priced them but I seem to remember they were about $60 per joint just for the part.

Sure you aren't at +1.1. If you were at -1.1 you would be fighting just to keep it going straight down the road. The wheels would want to flop to one side.

lpennock said:

It has been a few years since I priced them but I seem to remember they were about $60 per joint just for the part.

Sure you aren't at +1.1. If you were at -1.1 you would be fighting just to keep it going straight down the road. The wheels would want to flop to one side.

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According to the printout the alignment shop gave me:
FRONT LEFT: Camber = -1.1*; Caster = 5.1*; Toe = 0.13*; SAI = 10.9*; Included angle = 9.8*
FRONT RIGHT: Camber = -1.1*; Caster = 5.4*; Toe = 0.13*; SAI = 11.0*; Included angle = 9.9*
FRONT: CROSS CAMBER = -0.1*; CROSS CAMBER = -0.2*; CROSS SAI = 0.0*; TOTAL TOE = 0.25*

That's what I have, though I'm sure the ranges are for a stock height XJ. Yes, it's a handfull to drive, especially at higher speeds.
I don't think degree shims are the solution, as this is a four-link coil conversion rear suspension. I think, to get more angle, I need to have the upper control arms lengthened to roll the diff rearward and raise the pinion up. This means the spring pads are gonna have to come off and be re-welded on at the new flat angle too. Here's a pic of the components in the Teraflex Grand Up kit. I've been told it's based on the same setup under a Range Rover.

Osmosisfrank said:

According to the printout the alignment shop gave me:
FRONT LEFT: Camber = -1.1*; Caster = 5.1*; Toe = 0.13*; SAI = 10.9*; Included angle = 9.8*
FRONT RIGHT: Camber = -1.1*; Caster = 5.4*; Toe = 0.13*; SAI = 11.0*; Included angle = 9.9*
FRONT: CROSS CAMBER = -0.1*; CROSS CAMBER = -0.2*; CROSS SAI = 0.0*; TOTAL TOE = 0.25*

That's what I have, though I'm sure the ranges are for a stock height XJ. Yes, it's a handfull to drive, especially at higher speeds.
I don't think degree shims are the solution, as this is a four-link coil conversion rear suspension. I think, to get more angle, I need to have the upper control arms lengthened to roll the diff rearward and raise the pinion up. This means the spring pads are gonna have to come off and be re-welded on at the new flat angle too. Here's a pic of the components in the Teraflex Grand Up kit. I've been told it's based on the same setup under a Range Rover.

Click to expand...

My mistake on your numbers. You said Camber I was thinking caster. The camber you have is a little off but I don't think I would worry. Normal range is around -.75 to +.5. With your specs it shouldn't be that bad to drive. I'm running pretty similar numbers and mine drives fine but I am only running 5.5" with 33's.

Osmosisfrank said:

According to the printout the alignment shop gave me:
FRONT LEFT: Camber = -1.1*; Caster = 5.1*; Toe = 0.13*; SAI = 10.9*; Included angle = 9.8*
FRONT RIGHT: Camber = -1.1*; Caster = 5.4*; Toe = 0.13*; SAI = 11.0*; Included angle = 9.9*
FRONT: CROSS CAMBER = -0.1*; CROSS CAMBER = -0.2*; CROSS SAI = 0.0*; TOTAL TOE = 0.25*

That's what I have, though I'm sure the ranges are for a stock height XJ. Yes, it's a handfull to drive, especially at higher speeds.
I don't think degree shims are the solution, as this is a four-link coil conversion rear suspension. I think, to get more angle, I need to have the upper control arms lengthened to roll the diff rearward and raise the pinion up. This means the spring pads are gonna have to come off and be re-welded on at the new flat angle too. Here's a pic of the components in the Teraflex Grand Up kit. I've been told it's based on the same setup under a Range Rover.

Click to expand...

you could cut off and reweld the coil buckets, or you could get some custom arms made(like you mentioned earlier). i guess it depends on your budget and how much hassle you want to go through. i dont know what your fab skills are, but it is possible to make your own adjustables, or fixed if you know what length they would need to be. also with a triangulated 4 link do you need the pinion 1* down for axle wrap? is i didnt think that there was much axle wrap with links instead of leafs.

boomhauer said:

You need degree shims, your pinion is pointed way to low. -B

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Read post #1,his rig doesnt use them!

Osmosisfrank said:

The t-case is stock, NP242. No shims or drop kits. The slip yoke eliminator on the rear: I don't really know. I bought the driveshaft and SYE from Teraflex. Installed, $350. That kinda hurt. I think I could have done it myself for cheaper getting a Tom Woods unit.

Click to expand...

What does the front axle pinion angle look like?
If it is off, like the rear, you will get vibrations from it too.

RCP Phx said:

Read post #1,his rig doesnt use them!

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Whoops, coil conversion, my miss, thanks RCP. -B

Could you not try a t-case drop to help that angle. I know you have the SYE BUT a little help from the drop could keep your fillings in.

The LCA's on that rear kit look to be length adjustable. Are they? If so, shorten the lower links and it should bring the pinion angle up to par. If not, cut one of the ends off and make it adjustable. If they are tube arms and are thick enough, thread the inside of them or get threaded inserts, then get a threaded joint end to replace the eye and bushing.

Osmosisfrank said:

minimally adjustable" rear setup. The rear LCA's are adjustable, but the tops ar not. The lowers are adjusted all the way in, as short as possible, and the tops are fixed.

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already is