Modified rear shock location for a TJ

[Stu Olson]

So....I am considering the modified rear shock setup.

A question: If the TJ was involved in a rear end collision (it was hit from the rear), what might the results be given the modified frame rails? Would they be more subject to failing at that spot? Any ideas on this?

[Jeeper]

Stu, what modified location? Are you talking about the upper mounts similar to the one's I had where you had to drill a hole in the frame about 2" above the stock mount?

Jeeper

BTW...I'm almost done Finally got to the wiring this past weekend

[Stu Olson]

Steve,

Some of the CA guys run them on their rigs. It entails changing the lower and upper mounting points for the rear axle. A bit more involved than drilling a couple of holes.....Blaine had a 30 minute shock relocation primer with me this morning.


Blaine,
Let me know when 220 is available. I am thinking this might be the best way for me to accomplish my goal.

[Deaver]

I'd like to learn more of this. What's involved?

[mrblaine]

Originally posted by Deaver
I'd like to learn more of this. What's involved?

[karstman]

Sweet setup Blaine!
How much additional shock length did you net?
I really like how the bushings are now oriented in such a way that they actaully work. The factory setup is a joke.

Has the lower mount been any more or less prone to damage with the shock mounted on a stud?

later,
mark

[StealthTJ]

Blaine,
Is that peice that's cut and welded into the frame a Ford shock mount -> E5TZ18183A ???



Fred

[mrblaine]

Originally posted by karstman
Sweet setup Blaine!
How much additional shock length did you net?
I really like how the bushings are now oriented in such a way that they actaully work. The factory setup is a joke.

Has the lower mount been any more or less prone to damage with the shock mounted on a stud?

later,
mark

The rear shocks are now 9005's. Used to be 9116's I think, but don't quote me. You get some additional length, but you can dial in as little or as much as your springs allow.

Considering that I moved them over behind the LCA's, they are much less prone to damage.

[mrblaine]

Originally posted by StealthTJ
Blaine,
Is that peice that's cut and welded into the frame a Ford shock mount -> E5TZ18183A ???



Fred

Fred, it is the upper section of a Ford Shock mount, not exactly sure of the part number, but I will look at the ones in the garage and find out for you.

Scott Hill on here actually found the first ones for me and then I bought a bunch from Ford for about 13 bucks each. Much easier than me fabricating them.

I got your PM, give me a few to think a bit.

[StealthTJ]

Thanks Blaine.. No rush (on the thinking ).. I always appreciate your thoughts and ideas. You normally have some great ones

I'm having Scott Sides look at the Jeep (he's doing some welding for me. Welding in the cage and some other small things). He's going to see what he can come up with regarding arms. His original thought was maybe triangulation for the rear, but there isn't much room back there. We're talking about the front still. He's done a fantastic 3 link on the front of his super built up XJ and it works great. It was done on the HPD30 first, but he's since put a HP9" in and has the same setup, arms that is.


Thanks,
Fred

[Tumbleweed]

Stu: To address your strength question. That Ford shock tower is pretty stout and I believe that the location of where it is placed on the frame rail is the key to the strength. If I remember correctly; there is a cross member that runs right behind the new mount. Many people will be skeptical about cutting their frame rails but keep in mind that you are adding a bunch of steel, also. I think if you add up how much you are adding vs what you took out-probably a draw. Blaine and I had a brief discussion on this awhile ago and I looked at his set up at JV. I was impressed!

[Stu Olson]

Tumbleweed: The question I posted concerning the strength aspect was for the benefit of someone else. I have no doubts as to putting one in my TJ. Blaine and I had what was probably the same conversation.....I crawled under and looked and there certainly is some other reinforcing already done in that area.

[mrblaine]

Originally posted by StealthTJ
Blaine,
Is that peice that's cut and welded into the frame a Ford shock mount -> E5TZ18183A ???



Fred

That be it Fred.

[StealthTJ]

Thanks Blaine !!
Still thinking about the other things





Fred

[JEEP_TJ_FREAK]

Doesn't that bind up pretty good? I keep thinking that the bushings are both facing the same direction and neither into the arch of the axle as it moves. Am I just not visualizing this correctly or will those bushings just flex that much?

[Stu Olson]

I've seen them work on the rocks. I did not notice any binding.

[mrblaine]

Originally posted by JEEP_TJ_FREAK
Doesn't that bind up pretty good? I keep thinking that the bushings are both facing the same direction and neither into the arch of the axle as it moves. Am I just not visualizing this correctly or will those bushings just flex that much?

This comment surprises me coming from you. I have seen your posts on suspension and you have a better grasp of what it does moreso than anyone I have seen post.

The rear axle moves in two separate and distinct arcs. One is controlled by the four link and the other is controlled by the track bar during articulation. Both arcs are similar in size with the arms producing the smallest radius due to their shorter length. One moves up and down basically parallel to the frame and the other moves up and down perpendicular to the frame as in the diff being the center of that arc.

Because of the two opposed arcs the suspension moves in and the relative amounts of degree change, there is no perfect alignment of the shock pins to each other. Just pick one and live with it.

The worst thing you can do is angle the shock and orient the pin so that the movement against the shock is trying to force it back and forth on the bar pin. That becomes the first movement of the shock before it starts any dampening and really helps to decrease a shock's performance.

[Chris L]

Blaine, I ordered these shock towers and should have them tomorrow. Any more details or pictures about where and how deep to cut the frame? How much of the shock tower needs to be cut off?

[Scott Hill]

To chime in on this one.

BEST mod for handeling and stability it is the difference between a disconected front sway bar and an antirock.


Scott

[Robert J. Yates]

Originally posted by Chris L
Blaine, I ordered these shock towers and should have them tomorrow. Any more details or pictures about where and how deep to cut the frame? How much of the shock tower needs to be cut off?

You notch the frame only that which is needed to accept the shock tower bracket so that it is flush against the outside of the frame. You will not be able to reach behind the bracket with the mig gun so you will need to drill 4 holes along the back of the tower so that you can plug weld it to the frame. As far as how much to lop off, there is a brace for the corner of the tub that will allow only so much height without hacking the brace, none of us have hacked the brace so if you chose to do it the same way, that will set the depth of the tower and determine your cut-off line.

[Scott Hill]

Robert,

Clean out you mail box here


Scott

[Stu Olson]

New shocks are sitting in the garage. UPS person dropped them off today.

[Robert J. Yates]

Originally posted by Scott Hill
Robert,

Clean out you mail box here


Scott

DONE

[Stu Olson]

Robert,

Donna has her calendar cleared out so she is coming along for the trip. (gee, it won't be such a boring drive this time!)

I'll give you a call some time this week and touch bases with you. The current plan is to get to your place on Friday afternoon and leave for Phoenix Monday morning. In between those days, we'll watch Garry on Saturday and wrench at Blaine's on Sunday.

[TDW]

Three questions:

What are you guys using to cut the frame?

Is the only modification to the new shock tower (other than drilling holes for the plug welds) is cutting it to length?

Are you mounting the shock at a predetermined angle other than what will fit?



edit: added another question

[Art Welch]

I can tell you what I did but can't guarantee if it matches what is setup on Blaine's, Robert's, or others.

What are you guys using to cut the frame?

Plasma cutter. I think you could do all of the cuts except those on the back top edge of the frame rail with a grinder if necessary. Maybe even those if you are more skilled with a grinder than I am (which wouldn't be saying too much).

Is the only modification to the new shock tower (other than drilling holes for the plug welds) is cutting it to length?

Yes

Are you mounting the shock at a predetermined angle other than what will fit?

Made it as vertical as possible without removing support for the side to side cross brace between the frame rails above the spring perch.

[Ace!]

Originally posted by Stu Olson
So....I am considering the modified rear shock setup.

A question: If the TJ was involved in a rear end collision (it was hit from the rear), what might the results be given the modified frame rails? Would they be more subject to failing at that spot? Any ideas on this?

Stu, I read through the replies, but didn't really see the answer to your question. That portion of the rear of a TJ frame is the "kickup" and is designed to absorb energy. By modifying it in the way I see it from the pictures, it has been changed in it's ability to absorb energy. I think the frame rail is more likely to bend other than the way it was designed. I've seen several TJs involved in rear ends, rollovers, and front end impacts, and I know what it's supposed to do when the rear of the vehicle takes a significant impact. I think the frame rail is more likely to bend outward instead of under with that mod.

I think the suspension of the TJ allows this mod to not stress the frame as much as some setups, and as such would make for a modification not likely to cause significant damage to the vehicle or occupants when not involved in a rear impact (i.e., I think the frame would last a considerable time, maybe indefinitely offroad). I also think the mod if done correctly (which the pictures show it to be) would not significantly weaken the overall frame, just change it's engery absorbing/transfering properties. If I were using my Jeep as an offroad only rig, I think there would be no issue with this mod. On road, and in a rear impact, I think there would be significant energy not properly displaced.

[Daddy Longlegs]

Ace,

Those were my concerns. The overall mod looks good but I'm not sure I'd like to find out the hard way whether its crash worthy.

I wonder if Stu would be willing to sacrifice his TJ for testing purposes in order to possibly save the lives of fellow Jeepers comtemplating this mod?

Scott K

[Jeff Weston]

Is the frame as strong after the mod as it was before? No. Is it strong enough? It appears to be so far for everybody who has done it. One thing to consider is the fact that most frames used to be constructed entirely of open channel. Look at any early Bronco, FJ40 and even most CJ's and you'll see open channel frames. I don't think CJ's frames were boxed until '78 or '79 and at that, they are not completely boxed from end to end. This modified "mini-boxed" area is probably still stronger than those older frames.

If you get rear ended hard enough to trash the frame that bad, your tub is already shot. The other guy's insurance will be footing the bill either way. Nothing is indestructible. If you saw Brad's TJ in person after the front end got wiped out and the frame displaced by several inches, you'd know the wonders that frame shops can do.

If I had the ability, it'd already be done. Instead, I keep working those lower shock mounts to no end. I think there is more weld than original material on them now.

[mrblaine]

Originally posted by Ace!
Stu, I read through the replies, but didn't really see the answer to your question. That portion of the rear of a TJ frame is the "kickup" and is designed to absorb energy.

I don't know what a kickup is, but I do know that there are significantly sized holes at the very start of the hoop that goes over the rear axle. They are in the middle of a transition from horizontal to the first upward bend in the frame. I don't see how the frame can absorb energy in and of itself as it is tied into the tub fairly well in that rear area. In order for the frame to absorb energy, it would have to be separate. If you said it was part of an energy absorbing structure, I would then agree.

By modifying it in the way I see it from the pictures, it has been changed in it's ability to absorb energy. I think the frame rail is more likely to bend other than the way it was designed. I've seen several TJs involved in rear ends, rollovers, and front end impacts, and I know what it's supposed to do when the rear of the vehicle takes a significant impact. I think the frame rail is more likely to bend outward instead of under with that mod.

In order for the frame to bend outward in that area, a significant length of double and triple welded crossmember will have to be separated from the frame. That crossmember is located just inside the shock relocation area and actually spans the cut on the inner wall of the frame. As far as knowing what it's supposed to do, I don't think either one of us can do anything but speculate. I have discussed this with some mechanical engineers and they feel the same as I do.

I think the suspension of the TJ allows this mod to not stress the frame as much as some setups, and as such would make for a modification not likely to cause significant damage to the vehicle or occupants when not involved in a rear impact (i.e., I think the frame would last a considerable time, maybe indefinitely offroad). I also think the mod if done correctly (which the pictures show it to be) would not significantly weaken the overall frame, just change it's engery absorbing/transfering properties. If I were using my Jeep as an offroad only rig, I think there would be no issue with this mod. On road, and in a rear impact, I think there would be significant energy not properly displaced.

I was actually more concerned about using a snatch strap to yank stuck vehicles. I used to be anyway. That was until my rig was used to haul out a serious stuck in the little sluice and ruined a rear bumper from the force with no apparent displacement of any of the frame members.

This energy displacement theory is a little bizarre coming from an advocate of big heavy bumpers which definitely alter the way energy is transferred compared to the stock bumpers.