Another question about a HP rear

[Joker11]

Matt,
I am running a ZF 5spd and a Behemoth Underdrive StrongBox and then a Dana20. The length, plus a 5.5inch suspension lift does become a crazy angle.

If it were stock trans, stock transfer case and no lift, yeah, I could see not having a crazy angle.

Based on my searching so far, I want to get a True Hi9 and keep the rest of the rear the way it is for now. I don't want to buy new axles, bearings, brakes, and all that would be involved. I want to correct the driveline first. Then go from there. So that rules out the Dana 60 for right now. Not forever, but for now.

 

[mattt]

Understood. That combo and lift certainly has some issues to overcome, but it sounds like you're on the path to a correct combo. My combo is AOD/AA Adapter/D20 which is longer than stock, but not long enough to get into pinion angle issues to address.

 

[kholding]

Mattt, it was actually Currie that welded the perches on at the stock angle. When I ordered the rear end I gave them all the info including my lift size. The ball got dropped, but it wasn't the shops fault at all.

 

[mattt]

Ok, I thought the rear axle was ordered by the shop to install in your Bronco. However, if you ordered it and drop shipped it there, and if the perches were already fully welded, then you're stuck. There would be no way for Currie to know where to reset the leaf pads to compensate for a lift. It's all determined once you install in the Bronco and set it on the ground on it's wheels. Now, had you asked Currie to just tack the leaf pads in stock position, it would've been an easier fix. Nonetheless, given how much effort was put into your build there, I would have expected the shop to suggest fixing or just take it on their own & fix that obvious pinion angle problem. Have you measured with the new HP9....you may still have pinion angle to correct?

 

[kholding]

Agreed. Lesson learned (one of many during the build). The pinion angle now is good. It all worked out but would've been cheaper to have done it right the first time!

 

[Joker11]

In a single shaft driveline, the pinion should be an equal degree as the plane of the transmission output shaft.

in a two piece driveline, your pinion angle is going to match the output of the cv joint. But the cv joint angle will depend on where the pinion is.

like a catch 22. I wonder which comes first, the chicken or the egg?

Or would you just measure the difference between the angle of the transmission output shaft and the angle of a 0degree pinion angle and split the difference?
So if the difference was 12 degrees, you would shim the pinion angle up 6 degrees and the cv joint down 6 degrees.

This makes sense.

When manufacturers make angled shims and stamp 6 degrees on it, that must be the angle of the shim, but the net effect at the pinion may not equal 6 degrees.

I can see why some driveline angles are so far off. You really need to be on your toes and get it right.

I really want to get it right the first time.

 

[mattt]

Agreed. Lesson learned (one of many during the build). The pinion angle now is good. It all worked out but would've been cheaper to have done it right the first time!

I hear you....been there, done that, on the lessons learned during my build. 2 steps forward & 1 step back means it takes forever....at least in my case ;D

I just finished mine up last month. The pic shows what a correct setup looks like.....if I remember correctly, I think we set the pinion down 2* to correct for leaf spring axle wrap when on the skinny pedal. I would still put a protractor on yours just to verify, even though you now have the HP housing. Since you haven't messed with the housing/leaf mounts, a few degrees off might be hard to see to the naked eye.

Lots of good info here, http://www.4xshaft.com/ Click Tech Info(upper right corner) and at bare minimum read Geometry 101.

 

[DirtDonk]

Right you are Joker. We've had members here install them and report their changes, and I can't remember the precise change, but it's something like 9 or10 degrees for a 6 degree shim on one of our rigs.

And the real world doesn't always work according to the book. With pinion angle changes during use being so prevalent on Early Broncos, we usually just use "1° to 2° below the driveshaft centerline" as the simple rule of thumb. More often than not, more than two degrees down-bubble results in vibration upon deceleration, and less than one degree down (or anything above the centerline) usually results in vibration during acceleration.
For all I know though, that matches what you said!

We only offer the one size steel shim (6° http://www.wildhorses4x4.com/product/Steel_6degree_shims) because that's what most often fixes the standard issue with the modern thick leaf packs. But it's not going to be perfect for everyone. Just most, luckily...

Paul

 

[DirtDonk]

Gotta love consistency!
Looks like mattt's experience mirrors what most of us have found.

Paul

 

[Joker11]

Now my issue is which way to go. Currie has a reputation and a history.

True Hi 9 has had some bad word of mouth. Their gears are unique and not interchangeable with a factory 9inch case.

I am not a competitor or a hardcore rock crawler. I don't want to beat up my ride. But I want it to be trailworthy.

Argh....

 

[bax]

my hi 9 has been doing fine for 2 years. no issues other than a leaking ARB seal.

 

[Joker11]

Bax, the ARB air locker seal?

I never intended on an air locker. I wanted to stay with my Detroit.

Now I am going to start a new thread on the question of a front locker. I don't want to derail this thread with it.

 

[bax]

yes the air seal on the carrier was leaking. Front should be a LS unless you are using it off road a lot. Then a detroit or a selectable is a good option.

 

[DirtDonk]

Currie has a good reputation and history as a company, but you still have the known limitations of their high-9 to deal with and factor into your build. What have you heard about True Hi-9 that is negative? I'm curious as I have not heard anything.

Now what about gear ratio? Does the 8.8" gear set that Currie uses have "small pinion syndrome" where the pinion gear gets smaller with lower ratios? Like Dana axles, where there's a point of diminishing returns, this might end up being pertinent to your decision.
Depending on tire size, the typical Dana 44 can handle up to 4.56 or 4.88 without too much issue, as long as you know not to abuse it. Jeep guys bust their 4.88's all the time though, so it's something to think about. Worse in a D30 of course, and less of an issue in a D60, but what do we know about the 8.8 and it's ratio/strengths?

On the flip side of that coin, if you're running a higher ratio with larger tires, that puts more stresses between the t-case and rear end as well. Does that put undue stresses on a pinion shaft then, with 3.50 gears say?
Then again, your uber-low gearing with the 1st gear of the 4500 and the gear reduction box, then the 2+ reduction of the D20, if big tires and tall gears, a weak gear set in the rear end might be an issue even in light wheeling if you have a healthy motor and heavy right foot.

Just throwing out some thoughts that popped into my head for discussion. Don't really know any of that might pertain to your setup, but deciding between the two brands might come down to strength after all, in spite of company issues.
And doesn't Currie recommend a tire size of 33 and smaller? Or is it 35 and down? Even if 35 that puts you at or near their own rated limit, which might make all that other stuff you're running and planning come into play in your decision again.

That should keep you tossing and turning at night for awhile!

Paul