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JK suspension in a TJ problems

8K views 39 replies 4 participants last post by  HSEXC 
#1 ·
Hello everyone this is my first post here and i was hoping I can get some help. I have a 99 tj 4.0l 5 speed. I read a lot of info on lifting the tj with the jk coils and springs and heard mixed reviews about it so I decided to give it a try myself. After install i got maybe an inch on the front and what seemed like 4 to 5 inches on the rear. The jeep looked ridiculous. So I had the bright idea of buying 3 inch coil spacers for a jk and installed them on the front springs. The result is still a 3 inch difference between the front and rear. I really want to try and leave at least 1 set either front or rear on so it wasn't a complete waste of my time and money. Does anyone have any ideas? Or anywhere I could go from here? Plus the ride even with 3 inch spacers is much improved. Please any input will be helpful. Thank you.
 
#2 ·
Not sure but I don't believe the JK rear coils will fit a TJ without making the hole bigger by heating the spring. That may be why you have the 3 or 4 in difference. The springs are not seating properly.
 
#3 ·
This is correct. You need heat or cut about 2in off so it fits in the coil bucket. Also what spring part numbers did you use?

A 1"/3" front/rear lift would not be surprising with the 4.0L. I got 2/2.5 when I did this on mine - but with v8 zj springs in the front.
 
#4 ·
Thank you so much for all your help. I think I'm going to cut it 2 inches. From any of your experiences do I need bump stop extensions? Because if I'm not mistaken i believe the 3 inch spacers i used in the front to attempt to level it out replace the bumpstops. Or is that incorrect?
 
#7 ·
Just to be clear - you are not cutting 2in from the height of the spring, but rather just a small piece from the coil of steel at the top so that it fits in the coil bucket.

Depending on your budget i would look at getting v8 ZJ springs for the front instead of spring spacers. $50 used or $70 new.

You could add some bumpstop extensions as well. 1.5in should do it.

Here is before the lift:

And here is after
 
#8 ·
Ok so trim the top of the coil until it
fits in the bucket and get V8 ZJ coils for the front. Will the JK shocks have enough travel for the front ZJ springs? And 1.5 inch bumpstops extensions on all 4? Do you know a good site to get the ZJ coils from? I'd rather get them new for $70 than used from a yard. Thanks again and your truck looks awesome man hopefully mine can look like that soon.
 
#12 ·
Yep. JK shocks will be perfect for a 2-3" lift. For bumpstops you can either buy are pre-made sets or do what I did and order 2in diameter, 3in body lift pucks on ebay and cut them in half and buy longer bolts from the hardware store. I would get the ZJ coils on Amazon or rockauto. Keep in mind there is a forum discount code for rockauto in the vendors section.

Ok as promised here are the pictures of the jeep with the lift and the labels. The first picture is the way it sits now. The second image is the shock labels on the front the rears were too faded. The third picture is of the front springs from jk with the 3 inch spacer. The 4th picture is of the rear coil seated in the bucket. The 5th image is of the rear coil Spring labels. By the way the tires are 31x10.50.
That does not look like 4-5in of lift - did you measure before/after?. It looks about the same as mine. The problem is your front springs actually dropped you TJ so with the spacers you are probably only at 1-1.5in lift in the front. ZJ springs will fix that. It actually looks like the rear coil is seated ok. If you can take pictures with better light of the top and bottom of the rear coil I could say for sure.
 
#9 ·
I also have a question. I've been looking for zj springs and decided to look on rock auto for some and found them for $35! But my question is, doesn't that sound a little jeep for a pair of springs? Can I trust moog springs in that they will be strong enough to lift the front like OEM v8 springs and won't sag over time? Here's the link:

https://www.rockauto.com/catalog/moreinfo.php?pk=225458&cc=1315953&jnid=418&jpid=0
 
#11 ·
Those are probably good springs for a ZJ, but not the right ones for a swap.

What you are looking for is moog part# cc782 for a ~2" lift and cc784 for ~2.5" lift. Those lift numbers are for Jeeps with the i6 4.0L engine.
 
#10 ·
Ok as promised here are the pictures of the jeep with the lift and the labels. The first picture is the way it sits now. The second image is the shock labels on the front the rears were too faded. The third picture is of the front springs from jk with the 3 inch spacer. The 4th picture is of the rear coil seated in the bucket. The 5th image is of the rear coil Spring labels. By the way the tires are 31x10.50.
 

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#15 ·
I am not sure. Maybe 1-2in more. You should try some -19 JK front springs first if you have the 4 cylinder engine. If you go the v8 zj route then i would try cc782 to get somewhere between 2-3in.
 
#16 ·
Yes - well i should have said 2-3in. I have not personally used those yet and i cant guarantee an exact number. The cc782 springs are comperable to v8 zj springs, which lift about 2". cc784 springs are like the v8 zj overland springs and will give you 2-3in.
 
#17 ·
Ok guys a little update i just got my coils from amazon moog part #cc784. I really hope these are the right ones for the front because they look so much longer than the originals. I assumed they were the same size just stiffer. These are for the ZJ overland i believe. Take a look and let me know if you guys think this will work.
 

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#27 ·
Nominal cost of a zj/jk swap is $200. Even with a BL that is $350. Zone 4.25 is $530. But I do see your point. From what I hear the zone kits are highly recommended so I am sure you will be happy with whatever you choose.
 
#28 ·
Ok so I put the coils in. Jesus christ that took forever to get the clips just right to compress the spring was a nightmare, but after about 6 hours i was done. So now I have the ZJ coils in the front and the jk coils still in the rear as well as the jk shocks all around. I have to say I am pretty displeased with the results. I on purpose measured with one of the jk coils with the 3 inch spacer and in the passenger side and one of the new ZJ coils in the driver side with no spacers and the measurements were exactly the same. So now with both of the ZJ coils in the front with no spacers the jeep sits exactly the same as it did before. 6 hours of hard labor for nothing. I just don't understand this for the life of me. Should I put the stock tj coils that I still have in the rear instead of the jk coils? Or should I put the the front jk coils in the rear. So just so there is no confusion should I put either my stock tj coils in the rear or the front jk coils in the rear to level it out. Because as of right now it still looks just as retarded as it did before the ZJ coil install. Thank you everyone for your responses.
 
#31 ·
Just eliminating the coil spacers is a good first step. Now we need to fix that rake. Can you take some measurements of the front and rear springs as they sit compressed on the Jeep? Can you post as many pictures as possible of the rear springs? How about a pic of the Jeep on level ground? Using that info I can probably figure out what is going on.
 
#30 ·
Ok so I put the coils in. Jesus christ that took forever to get the clips just right to compress the spring was a nightmare, but after about 6 hours i was done. So now I have the ZJ coils in the front and the jk coils still in the rear as well as the jk shocks all around. I have to say I am pretty displeased with the results. I on purpose measured with one of the jk coils with the 3 inch spacer and in the passenger side and one of the new ZJ coils in the driver side with no spacers and the measurements were exactly the same. So now with both of the ZJ coils in the front with no spacers the jeep sits exactly the same as it did before. 6 hours of hard labor for nothing. I just don't understand this for the life of me. Should I put the stock tj coils that I still have in the rear instead of the jk coils? Or should I put the the front jk coils in the rear. So just so there is no confusion should I put either my stock tj coils in the rear or the front jk coils in the rear to level it out. Because as of right now it still looks just as retarded as it did before the ZJ coil install. Thank you everyone for your responses.[/QUOTE]
 
#34 ·
I am at 35" front/37" rear from ground to the bottom of the fender flare. So I guess I have a 2" rake. So either the JK rear spring is not seated correctly, they are giving you too much lift, or the ZJ springs are not working as expected.

Can you measure the actual compressed length of a front and rear spring now that they are installed on the Jeep? Then you can compare that to stock numbers to see how much lift you got and where your problem lies.

I would not put front springs in the rear. The Jeep was not designed to use springs that way. Post up some pictures and then maybe I can get a better idea of what you are working with.
 
#35 ·
I am at 35" front/37" rear from ground to the bottom of the fender flare. So I guess I have a 2" rake. So either the JK rear spring is not seated correctly, they are giving you too much lift, or the ZJ springs are not working as expected. Can you measure the actual compressed length of a front and rear spring now that they are installed on the Jeep? Then you can compare that to stock numbers to see how much lift you got and where your problem lies. I would not put front springs in the rear. The Jeep was not designed to use springs that way. Post up some pictures and then maybe I can get a better idea of what you are working with.
I wish they would give us the spring rate constants so we could actually calculate if the springs would work or not.
 
#38 ·
That is one way to do it, and it works - but its not a great idea. The front springs are designed so that the coils collapse and stack on top of each other. The rear springs are designed so that the coils collapse around each other. Using the front springs in the rear means that the coils will ride closer to coil bind and are more likely to get damaged over time. They are also not the right shape to fit in the rear coil buckets and be stable under load. I would not recommend it, but it may solve your problem.[/QUOTE]

Ok i understand now what you're trying to say. You're saying that it's not the right way to do it, but there is a possibility it will work for temporary use. Do you know of another way I can correct this damn rake on the front to level out the front and rear. I don't think the rear coils are the problem because I took pictures before and I think they're seated ok. What else can I do?
 
#39 ·
Ok i understand now what you're trying to say. You're saying that it's not the right way to do it, but there is a possibility it will work for temporary use. Do you know of another way I can correct this damn rake on the front to level out the front and rear. I don't think the rear coils are the problem because I took pictures before and I think they're seated ok. What else can I do?
Well the easiest next option would be to get some ~2" coil spacers and use those and your OE TJ rear coils. That should get you 2" lift in the rear. I would measure your front ZJ springs and if they are around 14" then a 2" coil spacer will set you back to factory rake. The other option is to play around with more JK rear springs in the 54-46 range if you can find some near you.

Zone Offroad 1-3/4" Coil Spring Spacers J2202
 
#40 ·
Alright, I want to bring back this thread as I am considering this swap again. John, do you remember if the zj coils gave you lift over the front stock tj springs? Because if I remember correctly, you said you swapped in the jk springs and got no lift, but then put it 3" coil spacers. That would be 3" of lift in the front right? Then you put in the zj coils and took out the coil spacers and it stayed the same. So in theory you got 3" of lift in the front over stock with the zj springs. Is that correct?
 
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