BrettM
NAXJA Forum User
- Location
- michifornia
So for various reasons I have decided to link the rear of my MJ. If you wonder about why I would do something as bass-ackwards as reversing the factory setup to front leafs/coils rear read THIS, then ask any questions you have.
I would have liked to do a dual triangulated 4 link, but I have decided that I want to leave the gas-tank where it is under the driver's side of the bed, forward of the axle. This left me with 2 options, parallel 3 link w/ panhard, or triangulated 3 link offset to one side. After researching both, I have decided I do not want to mess with some of the uneven characteristics of the 3 link w/ panhard, so I will be doing an offset triangulated (wishbone) 3 link. I will also be losing about 4 inches off the wheelbase in the rear, bringing me down from 115" to 111" while still not interfering with the gas tank.
Here is a picture of mine underneath (older picture, ignore the exhaust and basically everything besides the frame, gas tank and axle):
here is one done similarly, but mine would be on the other side:
Build materials
-By the nature of this system it will function in geometry exactly as though the wishbone was the full width of the frame and symetrical if the frame mount is relatively rigid. Therefore I will be making Delrin bushings for those two attachment points rather than Poly. This will attach to a crossmember which will just barely fit between the gas tank and cab. This presents the first question, what material for the crossmember? The three I am considering at the moment are (in order that I would like to use them) 1.25" .250 wall DOM, 1.5" .120 wall 4130 chromo, or 1.5" .250 wall DOM. This crossmember will span 40 inches without support.
-The upper wishbone will be made primarily from 1.75 .120 wall DOM with multiple gussets.
-Both lower links will run parallel to the frame and will be made of 2x2 .250 wall square tubing.
-Both ends of the lower links will be poly bushings, as will the axle end of the wishbone. Rather than use rod ends or cartridge joints (and for adjustability) I will be using a large threaded section to make these "twisty links". They will consiste of 1.25" B7 (chromo) all-thread with 12 tpi, threading into grade 8 coupler nuts, with a total of 20 threads of engagement. This type of link has been suffiecently proven in my mind by a guy named Brook Green from Alaska. He uses the same thing on his Chevy truggy whereas his are 1.5" thread, however his Chevy weighs roughly twice as much as my MJ, has a 513 Caddy motor under the hood, and runs 46" tractor tires. He has been running "twisty links" for several years of serious abuse and when he recently took them apart he noticed no increase in slop.
-some reading on "twisty links": http://www.pirate4x4.com/forum/showthread.php?t=358084
http://www.pirate4x4.com/forum/showthread.php?t=282710
http://www.pirate4x4.com/forum/showthread.php?t=240839
-For coils I will be using stock XJ coils. My MJ is only 3600 pounds and heavily weighted to the front, so I'm hoping the soft rate on the XJ coils will be about right. They will be on adjustable mounts, so that if I need to cut the coils some to increase springrate I can easily adjust the ride-height back. 14" travel Bilstein 5125 shocks to go with.
Suspension Geometry
All these numbers are still approximations because I won't be back at my MJ for another couple days, though they should be fairly accurate based on measurments I've taken before and written down.
-Anti-squat looks to be coming in at 70%, some adjustability in the mounts would allow that to go up about 20% or down 10%.
-Roll center is at 28 inches. Sprung COG is (guessed) at 40.5, making overall COG at 34.5".
-Roll axis is tilted back (oversteer) 8 degrees. This is the only number I don't really like, but sort of a necessary evil of the triangulated 3 link.
-39" upper, 43" lowers.
-68% antisquat at 5" compression, 113% at 10" droop.
This is essentially what I'm looking at:
Coil mounting
I am going to have the coils captured on both ends, and I think that along with a high roll-center and leaf springs up front will keep my MJ very stable. The coils will be mounted about 43" wide, directly under the frame rails.
The top mount will be this style:
but on a threaded adjuster (same 1.25"-12 allthread) like this:
The lower mount will have the coil feed through two small pieces of tube like this, and will have an internal bumpstop like an XJ coil front suspension:
Well, that's all I got for now. It all seems pretty clear in my head, but please give input anywhere you see room for improvement or problems you see
I would have liked to do a dual triangulated 4 link, but I have decided that I want to leave the gas-tank where it is under the driver's side of the bed, forward of the axle. This left me with 2 options, parallel 3 link w/ panhard, or triangulated 3 link offset to one side. After researching both, I have decided I do not want to mess with some of the uneven characteristics of the 3 link w/ panhard, so I will be doing an offset triangulated (wishbone) 3 link. I will also be losing about 4 inches off the wheelbase in the rear, bringing me down from 115" to 111" while still not interfering with the gas tank.
Here is a picture of mine underneath (older picture, ignore the exhaust and basically everything besides the frame, gas tank and axle):
here is one done similarly, but mine would be on the other side:
Build materials
-By the nature of this system it will function in geometry exactly as though the wishbone was the full width of the frame and symetrical if the frame mount is relatively rigid. Therefore I will be making Delrin bushings for those two attachment points rather than Poly. This will attach to a crossmember which will just barely fit between the gas tank and cab. This presents the first question, what material for the crossmember? The three I am considering at the moment are (in order that I would like to use them) 1.25" .250 wall DOM, 1.5" .120 wall 4130 chromo, or 1.5" .250 wall DOM. This crossmember will span 40 inches without support.
-The upper wishbone will be made primarily from 1.75 .120 wall DOM with multiple gussets.
-Both lower links will run parallel to the frame and will be made of 2x2 .250 wall square tubing.
-Both ends of the lower links will be poly bushings, as will the axle end of the wishbone. Rather than use rod ends or cartridge joints (and for adjustability) I will be using a large threaded section to make these "twisty links". They will consiste of 1.25" B7 (chromo) all-thread with 12 tpi, threading into grade 8 coupler nuts, with a total of 20 threads of engagement. This type of link has been suffiecently proven in my mind by a guy named Brook Green from Alaska. He uses the same thing on his Chevy truggy whereas his are 1.5" thread, however his Chevy weighs roughly twice as much as my MJ, has a 513 Caddy motor under the hood, and runs 46" tractor tires. He has been running "twisty links" for several years of serious abuse and when he recently took them apart he noticed no increase in slop.
-some reading on "twisty links": http://www.pirate4x4.com/forum/showthread.php?t=358084
http://www.pirate4x4.com/forum/showthread.php?t=282710
http://www.pirate4x4.com/forum/showthread.php?t=240839
-For coils I will be using stock XJ coils. My MJ is only 3600 pounds and heavily weighted to the front, so I'm hoping the soft rate on the XJ coils will be about right. They will be on adjustable mounts, so that if I need to cut the coils some to increase springrate I can easily adjust the ride-height back. 14" travel Bilstein 5125 shocks to go with.
Suspension Geometry
All these numbers are still approximations because I won't be back at my MJ for another couple days, though they should be fairly accurate based on measurments I've taken before and written down.
-Anti-squat looks to be coming in at 70%, some adjustability in the mounts would allow that to go up about 20% or down 10%.
-Roll center is at 28 inches. Sprung COG is (guessed) at 40.5, making overall COG at 34.5".
-Roll axis is tilted back (oversteer) 8 degrees. This is the only number I don't really like, but sort of a necessary evil of the triangulated 3 link.
-39" upper, 43" lowers.
-68% antisquat at 5" compression, 113% at 10" droop.
This is essentially what I'm looking at:
Coil mounting
I am going to have the coils captured on both ends, and I think that along with a high roll-center and leaf springs up front will keep my MJ very stable. The coils will be mounted about 43" wide, directly under the frame rails.
The top mount will be this style:
but on a threaded adjuster (same 1.25"-12 allthread) like this:
The lower mount will have the coil feed through two small pieces of tube like this, and will have an internal bumpstop like an XJ coil front suspension:
Well, that's all I got for now. It all seems pretty clear in my head, but please give input anywhere you see room for improvement or problems you see