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Rear Cantilever Setup - Problems/Questions

1K views 15 replies 7 participants last post by  H8monday 
#1 ·
Each day my Jeep gets torn down another piece at a time. I don't really know where I'm going, but know where I want to be. One of my MANY projects I'm working on is redoing the rear shocks. My problem before was they just weren't long enough, so now I'm planning on doing some sort of cantilever setup. I did a few searches but didn't find too much helpful info for me. First off, most the pics I've seen of these types of setups are with the shocks mounted to the frontside of the axle tubes. Is it possible to mount mine to the rear side and tilt them forward? The reason I'm asking is because I believe my traction bar will interfere with my shock. Anyone see any ill consequences of this? I think it'll clear the gas tank ok. The other problem I'm having is how to build the crossmember for the shocks to mount to. I have fuel lines on one side of the frame rail. Will these be hard to replace? Thanks a bunch guys!

 

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#4 ·
yeah, the red stripe was a dead giveaway.

im learing here too, ive got some rancho 9012 to go to my rear, and I was theinking the old H8 way of leangin them in, but I fear the anti wrap bar will interfear.

so hopeully we will all benifit fromthis thread!
 
#5 ·
The farther away you get from parallel with the motion
of the axle (not necessarily straight up and down) the less
effective the shock is.

For instance, at a 45 degree angle the shock only moves 50%
of what it would if parallel. So, the more the angle, the
stiffer the shock needed for the same effect.

And something to think about - shocks compress easier than
stretching - mainly they control rebound.
Notice most leaf spring rear ends have one in front of the
axle, the other behind.
That's not accidental - it's done that way to help control
axle wrap - both on acceleration and braking.
The one in back of the axle resists most on acceleleration
(it's stretching then), the rear on braking.



 
#6 ·
Here is how I did mine, but my fuel lines were already on the top of the frame rails and my traction bar is more to the center. If you mount the shocks on the back of the housing, can you do the upper mounts behind the axle also? or do you have to tilt them forwards for space requirements?
 

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#7 ·
That's something I may of forgetton to mention. I'm probably going to have to tilt them forward some for clearance issues. Think this will be a problem? What do you think I could about my fuel lines? Does anyone sell fuel line like they sell brake lines?

RRich - Thanks for the input. I wasn't sure on the numbers, but knew they don't work as affectively. Do you think if I put in some stiffer shocks, and have my traction bar setup, that I'll be alright? What are your thoughts on me mounting them behind the axle on the tube and have them point slightly forward?
 
#8 ·
Jammie-
H8 and many others have mounted thier shocks angled toward the center on top like you have them propped up with yer feet.
Square tubing across the top of the frame rails are a popular mounting structure.
Search H8Monday's posts from last spring for a pic of how he set his up.
 
#9 ·
Most anything will work, but to what degree?

Consider this - take it to the extreme - what if one end of
the shock was on the axle, and the other end was attached
to the frame but at the same height? Like the pic is
canted in but way more, really flat.
The shock would do absolutely nothing.

Remember the axle rotates with spring wrap - on braking or
acceleration - symptom is wheel hop, breakage etc.

Say on braking hard - the axle nose tries to tilt downward.
The shock attached to the axle behind the axle goes into
collapse mode, hardly resisting the torque.
The shock attached in front of the axle goes into stretch
mode, resisting much better - it's doing most of the
controlling.

That doesn't mean the axle doesn't rotate, it just slows it
down to a more tolarable level.
If it rotates too fast it can break things, cause wheel hop,
even cause a loss of driver's control.

And a little trick - you can multiply the effectiveness for
the wrap control by the lower axle shock mount itself.
Measure the distance from the center of the shock's lower
mount (pivot) to the center of the axle tube. That's the
moment arm.
Double that distance you double the wrap control without
affecting the "up/down" body control or stiffness.

But too long that long moment arm will work against you too.
As the body bumps up and down, the shock tends to try to
rotate the axle, so keep it reasonable.

Sometimes subtle changes in the geometry can be used to make
up for location and clearance problems.

The use of the radius arms completely eliminates the axle
wrap tendancies, so the shocks can now be placed wherever it's
most convenient.
Those are great pictures by the way, thanks.


"IF" there was a PERFECT way to do it -- everybody would do it
the same way.
 
#10 ·
Jaffer - I've seen the pics of H8's and other's rigs with similar setups. But all of their setups have the shocks mounted to the front of the axle tubes. I'm asking about mounting the shocks to the rear of the axle tubes. Make sense? I'm thinking I'll mount them on the rear side of the axle, then tilt them somewhat forward to clear the gas tank. Any problems seen with doing it like this?

RRich - I hate to say this, but your post confused me very much. I get the basic gist of what you're saying, but not quite sure what you are getting at. I understand the shocks in this type of setup don't do as good of job as if mounted the other way, but they will not need to control axlewrap(as that's what the wrap bar is for), and if I put in stiff enough shocks, they should work out pretty good, right? Slap me around if I'm wrong;) Thanks for you help BTW!!
 
#12 ·
Jammy,
Your idea will work just fine.
I would suggest using a quality Nitrogen Charged shock like the 5100 Bilstein, for more affective dampening and slightly quicker rebound on hard charging climbs.
I have found through quite a bit of testing that shocks cantilevered towards the center tend to handle side hilling very affectively, ( probably due to the down hill shock affectively handeling the sideload on a more vertical plane relative to the uphill shock). The result is more of a squating posture when powering out of steep sidehill position. In contrast, straight up and down shocks have a bit more of tendency to lift at the uphill rear quarter, and effectively reduce uphill traction and control. Shocks cantilevered towards the center do not however seem to handle straight up hard powered climbs as well as a vertical shock set up. Shocks angled forward at the top in the rear seem to be the most affective at dampening the rear, under hard powered climbs.
Your proposed set up may help to maintain good side hill stability, and still retain good dampening on the climb.
Like I stated earlier though, I would go with a relatively stiff nitrogen charged shock. The Bilstien 7100's are the real hot ticket, because they are custome valved(compression, & rebound, dampening, RTC,) for whatever your set up is. I run the 7100s with remote reservoirs on the rear of my rig (they are valved and charged to handle the steep forward angle, that I run them on).
 
#13 ·
Thanks for the info. What you said made some sense to me. My setup will be basically like yours, but instead of in front, it'll be mounted behind the axle and will tilt slightly forward. You see any problems doing it that way? Any clearance issues you can think of? What did you do with your fuel lines on the frame rail? In fact, what did you do for the crossmember? I'm thinking just some square tubing, but I haven't a clue how I'll weld the top of it. Any idea?
 
#14 ·
Actually I dont run my shocks like that any longer. In the search to find a suspension that would keep the tires to the ground under the high HP and my aggressive driving style, I tested about a dozen different configurations, in relatively controlled parameters. In the end, I found that canting my rear shocks forward (at about a 50* angle) at the top, and locating them outward on the axle, to just inside the frame rail, was the best geometry, for full unabashed, "make it all cost" extreme climbs. But I was also destroying shock seals on a daily basis. When I went to the 7100's in the rear, the combinaion out performed my best expectations. In fact I notice that Chris Durham went to a very similar set up, in his most recent suspension.

As far as clearance issues,.. that is so hard to tell since everything is a one on one basis with custom suspensions. You would be a much better judge to answer that one yourself, but I dont see any inheirant flaws with the suspension idea, as far as geomtry goes (other than my last post statement that you will need good high energy shocks. You will also need to be sure that your axle wrap is being controlled with a good anti wrap bar, or the potential to tear up your shocks at the pistons and/or seals will be almost inevitable. the reason is, that you will be puting your shocks on a pretty steep angle on full compression, and they will be on the back side of the axle tubes,.. if the axle is allowed to wrap you will be affectively increasing the angle at the lower mounting point, by whatever degree the axle rotates upward under power.
After you install it, go out and test it, without any predetermined hopes. If it doesnt feel good dont be affraid to change it,..thats how successful performance combos come together.
Good luck.
 
#15 ·
Thanks a bunch for your help. I guess I just need to dive right in and get started. I think I'll make my tranny crossmember and traction bar first, then go from there. BTW - What did you use for your crossmember? I've seen pics, but not sure what the actual frame is made from.

Also, what's my best route for mounting the actual shock to the axle and to the shock crossmember?

Thanks!
 
#16 ·
I just used a piece of 2"x2"x1/4" Square tubing for the cross member, and left over shock mounts that come in the box with new shocks. I prepped the tube and the mounts at all welding locations. Then I placed the tube between the frame rails and tacked it in place. I positioned the lower mounts where I thought they would work, and tacked them, then did the same with the uppers. When I was happy with the location, I broke the tack on the tube and removed it so I could weld the upper mounts on the bench, Then I replaced the crossmember and welded it about 50% from every angle I could reach then I did same for the lower mounts. I took it out and tested it on a ramp (rock) by driving all 4 tires up onto the rock and visualy looking for any potential problems with contact or binding. When I was happy with that, I went back and completed the welding to 100%. You really dont need much weld to hold the shocks in position for testing, in fact its good to have the mounts break away at the welds when testing rather than the breaking a shock(s) if something does bind. To save time removing welds, when I was testing different configurations, I was only stitch welding the mounts in position, and actually driving hard to test performance.
 
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