Suspension Design - pros/cons and customisation

[david bfreesani]

So this all started with someone test driving a Merc X, then went on to a "show off your flex" thread. But we have not got to actually discussing the various options when it comes to suspension. What are the advantages and disadvantages of IFS vs SFA, Coil vs leaf. I know there are some experts on this forum who can give some great insight and advise, just based on their experience.

I would love to see this thread maybe have some information for the guy wanting to design a suspension from the ground up. Or someone wanting to convert from leafs to coils, or even from coils to leafs (yes, I actually found a youtube video of someone doing that conversion).

Playing open cards from my side, I am hoping for some puzzle pieces to fall into place for my Sani SFA project, but we won't get into that right now. Lets see how this thread pans out.

[Wooky]

All suspension setups / designs are a compromise of sorts and not any one design can do all things equally well.
For me the best place to start would be with the question - "What exactly do I want this vehicle to do?"
This will give you a fairly good idea on how the compromise is going to have to work and what type of suspension setup will get you where you want to be.

The next question is ( this is the honesty section ) just how much time, effort and money are you willing to invest to build what you want with the knowledge that you might well never be able to sell it in the future.

[david bfreesani]

Here is my story, and why I need some advise/pointers. I cut out the Nissan D21 Hardbody IFS and was advised leaf springs are a quick and easy SFA. Not taking into account leag pack and axle position relative to things like an engine sump, it probably would have been.

Here is what I found.... the placement of the springs on the axle forced me to running directly under my chassis members. Along with the sump, this got me a 150mm lift. No way I can get the leafs closer to the chassis. In fact, in an attempt to keep it lower profile, I ended up with very short shackles. This does not work well, and I would have had to extend the chassis another 50mm to get a good angle on the shackle, or gone shorter on the leaf pack.

I guess the big problem with leafs I found, was the limited adjustability if you find things aren't working out exactly as you expected. One of my niggles has been my castor angle and the inability to change that without some major cutting, grinding and welding.

Anyhow, you get the picture of my frustration with my leafs compared to the adjustability I believe I would have with something like a 3 link on coils.

Things I could change easy, and would like the adjustability on would be:
1) wheel base
2) dropping COG. Coils would take up less space due to the fact that I would have more options as to where I can mount them
3) Castor and pinion angle adjustability.
4) Anti squat adjustment
5) Adjusting Roll Centre Height
6) Adjusting Roll Axis Angle

Sure there are some I have not even figured yet. Besides all these points mentioned, I get away from my awful handling characteristics I got with with my leafs. I have figured a whole set of problems I inherited from my front leaf pack, that I can only fix by replacing with a custom built pack. The truck seems to be very heavy, which puts my on a very stiff set of leafs, which again fight articulation.

Sent from my SM-G925F using Tapatalk

[david bfreesani]

Wooky, I hear you. Here is the deal. The vehicle will, like most our vehicles, be on tar 99% of the time. Leafs are horrible for this. When I started my SFA, I kinda hoped I would in a small way, have the handling and feel of the Patrol. I had only been in a competition Safari on two occasions, so did not really have anything to compare it with. Now after driving my leaf sprung Hardbody, I got an opportunity to drive in a friends Y61 Patrol a while back.. Dammit, it peeved me as to my primitive feel and handling. Some guys are saying that I should fit a Panhard over the leafs to control my lack of sideways stability.

All suspension setups / designs are a compromise of sorts and not any one design can do all things equally well.
For me the best place to start would be with the question - "What exactly do I want this vehicle to do?"
This will give you a fairly good idea on how the compromise is going to have to work and what type of suspension setup will get you where you want to be.

Well, a compromise would mean that I lack in some departments, but am good in other. At the moment I do not have on road handling, stability or comfort. I have less articulation than I had with the IFS. Only thing I scored was ride height and bigger rubber.

The next question is ( this is the honesty section ) just how much time, effort and money are you willing to invest to build what you want with the knowledge that you might well never be able to sell it in the future.

Well lets start with the fact that I have known for a long time that I will never be able to sell the Sani. Also doubt I am interested in doing so if/when I get it the way I want it.

Those that know me from the other forum, will know that this started as a forum sponsored build, as I was unemployed, and since have become unemployable, and finances are always non existent. Strange thing is this.... The advise on leaf springs, is that it is simple and quick, and it just works. Yip it does, and there is not much that you can change or customise because of that simplicity. Sure I can go have custom leaf packs made, test various Castor correction shims to see what works. On the other hand, the internet is littered with multi link suspension "experts". You just have to choose the right one to follow, and filter out the BS.

So budget wise, and time wise, I am probably on par with getting the next setup installed (leaf or multi link). The difference is, that if the leaf setup still does not work, I have to start over again. The multi link and coils setup would have a fair amount of adjustability, depending on how you design it.

I think you may be getting that I am leaning heavily to the coil setup.

[Wooky]

While digging around for info when setting up my SJ I found these quite useful regarding leafspring set up:

1/ http://www-rockbottom4x4-com.4165476.n2 ... 82330.html

2/ https://www.pirate4x4.com/forum/jeep-wi ... metry.html

3/ https://www.onedirt.com/tech/chassis-su ... ll-center/

There is another page that I can't find now that had more details specific to 4x4's.... will keep looking.

As to the caster / pinion angle have a look at "caster correction shims / wedges". I have been looking for some localy but no one seems to know what I am talking about. Will have to import some from the states or have them made up.

[david bfreesani]

Also struggling to find Castor correction shims. Some people telling me it's simple to make them.....mmm right ....

I started my front end setup based on incorrect info . Then changed it to something I was told would work on a Jeep with the similar size wheels and lift. To do that, I had to cut off the original spring perches and weld on new ones at 6 deg more angle. You guessed it, it's still not right, and I need to pull back the angle. Now I have arc welded twice on the exact same place on the tubes to get this far. How much heat abuse can you give that tube before you compromise it. I think I may already by past that point. So the next time I do anything on that diff, it has to be the last time.

[Wooky]

I hear a lot of frustration with your current setup and the lack of correlation between what you wanted to achieve and what you now have.
So no worries if you lean toward coils. I might go that way in future changes to the SJ

I am no expert on leaf springs by any means but have figured out that they might well look simple and old fashioned but there is a lot of art going into understanding how they work. And getting them to work well might actually be more difficult than going with a linked suspension.

What springs are you using currently?
How arched are the spring packs?
It sounds like the extra long leaves combined with the short shackle could really be doing you a disservice and that alone would make for a hard ride and lack of articulation.
How far are the spring perches inboard from the ends of the axle?

150mm is a lot of lift!!

Post some pics of your setup as it is now and lets see if the combined forum knowledge base can help....

[XJ Junkie]

Have you still got the blocks of wood in the suspension?

[david bfreesani]

Budget pushed me to use what I had. That happened to be a spare set of 1 tonner hardbody rear leafs. I planned the spring mounts on the front chassis extension I built out past the end of the chassis member as everybody was telling me it's best to have the shackle on the rear of the spring. That quickly went pear shape, as I had to drop 120mm to get the spring to sit horizontal. Believe me, I tried it with the spring at an angle between perch and the space I needed to fit a shackle in on the rear, and I had had an harmonic bump steer develop into a slow and increasing death wobble at anything over 40km/h. Back out with the grinder and swop the mount and shackle ends. Next problem was the off center locating pin on the leaf spring. This pushed my axle 60mm forward, and I was running into problems that the spring pack was inverting under the weight of the Sani.

Comedy of errors saw me with a military wrap and additional blade that was done incorrectly and I based everything on that. Ended up with very sharp angle shackle and spring pack that lays dead straight with blades trying to separate. Here some pics with the best articulation I can get out of my setup as it is.

Result seems to be the springs are binding on the military wrap and causes enough tension on the spring to make it bend to the sides if there happens to be any sideways pressure due to uneven road surfaces. My Castor is now at 7.5deg which is not working on this setup. If I go toward full lock, it gets to a point where the wheels get pulled further into lock. They will only straighten out up to a certain point of turning (if that makes sense). I need to pull back the Castor. But I have been holding back on that exercise while I work on a few other things. I basically pulled the car off the road last February until I can get a few other things sorted. Finances has made this a very slow process. I am hardly even looking at the suspension till I have a few other things sorted. Busy right now building new crossmembers and a carrier for the second transfer case. Reenen on the forum has given me some info as to the location of the oil pickup in the sump. If this pans out, I want to cut the sump above the front diff, which will give me space to do a suspension drop of around 50-80mm I think. If that is the case, I need to do the entire suspension over again. And leafs just don't fit under the car. A SUA would help, but drops it too much, and would require a whole new set of spring mounts anyhow.

I have 3 sets of coil springs from Y60 and Y61 patrols and from a Pajero with 2 sets of shocks laying in my garage which have been donated by forum members over the past 2 years now.

[david bfreesani]

Have you still got the blocks of wood in the suspension?

I may have used wood along the way to measure and level stuff out, but never took the road with it. I did however have 130mm steel spacer blocks on the rear end for a long time till I built the new drop mounts for the rear leaf springs.

[grips]

Whooky Ironm stock those shims / wedges. Used on SFA Hilux. As far as I knows most fitment centre as well.

[Mike Nel]

Very cool thread

One day when I have time, money and retired, I want to try and tackle something like this

[XJ Junkie]

That Sani is a death trap.

[david bfreesani]

That Sani is a death trap.

Hence my ambition to fix the dodgy suspension setup that is causing the problems. That said, its actually not as bad as I thought. I was always comparing to how it felt on IFS, but the other day I was sent to Joburg with a Hilux, and on a few occasions it felt exactly the same. And that for a vehicle that is way lower and lighter than the Sani.

Sent from my SM-G925F using Tapatalk

[XJ Junkie]

You’ve been trying to fix it for 10 years. It’s a death trap. I hope you don’t drive it around on the roads?