Driveline angles, MML, TC drop, round 2...help please :) - Jeep Wrangler Forum

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Old 02-18-2013, 04:36 PM   #1
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Driveline angles, MML, TC drop, round 2...help please :)

Ok guys,

I have the jeep handling much better (no wandering etc). I do however have slight vibes around 55mph. Would love some comments to make sure I am heading in the right direction.

Bit of history of what I did already (thanks for the info in there!)
http://www.wranglerforum.com/f5/sway...ns-207844.html

This is what I currently have (installed by PO):
-98 sport 4.0L, 4" lift, 33"x12.5" tires.

- 1" MML
- 1" TC drop (do I even need this??, or were these stock on '98 sports? not sure if the skid plate normally bolts directly to frame)
- Double cardan rear drive shaft w/ spicer joints
- Stock control arms (pretty sure I need adj rear uppers at a minimum)

So I crawled under the jeep & measured some stuff:

- Rear flange off tcase - 11 degrees
- Rear DC driveshaft - 14 degrees
- Rear pinion angle - 11 degrees (this is the cause of the vibes right??? Needs to be in line with DS aka 14 degrees, fixable with adjustable upper control arms??....)

- Front stock driveshaft - 7.5 degrees
- Front pinion angle - 9 degrees
- Caster angle - 5.5 - 6 degrees (measured on knuckle & top of ball joints)
- Stock control arms, lowers have cam bolts and appear to be holding after my one & only off-road trip

Not terribly worried about front anymore as the wandering issue has been resolved.

So.....adjustable rear upper CA's, dial the pinion angle to match driveshaft angle, hopefully get rid of the vibes?
Thoughts on removing Tcase spacers? What problems will I encounter after that??....

Thanks!!
Jeff

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Old 02-18-2013, 05:08 PM   #2
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Forgot, it also has a SYE (obviously) to go along with the DC rear driveshaft.

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Old 02-19-2013, 07:14 PM   #3
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This is what appears to be the tcase drop...???....
Hoping i can remove those after getting the adjustable rear upper control arms...thoughts?

Anyone ?

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Old 02-19-2013, 07:41 PM   #4
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Quote:
Rear flange off tcase - 11 degrees
- Rear DC driveshaft - 14 degrees
- Rear pinion angle - 11 degrees
This would all be good if you didn't have a double cardan shaft. Transfer case and pinion shaft angles are the same, which is what you would want. Drive shaft angle @ 14 degrees means your u-joint angle is 3 degrees (the difference between the pinion/ transfer and drive shaft) which is very good. Sounds like someone set it up correctly for a regular single cardan shaft.

BUT, since you have a DC rear shaft, the pinion shaft should be aimed almost directly at the transfer case output, about 1 degree below. You need adjustable upper rear control arms to adjust this. And you can lose the transfer case drop once you accomplish this.
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Old 02-19-2013, 07:49 PM   #5
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Same story on the front. You want your front pinion angle to be within 1 degree of the drive shaft angle.
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Old 02-19-2013, 08:44 PM   #6
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Thanks for the reply Patrick,

Confirms what i was thinking, just wanted to make sure before i go ordering parts.

Hopefully adding the adjustable rear uppers I will get rid of the vibes, and would be nice to gain 1" clearance by removing the tcase drop.

My guess is PO had the tcase drop because of the stock control arms...

At least they had installed the sye and dc drive shaft...one of the few things they did right....even if everything else wasn't finished lol.
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Old 02-19-2013, 08:50 PM   #7
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You'll also need an angled track bar bracket to keep the track bar bushing aligned after the rear differential is pitched up to align your pinion angle.
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Old 02-19-2013, 08:52 PM   #8
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You got lucky with getting all that. Gonna do the same myself as the PO of mine had a BB with shocks that were not original.
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Old 02-19-2013, 09:28 PM   #9
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I'll have to crawl under again and verify, but i think both front and rear track bars are aftermarket and I thought I saw a non stock looking bracket on the rear....
I'll double check tomorrow.

Thanks!
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Old 02-20-2013, 04:11 PM   #10
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Ok, front track bar is adjustable.
Rear is not (stock??), but it appears there is a relocation bracket on the axle side.



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Old 02-21-2013, 08:06 AM   #11
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i have the same set up. The rear bracket is common with most lifts. But once you roll the axle back with the rear upper CA's to get the pinion angle right for the SYE, you will need the angled track bar mount to keep the TB from hitting your gas tank. I have this one JKS Manufacturing OGS160 - JKS Manufacturing Rear Angled CV Trackbar Bracket for 97-06 Jeep® Wrangler TJ & Unlimited with Over 3" Lift - Quadratec. Also watch for the shocks hitting the spring pads. Some use shock relocation brackets, others just notch the pads.
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Old 02-21-2013, 05:01 PM   #12
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Doh! One more part to buy. Thanks, didn't realize i needed an angled bracket.
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Old 02-21-2013, 07:28 PM   #13
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Quote:
But once you roll the axle back with the rear upper CA's to get the pinion angle right for the SYE, you will need the angled track bar mount to keep the TB from hitting your gas tank.
It also keeps the track bar busing in line so it doesn't bind after the axle is tilted up/ back.
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Old 02-21-2013, 07:33 PM   #14
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Thanks guys!
Ordered the bracket, as well as some Savvy alum rear upper ca's, can't wait!

Also need to service my diffs and do a pinion seal....

Then lose the tcase drop!
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Old 02-21-2013, 07:47 PM   #15
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Originally Posted by Bigkidneys View Post
You got lucky with getting all that. Gonna do the same myself as the PO of mine had a BB with shocks that were not original.
Yah, some of the stuff was bad (wiring, skyjacker shocks etc), but alot was good, SYE, DC driveshaft, stereo, CB, brand new tires, extended brake lines, & re-geared.

The rest of this is just a learning process, slowly making it better!


I just thought of something too, after eliminating the tcase drop, that should get the front driveshaft angle closer to the pinion angle as well. Bonus!
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Old 04-24-2013, 12:07 AM   #16
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Originally Posted by Patrick H View Post
Same story on the front. You want your front pinion angle to be within 1 degree of the drive shaft angle.
So front AND rear pinion angle should be within 1 degree of driveshaft angle. Did I read that correctly?
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Old 04-24-2013, 05:44 AM   #17
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Originally Posted by OhSixTJ View Post

So front AND rear pinion angle should be within 1 degree of driveshaft angle. Did I read that correctly?
Yes you read that correctly and on some Jeeps it is possible to get both axles within 1°. On the rear this is very important. On the front axle depending on lift height you may have compromise between pinion angle and caster angle. As you increase pinion angle, caster angle decreases which effects steering. A balance must be found between the two. The good news is the front shaft can handle more misalignment than the rear because it is much longer.
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Old 04-24-2013, 08:51 AM   #18
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I never updated....
Getting the rear upper adjustable CA's & bracket installed solved my vibes. Pinion angle dialed in within 1 degree & all is well. Removed the T-case drop too so gained an inch of clearance.

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