1973 Bronco with 3.5" Duff Suspension Lift

[wake2wake]

Looking for input to everything I may need to do with installation of a James Duff 3.5" suspension "System B" with Heavy Duty Leaf springs instead of add-a-leafs.

http://www.jamesduff.com/eb/suspension_systems.html
It comes with:

3.5" Progressive Rate Coils,
6.25° 14 piece Bushing Kit,
heavy duty leaf springs,
Tracking Bar Drop Bracket,
U-Bolts, 4 Shocks & Boots

The website states no other changes are needed, however I have discovered reading some posts that this is not exactly true.

I have some vibration and have noticed my steering "floating" and pulling.

I recently installed 4 degree shims and was going to rebuild my rear driveshaft, however have learned that I may need to buy an extended driveshaft. I measured front of transfer case flange to front of rear differential flange = ~35".

I have not yet installed by drop bar bracket that came with the lift. I have read on some posts that in addition to the drop bar bracket I may need a drop pitman arm as well. In addition, I have read and received some input I may need an adjustable track bar.

Any insight/input from someone who has installed this type of system that could refer me to what components I may need and any helpful pointers would be greatly appreciated.

Thanks.

 

[DirtDonk]

Hey Wake, welcome! Sounds like you've been doing some good reading.

In my opinion, on your year EB, you ALWAYS need a dropped pitman arm if you're going to use a dropped trackbar bracket. The whole point is not only to keep the angles of the different links as shallow as is reasonably possible, but also to keep them as close to parallel as possible too.
So in lieu of any other mods that might effect things, I agree you need both.

The adjustable trackbar is not a necessity, as much as a very desirable option. As you have probably seen too, we're always claiming that "every Bronco is different" so while most won't absolutely need an adjustable bar, some might actually be borderline where it's not only a good idea, but necessary if they're going to get the axle precisely in the center.

That's the kicker, and what makes it more of an option. Your axle might not even have been centered from the factory! After the lift, the axle shifts to the driver's side. After the installation of the drop bracket, it's "supposed" to come back to center. But it doesn't always come back the exact amount it moved. It's a good guess, and probably is close enough for 99% of owners, but it might not be perfect.
There's just no way to tell where it's going to be until you're done, and get out the old tape measure and plumb-bob to see where yours sits.
The adjustable bar simply lets you fine-tune out any discrepancies, and has the side benefit of allowing you to twist the upper eye to perhaps more easily line up with the angle of the upper trackbar bracket too.

It's all good, but if you're on a budget you can certainly wait until you're sure you need one.

Paul

 

[DirtDonk]

Couple more things...

I have some vibration and have noticed my steering "floating" and pulling.

When does the vibration happen? All the time, or just under accel/decel?

I recently installed 4 degree shims and was going to rebuild my rear driveshaft, however have learned that I may need to buy an extended driveshaft. I measured front of transfer case flange to front of rear differential flange = ~35".

Here's another perfect example of every Bronco being different. I'd say about 80% of 3.5" users do not have to replace the shaft. But the other 20% do. Just the luck of the draw, or some other design parameters on the install of the lift kit.

Are your 4 degree shims, a tapered shim under the leaf springs? Is the rear pinion pointed up almost into the centerline of the driveshaft? If so, and you still have a 35" measurement, then yes, you need a new one.

I have not yet installed by drop bar bracket that came with the lift. I have read on some posts that in addition to the drop bar bracket I may need a drop pitman arm as well.

There's a big part of your vague steering feel. The now much steeper angle on the draglink and trackbar are having their way with reducing the directness of any steering input. You were correct to not install it without the pitman arm, but not having either of them installed before driving is giving you that loose and waffling feel.
Not only that, but because your axle is undoubtedly off-center by enough to make a difference, and your stock draglink can't compensate for the change in it's effective length needed to bring the steering gear box back to it's center position, your box is contributing to the weird steering feel too.
It's got a very important "on-center" position that needs to be maintained for the best road manners.

And your toe-in could be not quite right for your setup.
And your air pressures could be slightly off for your setup (did you change tires and wheels too?)

Just some more stuff to think about.

Paul

 

[DirtDonk]

Oh, and last, but not least... Caster.

You do have their bigger 6.25° C-bushings, which is good. But without knowing exactly what your caster reading is now, you don't know if that's not part of the trouble too.
Ideally you'd want something like 3 to 4 degrees "positive caster" for a mild street rig with modest sized tires, but you probably have something more in the 1 degree range. Maybe two if you're lucky.

So even though the deed is done, it is always good to know what your caster readings are. When you get a chance, take it to an alignment shop and have them give you a printout of your alignment specs. Since they won't be adjusting anything (unless you want them to set your toe-in) it shouldn't take but a few minutes and not cost too much.
Theoretically...

Good info to have for future reference or when tracking down some other handling gremlins.

Paul

 

[DirtDonk]

Guess I'm on a post-whoring quest tonight!
I forgot to mention the more important adjustable linkage bit. The draglink.
When it all comes down to it, an adjustable draglink is the best way to make sure that no matter what height variations you have with new/old springs that might sit inconsistently with their advertised lift, or over the years might sag out a little bit, an adjustable draglink lets you always center your steering box at ride height.

That's the basic function of the dropped pitman arm too, but they're by design an imperfect method. They do a good job of getting the working angle back down to a reasonable level, but are only so good at keeping the box on-center.

Paul

 

[surfer-b]

Donk has covered all the steering and vibration probs but I will suggest that you add extended brake lines from the frame to the axles if you have not already done this, just a safety precaution.

 

[wake2wake]

Thank you both for the great feedback.

The vibration starts around a speed of ~45mph.

Your "loose and waffling feel" explains the steering well, it is not a good feeling...

I will place some orders and get back to you after install. I will plan on purchasing extended center brake lines, dropped pitman arm, and extended rear driveline and then take the measurements you mention to determine if I need an adjustable track bar.

Thanks again.

 

[DirtDonk]

As you may also have come across here, are suggestions to do "the test" that we sometimes end up performing every time the Bronco does something to make us suspicious of the front end.
That's to have a helper row the steering wheel back and forth just enough to make the tires turn (more like a wiggle) just a bit in each direction.
You need to do this with the full weight of the vehicle on the ground, and just have the helper keep doing it while you lay/sit under the front bumper and watch every bit of linkage from the input shaft to the box, the frame where the box is bolted, to the draglink and tie-rod ends, to the ball joints and wheel bearings. And even the c-bushings and any other connected bit you can think of.

With the torque of the steering system applied against the weight of the vehicle on the tires, if anything is loose or worn out, you're going to see it with this method. It's used often as a very accurate diagnostic tool. One that just looking at, or pulling on by hand just can't duplicate.

Try that and see what all, if anything, is even slightly loose under there.

Good luck.

Paul

 

[wake2wake]

Pinion Angle and Universal Joint Operating Angle

I ordered and installed parts, however there is still a vibration issue.

Some updates since the last post (time flies...)

Installed:

• dropped pitman arm
• dropped trackbar bracket
• new extended rear driveline
• new extended front driveline

I have re-measured the pinion angle (thank you 70_Steve thread), however from what I have read on other posts I am a bit confused by the pinion angle and the Universal Joint Operating Angle. The two seem to be contradictory to one another, however I am new to this so any input would be greatly appreciated.

The angles measured are below (with the 4 degree shims in place)

Rear Yoke (differential) Flange Angle - 15.5 degrees (90 degrees vertical)
Driveline - 22.5 degrees
Front Yoke (Transfer case) Flange Angle - 3 degrees (90 degrees vertical)
Top of driveline (rear yoke to front yoke) = 35"
Bottom of driveline (rear yoke to front yoke) = 34.75"

Thanks.

 

[Whoaa]

Did you have this "same" vibration before the lift, or only after the lift and new parts were installed?

And kindly describe the vibration the best you can, there are only so many things that can cause this; wheel bearing, driveshafts, input/output shaft, bum pinion angle, a foul running engine, bent wheel..........

 

[DirtDonk]

The most important angle for our double-cardan style driveshafts and leaf spring rear suspensions is the relationship between the centerline of the driveshaft itself and the rear pinion. Pinion should point almost straight up into the centerline of the driveshaft.
Roughly 1° to 2° below the shaft centerline works best.

Your readings on those two seem suspect, but it's hard to wrap my head around.
If you take level ground as 0 degrees, and vertical as 90 degrees, how are you arriving at the 15.5 number at the rear yoke's surface? Are you basing it off the vertical, or the horizontal?
If we take the down angle of the shaft, and the up angle of the yoke face, assuming they would be at 90 degrees to each other with the pinion pointed straight up into the shaft, then are you saying your numbers indicate a difference of 7 degrees? Is the pinion pointed up or down compared to the shaft?
Either way, you're still way off. Need to get that difference down to about 2 degrees.

For our purposes here, ignore the upper joint angles for now, and just compare the shaft angle to the pinion angle. Basically the two shafts to each other.
Here again "assuming" a standard double-cardan shaft like would have been stock on an EB. It's not unheard of for them to be changed out for the more common (at the time) single-cardan style shafts, with only one joint at each end.

Any chance you can take some pics of your rear driveshaft, including the rear pinion directly from the side?
Pics lie when it comes to angles, but we can get a better grip on things with pics anyway.
Sometimes...;D

Thanks

Paul

 

[wake2wake]

Thank you Paul. I read up on how to attach a photo. Please see diagram I drew up to show the angles and length dimensions. The left side is the differential yoke and the right side is the transfer case yoke. The angle of the differential is 22.5 degrees I have the driveline removed right now, however if it helps I can re-install and take a picture later this week.

As for a description of the vibration. I do not remember the vibration prior to installing the new components, however at the time I was installing the new components I also had the transmission rebuilt (and re-installed). The vibration seems to be coming from under the driver/passenger seats and starts around ~45MPH and increases as speed approaches ~55-60MPH. It has been some time since I drove it, however I believe I remember feeling some vibration in the steering wheel as well. I would take it for a spin again, however am in the process of installing a new auxiliary gas tank.

 

[DirtDonk]

Thanks for the drawing. And yes, when you get a chance a pic of the setup with shaft installed might still help. But in the meantime, by your diagram I'd say you're still 5 degrees too low on your pinion angle.

IF you have a double-cardan style joint at the top (still wanting to make that clear since we haven't seen it yet, and some have been changed over the years) then you want to bring that rear angle upwards about 5 to 6 degrees to put the pinion at roughly 1 to 2 degrees down-bubble from the centerline of the drive shaft.

Depending on the thickness of your spring pack (how many leaves do they have?), you won't need as much shim angle. In other words, a 6 degree shim might rotate the pinion up 10 degrees. Due to the offset from the axle centerline of the spring perch at one end, and the pinion gear at the other.

Paul

 

[wake2wake]

Thank you Paul. I will try to put back together and take a picture later this week.

Yes, it does have a double-cardan style joint at the top. The James Duff HD Leaf Springs have 11 leafs. Any guidance on what degree shims may be needed would be greatly appreciated. I do have 4 degree shims installed now, which plays into "only" having a difference of 7 degrees (22.5 minus 15.5). Let me know if there are any additional measurements I can take to assist with making the best estimate for what degree shims I may need to get that angle down to the 1-2 degrees suggested.

Thanks again,
Casey

 

[wake2wake]

Some photos of the angles.

 

[Crush]

That looks pretty good to me. Just by the eyeball

 

[DirtDonk]

the first two pics do make it look pretty good. The third is kind of iffy, but pics like lie a dog when from different angles!
it certainly looks driveable at this point.

Usually we find that a 6° shim is what's needed, so your 4 isn't too far off. However, a degree at the spring perch nets more than that at the pinion (off center and all that) so that last two degrees might just put you in the sweet spot.

Another thing is that yours looks kind of high in the pics too. Might be just my eye, as again, every angle puts a different spin on things.
Is it sitting at the expected ride height at this point? If not, all bets are off as to what your angle is, as that changes (at least a little) by the height.
If we have not discussed that aspect yet, measure from the top of the axle tube to the bottom of the frame rail and you should expect to see approx. 9.5" at that point.
If it's more, then it should settle some before the final tally. If it is, then drive around and see what it feels like.

Paul

 

[DirtDonk]

And one more thing.... (ain't there always?)
When driving and you feel the vibration, does it get worse under acceleration? Or deceleration? Or do you detect it at that speed you mentioned just under trailing throttle (light cruise) instead?

If you can add those details, we might be able to send you down the right steps.

In general terms, if the pinion is low in relation to the driveshaft, you will get vibrations under light to no throttle.
If the pinion is high (yours certainly doesn't look like it qualifies for that) you will feel more vibration under acceleration.

Good luck. Might just need 6 degree shims, or you might just have to start looking in another direction!

Paul

 

[wake2wake]

Thank you for the replies.

I measured distance from the top of the axle tube to the bottom of the frame rail and got 10.75 inches, you have good eyes to pick that up! Does this have to do with the new HD leaf springs? I do not have a hard top, so it is probably lighter than typical.

With regards to everything looking OK visually, remember that I measured a pinion angle of 7.5 degrees (with 4 degree shims in place). Just wanted to make sure I do not need to bring it down to that ~2 degree angle.

I remember feeling the vibration in acceleration and deceleration, however I do remember the vibration being worse in deceleration (or coasting), if I accelerated the vibration would dampen a little.

I have been waiting to purchase parts until I get feedback, so I am not able to drive right now. I could either get 6 degree or 8 degree shims and then re-test it out. I was also thinking of ordering an adjustable tracking bar, any other parts you would suggest with the 3.5 suspension lift that I did not list previously?

Thanks.

 

[DirtDonk]

Yes, likely a little high due to both the springs being newish and the hard top being off. Even with stock springs, the rear would rake up a bit when the top was removed. More on some spring packages than others.

While it will change the angle slightly, usually this 1" height difference is not enough in itself to cause a bad angle and once you dial it in for one height, it's usually good for the other.
And yes, judging by the pics, and judging by the fact that it's worse in decel, I would say your angle readings are correct and that you still need some more angle correction.

To that end, you or someone is either going to have to do the math/geometry, or you're just going to have to keep trying shims until it's right on the money. With our springs (very similar to Duff's in overall thickness) the 6° shims are just right. And with the fact that the pinion angle changes more than the degree of shim you install, that extra two degrees of taper might just do the job.
No way for me to tell from here though, since we all know my geometry skills went out the window decades ago.

Maybe the best bet at this point, so you don't have to keep buying parts and doing the install labor, would be to experiment with what you already have. Loosen the u-bolts so you can rotate the axle and measure the amount of change it takes to reach that 2 degrees down from the centerline.
With some inconsistencies of the manual method factored in, I would think you could reach a pretty reliable conclusion by hand. If changing the angle at the springs by 2 degrees more (mimicking the 6 degree shims) puts your pinion down in that sweet spot area, then there 'ya go.

I don't remember larger shims being available, but that might not mean anything. 2's, 4's and 6's are the common aluminum cheapies I remember, with some companies even offering 1/2 degree graduations. And there are some companies that do sell steel like us, but in variations that we don't offer.
I would avoid the typical aluminum ones unless you find some that are thick and robust and look quality made. The simple cast ones with ridges that we normally see tend to not work well on older trucks like our Broncos.

On a side note, I can't tell by the pics because I can't see the eyes of the leaf packs, but presumably you have the double-wrap eye to the front (frame) and the standard or Berlin eye to the rear (shackle) ends?
I don't think this would make a difference in the angle of the dangle, but it does effect how things work overall. So just making sure...

Good luck.

Paul