Rear Pinion Angle

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Joined
Aug 24, 2012
Threads
19
Messages
132
Location
Texas
Website
www.reddirtoffroad.com
I've been searching up and down but can't find any info on the pinion angle. What does everyone have it set to? -1°, -2° etc? I know we don't want them zeroed out due to the pinion pushing up under acceleration. No performance mods just re-geared.

The shop is asking and my service manuals are at home.

Thanks!
 
By pinion angle did you mean the delta of the angle between the TC and the rear diff? You wont be able to change this without adjustable control arms. Is the vehicle lifted? I just re geared and installed a locker in my lifted 100. I can assure you there is no mention of any specific angles in that particular area from the FSM, ARB, or Nitro.
 
Yes. Well, technically between the center diff and the rear diff. Yes I have a full new link system. And yes she's lifted - with lockers and 4.88 gears.

I know they won't have an angle since it wasn't adjustable and adjustment changes depending on lift height. I'm just looking for someone who has adjusted to see what they did.

I'm pretty safe at 1-2 degrees. Just wanted to double check.
 
Post 2.0" lift I found I had some slight driveline vibes above 65mph. I could feel the vibes on acceleration then they go away off throttle which points to driven member (output flange Ujoint). First off I checked my U-joint working angles. I went to measuring the operating angles of the rear driveline, and found my pinion(rear) is wrapped too far upward compared to the output flange, the cause of the phasing imbalance.

I should have measured angles pre lift to compare against, but it drove smooth so I didnt think to measure them. Maybe someone with a stock rig could do this sometime.

Lift details: 2" ironman lift: Toy13b 2" rear springs, Ironman TBs , Ironman FoamCell pro shocks, 2" extended rear sway links
33" BFG KO2 275/70-18

Here are the post lift driveline angles:

Output Flange(trans) angle: 0.5 ( darn near straight as an arrow)
Prop shaft angle: 4.8 degrees
Rear Pinion angle: 4.6 degrees

Operating angle 1(propshaft angle - output flange angle) : 4.8 - 0.5 = 4.3 degrees
Operating angle 2 (propshaft angle - pinion angle): 4.8 - 4.6 = 0.2 operating angle


The difference between the 2 operating angles is 4.1 (it should be less than 0.5 degrees.)

If I have this figured correctly, I need to rotate the diff/pinion downward 4 degrees to offset the operating angles parallel to each other, and maybe another 0.5 degree down to compensate for minor axle wrap. I've read that 4 link suspensions dont wrap upward much under acceleration, especially on our under-horsepowered 100's.

I am wondering how the pinion got so far off on a 2" lift. Is that a normal variance? My control link bushings are prob toast which probably doesnt help. But there's not too much discussion here in the 100 section about correcting pinion angles to make notes from, and nothing noted in the FSM either (cause there nothing to adjust). Some shops just recommend replacing the ujoints and rebalancing the drive shaft as part of a lift; but that doesn't address or correct out of spec operating angles which will cause premature ujoint failure and other drive line issues: both diff and trans.

I have MT adjustable Upper (& Lower ) rear control links on the bench to install- this should help correct the pinion angle, hopefully completely.

I'm wondering what more experienced 100 owners have done about this issue or given it thought?

Would appreciate any experienced input here.

Thanks
 
Post 2.0" lift I found I had some slight driveline vibes above 65mph. I could feel the vibes on acceleration then they go away off throttle which points to driven member (output flange Ujoint). First off I checked my U-joint working angles. I went to measuring the operating angles of the rear driveline, and found my pinion(rear) is wrapped too far upward compared to the output flange, the cause of the phasing imbalance.

I should have measured angles pre lift to compare against, but it drove smooth so I didnt think to measure them. Maybe someone with a stock rig could do this sometime.

Lift details: 2" ironman lift: Toy13b 2" rear springs, Ironman TBs , Ironman FoamCell pro shocks, 2" extended rear sway links
33" BFG KO2 275/70-18

Here are the post lift driveline angles:

Output Flange(trans) angle: 0.5 ( darn near straight as an arrow)
Prop shaft angle: 4.8 degrees
Rear Pinion angle: 4.6 degrees

Operating angle 1(propshaft angle - output flange angle) : 4.8 - 0.5 = 4.3 degrees
Operating angle 2 (propshaft angle - pinion angle): 4.8 - 4.6 = 0.2 operating angle


The difference between the 2 operating angles is 4.1 (it should be less than 0.5 degrees.)

If I have this figured correctly, I need to rotate the diff/pinion downward 4 degrees to offset the operating angles parallel to each other, and maybe another 0.5 degree down to compensate for minor axle wrap. I've read that 4 link suspensions dont wrap upward much under acceleration, especially on our under-horsepowered 100's.

I am wondering how the pinion got so far off on a 2" lift. Is that a normal variance? My control link bushings are prob toast which probably doesnt help. But there's not too much discussion here in the 100 section about correcting pinion angles to make notes from, and nothing noted in the FSM either (cause there nothing to adjust). Some shops just recommend replacing the ujoints and rebalancing the drive shaft as part of a lift; but that doesn't address or correct out of spec operating angles which will cause premature ujoint failure and other drive line issues: both diff and trans.

I have MT adjustable Upper (& Lower ) rear control links on the bench to install- this should help correct the pinion angle, hopefully completely.

I'm wondering what more experienced 100 owners have done about this issue or given it thought?

Would appreciate any experienced input here.

Thanks

My angles sound just like yours with a 2" rear lift... the rear diff is almost inline with the rear drive shaft. I'm betting this is where my vibrations at highways speeds (under load only, just like yours) are coming from. Gonna pick up some adjustable lower links and see if I can't beat the crap out of this gremlin.
 
I learned heaps during this project.

Yes adjustable links will fix pinion angle alignment; uppers more effectively than lowers, and together (adj. upper & adj. lower) requires less in/out adjustment per link arm. Be aware that the MT Upper links currently have virtually no inward adjustment to make them shorter than OEM (only about 5mm). I say currently, because next run MT are going to shorten the body on the uppers by 12mm to add more inward range of adjustment. MT was responsive to input from my install notes.

Determine your operating angles (see my previous post) This maybe widely overlooked on most 100 lifts, or at least not discussed. But just a couple of degrees out of phase and you'll get vibes, and things will only get worse over time if left unattended. Good idea to take before & after measurements. There is a good 1.99 Iphone app that you can use to get your angles: Plaincode development: Clinometer. Tremec also has a free driveline angle app. But with the size of the phone and getting a good flat surface read on the flanges its not so easy. Best solution for about $30 HF sells a very good, small digital angle finder with magnetic mount- fits on the output flange & pinion flange between the bolts perfectly. HF Digital Angle Finder

I think in most cases with lifted 100's that pinion will need to be corrected downward. How much depends on tire height & spring height. In my case it was 4 degrees off. To point pinion angle downward, you need to shorten the uppers, or lengthen the lowers to get the same result. The challenge with trying to adjust the pinion with just the lowers, is that it will push the axle back more than rotating the axle downward. Depending on how much you need to adjust it could move the axle back far enough that with oversized tires you might have clearance issues in the backside of the wheel well. Adj. upper links will rotate the axle more directly if that makes sense. Personally I think budgeting to replace both upper & lower at the same time is the best solution.

The end result was I shortened the uppers -5mm compared to OEM stock length, and lengthened the lowers +5mm compared to OEM stock length. This dropped my pinion 4.5 degrees. I got really lucky on the first try. So in my case 2mm link arm adjustment to 1 degree angle change. There may be different results with just adjusting uppers or adjusting only lowers.

There is a decent thread on Upper & Lower link install here: rear upper and lower control arms

If you want to study pinion angles this is a good overview resource: Pinion & U-Joint Angles
 
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Thanks for doing all the work and write up. This will help a lot and takes a lot of guess work and trial and error out when doing this for the first time.

Did MT give an ETA on the shorter uppers?
 
Remarkably better, vibes are for the most part gone. I have some very slight feedback in the driveline that is constant: it may be the fronts, or possibly the rears giving early warning, but it is so slight its hardly noticeable. At least I know my rear driveline is in optimal alignment.

My truck has 171k and I just finished the lift by adding the rear springs a couple of weeks ago to make ready for a new rear bumper & tire carrier. I drove it for a few hundered miles with that 4 degree offset before I fixed it. That may have been just enough excessive torque and oscillation to accelerate the wear on my already tired cap bearings. I have new U-joints ready to install for both driveshafts, but I wanted to get the operating angles sorted out before installing new parts.

I dont know when MT will be making new production, reach out to John or Mark to find out. You could ask them to machine off 10-12mils for you if they still have existing inventory. I made do with mine, splitting the difference between upper and lowers and it worked out ok.

When it comes to installing the link arms there are several tips to make the job easier. I will add my learnings to the other thread (rear upper and lower control arms) when I get a little more time.

Good luck-
 
I ran into the same issues with the uppers. I had to then resort to extending the lowers to continue to rotate the pinion downward. I went 3 degrees and should have done another 1-2 additional. I'm about to put on some new lowers from Rokmen Off-road that has their new in house EnduroMax™ Bushings. These are maintenance free, no greasing, and more comfortable than poly. They've cycle tested and these bushings will likely never need to be replaced - but can be if needed.

That being said, my MetalTech lowers will be available soon.
 
@abuck99 Do you happen to recall how many turns per joint you got for your ~5mm adjustment? I have almost identical measurements to yours and I'm about to make some upper and lower corrections... looks like I only have 1-2 full turns available on the uppers at most. I'll be mostly working in the dark so counting turns is preferred to actual measurement ;) Thanks a lot for your info, glad you got smoothed out and got MT to improve the design a bit.
 
@AimCOtaco

Sorry, I didn't keep track of turns I used measurements. On the uppers I turned them in as far as they would go ( and line up) which was -5mm compared to stock arm. I then added +5mm to the lower (combined total of 10mm). That yielded about 4degrees of pinion angle correction. Kind of got lucky on the first try.
 
@abuck99 Do you happen to recall how many turns per joint you got for your ~5mm adjustment?
Just finished installing Metal Tech's: 1 full turn on lower + 1 full turn on upper = 1 degree of rotation
Starting rear pinion angle = 4.6 deg, End = 0.5 deg
Output flange = 0.5 deg
~ 2.5" lift
Hope that helps
 
Thanks a lot guys, I'm hoping to adjust once and check and not have to do it repeatedly. Having to do them all 1 at a time and then re-check would be tedious. I can tell by inspection that my uppers only have about 2 turns left in them so I'll go with 2 turns all around and get at least 2 of my 3 degrees tuned out. Some day when I have a bit more time or have the axle out I may turn down the uppers (turn on a lathe, not turn the Johnnys) a bit and tune out the last of it.

Thanks all,
 
Good luck and post up your results.
 
I was measuring a T-case flange to rear pinion flange difference of 3 - 3.5 degrees (didn't measure closely, just determined the need to improve). After rotating the rear pinion downward by shortening the upper links by 2 turns each and lengthening the lower links by 2 turns each I'm now measuring a difference of about 1.3 degrees. This is unloaded and half fueled so for typical loaded highway travel it will be a bit less and I'll check again next time I'm in full on fun mode.

For reference, this is with Metal Tech rear links, Slee Panhard, OME 864's, and Slee's Remote Reservoir Shocks. This produces a big lift even with drawers, full rear bumper, and roof rack. Very happy with how the rear is handling at this point.
 
Just ran across this post, I recently went through the same process. I was chasing down some vibrations and decided to measure my driveshaft angles. I have MT upper links and factory lowers (it's probably time to replace those too) and ended up cutting about 1/2" of of the tubing to be able to shorten them enough to get my diff pointed correctly. All better now.
 
Guys running MT uppers and lower links, have you noticed less suspension articulation now that everything is tighter in the rear? I noticed a more harsh ride after installing uppers and lowers and there also appears to be less suspension travel now that everything is tight. Has this been discussed anywhere? I did a search but could not come up with anything.
 
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I didn't notice any less travel with MT UCA and LCAs.

The johnny joints will allow a little more free articulation so it would be improved. Worn control arum bushings will provide a little more slop and that will deliver vague mushy back end- and maybe you're feeling that difference.
 
I didn't notice any less travel with MT UCA and LCAs.

The johnny joints will allow a little more free articulation so it would be improved. Worn control arum bushings will provide a little more slop and that will deliver vague mushy back end- and maybe you're feeling that difference.

Hmm, maybe that's it. I should have taken measurements before i install the MT components. Oh well....
 

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