Ok so i thought i had a good grip on building a link system, but i guess not.

So from the beginning i put a set of 404 mogs under my Yj. Cut the rear frame and tube it all back in to the cage to make room for the coilovers. Then made a engine cage to stop the front frame for twisting with all the grearing. Took the jeep out and with in 10mins the front pinion rolled and cracked the new drive shaft. Bent the hell out of the front lower frame link mounts.

SO cut them off and made them all out of 1/4 plate. During that time i also redid all the tabs on the axle it self and to battle the roll i made the upper link towers 4" taller.

Then took it out and the rear cross member failed. So back to the shop i went and made that all out of 3/8 plate.

Now she is back together and i noticed the front pinion when i hold the brake and give it gas rolls up about 8" (no joke). It does the same thing when i clime something ( 8" down).

First Y is it doing that? Clearly i screwed something up, but what.
Second How can i stop it. Or is it just something that a 404 mog does cause of the 9" long pinion and all the gearing.


I have 42" pitbulls, atlas 11.1 t-case and a ax-15.

Please help me. I'm getting tired of this thing not working.

http://i205.photobucket.com/albums/bb18/flash-871/jeepbuild002-4.jpg

Do i need to take the upper links to the center more or lower my lower links below the axle housing more.

http://i205.photobucket.com/albums/bb18/flash-871/001.jpg\

This is about where the lower links are mounted. Its a different set of tabs now but in the same place.

I think you need to lower the lower links, everyone I have seen that trys to place the mounts on the face have a problem with the links tearing loose or not controling the axle. The reduction boxes put a lot of pressure on the link points.

I think you need to lower the lower links, everyone I have seen that trys to place the mounts on the face have a problem with the links tearing loose or not controling the axle. The reduction boxes put a lot of pressure on the link points.

I attempted to discuss this on Greg 72s build thread, but then Triaged posted that it doesn't matter how high or low you place the lower links, so long as you have enough vertical separation. I dont' necessarily agree, and believe that when you mount the lowers at axle centre height there are a few degrees of axle roll where the lower links are neither in tension or compression, but the axle end of the links are just swinging up or down a little.Regardless, Xcrawlers setup doesn't appear to have enough vertical separation between the upper and lowers for portals..
Ag.

I've got about 12" separation on mine with the lowers about 2" under
the axle & never had a problem on 42 Iroks..

Jeff

OK ill start with the lower links and move them down below the axle. looking for 10" of separation but i'll shoot for twelve. Any pic's. Thanks guys. That way i can see some setups that work.

OK ill start with the lower links and move them down below the axle. looking for 10" of separation but i'll shoot for twelve. Any pic's. Thanks guys. That way i can see some setups that work.

Can't tell if you have compliant bushings anywhere, if not are your link frame mountings adjustable for vertical separation to match the revised location of the lower links?
AG

Yes the whole front is adjustable with jonny joints on each end. Should i have put a adjustable bushing at the frame end instead?

you need the center of the bottom links even with the centerline of the tire, MINIMUM.
NOT the center of the tube. the tire.
the axle does not do jack shit, the torque multiplication takes place in the box, and THAT output force is what you are attempting to fight. (unsuccessfully)

I know that it probably pains you to have super high clearance axles, and then links hanging down in the way. get used to it, tuck them next to the boxes as well as you can.
Triaged 4 link calc is a great tool, but you need to 'plug in' the center of the tire/wheel when playing with mogs. all other axles (60's, 9's) are using the torque off the center of the axle. Mogs' torque is 4.5" lower, a shit ton of difference.

I think Dan's comments (Triaged) were trying to suggest that the torque creates a lever arm at the tire's contact patch, and had no relevance to the axle centerline...???

I've asked him about that on a couple of occasions, since I had this image in my head of all the torque trying to create "rotation" around the axle centerline (or in the case of the portal, around the lower output gear centerline).... my hope is that I understood him correctly in his description, because clearly if you look at my 4-link design it puts both the upper and lower link mounts WAY above the output gear centerline.

My Mog-9 Link setup (Rear axle): Wheel center = 19", Lower Link @ 23" and Upper Link @ 33"

http://i904.photobucket.com/albums/ac249/gregblanchette/K5%20Gallery/Suspension1.jpg



The best way I can describe it (assuming that my interpretation is correct) is to place a measuring tape at the ground where the contact patch is and them measure up to your lower link mounts and THAT is the length of your lever-arm resisting the torque.

I think for the OP here, the problem is a combination of a "too small" link separation combined with a compressible joint material. I'll bet that the torque is compressing the hell out of those joints (pushing some, pulling others) and the amount of slop is translating into that 9" of pinion motion. Considering how long the pinion snout is.... it would visually exaggerate any free-play in the link ends.

(This is my best guess.... at times like these I really wish I had pursued a degree in M.E. instead of Computer Science)


:usa:

The problem with the picture of the links you are showing on the calculator is your lower link is about 6 to 7" above the centerline of the drive axle. All the torque is placed at the center of the wheel which causes the reduction boxes to want to rotate around the housing. If the lower link was below the housing it reduces the torque of the box and controles the movement of the pinion, it will reduce your ground clearance but you will still have about 8" more than a 60.

Original comments from Dan...... FYI

http://pirate4x4.com/forum/showpost.php?p=11989404&postcount=112


:usa:

I have about 10" maybe more of separation in the rear. The links are shorter then the front and frame mounts are all fixed bushings that cant be adjusted. The rear doesn't roll at all.

http://i205.photobucket.com/albums/bb18/flash-871/4-18-09002-1.jpg

http://i205.photobucket.com/albums/bb18/flash-871/4-18-09005-1.jpg

http://i205.photobucket.com/albums/bb18/flash-871/4-18-09003-1.jpg

So maybe you are looking at both joints moving and seeing the pinon moving so much cause of it. I went wheeling this last week end and my buddy watched the pinion when i was in the rocks and he said it didn't really move. But when i was coming down any hill the pinon rolled up so much the drive shaft would bind up. How many of you guys have bushings on the frame end?

How many of you guys have bushings on the frame end?

all heims on my rig

all heims on my rig

Slighty off topic,Are all your links equal length and parallel when viewed from the side ?
Ag

Ok... so I have never done one of these before but...

It seems to me that the more longitudinal (front to rear) separation you have between your upper and lower axle end link mounts the more vertical seperation will be required. This relationship should be fairly sinusoidal.
As you apply braking force to the wheel the axle wants to pivot about it's link mounts. Also when you stop weight shift as a function of your center of gravity will cause a change in front suspension loading. As your front suspension loads most upper links will become "longer" in the longitudinal dimension. At the same time most lowers will become effectively "shorter" this will lead to pinion roll. The easiest fix for this would be to move your upper axle end rod mount back until it is directly above your lower. Lowering your lower mount and moving it forward would effectively do the same thing with the added bonus of shortening the effective lever created by the tire and portal box.
Shortening your lower link rod and moving your lower link frame mount forward should result in reduced nose dive as well.

Or at least that's what I get at first glance.=)

Sounds like a description of traditional pinion angle change under bump and droop? :confused:

I spent a lot of time playing with my calculator and messing with upper link lengths (and mount positions) until I had a total pinion change of only 5 degrees through the entire suspension travel (6" of bump, 10" of droop). Some combinations showed a lot of pinion change on bump and almost nothing on droop, other combos were the exact opposite.

If memory serves, controlling massive swings in pinion angle change is why there is a rule-of-thumb about keeping the upper links at 70% of the lower link length.

Maybe the OP should post up the suspension specs so we can see what the calculator says?


:usa:

I have had my lower link mounts (front and rear) on the axle centreline for about 6.5 years now with no problem.
Running about 10" separation on the front and about 11" in the rear. Double triangulated 4-link with all 1" heims front and rear.

I've never looked to see if my pinions roll up under torque, but the front one definitely can't be because if it did more than an inch or so it would be making love to my starter motor.

Slighty off topic,Are all your links equal length and parallel when viewed from the side ?
Ag

the rear links are, it is double triangulated.
the front has the lowers parallel and the top links (slightly) angled enough to keep the axle in place. (engine hogs up the room)

I am no expert so take my advice with a grain of salt.


First are you sure your suspension is not unloading and compressing causing the pinion to move up and down?

Also the long pinion really exagerates the pinion movement.

If your upper and lower links are alot diffrent in lengths it will cycle like you describe.

I also respect everyons opnions but i have had sucess with mounting my lowers center of tube. But you will have huge forces applied as far as leverage. you need to compensate (sounds like you did)
I went Cromoly tabs with cromoly weld inserts in the tabs. no failures to date.
Many stupid miles loged.

Mark

I am with tjmark with the suspension loading/unloading.? thats a common issue with any linked suspension.
with that said your frame mount separation comes into play, you need some, but not as much as on the axle end, too much/too little and you will get that nasty pinion movement. every rig is different there is alot of great info on here. and i am no one to tell you how to build a mog axle link'd setup, mine isnt driving yet. good luck

I am with tjmark with the suspension loading/unloading.? thats a common issue with any linked suspension.
with that said your frame mount separation comes into play, you need some, but not as much as on the axle end, too much/too little and you will get that nasty pinion movement. every rig is different there is alot of great info on here. and i am no one to tell you how to build a mog axle link'd setup, mine isnt driving yet. good luck

Not disagreeing with anyone as I'm always willing to learn, but could someone riddle me this?
Heim joints have no compliance. A parrallel equal length 4 link with heims on all ends will keep the pinion parrallel with the frame as the suspension cycles from fullbump to full droop,and won't produce much twisting force on the axle housing during cross axle articulation.If vertical separation of the links at the frame is reduced relative to the axle, then the link pair on each side starts to behave a bit like a long radius arm, that depending on its effective length would produce a certain degree of antidive, in addition to keeping the pinion aiming at the t/case.However, just like a radius arm setup that has been fitted with rigid non compliant axle bushings,a non parrallel 4 link in theory should not articulate at all because during articulation the pair of links on the left side of the rig wants to twist the axle tube say in a clockwise direction while the links on the right side wants to twist the axle tube anticlockwise.
My question is this. How do you build a heimed 4 link with a reasonable degree of front antisquat, that also gives good articulation without tearing metal or straining the heck out of all the links, joints, axle housings etc?
AG.

Not disagreeing with anyone as I'm always willing to learn, but could someone riddle me this?
Heim joints have no compliance. A parrallel equal length 4 link with heims on all ends will keep the pinion parrallel with the frame as the suspension cycles from fullbump to full droop,and won't produce much twisting force on the axle housing during cross axle articulation.If vertical separation of the links at the frame is reduced relative to the axle, then the link pair on each side starts to behave a bit like a long radius arm, that depending on its effective length would produce a certain degree of antidive, in addition to keeping the pinion aiming at the t/case.However, just like a radius arm setup that has been fitted with rigid non compliant axle bushings,a non parrallel 4 link in theory should not articulate at all because during articulation the pair of links on the left side of the rig wants to twist the axle tube say in a clockwise direction while the links on the right side wants to twist the axle tube anticlockwise.
My question is this. How do you build a heimed 4 link with a reasonable degree of front antisquat, that also gives good articulation without tearing metal or straining the heck out of all the links, joints, axle housings etc?
AG.

It hurts my brain to think about this question too much, it's a good one :laughing:

Are you describing a system with all links parallel in plan view, and the addition of a panhard or watts link? There IS bind there due to the axle not wanting to be rolled like a cone (one too many constraint points).

But, providing at least one pair of the links is triangulated enough to remove that 5th link, you have the perfect amount of constraint and no bind even if the separation at the frame is reduced to nothing.

Even if parallel in plan you can remove one upper or lower link (and leave the lateral constraining panhard or watts) and it will cycle without binding (once again back to the perfect amount of constraint), but that puts all the torsional load through the length of the housing itself.

I think you CAN build your sold-jointed, high travel 4-link with a good deal of anti-dive by converging the constraint points at the frame vertically without difficulty.
The problem becomes steering. If you need mechanical steering you really need to run a drag link parallel with a lower link. Which, on a 4x4 application, will more than likely need to run to a bell-crank setup on the housing. I can't imagine being able to package it hot-rod cowl steering style straight to the steering arm.

It hurts my brain to think about this question too much, it's a good one :laughing:

Are you describing a system with all links parallel in plan view, and the addition of a panhard or watts link? There IS bind there due to the axle not wanting to be rolled like a cone (one too many constraint points).

But, providing at least one pair of the links is triangulated enough to remove that 5th link, you have the perfect amount of constraint and no bind even if the separation at the frame is reduced to nothing.

Even if parallel in plan you can remove one upper or lower link (and leave the lateral constraining panhard or watts) and it will cycle without binding (once again back to the perfect amount of constraint), but that puts all the torsional load through the length of the housing itself.

I think you CAN build your sold-jointed, high travel 4-link with a good deal of anti-dive by converging the constraint points at the frame vertically without difficulty.
The problem becomes steering. If you need mechanical steering you really need to run a drag link parallel with a lower link. Which, on a 4x4 application, will more than likely need to run to a bell-crank setup on the housing. I can't imagine being able to package it hot-rod cowl steering style straight to the steering arm.

By parrallel I was imagining both in plan and when viewing the links from the side. From scribbled drawings on the back of a beer coaster, if the upper and lower links have a convergence angle when viewed from the side, then theoretically the suspension can't articulate if the links have heim joints on both ends.The fact that there are rigs setup like this that do articulate suggests that metal somewhere at the axle or frame is being stressed or flexed in some way to compensate for a lack of compliance in the heims.There are firms over here that replace the Radius arms on both Nissan Patrols and Toyotas with flexibly bushed parrallel 4 links(plus panhard), so it would seem that even with compliance,articulation and good antidive geometry are mutually exclusive characteristics with 4 ink arrangements.It could easiy be crap, but my minds eye is seeing a link between low front antdive numbers and Xcrawlers busted driveshaft and crossmember issues that may not be altogether due to vertical separation of the links at the axle.
Here's a bit more possible crap thinking. A rig that has a front suspension with no antidive when braking, conversely would rise under accelleration, with the sit up and beg attitude compounded by the low rear antisquat numbers favored by many. With a parrallel 4 link keeping the pinion parrallel with the frame, but with the suspension rising,the driveshaft universal joint angles would be significant even without axle wrap.
AG.

PS,Your mention of cowl to axle steering reminded me of a fairly stock and light flatfender I saw about 30yrs ago that had a rack and pinion unit bolted directly to the axle, with a universally jointed, slip jointed shaft running directly up to the steering column.The same effect on bump steer as full hydro for about 20 bucks,back then.

Agrover,

I wish I had some clever way to explain the 4-link function vs. radius arm distinction but I can't.

I can tell you from empirical evidence that there is no bind from the simple fact that I can cycle my suspension "by hand" from full bump to full droop and articulate one-side-at-a-time with no binding. (I'm running 8 heims on a 4-link rear).

I'm not Superman, so I know my strength is not adequate to bend link mounts or apply large torsional forces to them. Also, since my project is only a frame on jackstands there is almost NO weight to counteract me when I lift the axle...... if my links were binding anywhere, the frame would immediately start coming off the jackstands as I lifted the suspension to cycle it.

On a different note:

I've been contemplating a bell-crank steering setup for a long time, and I'm always on the lookout for photos of offroad vehicles that have used it (not many). There was one called "Fire Ant" a long time ago...and I hear rumors from time to time that there are newer trucks doing it too.

I like the idea of an axle-mounted rack&pinion but would wonder what sort of donor vehicle would have one strong enough to turn 39's without adding the complexity of hydro assist to it??


:usa:

Do you have some better pics of the frame attachment points? I suspect that your crossmember is moving under load judging by the your first pic that shows the crossmember. I have NEVER had a problem with that kind of movement, and I even use soft poly bushings on the axle end of my arms. All my lower axle mounts are flush with the bottom of the tubes and I have about 10" seperation at the diff with maybe 4" at the frame. So, the only thing that will cause it to move that much, is if either your link material isn't strong enough to prevent if from flexing under load, or you frame mount is flexing. Just my $0.02.

Agrover,

I wish I had some clever way to explain the 4-link function vs. radius arm distinction but I can't.

I can tell you from empirical evidence that there is no bind from the simple fact that I can cycle my suspension "by hand" from full bump to full droop and articulate one-side-at-a-time with no binding. (I'm running 8 heims on a 4-link rear).

I'm not Superman, so I know my strength is not adequate to bend link mounts or apply large torsional forces to them. Also, since my project is only a frame on jackstands there is almost NO weight to counteract me when I lift the axle...... if my links were binding anywhere, the frame would immediately start coming off the jackstands as I lifted the suspension to cycle it.

On a different note:

I've been contemplating a bell-crank steering setup for a long time, and I'm always on the lookout for photos of offroad vehicles that have used it (not many). There was one called "Fire Ant" a long time ago...and I hear rumors from time to time that there are newer trucks doing it too.

I like the idea of an axle-mounted rack&pinion but would wonder what sort of donor vehicle would have one strong enough to turn 39's without adding the complexity of hydro assist to it??


:usa:

Greg,I'm really trying to get my head around this, and like Wendle my head is throbbing,and I can't see where I'm going off course.
My basic 6th grade geometric calculations based on your suspension link diagram on page one indicate that your antidive geometry and forces are negligable.Unless I misunderstood discussions on other threads, an instant centre 145'' behind the front axle, represents a radius arm of the same length.Imagine a pair of 145'' long links, one each side, solidly welded to the axle to represent the non compliance of heim joints.Now lift the axle vertically a distance of 10''. According to my protractor the axle housing has rotated 5 degrees to increase the castor angle by the same.During cross axle articulation, if you get 20'' of vertical difference between the left and right hand side pair of links, there is a combined force that is trying to twist each end of the axle housing 5 degrees in opposite directions, a total of 10 degrees. Because your housing isn't actually twisting, where is the 10 degrees being absorbed ?Lash in the heims? bowing of the links? flex in the frame? all of the above?
AG.

Edit. OK I think I have it now. After playing with my compass on your diagram and putting numerous pin holes in my computer screen I now think I understand that the position of instant centre doesn't necessarily replicate the effective radius arm length.

The heaviest rack and pinion units I've seen over here were fitted to GM built Bedford CF 1.5 ton duall rear rear wheel vansabout 25 yrs ago, which I guess would be broadly similar to your Chevy delivery vans.
Do the Chevies have racks?