Rear coil suspension

I know we hashed through this a few months ago, but I lost the links. Anyone have a link to a good writeup for building rear coil suspension? MacGuyver had some great pics but the site has moved. I need help with putting together the unibody side mounts for the links. :helpme:
TIA
Mattk

here's a pic for ya

Brad

Here are a few I posted a while back. I hope they give you some ideas.

http://home.att.net/~j.kaczmarski/wsb/media/123450/site1029.JPG

http://home.att.net/~j.kaczmarski/wsb/media/123450/site1030.JPG

http://home.att.net/~j.kaczmarski/wsb/media/123450/site1033.JPG

http://home.att.net/~j.kaczmarski/wsb/media/123450/site1034.JPG

http://home.att.net/~j.kaczmarski/wsb/media/123450/site1035.JPG

http://home.att.net/~j.kaczmarski/wsb/media/123450/site1036.JPG

http://home.att.net/~j.kaczmarski/wsb/media/123450/site1038.JPG

-Jon

Impossible!

Can't be done. :looney:

No way. :dunno:
Rear coils won't work. :twak:

Jon, Nice work by the way. Exactly how did you decide on and measure the "frame" end mounts for the control arms? I'm a smart guy, but the details of optimizing anti-squat geometry elude me. I just want to copy a design that works (of course I will give credit where it's due if anyone asks)
Also, I remember you saying that the lift was more than you expected. How has that issue resolved itself? I was thinking about cutting the frame rails out where the springs will sit, reinforcing the area with some plate and mounting the spring on an ACOS mounted more or less at the level of the floor of the trunk. I only want about 7 inches of total lift on the rear. Sound reasonable? TIA
mattk

Uh, i shouldn't have seen this thread. I just was deciding against a coil spring conversion but you guys got me interested.

What i'm thinking about is a coilover conversion front and rear. Has anybody done this already? I'm not very experienced with this type of suspension so i would need some help in determining shock length, mount points and coil springs.

mattk, forget the ACOS in the rear, capture the springs on both ends. As for lift, fab your axle spring pads and your upper mounts and see how much "lift" these are going to provide. I have a spreadsheet to help you determine springs to use. I will be glad to help you with spring lengths, rates, and resulting lift. My current setup is a set of stock TJ front coils. They give me about 13" from the bottom of the "frame" to the top of the axle tube. They are very soft so I am thinking of changing them. One of the nice things about running coils is that you can change your spring rate by simply swapping coils. I can swap mine out in less than 30 minutes.

XJoachim,

My original plans were to eventually run coilovers all around. I have since decided to stick with the coils for the rear. The front is getting coilovers as soon as I work a few other problems out (and I can get my wife to let me spend the money).

Matt- I went through more drawings than I can remember trying to get the geometry right. The unibody certainly doesn't make things easier. And, to complicate the issue even more, I moved the axle back ~5" at the same time. If you can stand to trudge your way through the the threads on Pirate, there are some great nuggets of information. Pig seems to be one of the best sources. I'll have ~75-100% anti-squat when I finally get it on the road again. If you'd like I can take some detailed measurements and pics, let me know what you need.
I ended up cutting stock XJ coils to get the right height. I tried to use combiations of TJ front and rears, but like TN William said, they all seemed to be too soft. I don't know how much weight I saved by cutting the roof, but stock TJ fronts gave me 17" from axle to frame. I also captured the coils at the axle and frame, and just change coils the adjust the height. You should be able to get free stock springs pretty easily.
Does anyone have a stock measurement from the axle to the frame? I still don't know exactly how high its sitting.
-Jon

On mine we boxed the frame with 3/8th steel where we mounted the control arm brackets. We made a cross member to go btw the uniframe in the back where the coil perches are. I want to make a way for the coils on mine to be connected at the top, they are attached at the bottom and I think I want to get them to attach at the top.

I tried running front TJ stock coils but the ass end of my jeep just pushed them down to the bumpstops. I then used procomp 2in lift front TJ springs and they were still too soft. I am currently running RE 4.5 TJ rear coils with great sucess.

We moved my rear axle back about 1.5 inches when my conversion was done.

I wish my pics were still up, but I got photopointed again

so I am once again w/o photo posting space...

mac 'i guess i got to divy up some $$ for photo posting' gyvr

Where would you place coilovers in the rear? The control arms are no problem, but where do i attach coilovers to run the longest shock possible without cutting through the floor (which is a bad idea for me because we have a lot of water ccrossing and mud)?

Also what suggestions on spring rates do you have? In the front i guess i will go a 17" travel shock with dual springs. But what to do with the rear?

17" travel coilovers in the front? Do you realize how long that shock will be? If you set it up for 35% up and 65% down travel the shock will be (depending on brand) about 30" long at rest. Do you have 30 inches (plus mounting tabs) between the top of your axle and the location for the top of your new shock tower (which will have to be inside your engine compartment)? I don't want to discourage you but 17's may be overkill. I am having trouble working out 14's.

In the rear you will have to cut the tops of the inner wheel tubs. There just isn't enough room to keep them outside.

Jon, the plan for now is to make the arms long enough to go from the axle in near stock position to a point near the cardan joint at the back of the T-case. This should swing a good arc and help driveshaft wear. Good idea? From what I have read, the most important issue is the relative position of the frame end mounting points to each other. How many inches behind and above the lower arm mount is the upper arm mounted?
Mac, I plan to attatch the XJ front coils at the bottom, and run a crossbar like your setup. Where are your arms mounted to the frame? Are they similar in position to Jons? Are you satisfied with the geometry?
Part of the reason for the ACOS besides adjustibility, is that the coil should be able to fall a few inches off the upper mount and go right back where it came from using the bumpstop as a guide. There will also be adjustible limiting straps at either spring.
Thanks for the info and pics so far! Keep it coming!
mattk

TN William said:

17" travel coilovers in the front? Do you realize how long that shock will be? If you set it up for 35% up and 65% down travel the shock will be (depending on brand) about 30" long at rest. Do you have 30 inches (plus mounting tabs) between the top of your axle and the location for the top of your new shock tower (which will have to be inside your engine compartment)? I don't want to discourage you but 17's may be overkill. I am having trouble working out 14's.

In the rear you will have to cut the tops of the inner wheel tubs. There just isn't enough room to keep them outside.

Click to expand...

I realize how long 17" travel shocks are. I had a pair installed along with stud eliminators and they were great, just the coils were too short, i actually lost one while flexing.

Here is my plan: D60 front, D70 HD rear, coilover with long arms front and a 3 link rear, 44" tires I know i need the 17" in front and i know how and where to attach them. My problem is the rear mount points and appropriate shock length.

The arms mount of the bottom of the 'frame' about 34 inches from the front of the axle. The uppers are mounted on the inside of the 'frame' and they are triangulated to the top of the axle. It works great for me and offers all kinds of flex. If you have a roof in the back there is no way you'll ever be happy with stock front springs, they are just tooooo soft.

On day I will go to coilovers, but there wont be a back on my jeep and cutting through the floor wont matter.

mac '12in travel shocks' gyvr

Matt-
The links don't need to be mounted on the same plane as the T-case output. You can control driveshaft angle with the link location. My rear u-joint angle changes less than 2 degrees from full stuff to full droop with 14" travel shocks. Macgyver and I have similar set ups with the uppers triangulated and converging above the diff. All four of my links are 40", the uppers mount ~3" higher, and ~5" behind the lowers. I'll run a center mounted limiting strap, and let the captured coils control the droop at the wheels.

The axle mounts also have a great influence on geometry. The lower the LCAs are on the tube, the less torque stress they have, but it will increase the angle of the arms and raise anti-squat. Many "experts" recommend at least 6-7" of vertical seperation of the links at the axle. In general, the flatter you can mount the arms, the less AS you will have. Keep in mind, some AS is good, but too much can cause wheel hop, resulting in a loss of traction. The early generation Tereflex long TJ long arm kits had long lowers with short uppers. The resultant angles produced too much anti-squat, and also caused to front to "jack" and loose traction on steep inclines.

Also be aware, I am by no means an expert. This is my first attempt at suspension design, and all my work is based only on theory. I don't even know how well my junk will work when I get it completed. I have done as much homework as possible, but take my opinions with a grain of salt.

-Jon

Thanks again guys. Great info.
mattk

I will have a 3-link rear with a V-style upper link and i know where to mount them. I'm still in decision where to mount the coilover shock and what length to match the front 17" shocks. Any ideas?

I measured a fairly new (99?) stock non-up country XJ at the dealer yesterday. 6 1/4" from axle to frame rail. Hope this helps
mattk

Thanks. It looks like I'll end up with about 8" of lift with the cut XJ coils.
-Jon