General Tech A little help with a 4 link please!!!

[CrawlerCraig]

I have started my 4 link project, I have read and re-read tons of 4 link post here and on pirate, I have got the basic idea but would like some input before I start welding!

I'll post some pics to give u an idea what I've got so far see if you can help me tune it a bit more.....

A little info first,
Wheelbase 110
Cog 48 (bell housing bolt) tall I know.....
Frame 28
Axle height 19

The pic on the graph paper shows a 60in lower link on a 8degree angle below frame mount (seems kinda long)
The pic on the vehicle is a 60in link on a 10 degree angle to a side frame mount (keeps bracket from getting hung up)




As u can see the links go pretty far forward on the vehicle.... Good or bad? If I shorten them I will end up with more angle or I build the mount above the center on the axle.....

If something is wrong on the graph paper I wouldn't be surprised so don't be afraid to tell me!
My vertical separation at the axial would be around 10 but the frame end would be a lot closer

Is 10 degrees to steep? I've read 5 to 10 is acceptable..... I could make my uppers flat but that wouldn't leave much vertical separation at the frame end....

I based the graph off a pic on pirate so I know it's perfect!! Tell me if I missed interpreted it, thanks

 

[CrawlerCraig]

1 more graph drawing it shortens the links and puts anti squat to about 93%, the POC is about 3 inches lower than COG

The first graph puts the POC dead on COG so that would be 100% anti squat

I will be cutting the frame off right were the lower mounts go so don't mind the rock sliders supports in the way, and all the leaf spring hangers!

 

[N-Smooth]

You could always put the lowers on top of the axle if you have a stout axle/truss and room to still put the uppers 9-10" higher. It's just hard to get good numbers on tall rigs.

 

[UNSTUCK]

You have to remember that the calculators work best on a buggy. So you can build in your link mounts where ever you want. You are more limited with a stock frame. Sometimes you just have to mount links where they will fit and call it done. Why is the rig so tall? Anyway you could lower it 8 inches? Doing that would eliminate all kinds of problems. If you stay that high, mount the lowers to the bottom of the frame instead of on the outside of it. That will give you a bit more separation at the frame end. You're so tall they wont hang up much, if ever.

 

[STAG]

There is a link to a calculator in my signature if that is easier to you than using graph paper.


And read this article, very helpful info.

http://www.4wheeloffroad.com/techar...0307_four_link_suspension_part_2/viewall.html

 

[CrawlerCraig]

The reason it is so tall as it started as a 78 ford bronco with a 8 in lift,(leafs up front now, not coils don't ask) I have removed springs from the leaf pac to soften things up and it did lower a bit, I would have to try and mount the spring hangers outside the frame to get it any lower in the front and the spring perches in the axle won't allow me to move (don't have the cash for linking up the front up right now)

As for that Petersens article it's good and i have read and re-read in a few times it has helped quite a bit, but now that I can actully put pen to paper I just wanted a little help fine tuning it from people who have built or re built there's cause they found a design flaws

 

[brandonlmb]

I was over at my parents yesterday and saw you in your garage, I should of stopped over.

 

[CrawlerCraig]

I was over at my parents yesterday and saw you in your garage, I should of stopped over.

Really!?!?! Dang! Feel free to stop by next time ur down!

 

[bryson]

Hi Craig. :tara:

 

[CrawlerCraig]

Hi Craig. :tara:

Wow it's been a while!!! Hi to u as well! Glad to see ur still around, maybe when i get the pig done we can go wheelin!!

 

[flexyfool]

Here are rules of thumb for rear 4 links for typical rock crawling jeeps, toys, buggies, and small truggies.

1. Make the vertical separation of the lower and upper links at the axle be at least 8 inches. Less separation strains the joints and axle wrap can develop.

2. Make lower arms as parallel to the ground as possible.

3. Make upper arms as parallel to the lowers as possible. 2 & 3 give the squatting behavior that prevents the rear axle from walking under the rig when climbing. The rig bellies into a climb rather than sticking its ass up. High squat soaks up slams against ledges and gives a smoother ride overall. Rigs with too little squat ride stiff and have a herkyjerky shudder when climbing. Try to achieve 0-50 anti-squat # on the calculator.

4. Ensure 40 degree total horizontal angle to ensure side stability. Add up the angles of the 4 links. It should be over 40. More is not needed and can be detrimental. See 5 below.

5. Place as much horizontal angle in uppers to ensure a high roll center. This means space the uppers on the axle as close together as you can get them. Keep the lower relatively straight. A high roll center keeps the axle centered under the vehicle as it articulates. The axle moves rather than the body. This makes for a more predictable and stable rig and helps to keep the body out of the rocks in narrow places as well as the tires away from the body.

6. Don't use excessively long links that connect to the frame beyond the center. Very long links transfer forces to the front of the rig not the back. Forces from the rear axle should effect the rear of the rig not the front. 70" links are getting long.

7. Don't use excessively short links. Short links cause the geometry to change a lot through the suspension cycle. 30" links are getting short.

8. If using a CV joint off the transfer case, making the lowers shorter than the uppers can help to keep the pinion pointed at the transfer case. If using a U joint, make them the same length.

9. The lower and longer the vehicle, the less important 1-8 are. Low and long vehicles can get away with more deviation from the rules of thumb. A stock dimensioned Jeep, for example, can be quite sensitive to the geometry.

10. Use at least 7/8" rod ends and 1/4" wall tube for lowers.

11. Use a center limit strap. It will keep the ass from lifting when going downhill. It can keep the drive shaft from angling too far and binding or pulling apart. You don't need more than 6" of down travel at the center. Coil overs and plain coils can benefit from side limit straps to keep the coils seated. 14" and less coil overs and airshocks can benefit from side straps to take stress off the shafts at full droop. 16"-18" shocks don't seem to max out so side straps are not beneficial.

 

[UFAB]

60 in lowers are a bit long.

The longer, the bigger and heavier your lower links need to be.

7/8 heims work great.

The controlled front 4 link calculations only reflect how well the rear has been designed.

Good luck

 

[CrawlerCraig]

Thanks for the replies!!
I haven't heard of the 40 degree rule or guide, I think my lowers will be about 9-10 degrees and the uppers I can make anything so I guess shoot for around 5-8 so the links stay somewhat parallel. So that would be a total of 30-36 total degrees


I have 1 1/4 joints and lower links are 2in .250 DOM tube so they should be pretty strong

I will shoot for lower links in the 42-46 Area depending on what it take to keep the angle under 10