Move upper arm mount rearward to allow caster adjustment

[Woody500]

Realized a while back that cutting off upper a-arm mounts & moving them back would allow proper caster adjustment w/stock suspension.
An a-bodies thread about new CO suspension setup and fabricated spindles mentions thinking of moving UBJ mount to rear "about an inch". So that's somewhere to start.
Anyone ever relocate the upper mounts?
You could also mount them higher to use the later Tall Spindles.
'65 Barracuda is my project

 

[TrailBeast]

Realized a while back that cutting off upper a-arm mounts & moving them back would allow proper caster adjustment w/stock suspension.
An a-bodies thread about new CO suspension setup and fabricated spindles mentions thinking of moving UBJ mount to rear "about an inch". So that's somewhere to start.
Anyone ever relocate the upper mounts?
You could also mount them higher to use the later Tall Spindles.
'65 Barracuda is my project

Seems like using the offset bushings would be a lot simpler.

 

[DionR]

What would you do with the shock mount? It seems like that would have to move with the UCA mounts. And that might cause problems with the connection of the shock to the LCA.

Moving the mounts would give the option to use a stock UCA and still get 6 or 7 degrees of positive caster, but when SPC control arms do that for much less work it seems like the tough way to get there.

BAC/SPC 1.5 Upper Control Arm - Bergman Auto Craft

 

[Woody500]

Not if you're an ex fabbie. Its a easy job. Shock mount change may be tough, I'll have to mull that over.

 

[Woody500]

I've also searched to see if anyone has ever engineered B -Body lowers to fit sn early A; track width change, wheel rate change due to longer arm, ete etc etc.
Tire rub issues and more?

 

[Professor Fate]

B body lcas are actually shorter than A body ones- destroys the swing arc and nearly impossible to dial in correct camber, from what I've read.
I have read about C body lcas being adapted, but sadly I cannot find the link anymore. Seemed like a ton of work for minimal gain from what I remember.

 

[Woody500]

Thanks. I could never found any info about dimensions or differences between A & B Body arms. Does anyone have both to measure and take photos side by side, and stack to see any differences?

 

[DionR]

Firm Feel worked up a kit years ago to use ‘73-4 B-Body LCA’s. I think they were the same length as the A-Body but the LBJ is in the arm instead of the steering arm. I think the idea was to gain suspension travel though. Mopar Action had an article on it.

 

[Professor Fate]

Thanks. I could never found any info about dimensions or differences between A & B Body arms. Does anyone have both to measure and take photos side by side, and stack to see any differences?

About 1/2" different, c to c (BJ to pivot pin). A on top, B below it.
The pivot pins are a different diameter too, IIRC.

 

[66Valiant528]

Shocks with rod ends since you are fabricating.

 

[Woody500]

Ez fix of course. Thanks!

 

[72bluNblu]

73/74 B-body LCA’s are the same length as A-body LCA’s, other B and E body LCA’s are shorter.

Moving the mounts will likely affect more than just the caster too, randomly moving the mounts back 1” without plotting out the resulting geometry curves would be a poor decision.

For example, E body Hotchkis UCA’s move the front UCA mount to remove anti-dive from the geometry. Their A-body UCA’s retained the factory mounting locations, so, one might infer that moving the UCA mounting locations wasn’t beneficial when keeping the rest of the factory components, seeing as how they didn’t have an issue doing it for the B/E bodies.

 

[Woody500]

What would you do with the shock mount? It seems like that would have to move with the UCA mounts. And that might cause problems with the connection of the shock to the LCA.

Moving the mounts would give the option to use a stock UCA and still get 6 or 7 degrees of positive caster, but when SPC control arms do that for much less work it seems like the tough way to get there.

BAC/SPC 1.5 Upper Control Arm - Bergman Auto Craft

That link seems to show thise arms not available for earlier than 1967 models, so ...

 

[junkyardhero]

That link seems to show thise arms not available for earlier than 1967 models, so ...

the uppers all fit the same from 62 and up

 

[RustyRatRod]

Moving the upper control arm mounts back one inch will equate to a mile as far as alignment adjustment is concerned. Considering there are so many other ways to get increased caster, that seems really extreme. Also, some of these cars align just fine without the need for anything to give additional caster, so you may be jumping the gun. I don't recommend it. Proceed at your own peril.

 

[Woody500]

The 1'' came from another thread and seems a lot. Anyone have stock arcs plotted? Bumpsteer arcs, too. If i knew trig maybe I could get an estimate.
Also seen some old nascar parts that were cut, bent & rewelded out near balljoint for more caster.

 

[DionR]

I will post pictures later, but the 1” number came from my layout where I rotated the spindle to give 6 degrees of positive caster.

The distance between ball joint centers is just under 9.5” per my layout (no promises it is perfect), so each degree of caster is just under 3/16” of offset for the top ball joint. So 6 degrees is about 1”. Note that all of those numbers are rounded, so don’t freak out if the math above isn’t perfect.

 

[junkyardhero]

i think before you go hackasaurous wrecks on it, how about you establish how much caster you want/need?

as mentioned upthread, there exists aftermarket control arms that will give you near excessive amounts for pretty much anything you'd use on the street.

 

[72bluNblu]

It's one thing to do something like that if you're custom fabricating the rest of the suspension components, using different spindles etc.

It's just silly to do it so you can use stock components. Using the K7103 offset UCA bushings gets most people to +3.5° to +4° of caster pretty easily, which is more than enough unless you're running really wide tires and doing some kind of autoX/road racing. And installing those in stock UCA's would take a fraction of the time and have zero unwanted side effects.

The other thing is, if you are running 275's up front and need +6° of caster or more you also NEED to have a tubular UCA, because the 18x9's you need to run 275's will hit the stock UCA's at full steering lock and full suspension droop at the backspace you need to run those tires.. And if you have tubular UCA's even all the non-adjustable ones have more caster built in, so you don't need to move the mounting points. And if you're really serious then you want something like the double adjustable SPC UCA's, which can easily get you more than +8° of caster without moving anything at all on the chassis.

Heck, I had +8° caster on my Duster for awhile with non-adjustable tubular UCA's that had offset bushings installed in them, if you don't want to spend the money on the SPC's.

 

[DionR]

It might be overkill, but I settled on 7 degrees of positive caster as my target. Mostly because it seemed like a number I saw a lot on some of the later model cars I am kind of benchmarking.

Case in point, I like the idea of chasing the S197 Boss 302 as the style of car I want and that car has 7 degrees of caster. Pretty sure @72bluNblu runs 6 degrees and didn’t feel more was necessary. Nice thing is, if I “engineer” in 7 degrees, I can always dial it back some.

And 7 degrees is more than 1”, it’s almost 1.25”.

 

[DionR]

Here is what I think the spindle looks like in it's stock orientation. Ignore the shape of the spindle, the ball joints should match the factory.

Here is the spindle at 6 degrees of positive caster.

This assumes that the LBJ is in its stock location. You can gain some positive caster by pulling the LBJ forward using the strut rod, but I think that is a bad idea and introduces binding into the suspension.

Note that the OTR drops 3/4" between the two conditions, too.

Here's how things might look if the spindle had 7 degrees built into it.

 

[DionR]

I guess 1" was a bit of an exaggeration.

Here is the ball joint in it's stock location and at 6 degrees of caster and the difference between them. More like 13/18".

I know moving the mount on the spindle is almost 1.25" and some of that difference is the greater caster, plus moving it horizontally rather than in an ark like above. This also makes the spindle a touch taller before raising it some more.

 

[Bozwel]

problem is there is a ton of caster change due to the anti dive top arm geometry.

^^^^^ this is full droop (the plate is just leveled with the ground at droop not a measurement)

^^^^^ and with the brake locked this is the caster change as the top arm angles backwards, this isn't even full bump.


i was measuring bump steer but the plate showed how much caster change is present with even small ride height changes.

 

[Bozwel]

I'm messing with a '66 Barracuda to increase caster for a RHD Power steering rack conversion i'm doing.

i'm actually moving the K frame forward by 1/4 inch and doing away with bushes on the lower arms

 

[DionR]

I'm messing with a '66 Barracuda to increase caster for a RHD Power steering rack conversion i'm doing.

What's your plan for maintaining a reasonable ackerman angle?