Today I was crawling around under my 2007 F250 Super Duty Extended Cab w/ 6.0L PS diesel to work on the starter, as I recently documented at: https://www.ford-trucks.com/forums/1...woes-help.html .

I noticed a probably unrelated but possibly serious issue: one of the front mounting tabs on the driver's side radius arm is broken. Photo:


Broken front mounting tab on radius arm

It appears that at the front end of each radius arm there are two top tabs and two bottom tabs. A large bolt goes through each pair of tabs, and through holes in a bracket mounted between the tabs that supports and positions the front axle.

So, out of four tabs, I have three still intact.

No idea how long I have been driving around with the radius arm in this condition. The break does not look fresh, so who knows, maybe it's been like this for months. But I reckon it's probably a good idea to repair or replace this component, sooner rather than later.

My first thought was to try to weld it. But, I have seen and experienced horror stories concerning people doing arc welding on vehicles with sensitive electronic components and computers. If I was going to weld it, I would definitely remove it from the vehicle first.

Another approach would be to leave the arm in place and cobble up a splice piece that's bolted to the arm. I have been known to do this kind of repair frequently, but... this is a dang heavy truck, and this radius arm has to support a lot of weight. It may also be intimately involved with keeping the wheels in alignment.

So, replacement may be my best option. Do any of you FFF (Fellow Ford Freaks) have any advice regarding repair vs replace, and new vs. salvage, or for specific products you'd recommend?

 

My first attempt would be a used replacement.

 

Depends on your budget. If you can afford it, and they've got them in stock, just buy a brand new one and be done with it, the truck has been in service for the better part of two decades. May want to inspect the other side to see if there are any stress fractures starting on that side. If there are you'll be back under the truck soon, so replace it now before it breaks if needed.

If you're on a budget or you need the truck back and new ones aren't in stock, a good used replacement from a salvage yard would be adequate. No telling how long any of them will last, but used tends to not have the lifespan of new.

 

Disconnect your negative batt cables for peace of mind and you can weld on that thing all day long. But I'd want it on the bench anyway .....if for no other reason than to preserve rubber bushings.

I'm baffled by the failure mode -- it looks like a deliberate cut from an abrasive wheel.

 

I don't think it is a deliberate cut. The break has random curves that would be pretty hard to achieve with an angle grinder. My take is that it cracked, and subsequently the weight of the truck on the axle brackets was less evenly distributed, so the radius arm shifted enough to create a gap at the break.

A several trucks ago I purchased a 1985 F150 that someone had rolled. They cut off the crunched cab and welded a different cab in place. They told me they'd unhooked the battery before welding, but the thing ran really rough, and I wound up replacing the computer and a bunch of sensors that had apparently not liked whatever stray electric currents were coursing through the frame. Hence my suspicion of welding on vehicles.

 

I have been looking at sites that sell new radius arms. I see some of them specify that their product is designed for trucks with X number of inches of lift.

My '07 is pretty dang high off the ground (a friend complained about needing a parachute to get out of the cab). This makes me wonder if a PO "lifted" the truck but did not replace the radius arms, and this created stresses that broke this arm.

How do I tell:

A. Is my truck lifted?
B. Are the currently installed radius arms appropriate for the degree of lift?
C. If not, what would be appropriate?

 

Definitely not a deliberate cut, probably started as a stress fracture that propagated under use - it's not a spring chicken anymore.

You CAN weld on vehicles all day long, so long as you disconnect the batteries completely and make sure you've got proper grounding and use proper settings on your welder. It's more likely that your issues with that previous truck stemmed either from the previous owner lying or age, as electronics and sensors eventually wear out.

The issue with just welding it back together is that you need to keep the geometry right or your axle will no longer sit straight. You'll likely need an alignment after whatever you do, but at least a stock part will be known within a tolerance - there's always a possibility you won't get the old one back where it belongs if the metal has stretched as the crack propagated.

It is ultimately your choice, but I definitely recommend replacement over repair in this instance.

 

If its lifted, and you have stock radius arms, then there should be drop brackets at the pivot point to lower the arms and accommodate the lift. If they went on the cheap and stuck lifted springs on with no drop brackets then its going to change caster, going "negative" caster. Post a pic so others can see what the lift might be.

 

Is the pivot point at the rear end of the radius arm?

 

Yes, the pivot point is at the back. Smaller lifts (I think under 4" but don't quote me on that) can get away without the brackets, but even so it shouldn't cause THAT kind of a failure.

 

i wouldnt do more then an inch or two without new arms, drop brackets or some other way to get caster correct. my 3.5" lift came with drop brackets so that alignment can get back into spec.

 

The question is, what DID cause that kind of a failure?

 

That is the question...though it looks like it has been like that for a while.

 

Here’s a picture of the rear of right radius arm. Is this the kind of drop bracket you mean? Then a not real clear picture of the spring mount end.

 

this is a drop bracket. The 2 top holes are used to the mount you showed and the bottom hole drops the radius arm down 3"