Radius Arm Bushings for Duff Arms

[rcmbronc]

I am installing a 3.5" lift with Duff extended arms. I am wondering where to start with radius arm bushings for pinion angle. I will cut and rotate the knuckles for caster but I am just looking for a starting point for bushings. 4 degree, 2 degree or 0?

 

[jamesroney]

I am installing a 3.5" lift with Duff extended arms. I am wondering where to start with radius arm bushings for pinion angle. I will cut and rotate the knuckles for caster but I am just looking for a starting point for bushings. 4 degree, 2 degree or 0?

Ugh, You won't like this...

If you are going to do the caster correction, then you want to use the wedge bushings to establish the correct pinion angle. Factory was 8 degrees, and that was correct for a low pinion Dana 44 with factory radius arms. The long arms swing thru a different arc than the Dana 20 driveshaft. So as the suspension cycles, the relative angle between the driveshaft and the radius arm is different. Which means that your front pinion angle will only be exactly correct at one and only one suspension height. You want your front axle u-joint to be in perfect phase and alignment when it is rotating the fastest, and the longest. (which is typically at static ride height, fully loaded, at 65 mph on the highway) It's only a few degrees, and many will tell you it doesn't hurt anything. But of course there is the "right" way, and countless wrong ways to do this.

The other problem is that countless people order their suspension first, and then decide to modify their drivetrain later. You really do want to know your transfer case output location and get it locked down. If you set your pinion angle for the Dana 20 in the factory location...don't come back to me next month and tell me you decided to add a 5 speed, or swap to an Atlas, or clock your transfer case. You get one chance to get this right. Because once you "find" your pinion...that will determine EXACTLY how much you will cut and rotate your knuckles. Again, I am talking about a few degrees, but that matters when it's time to set your caster.

I happen to like Jim Cole's long arms, (Duff arms) and I usually do them with an Atlas, clocked up tight against the frame. I think I ended up with 14 degrees of pinion and 7 degrees of caster on the last one. In order to get the pinion right, I had to go with 4 degree bushings...but install them upside down.

So first things first (always...) MEASURE the suspension height gap between frame rail and axles. Front and Rear. You said 3.5 inch lift, so we are looking for 9.5 inches and 10 inches. Hang a protractor on your front driveshaft, and measure your driveshaft angle. hang a protractor on your pinion and get a pinion angle. (this part of the process doesn't care which radius arms you use...if any.) Keep in mind that your factory track bar is going to fight you to get the pinion right. If your Bronco is a project, and doesn't have all of its weight on it...then cut some wooden 4x4 gage blocks and strap it down.

Note that this is the ONE TIME where cutting wedges and re-welding might have some benefit. But at 3.5 lift, please DON'T. I would compromise a couple of degrees of u-joint angle to run a standard 0,2, or 4 degree bushing. So if you have to run a 2 degree upside down to get your driveshaft right...OK.

I just thought of something. WHY do you want to know this? Do you have any intention of installing the long arms and then doing your cut-n-turn later? Please understand that if you install your long arms and set your pinion correctly...your Bronco will be un-driveable until you do your cut and turn. Wierd and unstable things happen as you cycle thru zero caster. So don't even think that you are going to install long arms without doing the caster correction at the same time. That's just silly.

Have fun!

 

[bigmuddy]

With the Cage arms and a 2.5" lift I could not get a driveshaft to mate up to my dana 44 using a ZF 5 speed and Dana 20.
Had to go to a weird offset trunnion to get it to mate and work correctly. If I was doing a lot of mudding or snow wheeling I would have corrected it without doing a band aid fix. However, I don't and it's help up fine for the small amount of rock crawling and off roading I do.
That said, now that I have installed a 4R70w and an atlas II I need to go back and see how things fit up but I would consider doing a cut and turn on the dana 44 to lose the offset trunnion.
So, I wouldn't say it's not necessary with lifts at 3.5 or less.

To be completely open though I don't think they recommend the use of the long arms with lifts less than 3.5" but I have always assumed this was due to limited up travel?

 

[rcmbronc]

My intention is to set up the pinion angle using the bushings and then cutting and rotating the knuckles for the caster. This is on a friends truck. Fully assembled. Will be adding the new 3.5" springs with the arms. I used to have them on the front of mine (Cage) until I switched to a three link. I just did not know what bushings to start with to get the pinion angle. Like I said I will cut the caster after the pinion angle is set.

I know I used the Cage arms with 3.5" before but maybe I will call Duffs and see what they say. Could stay with standard length arms also if needed.

 

[toddz69]

To be completely open though I don't think they recommend the use of the long arms with lifts less than 3.5" but I have always assumed this was due to limited up travel?

That is correct. The arms will hit the frame on full compression.

Todd Z.

 

[bigmuddy]

That is correct. The arms will hit the frame on full compression.

Todd Z.

I know that is what is said, but I have had mine fully stuffed and not hit the arms but I suppose that's due to limitations up travel from where I have the bump stops sitting. Regardless, I like the ride on and offroad with them.

 

[DonaldDouchebag]

With the Cage arms and a 2.5" lift I could not get a driveshaft to mate up to my dana 44 using a ZF 5 speed and Dana 20.
Had to go to a weird offset trunnion to get it to mate and work correctly. If I was doing a lot of mudding or snow wheeling I would have corrected it without doing a band aid fix. However, I don't and it's help up fine for the small amount of rock crawling and off roading I do.
That said, now that I have installed a 4R70w and an atlas II I need to go back and see how things fit up but I would consider doing a cut and turn on the dana 44 to lose the offset trunnion.
So, I wouldn't say it's not necessary with lifts at 3.5 or less.

To be completely open though I don't think they recommend the use of the long arms with lifts less than 3.5" but I have always assumed this was due to limited up travel?

I’m just about to install some Cage arms with a 2.5” lift already in there. We’ll see how it goes! I have no idea what bushings to start with, either.

What’s an offset trunnion?

 

[jamesroney]

I’m just about to install some Cage arms with a 2.5” lift already in there. We’ll see how it goes! I have no idea what bushings to start with, either.

What’s an offset trunnion?

known to some as high clearance offset joint...

 

[rcmbronc]

I installed the axle with 2 degree bushings mounted up side down. Gave me the correct pinion angle. Then I cut and turned the knuckles for about 7-8 degrees caster.

 

[jamesroney]

I installed the axle with 2 degree bushings mounted up side down. Gave me the correct pinion angle. Then I cut and turned the knuckles for about 7-8 degrees caster.

That sounds about right. With stock radius arms, and the Dana 20...you want 0 degree bushings, (or for urethane, 2 degree mounted one up, one down)

Legend has it that the Duff Arms have 4 degree of built in correction. (although you make it sound more like actually 2???)

Would be curious to know your current pinion angle, and current driveshaft drop. I wouldn't ask you to pull the driveshaft to get the pinion angle, but if the Bronco is parked level, you can approximate the pinion angle from the front cover.

Sometimes people intentionally put 1.5 degrees of mis-alignment in the joint. Just wondering if you set yours dead nuts, or built in some angle.

Thanks.

 

[DonaldDouchebag]

known to some as high clearance offset joint...

Ah, thank you. I've seen those. Will keep them in mind if run into the issue you had.

 

[bigmuddy]

Ah, thank you. I've seen those. Will keep them in mind if run into the issue you had.

It's worked well for me but only until I cut and turn the axle one day.

 

[DonaldDouchebag]

It's worked well for me but only until I cut and turn the axle one day.

Nice. i'm glad I stumbled upon this thread. I'm just starting on redoing the front suspension and steering this weekend.

 

[DonaldDouchebag]

I determined that, with my 2.5" lift and stock radius arms, I'm currently running 7 degree bushings. With my new-to-me Cage arms I'm going to start with 2 degree bushings and see how that goes.

 

[bigmuddy]

I determined that, with my 2.5" lift and stock radius arms, I'm currently running 7 degree bushings. With my new-to-me Cage arms I'm going to start with 2 degree bushings and see how that goes.

It's been awhile since I set mine up but I went either 2 or 4 def bushing. Keep in mind part of the reason I ended up needing the weird joint was the use of the ZF tranny which changed the angle of dangle as they say.

 

[DonaldDouchebag]

It's been awhile since I set mine up but I went either 2 or 4 def bushing. Keep in mind part of the reason I ended up needing the weird joint was the use of the ZF tranny which changed the angle of dangle as they say.

Ah, interesting. I’m starting on this tomorrow and Monday—I’ll post back here once everything is in. (Waiting on some rod end cone spacers so may not get if all finished for a week.)