• Welcome to ClassicBroncos! - You are currently viewing the forums as a GUEST. To take advantage of all the site features, please take a moment to register. It's fast, simple and absolutely free. So please join our community today!
    If you have problems registering or can't log into your account, please contact Admin.

Eric's Extended Radius Arms

ntsqd

heratic car camper
Joined
Jan 30, 2005
Messages
3,225
Loc.
Upper SoKA
There is an important yet not often considered aspect worth thinking about. Drive-shaft plunge. Where the frame pivot is placed can have a very large influence on plunge. The most ideal location (with regard to just this aspect) would result in no plunge or extension of the drive-shaft thru the whole travel range. The lone desert racing rear 4 link that I've designed had this as a high priority concern from the team owner. He wanted no plunge/extension in 24" of wheel travel.

There's a couple reasons why this is important.
Ride quality at road speeds will suffer with excessive plunge because it is a resistance to movement. Makes the suspension ride that much harsher.
Articulation under power will also suffer for the same reason, even though they're designed to move under load they are not friction-free under load and the further they have to move the longer it will take, which will slow down the axle's movement.
And that's not to mention what those plunge-extend loads do to the U-Joints and output shaft bearings. To give an idea of the size of those loads I have seen a drive-shaft that would hydro-lock at desert speeds. It tore up the transmission in less than 100 miles. There were two causes, the primary was way too much grease in the slip-yoke (& a welded weep hole to keep dirt out) and the second was a suspension that required about 6" of plunge travel in the drive-shaft.
 
OP
OP
E

EricLar80

Bronco Guru
Joined
Jun 14, 2001
Messages
2,170
There is an important yet not often considered aspect worth thinking about. Drive-shaft plunge. Where the frame pivot is placed can have a very large influence on plunge. The most ideal location (with regard to just this aspect) would result in no plunge or extension of the drive-shaft thru the whole travel range. The lone desert racing rear 4 link that I've designed had this as a high priority concern from the team owner. He wanted no plunge/extension in 24" of wheel travel.

There's a couple reasons why this is important.
Ride quality at road speeds will suffer with excessive plunge because it is a resistance to movement. Makes the suspension ride that much harsher.
Articulation under power will also suffer for the same reason, even though they're designed to move under load they are not friction-free under load and the further they have to move the longer it will take, which will slow down the axle's movement.
And that's not to mention what those plunge-extend loads do to the U-Joints and output shaft bearings. To give an idea of the size of those loads I have seen a drive-shaft that would hydro-lock at desert speeds. It tore up the transmission in less than 100 miles. There were two causes, the primary was way too much grease in the slip-yoke (& a welded weep hole to keep dirt out) and the second was a suspension that required about 6" of plunge travel in the drive-shaft.

So, in the case of a radius arm suspension - the ideal location would be to put the pivot point for the radius arm in-line with the double cardan joint on the driveshaft, right?
 

ntsqd

heratic car camper
Joined
Jan 30, 2005
Messages
3,225
Loc.
Upper SoKA
I think that is close anyway. With the way that the CVJ in the front drive shaft moves ("bends") combined with the vertical offset of where the bracket can go vs. the 'Z' of the output flange, there might be a necessary dislocation that isn't obvious w/o modeling it or experimenting @ 1:1.

And, I'm not sure that I'd let this dominate the radius arm length decision, just that I'd consider it and see what compromises it forces if it were allowed to dominate. A small amount of plunge is acceptable if that means that other competing goals are better met.
 

toddz69

Sponsor/Vendor
Bronco Guru
Joined
Nov 28, 2001
Messages
10,079
I got to that point rather unintentionally on my setup. With Lars Bars, a 700R4 and 4 speed Atlas, the double cardan's pivot point is pretty close to the bars' mounting point on the frame.

Todd Z.
 

DirtDonk

Contributor
Bronco Guru
Joined
Nov 3, 2003
Messages
47,345
Pretty sure Lars did his arms about the time he did the NV4500 too. Which might have dictated the length for the same reasons.
Ford's original location is not that far off of this either I think. Isn't it about where the front u-joint in the CV head is?

Paul
 

toddz69

Sponsor/Vendor
Bronco Guru
Joined
Nov 28, 2001
Messages
10,079
interesting conversation

One of the 4,700 cool reasons to go on camping trips/expeditions with Lars and Thom - we have a lot of good engineering discussions and everyone learns something.

Lars did his 4500 and Atlas first. The extended radius arms hatched after we three were walking around at Fab Fords one year and saw the ~6" longer arms on Dennis Hogue's well-built Bronco. Lars took it from there.

Todd Z.
 
OP
OP
E

EricLar80

Bronco Guru
Joined
Jun 14, 2001
Messages
2,170
One of the 4,700 cool reasons to go on camping trips/expeditions with Lars and Thom - we have a lot of good engineering discussions and everyone learns something.

Lars did his 4500 and Atlas first. The extended radius arms hatched after we three were walking around at Fab Fords one year and saw the ~6" longer arms on Dennis Hogue's well-built Bronco. Lars took it from there.

Todd Z.

I was talking to Dennis over the phone some time ago regarding automotive wiring, and we got on the topic of radius arms - he is definitely a proponent of mid-length radius arms for "a lot of reasons." I didn't ask for the specifics, but he felt the vendor arms are too long.
 

74BroncoCO

Bronco Guru
Joined
Nov 3, 2004
Messages
2,374
What do you have planned for a frame mount?

I built my own radius arms from a kit that had the exact parts I needed. And after I sent my design for the frame mounts, he built those for me too. They are welded to the inside of the frame so they are inboard from the stock mounts. That allowed me to go slightly longer and gain some turning clearance, although my 35's still rub. But the arms are straight.

My setup is significantly different in that I cut off my wedges and welded a bracket that accepts two bushing per side (pretty much what all the fab shops sell). So with my top short link having a heim at one end, I can adjust my caster to some degree. And with an HP44 I can get away with gaining caster there easier than a LP44.

Admittedly I designed mine for maximum flex and would "deal" with the loss of road manners.

I like what you've done here and am interested in how it performs, and holds up. Sure the DOM is thick enough to resist bending in 99% of all situations. Being a CAD guy myself, this looks like a fun project!

My other question is if you've got anything planned for shock mounting?
 
OP
OP
E

EricLar80

Bronco Guru
Joined
Jun 14, 2001
Messages
2,170
What do you have planned for a frame mount?

I built my own radius arms from a kit that had the exact parts I needed. And after I sent my design for the frame mounts, he built those for me too. They are welded to the inside of the frame so they are inboard from the stock mounts. That allowed me to go slightly longer and gain some turning clearance, although my 35's still rub. But the arms are straight.

My setup is significantly different in that I cut off my wedges and welded a bracket that accepts two bushing per side (pretty much what all the fab shops sell). So with my top short link having a heim at one end, I can adjust my caster to some degree. And with an HP44 I can get away with gaining caster there easier than a LP44.

Admittedly I designed mine for maximum flex and would "deal" with the loss of road manners.

I like what you've done here and am interested in how it performs, and holds up. Sure the DOM is thick enough to resist bending in 99% of all situations. Being a CAD guy myself, this looks like a fun project!

My other question is if you've got anything planned for shock mounting?

Here is a picture that shows what I am building for the mount. It's a little different than the picture, but very similar. I will use Johnny Joints on the arms. The load bearing hole in the mount is made from 1020 DOM Tubing 1.5" OD X .375" wall, 9/16" long. The 3/4" ID through hole corresponds to the bolt size of the Jonny Joint and will keep the hole from being wallowed out because it will have 2.25 times more contact area than the 1/4" thick bracket material.

As far as shock mounting, I will probably just weld some tabs to the boxed section of the radius arm. The top landing, where the coil sits, was also made large enough for tabs for ORI struts to be welded to it, so that will be an option when/if I decide to move in that direction.

EkTIkzd.jpg
 

74BroncoCO

Bronco Guru
Joined
Nov 3, 2004
Messages
2,374
That should be plenty stout. My only comment would be that it will stick down below the frame considerably and could cause you to hang up there, especially if you need to back out of somewhere. This was quite important to me since I have a flat belly.


FWIW, my brackets are made from 1/4" and I have yet to see the holes wallow out, but I was able to make my brackets the same width at the planned JJ so I can torque the bolt down. I suppose with the sleeves you have, the same can be done.

In all honesty tho, I hang up on the front leaf spring hanger much more than anything on the front. And the rear pumpkin. Rear steer would solve that...
 
Last edited:
OP
OP
E

EricLar80

Bronco Guru
Joined
Jun 14, 2001
Messages
2,170
Being that my arms are not as long the typical extended arms, the mounts are going to be further forward than typical. I think it should be fine for my use.

I haven't had a flat belly since I was in my 20's. ;D
 

Yeller

Contributor
Bronco Guru
Joined
Mar 27, 2012
Messages
5,881
Loc.
Rogers County Oklahoma
Is there reasoning that your using a 3” joint (3/4” bolt) vs a standard 2-1/2(9/16” bolt)? Also in my experience a 5/16-3/8” bearing surface is more than sufficient.
 
OP
OP
E

EricLar80

Bronco Guru
Joined
Jun 14, 2001
Messages
2,170
Is there reasoning that your using a 3” joint (3/4” bolt) vs a standard 2-1/2(9/16” bolt)? Also in my experience a 5/16-3/8” bearing surface is more than sufficient.

Bigger bolt is bigger and it was an option. The joint is actually 2.812" mounting width. I don't know why summit says 3". The joint doesn't match the width of the frame, so the short length of DOM also makes it so it doesn't require spacers.

https://www.currieenterprises.com/ce-9114-22-2-12-johnny-joint-forged-1-14-rh-thread-2812-x-750-ball-2
 

Yeller

Contributor
Bronco Guru
Joined
Mar 27, 2012
Messages
5,881
Loc.
Rogers County Oklahoma
Thanks, was just curious if there was a design reason or because it was available and fits the frame a little better. Build on, I like seeing new designs. I build and design a lot of stuff but am archaic in my methods, usually chalk drawings on the shop floor or weld table. I've been asked if I would sell my drawings and I usually have to answer with "if you can figure out how to get them out of my head we'll both be rich":p
 

BanditBronco

Sr. Member
Joined
Jul 2, 2008
Messages
689
I dig them.

I have seen some lars bars built with 2" x 1/2" wall that sheared directly at the bend location on the tube. Also a few Duff's even though they run 5/16. Maybe the extra length implies extra leverage, maybe a scab plate on both sides of the tube located directly on the bend could help. Kinda like what protofab does on their bent section.

Would be cool to see FEA on them.
 

NicksTrix

Bronco Guru
Joined
Aug 1, 2001
Messages
6,386
i'd like to know how a 2x 1/2 wall tube sheared on a bronco, let alone a 5/16 wall. not saying it's impossible, but you'd think the chassis would be killed being it's only about .140 wall. the std front ends are only 5/16 wall so you'd think you'd be snapping tubes off there as well... maybe i'm all wrong... got any pics? that would be interesting to see
 

BanditBronco

Sr. Member
Joined
Jul 2, 2008
Messages
689
i'd like to know how a 2x 1/2 wall tube sheared on a bronco, let alone a 5/16 wall. not saying it's impossible, but you'd think the chassis would be killed being it's only about .140 wall. the std front ends are only 5/16 wall so you'd think you'd be snapping tubes off there as well... maybe i'm all wrong... got any pics? that would be interesting to see

Not sure if Casey's arms have a bend or not, but also shows how "fish mouthing" and even better not terminating on the same plane can help save a tube.

Same with when KyleQ broke one.

I am not saying it is common or even something to worry about, just something to think about when building.

Not finishing the baja 1000 because of a trailing arm failure that looks very similar to each of the above breaks will make you cut that triangle a little deeper with a sharper corner the next time.
 

Attachments

  • radius arm break 2.jpg
    radius arm break 2.jpg
    4.7 KB · Views: 296
  • radius arm break.jpg
    radius arm break.jpg
    62.3 KB · Views: 189
  • radius arm break 3.jpg
    radius arm break 3.jpg
    112.8 KB · Views: 185

Yeller

Contributor
Bronco Guru
Joined
Mar 27, 2012
Messages
5,881
Loc.
Rogers County Oklahoma
I managed to help bend a Duff's, but it earned it. Launched off of a 12' high near vertical wall, landed on the gas against a ledge. Was brutal violent to watch but the bronco and driver survived to keep going. I was spotting at a WERock event and had to scream at the driver "RUN MY ASS OVER" to coax him off the wall. funny all the spectators standing around vanished when I said that;D

So snapping one I would want see as well, It would literally take crash that other parts would not survive. If the one we bent hadn't been on a Spidertrax 609 I know it would have left parts behind, a bent housing at a minimum. Had it not bent, we might have bent the frame and or housing, it was violent. There comes a point when you have to say what would you rather bend or break. I know none of it but there are worse things that can happen.
 

NicksTrix

Bronco Guru
Joined
Aug 1, 2001
Messages
6,386
bandit, thanks for the pics. the one you can enlarge and see a side profile is a much thinner tube than a .500 wall tube. have you any pics of really thick wall tube sheared?
 
Last edited:
Top