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Rear four link

Roxtar

Roxtar

NAXJA Forum User
Location
NW Indiana-Chicago area
In the process of building a rear triangulated four link using Fox 2.5" X 16" travel air shox.
I'm running the LCAs along the outside of the (sleeved) frame rails.
Looking for recommendations on link length.
 
kid4lyf said:
In the process of building a rear triangulated four link using Fox 2.5" X 16" travel air shox.
I'm running the LCAs along the outside of the (sleeved) frame rails.
Looking for recommendations on link length.
Click to expand...


Longer to reduce axle steer. Shorter to reduce dragging when drooped.

I would suggest something between long and short. :D

CRASH
 
CRASH said:
Longer to reduce axle steer. Shorter to reduce dragging when drooped.

I would suggest something between long and short. :D

CRASH
Click to expand...
Damn, I just looked at my tape measure and can't find the markings for "long" or "short"
I'll check with my Snap On man to see if theirs do.
 
kid4lyf said:
Damn, I just looked at my tape measure and can't find the markings for "long" or "short"
I'll check with my Snap On man to see if theirs do.
Click to expand...


Have you run the 4 link calculator yet? What kind of AS are you getting?

I wouldn't buy into the calculator results as perfect, but it'll get you into the ballpark. An AS of between 100 and 150% seems pretty darned popular for comp rigs that do a lot of climbing.
 
CRASH said:
Have you run the 4 link calculator yet? What kind of AS are you getting?

I wouldn't buy into the calculator results as perfect, but it'll get you into the ballpark. An AS of between 100 and 150% seems pretty darned popular for comp rigs that do a lot of climbing.
Click to expand...
Unfortunately, It'd be pretty difficult to do that because the heep is somewhat immobile. Both axles are off so weighing it to find the CG is impossible (for me).
I'm also limited as to what I could do with the results even if I had them. Since I'm not chopping it up the mounting points are determined somewhat by the constraints of the floor. Front link mount vertical separation will be minimal.
That's part of the reason I'm going with the air shocks. The unlimited tunability they offer should help mask some of the design limits.
 
I thought you'd have "trimmed" the mangled sheetmetal by now!

That poor Jeep.

kid4lyf said:
Unfortunately, It'd be pretty difficult to do that because the heep is somewhat immobile. Both axles are off so weighing it to find the CG is impossible (for me).
I'm also limited as to what I could do with the results even if I had them. Since I'm not chopping it up the mounting points are determined somewhat by the constraints of the floor. Front link mount vertical separation will be minimal.
That's part of the reason I'm going with the air shocks. The unlimited tunability they offer should help mask some of the design limits.
Click to expand...
 
CRASH said:
I thought you'd have "trimmed" the mangled sheetmetal by now!

That poor Jeep.
Click to expand...
We can rebuild her.
Make her bigger, faster, stronger



I call her Phoenix.
She will RISE from the ashes.
 
kid4lyf said:
Unfortunately, It'd be pretty difficult to do that because the heep is somewhat immobile. Both axles are off so weighing it to find the CG is impossible (for me).
I'm also limited as to what I could do with the results even if I had them. Since I'm not chopping it up the mounting points are determined somewhat by the constraints of the floor. Front link mount vertical separation will be minimal.
That's part of the reason I'm going with the air shocks. The unlimited tunability they offer should help mask some of the design limits.
Click to expand...
top of the bellhousing is the general approximation of COG used by many. if you're running parallel lowers (not triangulated) CRASH is exactly right, you need long to avoid flex-steer, and short to not drag them on everything, the compromise of the two is your decision. I'd just shoot for 30-36 inches. are you going through the floor for the uppers?
 
My uppers measure 37" and my lowers are 35".The seperation is about 5".I have 16" Fox Airshox on it.The lower mount is flush with the bottom of the unibody/cage.
IMG_0473.jpg
 
Well, got the axle in. Lowers ended up at 34" and uppers at 40"
 
the longer uppers will be good for pinion angle through travel, but bad for antisquat, the antisquat will increase when the rear end lifts, making it want to lift even more. also, it looks as though your frame mounts are on the same horizontal plane with no vertical seperation, this will also create a very high antisquat. I center limit strap may make it "good enough", but it's hard to say.
 
BrettM said:
the longer uppers will be good for pinion angle through travel, but bad for antisquat, the antisquat will increase when the rear end lifts, making it want to lift even more. also, it looks as though your frame mounts are on the same horizontal plane with no vertical seperation, this will also create a very high antisquat. I center limit strap may make it "good enough", but it's hard to say.
Click to expand...


It looks like the rear is going to act like a radius arm setup, not good for the AS......

CRASH
 
CRASH said:
It looks like the rear is going to act like a radius arm setup, not good for the AS......

CRASH
Click to expand...
exactly.

hence the reason I recall Beez saying you can't do a good 4 link rear on an XJ without going through the floor. or you could but the lowers under the frame rail, but then you lose a bunch of clearance.
 
That's what I was referring to. By going to the top of the rail for the uppers and the bottom for the lowers I managed just over 2" of vert separation. The AS will be high.
It's actually pretty close to both the D&C and RockKrawler setups.
If you look at them they have the upper and lower mounts very close to each other. Not the optimum setup but the only way around it is to lose the floor or mount the lower links below the rails, losing ground clearence.
Everything's a tradeoff.
It will be easy to move the lower mount down an inch or so if it absolutely needs to be. I just don't want to give up the clearence unless I have to.
 
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