Build-up plan XJ to MJ

TNT

TNT

Seasoned Veteran
Location
S.E. WI
This is what I'm thinking right now.
Hopefully this is concidered Advanced Fabrication and Engineering.

My plan and some background: I build as many parts as I can instead of buying them...

I'm looking for some fun at speed, but also general offroad use. I've got a bad back, so I'm really interested in the prerunners ability to go fast in the rough and absorb the terrain. I figure a good prerunner type set-up will ride and handle the best, will be my daily driver and am willing to give up the hardcore rockcrawling(unless my body can take it). I'm buying a '89 2wd short box MJ to use for the build. The longer wheelbase will help the ride and the longer springs should ride better also. The plan is to get good shocks, bumpstops and limiting straps. I plan on trussing the front/rear diffs and raising the front axle mounts about 2.5". I will probably run 33x10.5-15's for tires and will cut the fenders for maximum up travel. Lift will be about 5" with 10"-12" of travel or more. Control arm type,design and length are still up in the air. It should have about 5"-6" of up travel. A traction bar will attach to the rear truss to control axle wrap from the spring over. The driveline and interior from my 95 XJ 4.0 auto setup will be swapped over. The steering and trackbar will be raised for improved angle and durability. The MJ box will be bobbed and trimmed for clearance. The frame will be reinforced and a rollcage(probably an exo/internal combo) of some type will be added. The XJ fuel tank and battery(due to the fender trimming) will be bed mounted in a box along with the spare. Rocker guards will be welded into the body. Custom bumpers will also be used.

Any suggestions or input would be great. I will be starting this shortly and want to nail down a plan.

I have a HP D60 and C&C 14 bolt I could use but don't want the added unsprung weight. I'll probably just sell these off to help finance the build.
 
Just a few comments from things I've done.

The front springs need to be stiff. One of the stiffest off the shelf coils out there are the Skyjacker 8" coils, and I run them with one coil cut off, which makes them even stiffer......I think they are just right. Bumpstops are real important, and what I've found that works the best are poly coil inserts made for Ford Ranger pre-runners. They float inside the coil and are pretty soft, mine compress more than 3". With the stiff coils and soft bumpstops my front works pretty good, I would recommend that combination to anyone. A number of us around here are running the Bilstein 7100's in front with 275/78 valving, which seems to be a good choice, I like them on mine. The 7100's come in a short body version that gives you a 12" travel shock in a 10" shock length, which makes it easier to fit the shocks on our XJ's.

I also run 57" long MJ rear leaves on my XJ, or at least the main leaf. I've had problems with the rear being too stiff, so the back wants to buck, which means the ass end of the rig kicks up in the rough stuff. You want as soft a spring rate in the rear as you can get away with, and good bumpstops, and a good shock. I'm running Bilstein 5150's right now, that are 255/70 valving, and it seems to be pretty close. I'm still trying to get the bumpstops working like I want, and I think I'm going to have to go to hydraulic/air bumpstops to get what I'm after. Since I built a buggy now and funds are too short for air bumps, I'll probably try the biggest (non-XJ) poly bumpstop I can get and live with it. I've tried various longer XJ bumpstops, drilled holes in them to make them softer, and I haven't been happy with any of them. Other than the rear still bottoming a little harder than I want it to, the whole setup works pretty well.

You should be able to run a longer shock on the rear of the MJ than I can run on the XJ, so more travel with softer rear springs should be doable for you.
 
The front set-up sounds like a good combination. I prefer running without a swaybar and it sounds perfect for that.

Your still running the lower mounted mid-arm front control arm set-up? How's that working out?

With an MJ I should be able to stuff the rear tires further into the wheelwell than on an XJ. I can always increase the wheelwell size. I also plan on the upper shock mounts being moved into the bed. It will probably be built to run a forward rake for a stance.
 
WheelinJR said:
A little off the suspension topic of the build, but a suggestion.

Buy a good quality off-road suspension seat, your back will thank you. You may have already had that in mind.
Click to expand...
Good Point. I understand Mastercraft has a suspension seat that is not a "Fixed Back" design. Richard as always thanks for taking the time and confirming a few of these issues. I'm getting ready to change my front bumpstop and looking to soften the compression. Is what your talking about similar to what Avery and others are using? Just want to make sure I get it right this time. Thanks in advance. Russ
 
TNT said:
The front set-up sounds like a good combination. I prefer running without a swaybar and it sounds perfect for that.

Your still running the lower mounted mid-arm front control arm set-up? How's that working out?

With an MJ I should be able to stuff the rear tires further into the wheelwell than on an XJ. I can always increase the wheelwell size. I also plan on the upper shock mounts being moved into the bed. It will probably be built to run a forward rake for a stance.
Click to expand...

Yes, my arms are a few inches longer than stock. The frame LCA mounts are 2.5" rearward and 1" lower than the stock mounting position, and the axle mounts are even with the tube. This gives a pretty good angle on the arms with good ground clearance. Like has been said over and over, it's the angle of the arms that makes the biggest difference, the actual setup can be drop brackets, mid-arms, J arms, or long arms, it doesn't make much difference so get what you prefer.

With the RE ZJ springs and the old Pro Comp shocks I ran I still prefered to run a sway bar, but with the Skyjacker coils and monotube shocks it feels real good without one, so I took it off.

The reason off road race rigs and pre-runners have a rearward rake (down in the back) is for better weight distribution coming off the jumps.......you want the rear to stay down as much as possible. It's also one reason you want stiff springs in the front and soft springs in the rear. When clearing a jump, even a small one, you want the front springs to push up hard to raise the front, and the rear springs to push up soft so the rear doesn't kick up too much.....so you don't come down too hard on the front. Soft springs in the rear, and softer rebound valving in the rear shocks, also helps to keep the rear tires in contact with the ground for better traction and handling. When you're hauling ass, it makes a difference if your rear tires stay on the ground.

Year before last I hit a small bomb crater in JV (that I didn't see) and launched about 4 ft in the air, but I came down evenly on all four tires and it didn't feel bad. Be sure to truss your axles good, though. :)
 
pottenger said:
Good Point. I understand Mastercraft has a suspension seat that is not a "Fixed Back" design. Richard as always thanks for taking the time and confirming a few of these issues. I'm getting ready to change my front bumpstop and looking to soften the compression. Is what your talking about similar to what Avery and others are using? Just want to make sure I get it right this time. Thanks in advance. Russ
Click to expand...

Yes, Lincoln, Cracker (Avery) and I are running the same front bumpstops. I'm trying to post a link to them, but I can't remember where we got them. After trying a number of difference ones, these are the ones to use. They're like poor man's air bumps. I know they are originally for the front of a Ranger. They come in 6, 8 and 10" lengths, I got the 10" and cut them down to fit. The only problem with them is that they don't have a specific point to stop the compression, so you have to make sure you have enough clearance for every component on compression, and the shock length and bumpstop length tuned accordingly. Mine hit only a couple of inches into the down travel.

I'd put the seat at the bottom of the list. Get the suspension dialed in first......but that's just my opinion.
 
pottenger said:
Good Point. I understand Mastercraft has a suspension seat that is not a "Fixed Back" design. Richard as always thanks for taking the time and confirming a few of these issues. I'm getting ready to change my front bumpstop and looking to soften the compression. Is what your talking about similar to what Avery and others are using? Just want to make sure I get it right this time. Thanks in advance. Russ
Click to expand...

I was looking at the Mastercraft Baja RS Seat with the adjustable headrest and adjustable lumbar support.

Richard is always a great source of knowledge. His help is always greatly appreciated.
 
While we're on the subject, Daystar has a new product that I think should work very well. No matter what you're running, I would go buy these right now.

poly shock shaft bumps

I have shaft bumps on the coilovers on the buggy, but being able to get shaft bumps on any shock is a great idea.
 
I've been eyeballing those poly bumps. As I sit right now I can hard compress my suspension and still have a few inches of shock left and I clear everything aside from a little flare rub, but I want them there anyways.
 
Thanks for the info. Will get these ordered and give them a try. Thanks Again, Russ
 
WheelinJR said:
I've been eyeballing those poly bumps. As I sit right now I can hard compress my suspension and still have a few inches of shock left and I clear everything aside from a little flare rub, but I want them there anyways.
Click to expand...

Put some small wire ties around your shock shaft and go hit a few good dips and see how much the suspension is really compressing. It might surprise you. :)
 
Man I love these threads. Since your talking MJ stuff here TNT... let me ask you a few things.

Your considering removing the factory control arm mounts? I looked at these and was pleasantly surprised by the beef! Part of me does not want to touch them and just use them. Yet I really want a midarm setup 3 link identical to Goatmans. What have you decided to do with those mounts? Are you willing to cut them off? I am wanting to use the prerunner inspiration on my new MJ too.
 
Goatman said:
Put some small wire ties around your shock shaft and go hit a few good dips and see how much the suspension is really compressing. It might surprise you. :)
Click to expand...

I put that to the test yesterday. Driving down the road coming out of the trails. Rough gravel road hardly maintained somewhere around 15mph or so. Cruising along and didn't notice the abrupt drop in front of me. Came down hard and you could feel the front pretty much flatten the springs all the way down and the tires stuff in the fenders.

The trails we had been on previously were wet so there was mud all over everything. You could see on the shocks how far up they were clean. Still had a good 2.5-3 inches of uptravel left.
 
Scrappy said:
Man I love these threads. Since your talking MJ stuff here TNT... let me ask you a few things.

Your considering removing the factory control arm mounts? I looked at these and was pleasantly surprised by the beef! Part of me does not want to touch them and just use them. Yet I really want a midarm setup 3 link identical to Goatmans. What have you decided to do with those mounts? Are you willing to cut them off? I am wanting to use the prerunner inspiration on my new MJ too.
Click to expand...

Yes, I have seen the mounts an MJ uses. I'm very tempted to just raise the lower axle mounts 2.5" when I truss the front axle and knuckles. I will probably move the axle forward about 3/4" for added tire clearance. Then lift the front suspension about 4". I can cut the fenders, relocate the battery, airbox, and extend the wheels forward some so I can run 12" travel shocks. I should only need to limiting up travel about 2" with 33x10.50-15 tires. This should provide acceptable control arm angles.

If I left the rear springs under the axle and lifted the rear about 3" I could cut as needed to fit the tires without limiting up travel. If needed I could raise and enlarge the wheelwells. Some Denver springs might be the ticket. The rear shocks will be ran thru the bed and mounted to a shock hoop. The rear axle will be fully trussed and I can add a traction bar if needed.

For the steering a over the knuckle tierod that runs from knuckle to knuckle to eliminate toe change as the suspension cycles. The drag link would then be mounted to the top of the tierod. I will probably use the ZJ pitman arm that is on the XJ. This should provide good steering geometry.

The trackbar mount will be raised on the axle end and made as close to the same length the draglink is as possible.

For bumpstops the ranger coil inserts for there front sound good and a set of air bumpstops in the rear will probably be the plan.

By keeping it as low as possible and allowing the the maximum uptravel as I can it should handle great. Fast speed corners should be a blast because of the low center of gravity.
 
Goatman said:
Yes, Lincoln, Cracker (Avery) and I are running the same front bumpstops. I'm trying to post a link to them, but I can't remember where we got them. After trying a number of difference ones, these are the ones to use. They're like poor man's air bumps. I know they are originally for the front of a Ranger. They come in 6, 8 and 10" lengths, I got the 10" and cut them down to fit. The only problem with them is that they don't have a specific point to stop the compression, so you have to make sure you have enough clearance for every component on compression, and the shock length and bumpstop length tuned accordingly. Mine hit only a couple of inches into the down travel.

I'd put the seat at the bottom of the list. Get the suspension dialed in first......but that's just my opinion.
Click to expand...


Those bumpstops sound like what I'm looking for. As for the seats they will be almost last on the list since my '95 XJ seats fit me well and are quite comfortable. If I had to use my '94 seats they would get replaced in a hurry.
 
Goatman said:
While we're on the subject, Daystar has a new product that I think should work very well. No matter what you're running, I would go buy these right now.

poly shock shaft bumps

I have shaft bumps on the coilovers on the buggy, but being able to get shaft bumps on any shock is a great idea.
Click to expand...


These would be nice in conjuction with the ranger ones just to help protect the shocks and also to help eliminate a hard bottom out.

Thanks for your info on your suspension. How high is your upper mount above the axle?
 
I didn't read whether Goat mentioned it or not but there is a hole completely through those inserts. It just happens to be the same size as the bump stop tower. You need to make a plate that doesn't hang on the coil but is large enough to cover the hole. I made a set out of 1/4" and they bent, replaced that with a 3/8" cold rolled plate and it's been holding for a few years. Round the edges so it doesn't cut into the stop while it's shifting around.

I've been running these since 2001 and mine are just starting to get chewed up. When I'm not so lazy I'll flip them over and hopefully that will work for another 6 years or so. They haven't seemed to get any softer, crack, or anything else.

Also I believe http://www.mad4wd.com also carries those inserts.
 
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