Rear coilover/ORI mounting

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71fj40cruiser

71fj40cruiser

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Hopefully this does not come across as a dumb question, but here it is. I have a 40 with 80 series rear axle. It is 4-linked with ORI's with wheel base of 104" It currently has 4 speed with splitcase and I am looking to put an auto in and wanted to extend the rear axle a bit. My question is this, what impact would it cause moving the ORI's from behind the axle to the top of the axle? Just that move would gain about 4-1/2"
 
71fj40cruiser said:
Hopefully this does not come across as a dumb question, but here it is. I have a 40 with 80 series rear axle. It is 4-linked with ORI's with wheel base of 104" It currently has 4 speed with splitcase and I am looking to put an auto in and wanted to extend the rear axle a bit. My question is this, what impact would it cause moving the ORI's from behind the axle to the top of the axle? Just that move would gain about 4-1/2"
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Move the axle back far enough that the ORI are now on the front of the axle, if possible. In your scenario, you are either raising the body up to account for the raised lower mount, losing a bunch of up travel, or a combination of both.

Nice looking 40 by the way, share some more recent photos with us!

71fj40cruiser

Thread 'Buena Vista, CO'

Just got back from a week in the mountains. Had a great time, lots of scenery and good trails! This pic is on the Holy Cross trail
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71fj40cruiser

Thread 'Time to go wheelin''

I was able to go to Moab in June. What a blast:steer:

But it is time to go again. I am going to SMORR Friday night and wheelin' Saturday. It is supposed to be fairly cool, maybe some rain Friday, but clear Saturday.

Does anyone still wheel?

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It sounds like you will lose up-travel if you move your shock mount to the top of the axle, and 4.5” of lost travel is pretty significant. I agree with what Evan suggested, or move your tower backwards the same distance that you want to move the axle. Otherwise you will have to get a shorter shock, but that will limit your down travel.
 
To be clear, it would not raise the ORI 4.5, rather it would move the axle back 4.5". It would raise it half the axle diameter. about 1-1/2". I cannot move the upper mount because I cut the frame to place the upper mount in the proper place. My plan is to either modify the upper mount, (make it higher) to accommodate the 16" ORI or change to 14" ORI's. I do not plan on raising the body, if anything I am looking to lower it some. My main question is how would moving it from the back of the axle to the top affect the suspension geometry?

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Moving the eye will not change suspension geometry, the geometry changes when you move the axle and link lengths increase and angles change. I dont expect you’d notice any negative effects from the stretch, longer link lengths are generally favorable. If youre happy with the way the rig performs now, I’d put the axle where you want it for an acceptable rear driveshaft length with the new drivetrain, and the just lengthen the links to work with the new location. Then tackle the ORI’s.

If there are negative characteristics of the rear suspension now, it would be a good time to rectify them. Did you link it yourself the first time?
 
My gut told me what EWheeler stated but I by no means have the experience to say much - except that if your so inclined, I would take measurements as is, enter them into the link calculator on irate, note all the parameters and then enter the new measurements and see what changes, and dial it in so it’s the same or better.
 
71fj40cruiser said:
I did not do the original 4-Link. Justin with Redline set it up.
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Are there any handling characteristics you don't like? My rear 4 linked 40 has an old Proffit's kit (unsure if it was installed by Proffits) and it has a TON of roll steer. If functions just fine on the trail, but is a miserable vehicle to drive on the road as you're constantly fighting the roll steer.

I seriously doubt putting the shock eye on TOP of the axle will only lose 1.5" of shock shaft. I suspect you're going to be more like 3" with it directly on top. The centerline of the eye looks a bit below axle center line, and when you move it on top, you'll have to maintain a small amount of clearance from the eye to the tube, so you're not just adding half the tube diameter if the mount is truly on top of the axle. If you can offset the mount forwards from center a bit without causing binding of the spherical bearings in both eyes, you'll be able to keep it lower.

The front coil overs on my crawler were mounted such that at full droop, the bearings in the eyes were binding. This resulted in a broken shock shaft right at the bottom eyelet the first time I took it out after buying it. It is imperative that you cycle suspension full droop to full compression and confirm no binding in the eyes before you burn everything in.

Very cool 40. I've got the same cage from Justin in my '80. Also have a nearly identical photo as yours on Holy Cross on the same obstacle 15 years ago!
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EWheeler said:
I seriously doubt putting the shock eye on TOP of the axle will only lose 1.5" of shock shaft. I suspect you're going to be more like 3" with it directly on top.
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I suspect you are correct. Right now the mount is directly in line with the lower link mount. Bringing straight forward is not an option without moving the mount inboard, and I don't want to do that. It drives very well at this point, nothing unexpected in the characteristics. I mean as well as a 4 speed with 529's and 40 stickies will let you :grinpimp:
 
71fj40cruiser said:
I suspect you are correct. Right now the mount is directly in line with the lower link mount. Bringing straight forward is not an option without moving the mount inboard, and I don't want to do that. It drives very well at this point, nothing unexpected in the characteristics. I mean as well as a 4 speed with 529's and 40 stickies will let you :grinpimp:
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I was thinking that may be the case if you moved it to the front of the axle.

Couple of options to consider:

1. You could re-design/rebuild those lower axle link mounts to incorporate the shock eye mount between the link and the axle tube. It would slightly affect geometry and pinion angle change throughout the travel of the axle. It would require a custom bracket and some lateral bracing to resist the leverage of the mount being further away from the axle tube, but it's possible.

2. You could look at mounting the ORI to the lower link in a trailing arm configuration. See visual here:
Firemedic831

Post in thread 'Grampys Truck'

While the rear Chevy 63 springs work well they do not keep up with the front . So I am linking the rear but going with a trailing arm setup this time . And all my PSC stuff was at my door when I got home .

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If going the trailing arm route, just need to make sure you do something to resist wobble. This is usually done by either mounting the shock eye below the centerline of the trailing arm, or using wobble stops if the shock eye is mounted above the trailing arm centerline.
 
peesalot said:
The stress/load will change if you move lower mount to top of tube. You will have LESS stress on the link ends with the lower mount centered on tube. Other than the packaging issues already discussed thats it.
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He is asking about moving the shock eye, not the link mount.... but on that topic, almost all of 4 Wheel Underground's link kits have the lower links mounted above the axle centerline. He says flatter links are WAY more important than the small amount of added stress from having the joints mounted off centerline. I'd like to try it one day....

Here is a great page that I don't think many are aware of:

Suspension Encyclopedia | 4Wheel Underground

No matter what type of vehicle we drive, the suspension is the single most important element in regards to how it handles. With a poorly designed suspension, even a well-built ...
www.4wheelunderground.com www.4wheelunderground.com
 
I know, that is exactly what I posted, moving the lower shock mount to top of tube vs. offset will lessen the stress on the link ends.
Having the axle end of your lower link at axle tube center or above actually increases the stress load.
 
peesalot said:
Having the axle end of your lower link at axle tube center or above actually increases the stress load.
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To clarify, are you referring to the lower link of the ORI or the lower control arm? I wasn't so much concerned about the stress load as I have not had an issue in several years with it in the current set-up. I was more concerned about how the suspension might or might not react to the movement of the lower shock mount from offset to the rear to the top of the axle.
 
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