longarm/math gurus?

[BigAl]

I put a 6.5" BDS longarm kit on my buddies Cherokee this weekend. We used 8" skyjacker springs. The kit called for 32 3/4 lowers and 28 3/8 uppers. Does anyone know how to calculate the correct length of the arms with the 8" coils rahter than 6.5?

 

[goodtimes]

Are both upper and lower arms adjustable?

Given the info you provided, the upper arms should be 28.9", and the lowers should be 33.2"...to keep the axle in the same for/aft position relative to the wheel wells. The problem is that this will not work because of the unequal length arms. It will throw your castor (and pinion angle) way off at curb height.

Typically, I go about it this way:

Step 1: Start with a rough guess at the arm length (in your case, I'd start the lowers around 32" and the uppers around 28.5...make both the lowers the same length, and both the uppers the same length), then install the axle.

Step 2: Dial the pinion angle in using the adjustable upper arms (keeping both left and right the same length).

Step 3: Adjust axle position using both upper and lower arms (maintaining the pinion angle, and still keeping both lowers the same length as each other, and the uppers the same length as each other). At this point, your axle is centered under the wheel well, and the pinion angle is close.

Step 4: Re-check the pinion angle, fine tune it as needed. Any pinion angle adjustments should be pretty small if you did step two carefully.

Step 5: Lock everything down and test drive it.

With that much lift, you may need to look into castor correction....which can be a pain in the butt, so hope you don't need to do it.

 

[OverlandZJ]

goodtimes is spot on.

I still need to dial in my LA's for the right compromise of pinion angle and castor. But i'm close.

I'd like to see pics of the BDS system. I'm running RE arms and Claytons crossmember.

goodtimes...in your experience do you usually attempt to get around 6-7* castor?

 

[goodtimes]

On the short wheelbase jeeps (like my TJ), 6 degrees is awesome...if you can get it. I am between 4 and 4.5 degrees, and that is all I can get with the arms that I am using (Rubicon Express). As it drops off towards 0, the handling goes out the window.

 

[BigAl]

Are both upper and lower arms adjustable?

Given the info you provided, the upper arms should be 28.9", and the lowers should be 33.2"...to keep the axle in the same for/aft position relative to the wheel wells. The problem is that this will not work because of the unequal length arms. It will throw your castor (and pinion angle) way off at curb height.

Typically, I go about it this way:

Step 1: Start with a rough guess at the arm length (in your case, I'd start the lowers around 32" and the uppers around 28.5...make both the lowers the same length, and both the uppers the same length), then install the axle.

Step 2: Dial the pinion angle in using the adjustable upper arms (keeping both left and right the same length).

Step 3: Adjust axle position using both upper and lower arms (maintaining the pinion angle, and still keeping both lowers the same length as each other, and the uppers the same length as each other). At this point, your axle is centered under the wheel well, and the pinion angle is close.

Step 4: Re-check the pinion angle, fine tune it as needed. Any pinion angle adjustments should be pretty small if you did step two carefully.

Step 5: Lock everything down and test drive it.

With that much lift, you may need to look into castor correction....which can be a pain in the butt, so hope you don't need to do it.

Yes both the upper and lowers are adjustable, that makes sense, as long as caster and pinion are okay then who cares how long the arms are. The steering doesn't bind and we did bushwacker cut out flares so the the wheel can sit a little forward with no issue. I ended up with 33 lowers and 28 5/8 uppers.

THANKs

 

[BigAl]

goodtimes is spot on.

I still need to dial in my LA's for the right compromise of pinion angle and castor. But i'm close.

I'd like to see pics of the BDS system. I'm running RE arms and Claytons crossmember.

goodtimes...in your experience do you usually attempt to get around 6-7* castor?

I'm stuck in Kalamazoo MI on business:smilies27 I'll post some pics when I get home. I have only seen a rustys and this BDS but the BDS is really well made and was a breeze to install:bowdown:

 

[BigAl]

Here is the BDS kit, I tired to take some odd angle pics to show all the components. You can see where I cut off the stock LCA mounts

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[OverlandZJ]

I like the 4 arms vs a radius style arm. Hows the ride?

Replace those zerk fittings with plugs, and reinstall the zerks when your greasing the chassis.

Nice looking rig.

 

[BigAl]

Hows the ride?
Replace those zerk fittings with plugs, and reinstall the zerks when your greasing the chassis.

It rides really nice. Better than most vehicles on tires that big. That's a good idea on the zerks, especially on the lowers, they're begging to be ripped off

Nice looking rig.

Its a 95 with 103K. It was a Park Ranger Jeep, bought at auction for $1100 b/c it said bad steering on the window. Replaced the steering box and all is good. It has zero rust and was really well maintained from what can be seen.:safari-rig: