Buffer plate for radius arm pivot boxes

[Mikes Early Bronco]

Hi all,
I came across a write up regarding leaf spring hangers and welding them to a frame. Although the material pertains to a trailer, they’re are some relative practices to welding on a Bronco frame. Later in the article they review the use of a buffer plate that allows for parallel welds on the frame only, and cross welds on the plate that don’t touch the frame but still offer support. You can read the article here: https://mechanicalelements.com/welding-on-trailer-spring-brackets/
Why do I bring this up? I’m moving at a slow pace on my 77 this month. I’m back to work welding in the pivot boxes for a set of Solo radius arms. I was going to apply the buffer plate method with the boxes. My only concern is no seal between the buffer plate and frame to prevent corrosion. Has anyone taken this route and do you have any advice? Thank you. Have a great weekend.

First pic shows buffer plate. Last two are mock up with out the plate

Mike R

 

[DirtDonk]

Interesting question and subject.
Haven’t even heard the term before myself, so obviously no help here. But I’ll go check out the article anyway and maybe learn something.
In the meantime, back to the top for you.

 

[Mikes Early Bronco]

Interesting question and subject.
Haven’t even heard the term before myself, so obviously no help here. But I’ll go check out the article anyway and maybe learn something.
In the meantime, back to the top for you.

Thank you sir. It seems like a great to solution to getting the job done while keeping as much strength in the frame as possible. And it’s possible a cross weld on a frame won’t harm anything, but when I think of the precious cargo that’ll be riding along, every bit of strength is piece of mind.

 

[DirtDonk]

Looking at the mounts, normally radius arm mounts also have extensions that run up the side of the frame.
Some are one side only, while others are both sides. Creating essentially a C channel that slips over the frame.
Lots of weld area and lots of reinforcing metal.
Seems like mounting radius arms in just one plane like pictured isn’t as strong as the traditional methods.

 

[Yeller]

Either will work and unless you live and drive in salt country or play in acidic mud a lot the corrosion is not an issue. If real concerned coat everything with zinc weld through primer prior to assembly.

This version would be my preferred method but it will all work. With this mock-up there is no need for a buffer plate and it is stronger than the other with one.

 

[jamesroney]

Hi all,
I came across a write up regarding leaf spring hangers and welding them to a frame. Although the material pertains to a trailer, they’re are some relative practices to welding on a Bronco frame. Later in the article they review the use of a buffer plate that allows for parallel welds on the frame only, and cross welds on the plate that don’t touch the frame but still offer support. You can read the article here: https://mechanicalelements.com/welding-on-trailer-spring-brackets/
Why do I bring this up? I’m moving at a slow pace on my 77 this month. I’m back to work welding in the pivot boxes for a set of Solo radius arms. I was going to apply the buffer plate method with the boxes. My only concern is no seal between the buffer plate and frame to prevent corrosion. Has anyone taken this route and do you have any advice? Thank you. Have a great weekend.

First pic shows buffer plate. Last two are mock up with out the plate

Mike R

Don't forget that the entire structural analysis of the trailer leaf spring hanger is completely different than the Bronco radius arm.

The leaf spring on a trailer supports the entire load of the trailer, so the majority of the load is in the vertical plane. The only time the leaf spring sees longitudinal load is when the trailer brakes are applied. Otherwise, the axle basically coasts.

Contrast that with the front radius arm hanger on a Bronco which sees essentially zero vertical load. The coil spring sits directly on top of the axle, and so the frame end of the arm carries no weight. There is a vertical component from the reaction force when the brakes are applied, and when the front axle is driven. But the vast majority of the load on a bronco radius arm comes from the longitudinal force of braking, and driving. In 4x4, the front axle tries to pull itself out from under the Bronco, and the brakes try to push the front axle out the back of the Bronco.
(oddly enough, I'm going to say that the greatest load on the radius arm frame mount occurs when the operator applies the service brake, while applying power in 4xLo, against a rock or boulder. The rear axle tries to push the frame forward, and the brakes tries to push the frame rearward. With a really good crawl ratio, the loads are pretty impressive.)

So the design that @Yeller proposes is vastly superior to U-bracket that is prevalent in the trailer application. You need some kind of ears or tabs to prevent forward and rearward motion. It's one of the things that I like least about the short Duff Radius Arm frame bracket. With time, the ears come loose on the frame, and the bolts loosen, and the brackets start to wiggle. So you really must weld them.

@DirtDonk also makes a great point. Take a good look at the lower control arm pivots for a 97-06 Jeep TJ. They have pretty good rust resistance. The structural welds are up from the frame flange about an inch, and there's a small cosmetic weld across the frame rail to keep it tidy. (yeah the frames rust out, but its from the inside of the box tube...)

 

[Mikes Early Bronco]

Either will work and unless you live and drive in salt country or play in acidic mud a lot the corrosion is not an issue. If real concerned coat everything with zinc weld through primer prior to assembly.

This version would be my preferred method but it will all work. With this mock-up there is no need for a buffer plate and it is stronger than the other with one.
View attachment 908389

Thanks Yeller! After mulling it over and help from y’all, I decided to ditch the buffer plate and proceed with the original setup in the pic. I’m not sure why the pivot boxes were made with only one ear on the outside but I’m going to roll with it.

 

[Mikes Early Bronco]

Don't forget that the entire structural analysis of the trailer leaf spring hanger is completely different than the Bronco radius arm.

The leaf spring on a trailer supports the entire load of the trailer, so the majority of the load is in the vertical plane. The only time the leaf spring sees longitudinal load is when the trailer brakes are applied. Otherwise, the axle basically coasts.

Contrast that with the front radius arm hanger on a Bronco which sees essentially zero vertical load. The coil spring sits directly on top of the axle, and so the frame end of the arm carries no weight. There is a vertical component from the reaction force when the brakes are applied, and when the front axle is driven. But the vast majority of the load on a bronco radius arm comes from the longitudinal force of braking, and driving. In 4x4, the front axle tries to pull itself out from under the Bronco, and the brakes try to push the front axle out the back of the Bronco.
(oddly enough, I'm going to say that the greatest load on the radius arm frame mount occurs when the operator applies the service brake, while applying power in 4xLo, against a rock or boulder. The rear axle tries to push the frame forward, and the brakes tries to push the frame rearward. With a really good crawl ratio, the loads are pretty impressive.)

So the design that @Yeller proposes is vastly superior to U-bracket that is prevalent in the trailer application. You need some kind of ears or tabs to prevent forward and rearward motion. It's one of the things that I like least about the short Duff Radius Arm frame bracket. With time, the ears come loose on the frame, and the bolts loosen, and the brackets start to wiggle. So you really must weld them.

@DirtDonk also makes a great point. Take a good look at the lower control arm pivots for a 97-06 Jeep TJ. They have pretty good rust resistance. The structural welds are up from the frame flange about an inch, and there's a small cosmetic weld across the frame rail to keep it tidy. (yeah the frames rust out, but its from the inside of the box tube...)

Awesome points James! I should have taken better pics of the pivot boxes. They were made with one ear on the outside of each. I’ll supply a better pic. I would have preferred two ears per box as now I’m forced to weld along the inside (welded) seam of the frame. But they may have their reasons for it. Well with the help of all of you, I’m scrapping the buffer plate and welding directly to the frame. The direction of force you pointed out makes a lot of sense. Thanks for a very helpful response.

Mike R

 

[Mikes Early Bronco]

Thanks all. There’s no better place to bounce ideas off of professionals. As always I received tremendous help.

 

[toddz69]

Awesome points James! I should have taken better pics of the pivot boxes. They were made with one ear on the outside of each. I’ll supply a better pic. I would have preferred two ears per box as now I’m forced to weld along the inside (welded) seam of the frame. But they may have their reasons for it. Well with the help of all of you, I’m scrapping the buffer plate and welding directly to the frame. The direction of force you pointed out makes a lot of sense. Thanks for a very helpful response.

Mike R

That's a great design they have there for their radius arm brackets (arms are nice too). FWIW, Poly Performance used to sell something very similar to those brackets and Lars and I both have them on our trucks for our extended arms.

Todd Z.

 

[73azbronco]

Don't over engineer unless you can prove it is needed. Has anyone else done a doubler? Maybe, none to my knowledge. When you stiffen that one spot, you may make the spot right next to it much weaker. Reference all the engineering fails through history.

 

[Yeller]

There isn’t one on the inside to not interfere with crossmembers and in a bronco a tcase, there is a reason lol.

 

[Broncobowsher]

Don't forget that the entire structural analysis of the trailer leaf spring hanger is completely different than the Bronco radius arm.

The leaf spring on a trailer supports the entire load of the trailer, so the majority of the load is in the vertical plane. The only time the leaf spring sees longitudinal load is when the trailer brakes are applied. Otherwise, the axle basically coasts.

Contrast that with the front radius arm hanger on a Bronco which sees essentially zero vertical load. The coil spring sits directly on top of the axle, and so the frame end of the arm carries no weight. There is a vertical component from the reaction force when the brakes are applied, and when the front axle is driven. But the vast majority of the load on a bronco radius arm comes from the longitudinal force of braking, and driving. In 4x4, the front axle tries to pull itself out from under the Bronco, and the brakes try to push the front axle out the back of the Bronco.
(oddly enough, I'm going to say that the greatest load on the radius arm frame mount occurs when the operator applies the service brake, while applying power in 4xLo, against a rock or boulder. The rear axle tries to push the frame forward, and the brakes tries to push the frame rearward. With a really good crawl ratio, the loads are pretty impressive.)

So the design that @Yeller proposes is vastly superior to U-bracket that is prevalent in the trailer application. You need some kind of ears or tabs to prevent forward and rearward motion. It's one of the things that I like least about the short Duff Radius Arm frame bracket. With time, the ears come loose on the frame, and the bolts loosen, and the brackets start to wiggle. So you really must weld them.

@DirtDonk also makes a great point. Take a good look at the lower control arm pivots for a 97-06 Jeep TJ. They have pretty good rust resistance. The structural welds are up from the frame flange about an inch, and there's a small cosmetic weld across the frame rail to keep it tidy. (yeah the frames rust out, but its from the inside of the box tube...)

Another point about trailer spring hangers. They have to take massive lateral loads. At least a tandem axle trailer. The forces are the grip limit of the tires considering they slide around when making turns (intersections, parking lots).

 

[Mikes Early Bronco]

There isn’t one on the inside to not interfere with crossmembers and in a bronco a tcase, there is a reason lol.

Brilliant! That’s the missing link and I have yet to mock up the crossmember for the ZF5.

 

[Mikes Early Bronco]

That's a great design they have there for their radius arm brackets (arms are nice too). FWIW, Poly Performance used to sell something very similar to those brackets and Lars and I both have them on our trucks for our extended arms.

Todd Z.

Thanks Todd. That holds a lot of weight. I’m anxious to install them and get this thing on wheels.

 

[Mikes Early Bronco]

Don't over engineer unless you can prove it is needed. Has anyone else done a doubler? Maybe, none to my knowledge. When you stiffen that one spot, you may make the spot right next to it much weaker. Reference all the engineering fails through history.

Great advice and something I need to be reminded of constantly. I’ll overthink a bowl of cereal sometimes.

 

[DirtDonk]

Yet, sometimes they need it!