Help with calculating caster

[Shimmy]

Some of you may remember my earlier thread on how I've basically got no caster on my 3.5" SL bronco. I need ya'lls help with calculating my estimated caster. Am I understanding this correctly? Here's what I've done:

James Duff Long travel arms (4* caster built in)
4* C bushings

Don't i gain more caster due to the long travel arms mounting further back on the frame? I'm estimating about 10-11* worth of caster factored in here? Or am I totally not understanding this?

EDIT: the reason i'm asking all this is because with 7* bushings and stock radius arms/mounts, I was at .5* caster.

 

[lars]

Pretty simple. Take it to an alignment shop and have it checked, accurately.

It's no secret that during the years Broncos were being produced, that Dana's quality control was less than stellar. Caster numbers were all over the place. 20 years ago I got tired of the wandering. I had a 3-1/2" lift with supposed 7° bushings. Measured caster was less than 1°. I removed the 7° bushings, put in 2° bushings (zero degree bushings weren't available) then had it checked again. It was almost undrivable at that point. Knowing what the numbers were (negative, the worst possible) I fabbed a jig, then ground the inner C's off my Dana 44 and rotated them back until I had an estimated 5° positive, then welded everything back together and reinstalled the axle with the 2° bushings. Had the caster checked yet again and confirmed that I'd hit my target.

That transformed the handling of my Bronco. Made it stable like any modern vehicle.

 

[Shimmy]

Pretty simple. Take it to an alignment shop and have it checked, accurately.

It's no secret that during the years Broncos were being produced, that Dana's quality control was less than stellar. Caster numbers were all over the place. 20 years ago I got tired of the wandering. I had a 3-1/2" lift with supposed 7° bushings. Measured caster was less than 1°. I removed the 7° bushings, put in 2° bushings (zero degree bushings weren't available) then had it checked again. It was almost undrivable at that point. Knowing what the numbers were (negative, the worst possible) I fabbed a jig, then ground the inner C's off my Dana 44 and rotated them back until I had an estimated 5° positive, then welded everything back together and reinstalled the axle with the 2° bushings. Had the caster checked yet again and confirmed that I'd hit my target.

That transformed the handling of my Bronco. Made it stable like any modern vehicle.

Right, i understand that, but am I correct in understanding that the long arms alone will net me more caster too?

 

[lars]

Right, i understand that, but am I correct in understanding that the long arms alone will net me more caster too?

I made my own long arms. Extended by 6" (peanut gallery, control yourselves). That netted me 3/4° more caster. Measured by my local alignment shop, before and after. A nice bonus but not enough.

As others have written here, pretty much every Dana 44 ever installed on an early Bronco needs a cut and turn, especially if you lift it. A big PITA but the first time you drive it with 5-ish degrees of caster and no front driveline bind you'll forget all about the hassle.

 

[jamesroney]

I made my own long arms. Extended by 6" (peanut gallery, control yourselves). That netted me 3/4° more caster. Measured by my local alignment shop, before and after. A nice bonus but not enough.

As others have written here, pretty much every Dana 44 ever installed on an early Bronco needs a cut and turn, especially if you lift it. A big PITA but the first time you drive it with 5-ish degrees of caster and no front driveline bind you'll forget all about the hassle.

“Every Dana 44 ever installed on an early Bronco needs a cut and turn.”

Fixed it for you…

 

[DirtDonk]

I think you’re adding too many factors in your head Shimmy.
You started with 7° of caster correction (let’s ignore the lift and all that stuff for now) and you had roughly half a degree negative.
You have since removed the 7° and re-added 8°. Basically netting yourself only one degree of additional positive caster.
You say it reads zero and that’s about a half a degree from where you were before which to my way of thinking is within the realm of variations between alignment machines, alignment technicians, and just mother nature.

Could have settled the springs in slightly in between those modifications too, or the radius arms change the overall lift slightly by having a different angle on the head where the spring cups mount. Coil springs can vary just by how much they are twisted.

All that means is that your change of roughly half a degree after all that work is pretty much expected. Remember you already had 7° then you took it out. Then you added back 8°. So you basically only changed your caster by approximately 1° with the addition of the arms and 4° bushings.
The length of the arms has nothing to do with caster other than how each manufacturer creates the arm specifically to change the caster.
Long or short, the rated caster is what you get. So 4° for the arm, 4° for the bushings. Period…

It’s all about how the axle tilts relative to the chassis and ground.

 

[Broncobowsher]

Long arms (in general) do not change caster, it is the caster correction built into the long arms that changes caster.
The arms have the head that attaches to the axle installed in a rotated position. Does the same thing the offset bushings do.
There are other old school ways of getting more caster out of the arms as well. Alignment shops would bend the arms. That would rotate the axle and get you the caster. There were also radius arm drop brackets. Drop the back of the radius arm where it attaches to the frame and that will rotate the axle and get you the caster back.

But there are limitations. The more you rotate the axle to get better caster numbers, the worse the U-joint angle gets at the front driveshaft. In general a 3½" lift and 7° bushings is the limit. The front U-joint is running a steep enough angle that vibration and general binding are boarderline. At the same time the caster is usually right about zero. Sometimes it works, sometimes it doesn't. Back to that build variation thing. The magic fix is a cut and turn of the outer Cs. Take out the caster correction, might even have to put some bushings in backwards if you have long arms. Bring that U-joint angle back into happy land. Put your caster back in by rotating the C on the axle, and put a lot in. 12° of rotation tends to fix a lot of it. Now you have good U-joint angles and good caster angles. If you want to run a lift and have good street manors, and still have a functional front driveshaft, that is about the only way to do it.

 

[Shimmy]

thanks for everyone's input. I guess i was thinking that long arms would net me additional caster or do the same thing that drop brackets would do.

 

[DirtDonk]

Only what's advertised by that particular arm's manufacturer.

Paul

 

[lars]

“Every Dana 44 ever installed on an early Bronco needs a cut and turn.”

Fixed it for you…

That was funny.

I first got the idea to do the cut and turn almost 20 years ago, after hating the steering on my Bronco for the previous 6. My boss at the time had a 78 big Bronco that was box stock except for a 1" lift and 33" tires. It stopped went and especially steered without histrionics. I started looking for reasons why and eventually settled on caster. Ford's spec for it was around 6° as I recall. The EB spec was/is something like 3°. I heard all sorts of reasons attempting to explain away the difference, nearly all of them wrong.

The real reason: manual steering requires a compromise on caster or it's too hard to steer, wheel kicks back, etc. When Ford made power steering standard for the last couple of model years, they didn't bother to change the caster spec. The big Bronco was designed from the ground up to have power steering. After looking at the caster spec for a bazillion other live axle 4x4 vehicles that came standard with power steering, I realized that none of them had a caster spec less than 5°, and most required more than that. Duh.

Rotating the axle with C bushings seemed like a bandaid to me, and in exchange for using them (and still having too little caster) the front u-joint at the Dana 44 bound up. Great. That was one of the reasons I reverted to 2° C bushings when I rotated the C's.

At the time (2003) I couldn't find anyone to do it for me, so I did it myself. Now there are shops that will, at least in the Sacramento area. Since then I've been making the case for doing so regularly, but it seems like most are intimidated by the hassle. What ever.

 

[lars]

Long arms (in general) do not change caster, it is the caster correction built into the long arms that changes caster.

Actually, they do, regardless of any additional built-in caster, which I wouldn't have wanted due to the aforementioned pinion angle issue.

Think about it. As you slide the frame mount back, the angle between the arm and the ground has to get shallower, assuming a horizontal frame rail. Result, a change in caster, albeit a small one.

My arms are based on OEM radius arms, extended 6". I calculated that moving the mount back (dimension from bottom of frame to pivot point remained constant even though I used Johnny joints instead of stock bushings) would increase the caster by about 3/4°. A subsequent alignment check confirmed that.

 

[Shimmy]

i'd have to take my axle to a shop to do a cut and turn. i don't know how to weld. i was chatting with a local shop and for the life of me couldn't get an estimate out of them. they just kept saying "oh it's spendy!"

if anyone knows of a shop in washington let me know

 

[lars]

i'd have to take my axle to a shop to do a cut and turn. i don't know how to weld. i was chatting with a local shop and for the life of me couldn't get an estimate out of them. they just kept saying "oh it's spendy!"

if anyone knows of a shop in washington let me know

Where in Washington?

 

[Shimmy]

Where in Washington?

Maple Valley. I'm about 45 minutes east of Seattle.

 

[lars]

Maple Valley. I'm about 45 minutes east of Seattle.

Track down "nvrstuk" on this board. He's in Ellensburg, obviously further east, but he may know of a shop that can do it.