3rd link?

[fordbrian333]

is there a benifit to running a radius arm style third like right to a lower link rahter then a 3rd full length width? or the opposite way around?

 

[Hahnsb2]

Just that it's simpler than running an upper link. It works, flexes well assuming you only run an upper link on one side, but pinion angle changes with suspension travel and I've heard under hard breaking one side tends to dive more than the other.

 

[--weezl--]

found this interesting video which shows an issue with the 3 link...

http://www.youtube.com/watch?v=AcPqpIWLf84

 

[1slow5oh]

With the Radius arm style setup you are putting more stress on the two lowers under braking and any forces applied. The third arm running to a single point on the lower puts stress on the single point and arm....

Running the third arm separate lessens the force on one single lower. The force will be applied to a separate mount. I dont see caster adjustment being an issue with either as long as the joints have the adjustability.

I'm sure I will think of other reasons once I post this....

BTW these are theoretical problems. I have seen both used and work....and it depends quite a bit on material used and suspension design....

 

[BONES]

The youtube scale RC 3 link has no pan hard that's why it moves around like that, add a pan hard and you eliminate that irregular movement all together.

As long as you build your lower links strong enough the upper link can mount to it without issue. One benefit of mounting it to the lower link is you can get away with using less material as the upper link will generally be shorter than if you mounted it to the frame.

I have a wristed rad arm set-up on my sas bii and under hard braking, like locking up the tires, I haven't noticed it dip to one side at all, she nose dives right to the bump stops and slides to a relatively straight stop in short order. Not saying yours will or will not, but mine doesn't exhibit any one sided dive anyways. Maybe because mine only has 5" up travel to the bump stops??

While pinion angle will change under full axle movement up and down with a rad arm type set-up, the changes while driving will be very minimal unless you air it out all the time at higher speeds and achieve full 2 feet of droop in the air, could make for a twitchy landing, but I doubt that will ever be your problem.

Having the 3rd link mount to the frame, you could make it the length it needs to be to keep castor angles through out full travel, but again, unless your airing it out at higher speeds that really is a none issue imo.

I'm not saying that you should go one way or the other. Just some thoughts I had on your question.

 

[fordbrian333]

ok thanks guys, i set it up as two radius arms with the third going to one of the lowers, im using 2inch o.d. .250 dom for the links with curries 21/2 jonny joints so i dont think strengthis really an issue (atleast im hoping), its only got about 3 inches of up travel and alottt of down (im running hydraulic rams as air shocks, the truck isnt getting driven on the road so im not worried about the ride quality and a freind of mine runs them on his camanchee and they work great)

 

[--weezl--]

i was thinking about this over the last few weeks (back of my mind) as for pinion angle, depending on where you mount your upper link(s) you can control your pinion angle completely, if you were to mount your upper links to somewhere linear to the lower links (ie, take a metal rod and all of your mounting points would be a perfectly straight line) the pinion to driveshaft angle would remain the same regardless of wheel travel (provided the link mounting point is close to lining up with the rear of the transfercase... you can also mount the upper links slightly above the lower links, but the same distance from the diff, and as the axle droops, it will increase the pinion angle slightly, but also rotate the diff slightly, reducing the need for a DC driveshaft on that end, it would still have a sharp angle with enough droop, that your front u-joints would bind up and get damage , but putting a dc on one end of your driveshaft i'm sure is cheaper than putting 2 on your driveshaft