Eco diesel Suspension bottoming out on normal roads

[CerOf]

That’s not correct. There is preload on the spring already from the shock limiting the free length. Otherwise, the spring would rattle around when the shock is completely extended. A spacer increases preload and ride height. Spring RATE does not change with a spacer.

With the Jeep on level ground with factory spring and shock:
Unbolt the bottom of the shock.
How much does the shock extend downward?

I’d be willing to bet the shock will extend more than 1” below the stock ride height with the stock spring.
If the above is true, then a 1” spacer would not make the shock compress the spring creating additional pre-load.

If the shock does not extend 1” or more, you would need to use a floor jack to push the axle/lower shock mount up so the bottom of the shock could be lined up and bolted back; compressing the spring. This would narrow the distance between the bump stop and it’s landing pad; increasing pre-load.

ive run spacers on a ZJ, WJ, and JKUR; with stock shocks, and have always had the shock extend past it’s mount in the axle with a factory spring at the Jeep’s static ride height.

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[PackMule]

That’s not correct. There is some preload on the spring already from the shock limiting the free length. Otherwise, the spring would rattle around when the shock is completely extended. A spacer increases preload and ride height. Spring RATE does not change with a spacer.

Great dialogue on this issue... I'd like to get something clear on this...

So Gulf_coasterHTX put in the full Terraflex spacers, which appear to have put in 1.5" spacer on the top of the springs, and 1" pads down by the strikeplate. And this would effectively add 1/2" to the uptravel (3-1/8 after spacers, 2-5/8 speculated as before spacers).

I assume then this has increased the overall travel allowed by the suspension (e.g. increased it from a target of 7.88" of travel to 8.33"). And since the shock mounts have not changed, the shock is actually cycling 1/2" farther than before. Correct? That is assuming that the stock shock actually had that much margin to add, and probably takes away a bit of shock pre-load. Right?

If the above is true, what is the cycle limit of the stock shock? e.g., could you put in a 1" spacer on the top, with no pad on the lower strikepad, and gain 1" of increased travel? Or if so, would you be tacking away too much stock shock pre-load, and/or risking overextending the stock shock during downward articulation?

Just wondering what the limits are on the stock shocks before you are asking for trouble, and should have gotten new springs/shocks. It appears 1/2" seems to be "ok"... as that's what the Terraflex spacers have, that lots of people "level" their jeeps with. But at some point you probably cross a line that is not good to cross.

Any Idea where that line is?

 

[PackMule]

With the Jeep on level ground with factory spring and shock:
Unbolt the bottom of the shock.
How much does the shock extend downward?

I’d be willing to bet the shock will extend more than 1” below the stock ride height with the stock spring.
If the above is true, then a 1” spacer would not make the shock compress the spring creating additional pre-load.

If the shock does not extend 1” or more, you would need to use a floor jack to push the axle/lower shock mount up so the bottom of the shock could be lined up and bolted back; compressing the spring. This would narrow the distance between the bump stop and it’s landing pad; increasing pre-load.

ive run spacers on a ZJ, WJ, and JKUR; with stock shocks, and have always had the shock extend past it’s mount in the axle with a factory spring at the Jeep’s static ride height.

Ok... you answered my question before I asked it!!!!

This would be a good check to do while installing a spacer kit to see where the shock downward travel limits are, ... but would also need to know where the compressed limits of the shock are to ensure the bumpstop hits before the shock is over-compressed.

 

[CerOf]

To simplify pre-load:

The preload is set by the weight of the Jeep.

the shock and/or sway bar end links limit the suspensions downward travel.
the bump stops and/or shocks limit up-travel.

To change pre-load, you’d need to run shocks that are shorter than static ride height or you need coil overs with adjustable pre-load.

 

[Gruffid]

I wonder if there is a way to Frankenlift the MOPAR 2” diesel lift for the front springs, and the rest of a 2” full suspension lift from another company like Clayton or pick your favorite kit, but excluding the front springs?

personally, I’d rather go with the Clayton 2.5” overland kit, but they don’t make one for the diesel specifically.

 

[Scruf]

To simplify pre-load:

The preload is set by the weight of the Jeep.

the shock and/or sway bar end links limit the suspensions downward travel.
the bump stops and/or shocks limit up-travel.

To change pre-load, you’d need to run shocks that are shorter than static ride height or you need coil overs with adjustable pre-load.

This is correct.

If the ride height of the Jeep did not change, then yes adding the spacer would increase the preload of the spring because the spring would have to compressed more to fit into the same space.

But with or without the spacer, the length of the spring with the weight of the Jeep on it is the same. The spring rate is unchanged and there is no additional preload.

*edited - removed incorrect statement

 

[Renegade]

There’s way too many opinions in here that I don’t agree with, but to clarify, I am not advocating to add the bump stop spacer. This would decrease overall suspension travel unless longer shocks or extensions are used. Y’all can take my advice with a grain of salt, but if you don’t understand, I recommend reading up on suspension tuning (like from Accutune, that I linked earlier). The weight of the Jeep sitting on the springs has nothing to do with preload, that’s the ride height. Preload is the amount the spring remains compressed when the suspension (shock) is fully extended. Preload is measured with NO weight on the suspension. And yes, the spring is still slightly compressed when the shock is fully extended.
Resources:
https://accutuneoffroad.com/articles/

 

[Gulf_coasterHTX]

Adding the coil spring spacer does not add any additional up travel because you are still working with the same length spring. Which means that adding in the bump stop extension will make the Jeep more likely to bottom out because you are reducing the amount of available up travel before the bump stop contacts the stop.

I haven't followed line by line the posts but not sure if I understand this conclusion based on previously reported measurements - if stock diesel Sport S has 2 5/8" gap, this would allow for that spring to compress 2 5/8". After adding 1.5" spacer and 1" bump stop extension, I have 3 1/8" gap, allowing for 3 1/8" additional compression, or an additional 1/2" available up travel, correct?

 

[Renegade]

I haven't followed line by line the posts but not sure if I understand this conclusion based on previously reported measurements - if stock diesel Sport S has 2 5/8" gap, this would allow for that spring to compress 2 5/8". After adding 1.5" spacer and 1" bump stop extension, I have 3 1/8" gap, allowing for 3 1/8" additional compression, or an additional 1/2" available up travel, correct?

You raised your ride height, but decreased your overall suspension travel. This is because of the added bump stop spacer you added without increasing the shock extension.

 

[CerOf]

I agree the spring retains compression when the shock is fully extended.

Pre-load refers to the compression/tension on the shock before any load is applied. Hence “pre” in pre-load.

Only way to increase preload on a coil sprung Jeep is to run a shock that is shorter than stock while the full weight of the Jeep is on it or to switch to coil overs.

Going to a shorter shock is silly. This is why they make progressive, dual rate, triple rate, etc. coil springs.

Pre-load is most commonly discussed with coil-overs where the pre-load is adjustable either by turning a collar or inserting a spacer between the top of the spring and the top hat of the coilover assembly.

 

[Renegade]

I agree the spring retains compression when the shock is fully extended.

Pre-load refers to the compression/tension on the shock before any load is applied. Hence “pre” in pre-load.

Only way to increase preload on a coil sprung Jeep is to run a shock that is shorter than stock while the full weight of the Jeep is on it or to switch to coil overs.

Going to a shorter shock is silly. This is why they make progressive, dual rate, triple rate, etc. coil springs.

Pre-load is most commonly discussed with coil-overs where the pre-load is adjustable either by turning a collar or inserting a spacer between the top of the spring and the top hat of the coilover assembly.

Adding a spacer increases the preload on the spring, the same as dialing up the same amount of preload on a coilover.

 

[Scruf]

I haven't followed line by line the posts but not sure if I understand this conclusion based on previously reported measurements - if stock diesel Sport S has 2 5/8" gap, this would allow for that spring to compress 2 5/8". After adding 1.5" spacer and 1" bump stop extension, I have 3 1/8" gap, allowing for 3 1/8" additional compression, or an additional 1/2" available up travel, correct?

I edited my comment above. Since the bump stop is part of the upper coil spring bucket, then adding a spacer on top of the coil spring effectively moves up the bump stop as well. So while you have not added any upward travel relative to the stock coil spring, you do add upward travel relative to the bump stop (as represented by your measurements). I apologize for the confusion.

 

[CerOf]

Adding a spacer increases the preload on the spring, the same as dialing up the same amount of preload on a coilover.

Question: Does the length of the spring stay the same when you put a 1” spacer lift on top?

 

[Renegade]

Question: Does the length of the spring stay the same when you put a 1” spacer lift on top?

Available suspension travel remains the same. The ride height changes, allowing for an increase in available u-travel from ride height, and proportionately decreasing suspension droop from ride height.

 

[CerOf]

Available suspension travel remains the same. The ride height changes, allowing for an increase in available u-travel from ride height, and proportionately decreasing suspension droop from ride height.

But does the actual length of the spring itself change when you have a 1” spacer?

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