I am in the process of doing lots of research on 3 and 4 link rear suspension design for my XJ. The basic idea is that I want to put a 14 bolt underneath it, 6 inches farther back than the stock axle, and have it be a link suspension with coilovers.

The problem that I have run into is that due to the way the unibody is shaped, I cannot run links that are parallel top and bottom and close to equal length, unless I:

1.) Chop the hell out of the floor pan underneath the rear seats to be able to mount the top links higher.

2.) Have the bottom links mount to the frame about 6" below the bottom of the pseudo frame-rails.

3.) Mount the tops and bottom links about 4" apart vertically.

None of these options appeal to me.

I want to keep the top and bottom links parallel so that I get the least amount of anti-squat. I mainly do rockcrawling, so not getting wheel hop is very important.

I think that I can do a 3-link where the top link is about 2/3 the length of the bottom links. The roll axis will be decent. I'll still have some rear steer at full flex, but I don't think it will be a terrible amount.

My basic concern is, as long as I can keep the arms parallel and the roll axis as flat as possible, does it really matter that the top arms will be shorter than the bottom arms?

I know that as the entire axle droops, this will cause the pinion angle to decrease, but I don't plan on jumping this vehicle, so as long as I have the pinion pointing at the center of the rear u-joint on the CV joint when the suspension is at rest, I should be okay.

Just looking for sanity checks. If I am on crack, please tell me so.

Thanks,
- eliot -

Why do you want it to squat?? This makes no sense for rock crawling. Why would you want to make the rear squat towards the rocks, reduce traction, hinder climbing, and increase front tire pick??

Yes, it does appear that you are on crack. Maybe you should study link designs that are *proven* to work well for rock crawling instead of going on all the unproven and mis-guided "theory" that is blabered on the board.

Did I say I wanted it to squat?

NO.

I said I don't want a lot of anti-squat, because I don't want to have wheel hop. Wheel hop is caused by excessive amounts of anti-squat combined with climbing steep grades. Keeping the top and bottom links parallel leads to the least amount of anti-squat for a link rear suspension.

Maybe I should have rephrased the last bit to say "constructive criticism appreciated."

Thanks,
- eliot -

Originally posted by norton
Did I say I wanted it to squat?

NO.

..."

Not flaming or anything, just trying to help...

Err, not in those exact words, BUT when you make the links parallel (in a traditional link setup), you are creating the perfect conditions for maximum squat.

I'm not so sure that having anti-squat is going to guarantee wheel hop, but having limiting straps to reduce axel droop (not articulation) might eliminate/reduce wheel hop. I think that anti-sqaut causing wheel hop is probably just with setups with very short link bars, which allow the axle to walk under more.

I understand where you are coming from. As it is currently, if I mounted the lower links so that they were equal length and parallel to the driveshaft, I'd have about 50-60% anti-squat. To get it any less, I'd have to raise the mounts at the axle side or lower them at the frame side.

I looked at the picture of your buggy. It's looks like you have about 90-100% anti-squat. Have you measured it or played with the link mountings to see how it feels with more or less anti-squat?

- eliot -

I haven't played with any of the links to see what the changes would be.

The advantages to this design are:

1. Because the straight links are parallel to the GROUND, there is little to no rear steer.

2. Anti-squat can be reduced/eliminated with a simple strap in the center. I have a strap that allows about 4 to 5" of axle droop, and it's that much cause I like to baja down the trail. :)

3. Outside links are up out of the way.

4. Lower angled links protect the driveshaft.

I'm not saying that this design is best for everything though, it might be harder to do on non HP axles.

Sounds like you are on the right track to me.

I dont think there is anything wrong with shorter upper links if your running a triangulated four link. If your are running four parallel links plus a panhard then the shorter links will cause some binding cause they will fight each other as it articulates.

I would mount the links up fairly high on the diff housing. Like have the lower links in line with the axle tube and the uppers as high as you can get them.

My landrover (range rover links and chassis) has a stock rear upper A frame that would only be 30in long but I extended the lowers from 36in to about 54in and its starting to work well.

I think that the most important thing is to make them long so that when you drive up hill and rear springs unload (extend) then you dont get much of an increase of anti squat.

Sam

The 3 link that you are proposing will work very well even if the links are mounted on the same plane on the frame. the rear may "swing" (pinion rotate up and down with the control arms) depending on the difference in length on the control arms. The 3 link on the front of my truck is mounted on the same plane with allmost the same lenth bar the pinion moves like a Ford radius arm set up but I've had zero hop out of either axle and I run a 3 link front and rear, I've even done wicked reverse front swings in front wheel drive and the rear brakes locked with out an issue. Remember we don't run 200mph, if the geometry isn't perfect but you have excellent axle control it will still work perfectly, as long as you don't have too much anti squat so that the truck bounces when the rear suspension unloads, and as long as your control arms are long enough and don't stand straight up you'll be fine.

What is wrong with option 3? I tried to find out the answer to this in a previous post (http://www.pirate4x4.com/forum/showthread.php?s=&threadid=82028&perpage=25&pagenumber=2), but I got no replies.

I really hate to go into it all over again, but everyone that's anyone in the rockcrawling world runs their suspension this way. I posted pics of Shupe and Campbell for examples, but just about everyones ( that were 4 link) was that way. The rear links are in no way parallel.

I have mine done this way and I will say it is never driven on the road except to get to the trailhead, but it is a great working suspension. I have absolutely no wheel hop or any other drivetrain woes.

If it is so imperative that links be parallel, then why do the "professionals", who have money to burn, not go to all lengths to make theirs that way?

EDIT: This for a triangulated 4 link.

Sorry 350 Samurai I sort of lost that thread.
Ill reply over there now

Sam

Norton, it sounds eo me like you have done your homework. Now start choppin buddy. You might want to do a mock up and post pics. That way we can give you some better feedback. Its just kinda hard to say, "thats going to work well" by just reading some text.

The reason option 3 is unattractive to me is that my mounting the links only 4 inches apart at the frame and axle is going to put a lot of stress on the top link under heavy acceleration and deceleration.

Since the lower links are going to be in line with the axle tube, they aren't going to do anything to absorb the rotational force of the axle. The top link is going to have to do all that work. The farther the top link is mounted away from the axle, the less force it has to deal with (simple torque calculation). Say the top link is mounted 4 inches away from axle centerline. One mounted 8 inches away would have to handle only half the force.

Having an axle link rip off doesn't sound too exciting to me, so I'd like to be able to place the top link at least 6 inches away from the axle centerline. I'll probably go with 8 inches.

- eliot -

Originally posted by norton
The reason option 3 is unattractive to me is that my mounting the links only 4 inches apart at the frame and axle is going to put a lot of stress on the top link under heavy acceleration and deceleration.

Since the lower links are going to be in line with the axle tube, they aren't going to do anything to absorb the rotational force of the axle. The top link is going to have to do all that work. The farther the top link is mounted away from the axle, the less force it has to deal with (simple torque calculation). Say the top link is mounted 4 inches away from axle centerline. One mounted 8 inches away would have to handle only half the force.

Having an axle link rip off doesn't sound too exciting to me, so I'd like to be able to place the top link at least 6 inches away from the axle centerline. I'll probably go with 8 inches.

- eliot -

I agree with you there. I misunderstood you, I thought you were talking about a triangulated 4 link. I have a 3 link in the front and it is 11 inches from the centerline, but I have rockwells, so I need all the extra I can get.