FJ55 4 Link help (1 Viewer)

[F4MDTWR]

Help…

Does anyone have the dimension for a 4 link (rear) set and 3 link (Front) set on an FJ55? I tried using the 4 link calculator but got lost almost instantly. If some can help, I would truly appreciate it. Here are what my plans are….

SBC 350
SM465
Np205
Dana 60 (Front)
14 Bolt (Rear)
40” Tires
Wheelbase is roughly 116”-120”

Hope this helps…

 

[EWheeler]

You want to copy someone's homework? Show them you have put in the time & effort to understand the concepts. If you instantly got lost in the 4 link calculator, you need to do a lot more research. Head over to Pirate and get your read on homeboy.

 

[brokenparts]

yep, tons of info out there. I just went through the struggle of learning link suspension. Many nights (to say the least) of reading and playing with the calculator. There really is no "secret" formula or "set" info. What you need to do is get somewhat familiar with terms like anti-squat/anti-dive, roll center, instant center (this one is a little tricky at first) and then just go out to your rig and see what'll fit at ride height The calculator will start making more sense at that point and you can start manipulating according to what fits in the "real world". I must have spent 6 or 7 hours under my rig just staring before I even cut one link.

Good luck and dont be afraid to ask questions along the way... you just need a little more background. It'll be worth it in the end.

 

[brokenparts]

if you can manage to sift through the crap there is decent info in both of these threads:

THE GOD OF SUSPENSION...[for those of you who don't know] - Pirate4x4.Com Bulletin Board

Link suspensions for dummies? - Pirate4x4.Com Bulletin Board

Head to your local book store too... Most info you'll find will fall under drag strip and oval racing but many of the same concepts apply in the 4x4 world too.

 

[EWheeler]

Here are some threads pertaining to linked suspensions that I have saved. The ones posted by Brokenparts seem to be the most popular on Pirate, but these have a few bits of useful info.

[FONT=&quot]Center of Gravity and Roll-Over Angle - Jeepaholics Anonymous[/FONT]
[FONT=&quot]4 link with coils, link config question - Pirate4x4.Com Bulletin Board[/FONT]
[FONT=&quot]another ? for the suspension link gurus! - Pirate4x4.Com Bulletin Board[/FONT]
[FONT=&quot]Help me fix my broken front suspension geometry - Pirate4x4.Com Bulletin Board[/FONT]
[FONT=&quot]Rear Suspension - Instant Center - Mini Truckin' Magazine[/FONT]
[FONT=&quot]Anti Squat, the final answer - Pirate4x4.Com Bulletin Board[/FONT]
[FONT=&quot]https://forum.ih8mud.com/hardcore-corner/214490-front-rear-x-link-60-series-cruiser-ute.html[/FONT]
[FONT=&quot] New Version of my 4-link Analyzer & Request for Help - Pirate4x4.Com Bulletin Board[/FONT]

 

[brokenparts]

Here are some threads pertaining to linked suspensions that I have saved. The ones posted by Brokenparts seem to be the most popular on Pirate, but these have a few bits of useful info.

[FONT=&quot]Center of Gravity and Roll-Over Angle - Jeepaholics Anonymous[/FONT]
[FONT=&quot]4 link with coils, link config question - Pirate4x4.Com Bulletin Board[/FONT]
[FONT=&quot]another ? for the suspension link gurus! - Pirate4x4.Com Bulletin Board[/FONT]
[FONT=&quot]Help me fix my broken front suspension geometry - Pirate4x4.Com Bulletin Board[/FONT]
[FONT=&quot]Rear Suspension - Instant Center - Mini Truckin' Magazine[/FONT]
[FONT=&quot]Anti Squat, the final answer - Pirate4x4.Com Bulletin Board[/FONT]
[FONT=&quot]https://forum.ih8mud.com/hardcore-corner/214490-front-rear-x-link-60-series-cruiser-ute.html[/FONT]
[FONT=&quot] New Version of my 4-link Analyzer & Request for Help - Pirate4x4.Com Bulletin Board[/FONT]

hahahaha, yep I've read quite a few of those too.... great links (pun intended)!

 

[BellyDoc]

Like everything else in building a trail rig, linked suspension design will be about picking compromise points as you balance one thing against another. The more you learn about it, the more you find out what the things are involved in the compromises. THAT'S why you have to do a lot of homework on the topic and THAT'S why there's no simple "answer" as to how you do this. There are infinite ways to do it and either you spend a lot of time learning about the choices or else you take a stab at it with no idea, and then have no idea what to do next when the outcome is less than expected.

Here are some of the compromise balances that you have to consider:

1) Ease of construction vs. obtaining the geometry that you design.

This is one of the toughest, because to some degree the positions of pre-existing parts like frame rails, drive shafts, exhaust and the oil pan all tell you where links can and cannot go. On the one hand, you can put links where they'll fit and on the other, you can put them where you want (based on the link calculations) but then you have to do extensive modifications to the other systems to make space.

2) Triangulated geometry vs. ground clearance/ride height

On the one hand, it would be nice to make nice wide based triangles with links because this is what offers the most lateral stability and strength, but on the other hand, there's no good point in the center of the vehicle or the center of the axle onto which these triangle points can end in link mounts. You have to add those if you want them in the form of cross members and axle trusses. If you build in crossmembers, they're probably going to drop your ground clearance. If you add an axle truss, it'll affect the ride travel on the axle by taking up space between the axle and chassis. In the front, a well triangulated 4-link system can interfere with the oil pan so that the vehicle will have to sit taller. Another option is to do a 3 link/panhard front system to clear the oil pan (instead of a double triangulated 4 link) and this also gives you the option to run non-hydraulic steering, but the cost is a different geometric motion than the rear, with potentially more roll and bump steer.

3) Link length vs. wheel recession.

Short steeply angled links mean that for the suspension to go into up-travel, it also has to swing in a sort of "out-travel". This means that for the front wheel to take a bump over a rock, it has to cycle forward and up, directly AGAINST the force of the rock against the tire. In many ways, it's preferable for a wheel to "recess" as it goes up, i.e., for the wheel to go up and BACK as it absorbs the shock of hitting the rock. A linked suspension in which the front lower link sits perfectly horizontal at ride height would have the wheel actually go straight up and slightly recess, but a link that flat means that the belly is probably too low. It's as low as the axle! Links that angle down, but are longer will have a shallower angle and less "out-travel" (I had to make up that term since I can't find an accepted opposite word for "wheel recession"). However longer links are easier to bend when you come down on a rock that hits the link square in the middle.

These are just a few considerations that show how compromises play into a link design. You have to make choices between what's easy to build and what you believe to be ideally suited for your application.

It's not all about finding a target range for the anti-squat and jerking with the numbers till you find a design that gives you those numbers because when you're done with that, you still have to build it and your build has to meet a budget and has to stand up to the trail abuse that you're going to give it.

I'm 2 years into the build pictured below, and the strong majority of that time so far was spent on suspension... in fact, I'm still working on it!

 

[EWheeler]

Thanks to Doc's post, I just added this thread to my list.

I must say Doc, you are truly an inspiration. Your thread drug me into the Cruiser section over on Pirate about a year and a half ago and is what made me want to buy a 40 (and I did). Having recently graduated with my ME degrees, I feel fully inadequate reading through your build as your understanding and ability to apply subjects like Mechanics, Dynamics, and Metallurgy to your build exponentially exceed mine. The rate at which your fabrication skills developed were not human. Thanks for all of your well thought out & clearly communicated posts and also for lighting the fire for me to build my own rig (though it pales in comparison to yours). I'll get off my knees now

 

[woody]

... and then just go out to your rig and see what'll fit at ride height

TOO true....unless you are building from scratch, 'what fits' is the biggest limitation

My rear suspension ended up with 39" eye-to-eye links, uppers and lowers...uppers mount inside the frame rail and about 2" above the top of the pumpkin...lowers mount under the frame rails and to the outer front edge of the axle.

Believe me, there was a lotta time taken with metal screw eyes and wooden closet rods, punching numbers into the 4-link calculator, and then asking questions about the values that resulted.

Took me a year of research...but it was right the first time, and works very predictably.

 

[F4MDTWR]

Ewheeler,

Nice finishing touch on the "homeboy" comment. Ignorance never fails...

 

[F4MDTWR]

Doc,

Thank you for your reply, your post makes a lot of sense. I am using a life line on this. BTF out of Alabama is help with the build. They have built some killer rigs in the past (red bull crawler) and they are going to help with some of the build. Going to give it a try.

Great build, rig is looking SWEAT. Hope you get to enjoy it soon.

 

[BellyDoc]

Blue Torch Fab!? GOOD CHOICE. If I hadn't been so F'ing ignorant at the outset, I'd have bought tons of parts from them. They make a really good axle truss that I probably should have used and that's just a start.

Also, I genuinely appreciate the freebie support. I've gone and said out loud that I want to be done by KOH 2010 so that I can take it out there and drive it around to the places I want to be to watch the race!

Now I'm scared.