"Gonna do it right...maybe!!??" Fuller's new XJ build!!!

marty79 said:
Ok wow guys too much overload hold up. Let me get caught up tonight and go through the numbers. I have ? On several comment but can't right now..
Y'all hold your thoughts please give me time to be there and work in this new stuff. Thanks
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I'll be lurking around here later. Gotta do something to pass the time at work... :D
 
Jody Treadway said:
This. I "broke" my 3 link front on my old MJ during an ECORS race. The mount held, the link held, the 5/8" bolt held. But what didn't hold was the 3/16" steel crossmember my frame side mount was welded to. It ripped the steel out over 1" away from the weld. Just plain metal fatigue.
IMO- The ideal way to do the frame side mount on an XJ is to plate the inside of frame (did anyone mention that yet?) and weld a typical mount to a piece of plate that is them welded and plug welded to the plated frame. 3 link mounts see extraordinary forces on them.

To be clear, I broke my front axle pinion yoke with my crankshaft when my 3 link failed. Yes, you read that correctly.
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This is exactly why I always recommend a 4 link if even remotely possible. Help spread that load out some.
 
Jody Treadway said:
This. I "broke" my 3 link front on my old MJ during an ECORS race. The mount held, the link held, the 5/8" bolt held. But what didn't hold was the 3/16" steel crossmember my frame side mount was welded to. It ripped the steel out over 1" away from the weld. Just plain metal fatigue.
IMO- The ideal way to do the frame side mount on an XJ is to plate the inside of frame (did anyone mention that yet?) and weld a typical mount to a piece of plate that is them welded and plug welded to the plated frame. 3 link mounts see extraordinary forces on them.

To be clear, I broke my front axle pinion yoke with my crankshaft when my 3 link failed. Yes, you read that correctly.
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I will look over it and make sure I overkill it like I usually do anyways lol, thanks
 
As @RHSCTJ said, the camshaft height (or top bolt in the transmission bellhousing) is generally a good rule of thumb for COG height. But, the added weight of your cage likely took it higher than that. If you could post up some estimates of how much tube you have in the top of your cage, as well as the dimensions of the tubing and overall dimensions of the cage, as well as your estimated COG (based on above), I'd be willing to lend a hand with calculating your COG. Of course, posting my math so others may be critical. :D You never know, I could fat-finger my calculator.
 
marty79 said:
I will look over it and make sure I overkill it like I usually do anyways lol, thanks
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Looking back at how you have it mocked up now, it looks to be tabbed to the crossmember. Take it for what it's worth, but IF you keep it there, you NEED to connect a brace from the back of the mount to something solid, like the plated frame rails. It will fail if not braced overly strong and when it does, it's bad.
 
marty79 said:
Ok I can't understand this for the life of me. Any simple for dummies way of explaining it
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For the sake of time and trying to explain it through a keyboard don't try to understand AS, just shoot for what @Mac5005 said here

Mac5005 said:
That AS number is terrible.

Shoot for 60% It’s going to rise in droop and that will be worse.

Bc you aren’t using the travel to plot the AS at full droop, shoot for an even lesser amount bc it is going to rise in droop.

Make the upper chassis side mounts adjustable so you can try each hole and adjust to what you like.

Too much AS will cause rear wheel hop.

Too much AS at droop will cause excessive wheel hop on the hardest of climbs.

This is because the suspension will move towards droop as you jeep goes uphill.

This is because the direction of gravity is constant, but the angle of the springs to gravity changes.

This takes weight off the springs and places more weight onto the links, moving the suspension towards the droop position.
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Or if you feel like killing some time watch this.
 
marty79 said:
Antisquat... don't overload me lol
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It’s not an easy one but I’ll try to keep it simple.

When you move forward, the tires rotate forward also.

But the opposite force is that the axle tries to rotate backwards.

This is why the pinion in the rear always tries to rotate upward.

This means with a link suspension, when moving forward, the axle is pushing on the lower links( compression) and pulling on the upper links( tension).

The placement of the links on the chassis cause the axle to attempt to move away from chassis, under power.

That force to “push” the axle away from chassis is antisquat.

Now bc you are trying to accelerate forward, you have weight transfer to the rear, which typically squats the rear suspension some.

Antisquat is the forces in the rear link geometry that try to combat that squat based on forward accel.

All you need to know John:

Shoot for less than 60%. And make adjustable mounts for chassis side upper so you can tune for your driving style.

Too much AS will cause rear hop on climbs.

How much is too much? That depends on HP, tires, traction available etc.
 
The seat of the pants, what you'll feel explanation is this...

With high AS, when you stomp on the throttle the rear of the vehicle will rise instead of squat like you would expect on acceleration. Some AS is fine because it plants the tires on acceleration, but as others said too much will cause it to hop.

When we did the rear 4 link on my old samurai, the AS numbers were a little higher than we wanted (I don't remember what the calc actually said), but it ended up being ok.
 
LBarr2002 said:
The seat of the pants, what you'll feel explanation is this...

With high AS, when you stomp on the throttle the rear of the vehicle will rise instead of squat like you would expect on acceleration. Some AS is fine because it plants the tires on acceleration, but as others said too much will cause it to hop.

When we did the rear 4 link on my old samurai, the AS numbers were a little higher than we wanted (I don't remember what the calc actually said), but it ended up being ok.
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With little hp, dot compound tires it probably was. There are tons of guys running 100% AS on low power street tire rigs and are fine.

The more traction, the more torque, and the steeper the angle of ascent of an obstacle and it gets much much worse fast.

I never had rear hop for several years. Then I started running harder obstacles and now have stickies and it’s there.

I have 68% AS at ride height, and it increases much more in droop.

It always shows up on the hardest high traction obstacles that I can’t just crawl, which are usually the worst places on the trails to break/fix/recover from.

When I built it in ‘11 I didn’t fully understand and got it close enough. I’ve been too busy wheeling and working on other rigs to fix it.

Proves it’s far easier to get it right from the start with the vast majority of information on the topic coming to public over the last 2 years.



To anyone build for future. Eventually you may upgrade hp and sticky tires and run more extreme obstacles. If it will work for that setup, it will more than work until that time comes.
 
Ok y'all this is what I have so far..nothing set in stone but not much options to change link mounts without really going crazy cutting out unibody rails and such.

I even played with the numbers to get the AS down, the only factor that helps it mainly is longer lower links, in the 40s which would be real freaking annoying
IMG_20180308_233500413.jpg

This is a 3 link in the rear and similar, both 3 and 4 link require longer lowers apparently
IMG_20180309_000024166.jpg
 
marty79 said:
Ok y'all this is what I have so far..nothing set in stone but not much options to change link mounts without really going crazy cutting out unibody rails and such.

I even played with the numbers to get the AS down, the only factor that helps it mainly is longer lower links, in the 40s which would be real freaking annoying
View attachment 264221
This is a 3 link in the rear and similar, both 3 and 4 link require longer lowers apparentlyView attachment 264222
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General rule of thumb as a starting point is the uppers are 75% the length of the lowers.

So a rig with 40" lowers would have 30" uppers. Now this is just a starting point and many factors play into what you eventually end up with but having uppers that are way longer is a step in the wrong direction.
 
Also, to get the proper separation between the frame side mounts, you may need to either place the LCA mounts on a subframe or cut the floorpan for the upper mounts. Get the numbers right, then figure out a way to package them on your chassis.
These are dependant on amount of lift, etc.

Which is why you build at ride height...
 
Jody Treadway said:
Also, to get the proper separation between the frame side mounts, you may need to either place the LCA mounts on a subframe or cut the floorpan for the upper mounts. Get the numbers right, then figure out a way to package them on your chassis.
These are dependant on amount of lift, etc.

Which is why you build at ride height...
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ok so your saying more seperation between uppers and lowers will help get that number better?
I did this calculation with lowers being mounted where factory leaf springs are so I guess I could make mounts below body rails like i did the front which would help with about 4". I'll play around with it some later on...

Right now I'm SUPER DUPER EXITED about to head to Raleigh to visit my folks and meet up with a guy from here to buy some 39.5" on Allied Beadlocks....OMG OMG OMG I'm getting REAL beadlocks yall, no more screws into rims yeiiiii. I'm soo exited. Will get back at it next week and play with the numbers. Everyone have a blessed weekend.
 
WOW look what happened by lowering lower link mount just 4"..how's this look
IMG_20180309_073800672.jpg
 
marty79 said:
ok so your saying more seperation between uppers and lowers will help get that number better?
I did this calculation with lowers being mounted where factory leaf springs are...
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There are actual calculations for building a 4 link in regards to frame vs axle separation. The GENERAL (not the law, but a guide to GO BY for INITIAL starting point) formula is approx 75% separation at the frame as what you have on the axle.
For example, most times a typical over the pumpkin truss with link mounts on top will be around 8" from the center of those mounting holes to axle tube centerline. Using the above method for reference, the frame side would need to be 75% of 8", which is 6" separation.

AGAIN THIS IS JUST A REFERENCE POINT TO START FROM- NOT THE LINK SUSPENSION HOLY WORD

Plug those numbers into the calculator and see what the results are. And then you can make changes from there. This is why you see some frame side UCA mounts with multiple mounting holes.

Do not use your factory leaf spring mounts for the link mounts. They are neither designed for the loads they'll see as LCA mounts nor are they located in the proper place on the "frame".

You did plate the frame didn't you?

Set the chassis at ride height
Set the axles at ride height
Do the calculations
Make links fit based on those calculations

Buddy, you're making progress towards doing things right. Slow down and don't rush it at this point.
 
I think this is a thought out build, with the least amount of knowledge, I am calling John out on this one, I thought he was dead or jail! If he is listening get a bottle, flux is horrible! The model programs works, the correct math has been presented, application is suspect, as always. Next time you come by buy me a pack of smokes!
 
49willys said:
I think this is a thought out build, with the least amount of knowledge, I am calling John out on this one, I thought he was dead or jail! If he is listening get a bottle, flux is horrible! The model programs works, the correct math has been presented, application is suspect, as always. Next time you come by buy me a pack of smokes!
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It was good to see you bud. Get that yota done so we can hit the trails! Blessings to you bro
 
marty79 said:
WOW look what happened by lowering lower link mount just 4"..how's this look
View attachment 264229
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so guys this 3link setup looks really good as far as numbers..what do you guys think. I'm home now and ready to get back at it but wanna make sure you guys agree with this setup. Thank you
 
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