When setting up a link type suspension do you want the pinion side of the axle to rotate up-ward as the axle drops down? I would think you would cuz this would relieve your drive shaft angle or at least the angle from the driveshaft to the pinion. I would also thing you wouldn't want this up front cuz it would f**k up all your streering geometry up front, but i was thinkin more of doing it in the rear. In the searches that I did alot of people wanted to just make all the links the same length and have them parallel, which would keep the pinion level or at the same dereges to the ground at all times. This would inturn really jar up your driveshaft when the axle dropped excessively.
If you could make the top link or links just alittle less steep of an angle to the ground than the lower ones, i think you could accomplish this. As the axle drops down the top of the diff would rotate out and away from the driveline, which would bring the pinion up relieving the driveshaft angle. I've done some searching but none seem to consider this. Thanks

HUH?

I read that at least 5 times, and I am still trying to figure out what you asked, and why you asked it.

YOUR PINION SHOULD BE STATIC! Period.

The purpose of a multi-link suspension is to locate the axle, and keep the radius the same while allowing flexation.

j

I understand what you are saying, and I went with the non-parallel bars so that my pinion stay pointing at the transfer case all the time instead of staying perfectly parallel to the ground.

I have read over and over that this is not optimal and that you will get wheel hop and anti-squat.

I decided to check out the guys that are running the rockcrawling contests and see what they were running, since they are particularly concerned with suspension geometry and what works and what doesn't . All the top guys that are running a 4 link type suspension are running they're links not parallel, with the front of the links originating on the same plane.

I am not saying what is right or wrong, but I will say it seems to be working for the "professionals"(dare I say that :D ) and it works for me. I do not have any wheel hop or any noticeable anti-squat or it is so minimal that it is not a factor.

Here is Ken Shupes rear susp. Him and his truck won the Super Bowl this year.:)

Yes that is what I meant by having the pinion pointing at the t-case at all times. I also noticed and realized from that picture that it probably doesn't matter at all. Look at how much travel that travel strap has. The diff on a rockcrawler at least nomarlly doesn't drop down all that much, most of the movement is in articulation which mean most of the movement is on the outer most parts of the axle. The only real application that this would help alot is if your interested in baja or jumping the truck to where there would be lots of movement in the diff. I wonder also if this would cause any binding in the the movement of the axle. Would parallel links move more freely and drop down further? Doesn't anyone else knows if this would cause more anti-squat or now of any disadvantages at all? Thanks

You're overlooking one other thing to consider: With regualr trail use, you will bend a link eventually. Period. Maybe it'll take a rollever to do it if you make them really beefy, but eventually you'll succeed.

As you mentioned - since the diff doesn't move much and it isn't a huge factor what the pinion does when dropping nine miles, running four same-length links will let you carry one pre-fabbed spare should you ever destroy one on the trail.

That is a good point to consider! I was thinkin of running a 3 link type setup with coils or quarter-elliptical. Has anyone ever bent the top A link on a 3-link? I bet you could break it somehow on the trails but I haven't heard of anyone acutally bending it. Anyone have any more ideas about the pinion angle thing?
One more thing, came across an interesting site about quarter-ellipitical. Wanted some of your'lls opinions on it, scroll down to the bottom and check out how he didn't actually attach the spring to the axle at all. Supposedly he built it and it works so its just not all some theroretical bull shit.
http://home.off-road.com/~ebarbely/qtrellip.html

Originally posted by 350 Samurai


Here is Ken Shupes rear susp. Him and his truck won the Super Bowl this year.:)

do you have any other pics of Shupe's rear susp ?

- jack

ok,
After seeing that link, now I get what you are after.

My rear is somewhat like that. A-arm top link, two lowers, with non-retained springs. My springs will drop completely away from the frame only limited by shock travel. As for the pinion drop and angle, that is limited by the radius of the A-arm and the rotation of the joint. My A-arm uses a ball joint link so my range of motion is similar to a heim. The springs relocate via a cone that points downward from the frame.

It works fine and flexes like mad.

In my first post, I assumed that you mean the front. My appologies.

j

We never bent the top link, but we broke them before. The biggest thing to remember when building a 3 link is to have the upper and lower arms as close to the same length as possible. When you have your links matched and the rearend drops the upper and lower links will follow the same arc. When running diff length arms they will travel in seperate arcs causing binding problems and what I call "auto steer" where the rear end will turn as one side of the axle goes down. Draw careful pics of the axle in motion and you'll start to see what I'm talking about. As far as the material you use be sure it's DOM at least .250 thick. Anything less will bend the first time you put weight on it. We had our lower arms made from .188 wall DOM and kept bending them, we then went to .250 wall and haven't bent one yet.

If you make the links converge so that the pinion points at the transfer the rear suspension will hop on steep climbs. I wouldnt do it.

See the pic of Ken Shupes? See how tight the limiting strap is? Without the strap his suspension will hop on the climbs. That is why he has the tight limiting strap - he has way too much anti squat built into the thing.

Now does this setup work?? - well, oh course yes, he won Supercrawl.

Is this setup the best for a rockcrawnin rig (as apposed to a "rockracing" rig - sorry to use this term) ??
IMO - NO because the axle carnt droop away from the frame so when this rig get hung up in the middle the back axle wont be on the ground (if it didnt have the strap then it would be but then it wouldnt be able to throttle up hills)

Sam

if you have a dual cardan joint at the back of the case, you want the pinion to point at the t-case output, and should setup your links accordingly. If you have a single joint at the back of the case, you want the pinion to stay static. Keeping it angled actually makes it bind LESS than if you keep it pointed at the back of the case.

Eventually you will flex enough that you exceed the amount of angle available from joints. You have a few options: 1) call jess. 2) reconfigure all your links and put a dual cardan joint at the back of the case, 3) Put a limiting strap in, there is practically traction on an axle that is drooped that far anyway.

Keep in mind that there is a difference between travel and flex. you don't need a lot of driveshaft movement to have gobs of flex, but you do need a bunch of travel to have a lot of travel. When you flex, the axle pivots more or less around the pumpkin, keeping the shaft in basically the same spot. When you droop the suspension out 3' baja style, you need a good long travel driveshaft.

If you run a limiting strap on the pumpkin, you will not really limit flex, but you will prevent drooping the suspension enough to mess up the driveshaft.

Yes the design will have a lot of anti-squat, but wheel hop? I don't think so. Wheel hop is caused by the tires loosing and then gaining traction. That's the whole point of a 3 link, to eliminate wheel hop. Yes it will bounce up and down but you will not have traditional wheel hop like leafs. I've seen Shupee climb near vertical walls, under heavy throttle and the susp barely moves. The point of the strap is to keep the frame close to the rearend when coming down steep hills. It will not affect articulation just keep the rearend from pulling away from the truck. Think about when you're climbing a hill, your front tires get over the top and there's no longer any weight on the frame, the susp will pull down to keep the tires to the ground but your COG( the frame) will still be going up. Not very helpful when trying to climb steep hills. Thats why competitors startes limiting their front susp droop, to keep the weight close to the ground. Shupe's just gone and done the same thing to the rear for coming down hills.

Originally posted by jeepguru7
Yes the design will have a lot of anti-squat, but wheel hop? I don't think so. Wheel hop is caused by the tires loosing and then gaining traction. That's the whole point of a 3 link, to eliminate wheel hop. Yes it will bounce up and down but you will not have traditional wheel hop like leafs. I've seen Shupee climb near vertical walls, under heavy throttle and the susp barely moves. The point of the strap is to keep the frame close to the rearend when coming down steep hills. It will not affect articulation just keep the rearend from pulling away from the truck. Think about when you're climbing a hill, your front tires get over the top and there's no longer any weight on the frame, the susp will pull down to keep the tires to the ground but your COG( the frame) will still be going up. Not very helpful when trying to climb steep hills. Thats why competitors startes limiting their front susp droop, to keep the weight close to the ground. Shupe's just gone and done the same thing to the rear for coming down hills.

Nope - you are incorrect.

Anti squat causes wheel hop. We are not talking about AXLE WRAP!!!!!

IMO the strap is there for driving up steep climbs. Yes it does help for going down as well but given the setup of the links and the tightness of the strap it is obvious (to me anyway) that it is there to control wheel hop of the steep climbs.

. I've seen Shupee climb near vertical walls, under heavy throttle and the susp barely moves

This is because of the rear strap and the amount of antisquat hes got. As he climbs the axle jams against the tension of the strap as the axle tries to move away from the body. On climbs the axle carnt move - its lock up solid (although one wheel can move up and the other down but both carnt move up or down when the power is on)

Sam

First: For the record, I came in fourth in the Uroc finals, in Vernal, and tenth in the Supercrawl, in the Legends class. It's no win, but it should be some evidence that my rig works. I run a four link with the links paralell, and all the same length. You are correct, the pinion stays the same angle as the suspension cycles up and down. I think you have your thinking backwards. If you run shorter upper links and longer lower links your pinion will drop as the suspension drops (the opposite reaction you wanted). In order to make the pinion drop as teh suspension moves up and vice-versa you would need shorter lower links and longer upper links, or have all the links converge in a common plane at the mounting point. The second option would produce a lot of anti-squat. Anti-squat is determined by the imaginary (or sometimes real) point where the links converge when looking from the side, and the angle of the links to the ground. Opinions vary a lot about what works and what doesn't, but I've found that very little anti-squat works best for me. That's why my links are paralell, and not at a very steep angle to the ground. I think it is much more important to get proper anti-squat and roll steer properties than to get the pinion always pointing at the diff. Suspension geometry is a constant exercise in compromise, the key is to find a good balance. Hope this helps some. Is anyone still reading this? Didn't think so...

hey i read it. and i agree with what you are saying. long links and as parralle to the ground as possible. seems to work very well. that is my whole educated redneck enginering course.

Thanks Monkey-Spanker.:D

Originally posted by morpheus


do you have any other pics of Shupe's rear susp ?

- jack

This is the only other one I took Morpheus, it didn't turn out too well.

Thanks for all the advice, I'll keep um parallel. One last question and I would like a real world answer instead of a theroretical answer that I found in most of my searches. How much difference in roll-steer is there if you locate your lower links in a V shape inside of frame to the outermost part of the axle? I've read that if you have them perpendicular to the axle or basically connected from outside the frame staight back to the axle you will have more roll-steer. Is this true? Thanks

Originally posted by GhettoRig
First: For the record, I came in fourth in the Uroc finals, in Vernal, and tenth in the Supercrawl, in the Legends class. It's no win, but it should be some evidence that my rig works. I run a four link with the links paralell, and all the same length. You are correct, the pinion stays the same angle as the suspension cycles up and down. I think you have your thinking backwards. If you run shorter upper links and longer lower links your pinion will drop as the suspension drops (the opposite reaction you wanted). In order to make the pinion drop as teh suspension moves up and vice-versa you would need shorter lower links and longer upper links, or have all the links converge in a common plane at the mounting point. The second option would produce a lot of anti-squat. Anti-squat is determined by the imaginary (or sometimes real) point where the links converge when looking from the side, and the angle of the links to the ground. Opinions vary a lot about what works and what doesn't, but I've found that very little anti-squat works best for me. That's why my links are paralell, and not at a very steep angle to the ground. I think it is much more important to get proper anti-squat and roll steer properties than to get the pinion always pointing at the diff. Suspension geometry is a constant exercise in compromise, the key is to find a good balance. Hope this helps some. Is anyone still reading this? Didn't think so...

Agree totally.

Sam

PS I wouldnt worry about roll steer. If the links are long it wont be bad. And anyway just turn the wheel a little bit is you have to.

This is a good thread here. I have to add that I had my links set up to rotate the pinion angle as the suspension cycled. I am running 4 link/panhard. With the bars not parallel, my suspension would bind a little and really limit my droop. I changed one of the mounting points and now they are very close to parallel, and my droop is nearly unlimited.

Here's a couple of pics to help you see the difference in parallel-to-the-frame vs non-parallel-to-the-frame lowers.

http://mywebpages.comcast.net/jjacobs149917/suspension/four_link.jpg

http://mywebpages.comcast.net/jjacobs149917/suspension/four_link_parallel.jpg

Notice the difference in the roll axis difference between the two. The parallel lowers will cause the roll axis to be on the same plane as the lowers, where as it the non-parallel changes the way that the roll axis is determined.

The flatter it is, the less rear steer you're going to get. So you should be able to sketch up how your roll axis will be with your arms going from the frame to the outer axle.

I think that this is a good thread in redneck suspension design, stop throwing out tons of therory, big fancy words that I can't understand and get to the stuff that really works....

-Keep the links the same length, upper and lower
-Make the upper and lower arms parallel to each other
-The less angle on the arms the better


I will add a few questions....

-Arm length?? I think that anything over 36" is a waste?

-wishbone vs 4-link. If the arms are almost parallel to the ground is there really much of a difference in roll?

I keep trying to keep an eye out of what really works...it seems the simple stuff does. Isn't shaffers rig really pretty simple. It looks like the front and rear suspensions are almost the same. The same goes for Paule bulit rigs.

Originally posted by Mieser


I will add a few questions....

-Arm length?? I think that anything over 36" is a waste?

-wishbone vs 4-link. If the arms are almost parallel to the ground is there really much of a difference in roll?

I keep trying to keep an eye out of what really works...it seems the simple stuff does. Isn't shaffers rig really pretty simple. It looks like the front and rear suspensions are almost the same. The same goes for Paule bulit rigs.

I am no where as edumacated in rock theory, but I would think that the arm length would be a function of flex vs. bind. Given that the pumpkin is going to be relatively limited on travel verticaly, arm/link length would determine the range of motion. Even heim's have limits to their rotational and degree travel. Therefore a longer arm is needed to increase the relative arc without it binding.

Originally posted by JohnnyJ
Here's a couple of pics to help you see the difference in parallel-to-the-frame vs non-parallel-to-the-frame lowers.


Glad to see somebody throwin down for the Millikin Book.

I just started my crawler and this looks like the ticket for my rear suspension. Any info on the pivet points on the front of the bars?

My idea that I keep tossing around my head is to run Two wishbones on my rear susp. I'm thinking both uppers and lowers above axle centerline (i.e. Camo, Desert Toy) and have the traditional traingulated upper with the opening of the V near the t-case and the point above the diff. But, instead of two straight bars run another triangulate V with point on frame crossmember and spread portion on top of axle tubes. Figure about 8" height difference between upper and lower links at axle end with less at frame end to keep diff pointed at t-case.

So, what do you guys think of the Double wishbone, I think it would be the ultimate in terms of very little bind and should locate the axle just fine. Yeah spares are a bitch to carry, and if the single end fails you're kinda screwed, but breakage aside how will it perform???? Think about it.
Chris

I've seen double V 4-link suspension work well as parallel and non-parallel setups. There is no reason you couldn't use the same length links top and bottom.

I've seen double V 4-link suspension work well as parallel and non-parallel setups. There is no reason you couldn't use the same length links top and bottom.

Yeah, Ive seen the double V with 4 seperate links used and it worked well.
I haven't seen or heard anything baout how it would be affected if the points of the Vs joined and were mounted with one Heim instead. For one thing it's cheaper, 6 heims instead of 8.

Sam at sierrarockcrawlers.com has done it. Looks like it works pretty good. I don't think he has any rear steer.