Caster School Time

[JBronc]

Ok, take me to caster school....

I have a 3.5 lift using 7 deg bushings with stock radius arms and just purchased some new Duff long arms.

The Duff arms already have 4.25 deg of caster built into them but recommend using a 2 or 4 deg bushing with them.

So here I am wondering what to do. If I install a 2 deg bushing I'll only have a total of 6.25 degs (.75 less than I have now) and if I install 4 deg bushings I'll have a total of 8.25 degs (1.25 more than I have now).

So what will less or more caster do for the drivability? As it is my Bronco drives ok at speeds bellow 50mph but does wander on the freeway a little.

 

[nlped]

Can't help, but I am subscribed so I can go to school with you

 

[sp71eb]

I'm not going to be much help because this is from memory. I have a 3.5 lift with stock arms and 7 degree bushings and my align specs(from memory) are +.65 so in my thinking if your lift gives you similar results as mine you could use a little more caster than the 2 degrees. I would rock the 4 degree. That being said all lifts/trucks are different and this may mail entail you installing a set and taking it to a align shop and see where you are at.

 

[Jeff76]

First, correct usage of wonder *and* wander in the same post. Impressive! ; )

A year or so ago, I put up a questionnaire thread on caster, and you should be able to search for the results. General opinion is more positive caster seems to be better on streetable broncos. This impression could be because the broncos generally came with less than optimum caster from the factory. The game is driveline angle vs caster. In my experience with gradually increasing the caster, more caster improves straight line stability, return to center, and reduces (buffers?) bump steer a bit if your steering geometry is off a little.

If you have some minor issues at higher speed, a bit more caster might help. Changing those bushings the first time was daunting, but after the initial time. It's really not that difficult. I would probably go with the 1.25 improvement, try it out, then then increase if needed. That way you can dial it in. I'm sure there is a point of diminishing returns, but I'm not sure that point is the same on every bronco.

Jeff

 

[JBronc]

Thanks for the feedback guys.

I'm leaning more towards the 4 deg bushings. If it sucks going to the 2 deg bushings will just be another Friday night in the garage I guess...;D

 

[surfer-b]

Couple of things here
1: 8.25* caster would be good
2: In theory yes you should get 8.25* with the 4* bushings and the arms with the 4.25* built in, however a lot of times it doesn't always gain that amount, usually a little less from my exper.
3: you need to look at the pinion/d-shaft angle with the 4* bushings, too much and it could cause binding when you have axle drop/wheeling.

 

[bmc69]

I build 6-7 degrees in to every rig I build and have built...I have not personally had one with as much as 8 but I sure wouldn't be skeered of that number.

 

[bmc69]

First, correct usage of wonder *and* wander in the same post. Impressive! ; )

LMAO....

 

[OX1]

Ok, take me to caster school....

I have a 3.5 lift using 7 deg bushings with stock radius arms and just purchased some new Duff long arms.

The Duff arms already have 4.25 deg of caster built into them but recommend using a 2 or 4 deg bushing with them.

So here I am wondering what to do. If I install a 2 deg bushing I'll only have a total of 6.25 degs (.75 less than I have now) and if I install 4 deg bushings I'll have a total of 8.25 degs (1.25 more than I have now).

So what will less or more caster do for the drivability? As it is my Bronco drives ok at speeds bellow 50mph but does wander on the freeway a little.

4.25 degrees caster with what lift? If that is compared to stock, then the 3.5 lift may be putting you @ neg caster already (depends upon long arm length), assuming no correction from C-bushings.

 

[bmc69]

4.25 degrees caster with what lift? If that is compared to stock, then the 3.5 lift may be putting you @ neg caster already (depends upon long arm length), assuming no correction from C-bushings.

As I understand it, Jim, (and I've installed their arms so it works) their definition is the same as the one I use when building my own extended arms...the arm itself has 4.25 degrees of caster built in to it relative to the 0-caster (i.e ..straight) stock arms. So that 4.25 degrees is added in to the equation as you calculate the lost caster for various lift amounts and try to "put the caster back".

Every 3.5 lift I've done with stock arms, I used the 7-degree bushings and ended up in reasonable caster territory with no control problems.


It's always better to measure, measure, measure, IMHO..than to guess and try to calculate the end result from cumulative changes to the front end geometry.

 

[Apogee]

OX1 brings up a valid point, the radius arms with built-in caster are using the stock arms with zero caster correction as a baseline. Considering you'll lose a few degrees of caster with a 3.5" lift, I would definitely go with at least the 4 degree bushings to start.

FWIW, I run the 7 degree bushings with my CAGE arms on my '77 and have pinion angle issues because of it, however I do drive mine at 75 mph on the freeway and need to to track safely. The HP D44 going under it should address my pinion issues...and I may rotate the knuckles as well.

 

[garberz]

The Duff arms have about 4.25 built into them by just being longer. I would suspect they have 2.5 degrees built in to the arm itself and the rest is gained by simply locating the pivot farther back on the frame. The reason they recommend 2-4* bushings is because of the front pinion angle as surfer-b mentioned. I put the Duff arms on my buddies with 3 1/2" coils. He's running the 4* "C" bushings. That's about all the pinion angle can take. The drive shaft will bind when you flex it. He's using an offset U-joint up front to help. You can't have too much negative caster. Until you cut and turn the yokes, the pinion angle will determine your max caster. I measured the toe-in off the tires, 35". I set it at 3/8" toe-in. make sure you have enough toe-in, that helps with the wandering.

Mark

 

[bmc69]

The Duff arms have about 4.25 built into them by just being longer. I would suspect they have 2.5 degrees built in to the arm itself and the rest is gained by simply locating the pivot farther back on the frame.

That sounds about right; the long arms I've built over the years are 14" longer and include almost exactly 2 degrees of additional caster physically built in to the arms.

 

[OX1]

As I understand it, Jim, (and I've installed their arms so it works) their definition is the same as the one I use when building my own extended arms...the arm itself has 4.25 degrees of caster built in to it relative to the 0-caster (i.e ..straight) stock arms. So that 4.25 degrees is added in to the equation as you calculate the lost caster for various lift amounts and try to "put the caster back".

Every 3.5 lift I've done with stock arms, I used the 7-degree bushings and ended up in reasonable caster territory with no control problems.


It's always better to measure, measure, measure, IMHO..than to guess and try to calculate the end result from cumulative changes to the front end geometry.

OK, assuming not measuring. Arms are 33 inches, so you lose 6 degrees caster just from a 3.5 lift. If the new arms put back 4.25, and you add another 2 from bushings, you are really only back to stock caster.

Assuming larger tires are going with the lift, I'd put back the 4 degree bushings with the arms, that puts you a hair over 2 more than you were stock, all said and done. Even that may not be enough, but you'd probably be looking at pinion angle problems doing any more corrections with bushings/arms.

Bill is right though, need to measure and see where you are.
Or try it and if you don't like it, mod the axle later to fix
caster once and for all.

 

[jimnrenee's77EB]

caster problem

I have a 77 with the James duff long arms and a 3.5 inch james duff lift. I at first installed the kits 4 degree caster shims and had terrible problems with darting and only had 0.7 degree of caster with my front axle. I then ordered 7 degree bushings and my truck was controllable with no worries of darting into oncoming traffic at 60+ MPH. Just my 2 cents