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TnA's 86 Jimmy Shop Build / Product Development Thread - (Trailing Arms?!?!)
- Thread starter CFMi
- Start date
With the front all nicely linked and nice soft spring rates on the coilovers, they left the rear leaf sprung. It's a pretty un-balanced system. In other words the front suspension will articulate much more, and easier than the rear. Depending on the terrain this can be an issue. I like to see a more balanced setup - in other words the front and rear suspension have similar overall spring rates and similar travel numbers. Of course this is just limited to my small window of experience in the rocks out here. I'll try to explain further, so please bear with me if this doesn't make any sense, lol... Let's say you are running a trail, and there is a large (5 foot tall?) rock coming up on your right hand side. There is enough room to barely squeak by on the left of it, but the trail turns hard right just after it. So you can get the front end past it, but then when you turn, the rear end has to drag up and over it (I mean let's face it, you be driving a full-size Chevy! They don't turn like a Wrangler) . With a flexible rear you can make it, but with a small-travel, stiff rear suspension it causes you to flop over. The opposite can happen as well if the front is stiffer than the rear. I personally would rather have the front end a little stiffer than the rear though, since you can steer the front tires around obstacles easier than the rear - the rear just sort of drags along behind you. So I just thought it was weird that they spent mega-bucks on portals and coilovers for the front but left the rear leaf sprung. My comment on the need for a sway bar was not meant to offend anyone, hopefully I did not. But that being said, the front sway bar would stiffen up the articulation of the truck, making it closer to the rear - thereby balancing things out a little better - although limiting your articulation after spending so much effort to make it possible is a bit of a band-aid. Disconnectable sway bars, or even in-cab adjustable sway bars are the ticket here!! The you could adjust to what you are doing at that moment - high speed cornering, stiffen up the swaybar, got a rock to get over, loosen it up!
Hope that explains what I was meaning. If not, I'll try to explain further.
I really need to get an on-the-fly adjustable anti-sway bar designed!
I really like the idea of rear air bags, linked together with a valve that can either connect or isolate them. When connected they act like a negative sway bar actually pushing air away from the compressing side. And when "locked" out they act like regular springs. With that and a selectable sway bar, you could have a rear nice flexable but stable ride.
I've always been intrigued by air springs - whether that be a high quality air shock, or an airbag setup. I see some inherent problems with them though - you are limited to the "spring rate" of air - sort of. Depending in the chamber size, the spring rate changes. So by tailoring your chamber size, you can effectively change your spring rate. However, as your suspension moves, the chamber size changes, so your spring rate is constantly changing. And it's soft - real soft. Until you get a really small chamber, but then it exponentially increases as that small chamber gets even smaller. And then if your chamber for the air is flexible (like an airbag), then it gets even harder to control.
I think that with serious design time and figuring you might be able to get something that works decently with airbags. I like the idea of being able to change the volume of air in each bag individually, kind of like your idea with the valves. To take the valve idea further you could have an air source onboard and be able to actually pump them up or let them deflate at any time you'd like.
However, there are plenty of companies out there that are building air shocks in a highly developed and well thought out manner. For instance, King shocks are so confident in their air shocks they actually state you can use them as their own bump stop, therefore cutting your suspension costs even further. But if you look at pretty much any off-road racing team, be it Baja or King of the Hammers - you'll see lots of teams experimenting with air shocks, and then a lot of them end up going back to regular coilovers for their adjustability.
Then there is the fact that an airbag or any of your lines can spring a leak, and so there's a reliability issue as well.
All told, I'm still really curious about air spring designs, but I have yet to venture into that arena because of those things stated above. I have been thinking about building up my XJ after the K10 build, and I think I might just go with some King air shocks at all 4 corners to give it a go. Or possibly air shocks in the front and bags in the rear. We'll see how things go.
Thanks for bringing up the airbag thing, it's definitely a road I want to explore in the future myself
I just really love the idea that when an axle set are linked it does EXACTLY the opposite of a sway bar. It actually pushes the uncompressed side down. So, going with airbags, switchable linked valving, and a selectable sway bar, you get 4 levels of suspension articulation.
1) street: linked sway bar, disconnected airbags. Limited articulation, great street manners.
2) medium off road/high speed: linked sway bar, connected airbag. Good articulation, still controlled, limited body roll.
3) slower off road: disconnected sway bar, disconnected airbags. More body roll and articulation.
4) full rock crawling: disconnected sway bar, connected airbags. Maximum articulation and axle/body movement, no fun on the street. If its rear only, then nice way to get three wheel turns. Sexy, but easy to roll.
1) street: linked sway bar, disconnected airbags. Limited articulation, great street manners.
2) medium off road/high speed: linked sway bar, connected airbag. Good articulation, still controlled, limited body roll.
3) slower off road: disconnected sway bar, disconnected airbags. More body roll and articulation.
4) full rock crawling: disconnected sway bar, connected airbags. Maximum articulation and axle/body movement, no fun on the street. If its rear only, then nice way to get three wheel turns. Sexy, but easy to roll.
This.
Great idea! You could easily fit a dual bag system anywhere (large bag to hold the weight of the vehicle, smaller bag on the other side to control droop) and then linkage connect it to these arms, with a separate shock. I like this idea.
They make 18" travel airbags , some even have internal bumpstops
Do you have a link to these?
Eh. No link but I have the paper catalog for firestone airsprings , later on I can look up the part number.
But honestly depending on where you mounted the bag on the lower arm you would not need as much travel .
You would want the largest diameter bag you can fit , larger diameter means less pressure for a given load .
A few of us have played with bags up here and they do work prettt well for us .
But honestly depending on where you mounted the bag on the lower arm you would not need as much travel .
You would want the largest diameter bag you can fit , larger diameter means less pressure for a given load .
A few of us have played with bags up here and they do work prettt well for us .
Not exactly what I'm talking about, but has a beautiful pic of a bell crank install of a by-pass shock about half way down.
http://www.pirate4x4.com/forum/general-4x4-discussion/659056-air-adjustable-4-link-need-advice.html
http://www.pirate4x4.com/forum/general-4x4-discussion/659056-air-adjustable-4-link-need-advice.html
I'm confused, you guys talking about cantilever shock setup? Never heard of bell crank.
Basically the same, true cantilever has the load going past a pivot the the support. Where as a bell crank typically does it at 90 degrees. Typical of a indy car front. But all of them basically use links and pivots to get the job done. It allows you to use ratios for travel and place all the suspension weight on the chassis as opposed to the suspension. Also gets the expensive parts of the suspension up and protected.
Ok, no worries. I used to be a Firestone dealer too - but don't ever remember seeing anything with bumpstops built in. That is interesting, but truly not really necessary. If you are doing something with a mechanical advantage - i.e. 12" bag and 24" travel, then the forces upon bump would be doubled on the bag so I would think a normal air or hydraulic bumpstop at the axle would be best anyways.
That is cool for sure!
Yeah, pretty much the same thing. Definitely the same in concept.
Thanks! I wish I could spend more time doing this, but what time I do spend I try to take my time and do things right. It doesn't always work out but I like to think it does most of the time
You guys have been keeping me busy!! Sincere thanks to all who have placed orders with me recently and in the past! It means a lot to me 
So yesterday AM, I had to move the big truck, affectionately known as "Truckie" around here - and when I tried to start her up, she made a loud metal-on-metal sound and then started puking engine oil out the exhaust. Sad day.
Since I was planning on taking her apart some time in the near future anyways though, I really was just the motivation I needed to get going on that. So at 3:30 in the afternoon, I got her pulled in to the shop, and she looked like this:
At 7:30pm, she looked like this...
...with a pile of dirty but functional parts:
Here is the front axle the will be for sale soon (I have a buddy interested in it, but I'm not sure he wants it yet). It's an HD D44 with link mounts obviously, one-piece cast high steer knuckle, ARB, Yukon 4.88 gears, USA made Bearings, Moser axle shafts, Randy's Super Joints, etc...
And a pile of coilovers, now to be re-purposed for the K10!!!!!!!
It's kind of a sad day, to see her go away. I've owned her for about 20 years, and we've done lots and lots of trails together! She has been a really good truck, and is somewhat well known - heck she was even on the cover of a magazine once! But technology has come a long way since then, and I'm also really excited to start a new build for myself! On to new things!!!!!!
-Darren
Since I was planning on taking her apart some time in the near future anyways though, I really was just the motivation I needed to get going on that. So at 3:30 in the afternoon, I got her pulled in to the shop, and she looked like this:
At 7:30pm, she looked like this...
...with a pile of dirty but functional parts:
Here is the front axle the will be for sale soon (I have a buddy interested in it, but I'm not sure he wants it yet). It's an HD D44 with link mounts obviously, one-piece cast high steer knuckle, ARB, Yukon 4.88 gears, USA made Bearings, Moser axle shafts, Randy's Super Joints, etc...
And a pile of coilovers, now to be re-purposed for the K10!!!!!!!
It's kind of a sad day, to see her go away. I've owned her for about 20 years, and we've done lots and lots of trails together! She has been a really good truck, and is somewhat well known - heck she was even on the cover of a magazine once! But technology has come a long way since then, and I'm also really excited to start a new build for myself! On to new things!!!!!!
-Darren
Just read through the last few pages. You are steeling my air bag design. But if you make it work, I won't have to do all of the tech.
I have been discussing bags on a linked truck for towing and wheeling. There will always be a compromise somewhere, just have to figure out where.
I have been discussing bags on a linked truck for towing and wheeling. There will always be a compromise somewhere, just have to figure out where.
I'm not sure I'm going to go with airbags on the K10 build - I've got some decent coilovers from the big truck that I had been planning on using. However I have given it some thought over the years, and really think the idea of two bags per wheel (one to control compression, one to control droop) seems like the way to go. It has always seemed like something that would be hard to fit in under a vehicle - but the idea of a trailing arm with one shock and then a link up to a belkcrank or cantilever would allow you to have much more freedom on bag placement. I like the idea a lot, but I'm not sure I like it enough to change direction on this particular build.
I am really not very happy with the shock performance on the rear of the Jimmy though, so maybe when I look at re-vamping that suspension airbags might be the way to go there. On the Jimmy, linkage up to bags and also putting the shocks up and out of the way could allow you to run shorter bypass shocks (Raptor take-offs??) and still get a decent amount of wheel travel. Lots of ideas, not enough time or money to experiment with them...
