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Coil springs rub unibody rail at full flex

maxbraketorque

NAXJA Forum User
Location
PDX
During a flex check of my freshly installed front axle, I observed that the coil springs lightly rub against the unibody on the side that's compressed at full flex. Since this appears to be due the tilt of the axle causing the spring to bow inward, I'm guessing its a common event when fully flexed, but would be interesting to hear from others if its common.
 
Most likely attributable to the lack of lateral spring stiffness. I just looked and after being at 5.5" for 20yrs my paint there is slightly burnished!
 
Same issue on my 99 with 5" of lift and front to rear stiffeners. The front stiffeners put the unibody rail closer to the coil spring.

I did have a little bit more rubbing than I would have liked on my drivers side. The RE coil springs I used seem to have a slight bow when installed. That bow was pointing towards the unibody. I ended up just rotating both coils springs to get the bow facing forward. Seemed to help greatly, but a little bit of rub might not be avoidable.

You can also check the centering of your axle if the rubbing is more pronounced on one side.
 
Here are a couple of photos at a few inches away from full flex either on driver or passenger side. Just slightly rubs on both sides. On the driver side, its rubbing against the track bar mount. It just misses the rib on the mount, but it rubs on the plate. It rubs about the same on the passenger side. I have the axle slightly favoring driver side.

As I look at the photos, I wonder a bit whether deflection of the coil spring spacers is contributing a bit to inward bow of the coils.

RC45LA_driver_side_coil_rub_at_flex.jpg


RC45LA_passenger_side_coil_rub_at_flex.jpg
 
I had similar issues when I swapped in my ECGS D44. Had to clearance the Ironman 4x4 TB mount and the coil perches due to coils rubbing.

I played around with caster quite a bit which helped out with the coils bowing. What caster are you currently at? If you have adjustable CAs it might be worth adding some more caster in which would tilt the coil perch back, reducing the bowing tendency. This will point the coil perch more towards the bumpstop and allow the spring to compress in a (more) straight line. Of course only add caster if it doesn't mess up your pinion angle.
 
How about a pic at full articulation!
 
How about a pic at full articulation!

If you're asking me, I'll get to that eventually. I'm sure the springs will rub more. The only thing left to learn with more articulation is whether the tires will rub before the suspension is firmly against the stops.
 
The only thing left to learn with more articulation is whether the tires will rub before the suspension is firmly against the stops.

That should have been done before ever installing the springs. My comment was to see how bad it would get!
 
That should have been done before ever installing the springs. My comment was to see how bad it would get!

I measured based on tire diameter, and the snubber should be well onto the bump stop before a tire rubs. Here are a couple of photos showing the amount of tire stuff relative to the amount of spring compression. There's ~4 inches more of available wheel movement, but only ~2 inches until the snubber hits the bump stop. Its not a progressive of a bump stop as some people use, but I plan to rarely flex my XJ that much.

RC45LA_front_driver_flexed_driver_side_view.jpg


RC45LA_front_driver_flexed_passenger_side_view.jpg
 
Well that explains a lot as you've got the axle pushed forward a lot so the springs start out crooked!
 
Well that explains a lot as you've got the axle pushed forward a lot so the springs start out crooked!

The front axle is only moved 0.5" forward. It actually helps with fore-aft spring alignment. If the axle is level side-to-side, the upper and lower perches are actually pretty well aligned to each other at the amount of suspension compression shown in the photos in my prior post.

Here are a couple photos with the suspension evenly compressed further than the point shown in the flex photos. It can be seen that the axle-side perches are behind the frame side perches. When the suspension has a few inches less compression (like in my previous photos), the axle side perches move into better fore-aft alignment as the radius arm goes through its arc. And the perches are more parallel to each other.

Since you mention that there is mild coil rub with your XJ, and others have mentioned it, it seems to me that its at least fairly common. Perhaps it happens more strongly with some spring brands or spring lengths. And of course its going to be dependent on axle alignment.

RC45LA-driver-side-spring-perch-alignment-fore-aft-stuffed_web.jpg


RC45LA-passenger-side-spring-perch-alignment-fore-aft-stuffed_web.jpg
 
I had similar issues when I swapped in my ECGS D44. Had to clearance the Ironman 4x4 TB mount and the coil perches due to coils rubbing.

I played around with caster quite a bit which helped out with the coils bowing. What caster are you currently at? If you have adjustable CAs it might be worth adding some more caster in which would tilt the coil perch back, reducing the bowing tendency. This will point the coil perch more towards the bumpstop and allow the spring to compress in a (more) straight line. Of course only add caster if it doesn't mess up your pinion angle.

Forgot to respond to your question. Currently estimating that caster is 5-5.5 deg. The pinion shaft to drive shaft angle is right at 2 degrees. Return to center is good. So, its a pretty good compromise. I could dial in another degree of caster, but I'm not sure that it would help overall with spring alignment.
 
Yeah, if they're not rubbing during normal/on-street driving, I wouldn't worry about it. It's not uncommon to have the coils hit the frame during full compression. And having that 3/16" thick track bar bracket doesn't help on the drivers side. I shifted my axle over a smidge to help offset this.
 
Rubbing Snubbing,still a fine looking jeep my brother.
P.S. thanks for the pictures!⁸
 
Noone needs bump stops thats what Sawzall and sledge hammers are for. Shhhzzz these bumping stopping jeep guys.

If castor is actually 5.5deg thats good. Its shoukd track arrow straight down the rd. If it wonders your 5.5deg number may not be acurate.
Depending on pinion angle id be comfortable giving it a handfull more castor if it doesnt like to drive a straight line or return to center leaving turns.
But there are other reasons these jerps steer and drive like shit. Castor isnt the endall cure its just a # to help get geometry dialed in

Is this rig used off road much?

Sent from my SM-G781U using Tapatalk
 
Noone needs bump stops thats what Sawzall and sledge hammers are for. Shhhzzz these bumping stopping jeep guys.

If castor is actually 5.5deg thats good. Its shoukd track arrow straight down the rd. If it wonders your 5.5deg number may not be acurate.
Depending on pinion angle id be comfortable giving it a handfull more castor if it doesnt like to drive a straight line or return to center leaving turns.
But there are other reasons these jerps steer and drive like shit. Castor isnt the endall cure its just a # to help get geometry dialed in

Is this rig used off road much?

Sent from my SM-G781U using Tapatalk

Caster is only an estimate. Before I swapped in the D30HP, caster was measured to be 4.5 deg at an alignment shop. Return to center was sufficient, and it was no problem staying in lane at any speed. When I installed the D30HP, I shortened the short arm by 1/8" which, by my calculations, should have increased caster by 1 deg. And I lowered the front suspension by 1/2" which will also increase caster because its a radius arm suspension. Return to center feels a little stronger now, but either way, it was fine. I don't think I'll add any more because at full compression, the axle-side spring perch is already tilted back quite a bit.

Just easy double-track so far. Not really interested in rock crawling to rock crawl. I just want a rig capable of getting me to some remote lakes and streams to hang out for the day.
 
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