TC Vibration, Rear Pinion Angle Help

[marcussly27]

I just got off the phone with Advanced Adapters (they're very helpful by the way) and they are wanting me to adjust my rear pinion angle. So the story is I have a small rattle/vibration when accelerating at low speeds (guessing it's there when I'm going 70+ but I can't hear it). When I hear the rattle, I pull down slightly on the rear axle shifter and it stops. I thought I was going crazy but my wife heard it as well, and after speaking with AA they provided this feedback... "the rear pinion angle needs to be straight inline with the drive shaft, see if the axle can be rotated up". So how do I accomplish this? And based off of the images I attached, is there any other feedback to help the situation? Thank you!

 

[Apogee]

Based on the last picture, the angle of your driveshaft at the pinion appears to be near zero, so I'm not sure what you can adjust. With that said, most would recommend that you run 1-2 degrees of down angle at the pinion to account for pinion rise under load (assuming leaf springs) and so that the u-joint caps rotate ever so slightly on the cross to aid in lubrication and load distribution between the roller elements, this is assuming a double-cardan at the t-case.

Everything in your pics looks new, so it's possible you have a tight u-joint or maybe a transmission rattle (what are you running for trans?) or something along those lines. How many miles do you have on the new components?

 

[DirtDonk]

A gearbox noise can easily come from a slightly too high or too low pinion angle.
Based on your description of it happening under acceleration, your pinion angle would be too high already.
I agree with apogee that it looks virtually straight into the driveshaft at this point, which is in fact too high on a bronco. Advance Adapters is thinking more along the lines of a jeep with four link suspension where the pinion does not climb or drop much at all during acceleration/deceleration.
Whereas ours with leaf springs changes quite a bit. So if yours is starting at a straight position it’s too high already.

Definitely want it 1 to 2° down and that should theoretically eliminate the vibration on acceleration.
Any more than 2° and you end up with a vibration on deceleration instead.

The angles are usually adjusted with tapered shims. However, with only a 1 to 2° adjustment necessary on yours, I’m not sure what degree shim you want. Probably a minimal 1° shim.
Very hard to find probably and I think 2 1/2 used to be the minimum in the old days.
Probably someone makes a one degree taper, but that’s a pretty thin wedge!
I don’t know how thick it would be, but I think that’s what you need.

How about some more details while we’re at it. Looks like a fairly tall lift? How high is the suspension lift? What transmission along with that transfer case? Looks like an atlas?

And while we are at it number two, how about some pictures of the rear driveshaft and pinion from straight on sideways?
Camera angles are very skewed sometimes on the computer screen and phone screens, so a couple of straight side shots (if that’s not what those others were) would be helpful.

Thanks!

 

[Oldtimer]

And a straight on picture of taper shim currently installed.

 

[DirtDonk]

Good call!
With a shim and a block already, you have some fine-tuning available to you either with different parts or with some minor machining of existing parts.

But again, how high is your lift? In some cases a really high lift is going to be hard to get away from a vibration under all conditions simply because of the overall angle of the driveshaft being too steep.
Longer transmissions and high lifts are often incompatible and short wheelbase vehicles.

 

[marcussly27]

Gosh I love this place. Really appreciate all the help guys. So in the rear, I have a 3 inch lift total with 1/2 inch of that being the block which we added because of my large 285s which I'm swapping out for 265s, so that 1/2 block can be removed now leaving the 2.5 SL and 2 inch body lift which should keep the truck level as it's currently slightly 1/2 higher in the rear. I needed that lift combo to fit the Coyote Gen 2 and 6R80 trans. It is indeed an Atlas TC as well. Here are some photos, let me know if you want more. I believe some settling has occurred with the leaf springs which is why this rattle/vibration is new? The truck only has 1,500 miles on it. I drove it from July through October last year before the PS pump blew and I just got it back on the road a couple weeks ago after having some other items addressed. Still working through some kinks with my builder. Thanks

 

[DirtDonk]

Thanks for the additional pictures.
This new one of the rear driveshaft (#3) looks to me, if anything, like the rear pinion angle is too high. That would certainly explain vibration under acceleration.
The driveshaft angle looks far too steep for a typical 2 1/2 inch lift, but the 6R80 / Atlas combination would I believe explain that.

Your spring packs already have the tapered shims installed. That would initially be considered a good thing, but perhaps the heavy modifications elsewhere are what is driving the vibration.
Normally the shims used with this type of spring dial-in a stock set up in perfectly. You are no longer stock in anyway regarding most of the drivetrain however, so more custom touches might be needed to get the driveshaft lined up perfectly.
The same details mentioned earlier with the pinion angle down 1 to 2° from the driveshaft centerline still apply.
You just have to work harder to get there than normal.

 

[DirtDonk]

Oh, and I meant to mention, while you’re rooting around under your vehicle, take some additional measurements just to see where your suspension is really sitting now.
Put a tape measure between the top of the axle tubes and the bottom of the frame rails front and rear, and check the measurement against expected stock.
Generally stock height measurements are approximately 7 inches in the front and 6 inches in the rear. Anything over that is your lift and you can then verify how close you are to the 2 1/2 expected.

Just some more data to have for diagnosing issues.

 

[marcussly27]

I’m pretty much 3 inches of lift on the nose per this measurement. So what I’m thinking is I will remove the half-inch block and then adjust my rear pinion angle to get the 1 to 2° drop and that should solve my problems correct? Not sure how much that half-inch will matter with the angle of my driveshaft but it will help I believe. I should have a leveled out Bronco at that point because currently it dips slightly in the front compared to the rear. Thanks!

 

[bax]

That set up looks pretty good. Front pinion is off but that's another can of worms. Yes it looks like the rear pinion angle could come down just a little. But right now it better than 80 percent of the broncos out there. I have to question the noise. Pulls down a little on the rear shifter and it goes away. The Atlas will make noise if the shifters are out of adjustment. I would take a good look at that also.

 

[DirtDonk]

Sorry. That, that comment was meant for another thread so I’m not sure how it got here.

 

[bax]

Sorry. That, that comment was meant for another thread so I’m not sure how it got here.

I completely understand that Mr.Donk. As busy as you are you were bound to miss post eventually.

 

[DirtDonk]

I’m just surprised it hasn’t happened more often!
I’ll just blame it on my phone anyway…

 

[marcussly27]

Alright I think I have my marching orders. Remove the 1/2 inch block in rear, correct pinion angle to be 1 to 2 degrees down from center on drive shaft. Correct? I'm also moving to the 265 tires from the current 285s. Any thoughts on having a level bronco from a slight rake? That's where I'm headed in removing the 1/2 in the rear.

Thanks everyone

 

[marcussly27]

Also this is off topic, but what do you guys think about my front end set up? She handles pretty well but I'm insanely particular so if there's any tweaks to make it handle better I'm all ears.

 

[DirtDonk]

Alright I think I have my marching orders. Remove the 1/2 inch block in rear, correct pinion angle to be 1 to 2 degrees down from center on drive shaft. Correct?

Yes.
With that steep of an overall angle on the driveshaft, I'd probably try to keep it slightly under 2 degrees.
No science fact though. Just a gut feeling.

Any thoughts on having a level bronco from a slight rake? That's where I'm headed in removing the 1/2 in the rear.

Sounds fine. This is completely personal preference though, as Broncos came from the factory either level or with a slight rake. Depended on options and the individual Bronco. Mostly level was the more common stance I'd say, but a rake was not unusual.
Especially with roadsters, half-cabs and wagons with the top removed.

Paul

 

[DirtDonk]

Also this is off topic, but what do you guys think about my front end set up? She handles pretty well but I'm insanely particular so if there's any tweaks to make it handle better I'm all ears.

Good to see pics! How much have you actually driven it?
Does not look like it would work well overall, but not horrible for very short jaunts to check it out. Might not notice the misalignment of the trackbar and draglink right off the bat, but eventually it will rear it's ugly head.

Your draglink's overall angle looks very good, from using a dropped pitman arm. And it's got the right angle down at the tie-rod end where the grease fitting is pointed upward into the radiator area.
But the upper trackbar mount was not lowered to match. Yes, you have an adjustable trackbar which allows you to fine-tune the sideways location of the axle. But if you use a dropped pitman arm you must also use a dropped trackbar bracket to keep the angles as close to parallel as they can be.
So add a trackbar drop bracket to your list of things-to-do and you'll have even better handling and steering on the street. More "linear" feeling and less likelihood of bump-steer and wallowing.

You can fine-tune things like toe-in later as you drive it and get used to it's quirks.

Paul

 

[marcussly27]

Now that I have a better understanding of my front end and what needs to be done, I'm thinking I will eventually want to go with a TRO configuration along with a trac bar riser (rather then a drop). That should produce a better overall driving experience correct? From the pictures I've posted is there anything else that I should consider? Aside from the riser what else do I need?

I admittedly might be overthiinking this. Maybe just get the riser and call it a day?

One another note, I downsized to the 265s, removed my rear 1 inch blocks and I have absolutely no TC vibration/rattling issues. Some of that rattling might have been in my head. Plus it looks a lot better with the smaller tires, and I have NO RUBBING which feels so good. These new BFG Trail Terrains are really nice, much quieter on the road but they still can be mistaken for KO2s which is a plus. Thanks for your feedback on that one.

 

[reamer]

Mount your phone so it can take a movie of the pinion and drive down the road. accelerate normally and brake too. Do this a few times and You'll see the yoke possibly shoot up. (mount the phone securely)

 

[DirtDonk]

Now that I have a better understanding of my front end and what needs to be done, I'm thinking I will eventually want to go with a TRO configuration along with a trac bar riser (rather then a drop). That should produce a better overall driving experience correct?

No.

From the pictures I've posted is there anything else that I should consider?

Yes. Rotate your tie-rod so that the draglink's lower Zerk fitting is pointed up at a 60° angle. Or generally up at the bottom of the radiator.

Aside from the riser what else do I need?

Instead of a riser and re-thinking everything, just get a drop bracket to match the dropped pitman arm and call it a day.
You'll have to weld, which will mess up your nice new paint/coating, but you'd have to do a lot more with a riser. And then you'd have to mess with the pitman arm again anyway.

I admittedly might be overthiinking this.

Yep, I think so.

Maybe just get the riser and call it a day?

Or not, and call it a shorter day so you can spend less money, time and the frustration when it does not improve things as much as you expected.

One another note, I downsized to the 265s, removed my rear 1 inch blocks and I have absolutely no TC vibration/rattling issues. Some of that rattling might have been in my head.

Congrats on a big success! It might have been in your head, but likely as not you were actually feeling something and got rid of it by downsizing slightly.
What tire size did you go with? Just a bit at maybe 255's or 245's?

These new BFG Trail Terrains are really nice, much quieter on the road but they still can be mistaken for KO2s which is a plus.

Have you had time to play with air pressures yet? What are you running currently?

In the meantime, rotate your tie-rod by loosening the three clamps, twisting the center section "up" a bit to get the draglink pointed more upward, and then lock things down tight again.
Then the need for a drop bracket will be even more apparent than it is right now. You can clearly see in the last pic that your bars are not parallel because of the use of the dropped arm without the drop bracket.

Paul