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Shock length and leaf spring free arch question

W

Woodswanderer

NAXJA Forum User
Location
SEPA
Trying to understand how one affects the other. I get that overtravel is a bad thing and will tear seals, too short and it bottoms out and blows the shock rebound. What i cant wrap my head around is the free arch going into the equation. And adding bar pin eliminators into the equation, that adds about an extra inch of travel, correct?

I think this is why my ass end is weird after <5k miles...suspect the new springs blew the new shocks due to more free arch (5.5” vs 4”).

Stock shocks have an extra 0.81” of length when extended vs kyb (20.61” vs 19.8”), but less compressed length (12.73” vs 12.95”). Travel length of stock shock is just over 1” more than the KYB (7.88” stroke vs 6.85”).

gabriel hijacker shocks i have on hand should fix the problem, correct? They have a 7.73” stroke length, 20.77” extended and 13.04” compressed length up to 200psi max. Add the BPE’s and that becomes 8.73”/21.77”/14.04” respectively?

Thread used for stock shock/leaf arch info:

https://www.naxja.org/forum/showthread.php?t=966436


codename 99 problems: Daily driver/tow rig build thread
 
Unless your shocks are routinely topping out or bottoming out during your driving routines, I don't think your new leaf springs caused the death of your rear shocks.

If you are looking to spec new shocks, my approach for the rear leaf springs is that the installed fully extended length of the rear shocks should be the same or a little longer than the fully extended leaf springs. Definitely do not allow the shocks to bottom out before your suspension has reached max safe travel. Change bump-stops as needed. For a given shock length some shocks have more travel than others. Monotube generally have less travel than twin tube shocks.
 
maxbraketorque said:
Unless your shocks are routinely topping out or bottoming out during your driving routines, I don't think your new leaf springs caused the death of your rear shocks.

If you are looking to spec new shocks, my approach for the rear leaf springs is that the installed fully extended length of the rear shocks should be the same or a little longer than the fully extended leaf springs. Definitely do not allow the shocks to bottom out before your suspension has reached max safe travel. Change bump-stops as needed. For a given shock length some shocks have more travel than others. Monotube generally have less travel than twin tube shocks.
Click to expand...


Im hitting bump stops and getting body roll/bump steer. Also sagging the ass and the springs are flat with maybe 75lb in the rear. Springs are rated 755lb each...even on S shaped factory springs i wasnt bottoming out with this weight in the back. Shouldnt be happening with under 5k on them

I suppose the bump stops could be too long and could be cut down or removed. Can anyone verify the length of the originals from factory? (Mine were nubs)

Didnt realize monotube normally had less travel. Im not even 100% the shocks are blown, it feels like they may be


codename 99 problems: Daily driver/tow rig build thread
 
Specs on the springs:


OEM Number:52000545AB, 545 LL
Width:2-1/2 Inches
Length (A): 23 Inches
Length (B):28-5/8 Inches
Arc (C):5-1/2 Inches
Number of Leaves:4
Pack Thickness (D):1-1/8 Inches
Capacity:745 lbs.
Front Bushing:Included / RB-163
Rear Bushing:Included / RB-138
Location:Rear
Spring Construction:4/276

So i should have a shock with 28” of travel with these, max?


codename 99 problems: Daily driver/tow rig build thread
 
You're reading the specifications incorrectly. The length values A and B are the leaf lengths from the axle pinning point to the front mounting bushing (A) and the rear mounting bushing (B). If you already have the springs installed, then remove the shocks, get the vehicle off the ground to let the rear axle hang down, and then measure from upper to lower shock mount. The shocks should be at least that length.

The slightly more difficult step is determining the desired compressed length. A simple and safe estimation is to measure the up-travel to the bump stop and then add whatever extra travel you think can occur after contacting the bump stop. Maybe another 1-2 inches depending on your bump stop configuration. Subtract this total value from your extended length, and that will be your target compressed length. Since the shock is canted at an angle, it will actually never compress as much as your estimation, so this is a very safe approach to keep from bottoming out on your shocks which would be bad for the upper shock mount subframe.

A complication that occurs in these estimates is that as the axle goes through its travel, it rotates due to the changing arch angle of the leaf. This is due to a few different factors, but it does happen, and on lifted XJs, the extended length on the driver side is significantly longer. On my 4.5" lifted XJ, the driver side is ~1.75" longer at full droop. And not only that but the amount of required travel on driver and passenger side is different. The driver side will need more travel. I'm not trying to complicate things, but its good to be aware of these aspects, and for the relatively low lift of your XJ, these may be non-issues.

Keep in mind that while bar pin eliminators are sometimes needed for a few different reasons, they take up space and should be included in your length estimates. My recollection is that the JCR BPEs take up the least amount of space and are a nice design.
 
Thanks Max, that definitely clears a lot up 😊

I’ll do some measuring when i get the lift kit and install it. I suppose its quite possible the monotubes are the correct length and they may not be getting enough compression stroke with the bump stops installed. Most, if not all, of my issues come from the right rear. Easiest test would be to remove the bump stops and see if the banging goes away.

The more research i do on this issue also makes me wonder if the shackles arent set up correctly or are deflecting too much. Spring manufacturer says the front eye is correct and there should be some gap, but they need to be tight in the shackles and some cheaper ones that arent gusseted will deflect and twist under load.

When i did everything and installed the u bolts, the new ones came with washers and locknuts where the factory ones just had


codename 99 problems: Daily driver/tow rig build thread
 
Just to be sure that we're on the same page - the shackles are supposed to twist around the installation bolts via the rubber bushings.

I'm not sure I understand what you are saying about the shocks and bump stops. The bump stops are travel limiters. The axle should bottom out on the bump stops before the shock is fully compressed.

How far is the axle away from the bump stops when your XJ is normally loaded?
 
Pics of the gaps in the eyelets of the springs, not sure if it helps but the oem springs filled the body mounts tighter than this 🤷🏼*♂️

cae5fbcaf243b2ac3d9dd399cb58fd58.jpg

0402bb2404cf5a2668f356bc9a84c4ef.jpg

9b73bfd7b5fcc2e0a938f646fd5edc8b.jpg

ea01bb181e858f32e116d519b39d4b0b.jpg



I’ll have to measure the bump stop to axle clearance. These are the stops i used:


https://www.quadratec.com/products/918280_09.htm


codename 99 problems: Daily driver/tow rig build thread
 
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