Lower Links 101

Curtis Guise

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"Both ends of each trailing arm must be able to swivel in all directions."

When I think about it that makes sense, but then why do all the TT's and nice prerunners have a standard bushing in the front instead of a heim? And all of those trucks are built by excellent fabricators. For examples allot of the trucks on the skunkz page are like that.
 

crashesalot2003

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i was thinking, would it make sense to use some sort of uerithane bushing up front, to help eliminate most wobble, but still allow good articulation? just a thought


no brain, no pain
 

RacerX

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billymanfroy- When baldwin ripped those links off, he hit a rock the size of a microwave. That will tear anything up. A single link with a bushing and a hiem or two hiems will crumble the same.
 

FABRICATOR

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Most, if not all, Trophy Trucks use swivel rod ends ("Heims") at both ends of the lower control arms (LCA's). Pre-runners, depending on application, use either swivel rod ends or rubber/urethane bushings at the forward end. There will be lateral movement of the LCA's. Any connection that does not allow for this will either wear rapidly, force something to flex, or both. Resilient bushings (rubber/urethane) are good for keeping the arm from flopping, but don't live long when subjected to a lot of movement.

<font color=orange>The best ideas are the ones that look obvious to the casual observer.</font color=orange>
 

CRAIG_HALL

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What about the upper link or links? I've got a 9" yet to be installed but I've already welded on my upper and lower mounts. On top I'm gonna use two 7/8" high misalign heims (the ones with the shoulders) and not space them smaller ,but use 3/4" bolts. I felt two 3/4" bolts holding two heims would be stronger and last longer (load spread twice) than a single 1-1/4" heim that you have to misalign to 7/8" I think thats the size bolt. With a 7/8" bung (1.25 o.d.) you can run two 1.5 x. 120 wall tubes for links,plus you get minor side to side adjustment. I think you can get of these for the price of a single 1-1/4" and you can get 20 deg. with the 7/8". Hope it works I already welded the mounts!!

On the lower I'm gonna use a large uniball 2.125 o.d. 1" bore misaligned down to 3/4" I think. Do you really need the heim adjustment for length? arms would be jigged identical in length with the mounting brackets being located off of existing holes in my carrier bearing crossmember (97-ext.cab ranger).Lower arm lenght to be about 60 5/8". Uupper yet to be figured, around 53" I think. I'm going to use two set screws in the uniball cup to keep out any slight misfit. Unaballs are still cheaper than a big heim on the bottom.
 

partybarge_pilot

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Bushings up front will bind to some degree on articulation depending on how much wheel travel you have and how long your arms are. I have yet to see a TT with bronze bushings. All that I have seen are delrin or urithane. Both will give a little flex when needed. This also helps isolate some vibration from the frame.
 

Curtis Guise

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Before putting much thought into it I was considering turning out some Delrin bushings for the front pivot like I used on the inner pivots on my lower a-arms on my race truck. But I didn't think about the flex they would need to allow for the lower arms on a 4 link. Delrin will allow almost no flex compared to a urethane bushing. So it sounds like Urethane or a heim is the way to go?
 

NorCal_Prerunner

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Some measurements for Thom. I didn't quite know how to get the exact measurement for the bottom of the flywheel, so I measured the distance from the back/bottom edge of the block down to the ground.This is just for reference. It is the process of determining the link length and the geometry that we're after.


It's never too late to be what you might have been....
 

ntsqd

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Sorry I didn't get back to you on that, busy at work with some testing of a new caliper. It did several months worth of racing on the dyno today.

What we need is the elevation of the center of the flywheel/crankshaft at the clutch surface. This is the commonly accepted rough approximation for the Center of Gravity of vehicles not highly modified.
To get exact, you need to first get corner weights (or at least front/rear percentages) with the vehicle sitting level. Then do it again with the vehicle tilted at a large angle. You can apply the percentages gleened from the first weighing to the wheelbase to find where the CG is front to rear. With the second measurement in hand apply a little Trig to find the elevation of the CG.

My thot was to put the Instant Center on the commonly approximated CG. We could have a whole discussion about where it really should go, but I lack the background in dez rigs to debate it and that's not our point anyway. Putting it on the CG makes getting the basics down easier.
So draw your upper & lower arm LOA's from that point to where they will mount on the axle housing. As one post said, do this in something like AutoCAD. Then you can easily cycle the suspension a quiery the program for what the various angles change to. You can model it in graph paper & construction cardboard. With enough time you can derive the same information.

TS

I used swerve around my halucinations, now I drive right thru them.
 

ntsqd

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My take on the front bushing vs. rod end/spherical bearing debate is that a properly done bushing will stabilize the arm from trying to twist. Which will cost you some articulation due to binding. It does build in an un-tunable swaybar. I'm willing to live with that since it gives me control over what the arm is doing otherwise.
If the arms are designed with the kind of twisting that articulation will put into them such that the strain is spread out over a long area of the arm, then the induced stress won't be high enough to rapidly fail the arm at any one point. Make no mistake though that you have just created something with a limited life expectancy. If you want the arm to last the natural life of the vehicle, then a spheric in some fashion is called for.

TS

I used swerve around my halucinations, now I drive right thru them.
 

NorCal_Prerunner

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For progression of the post, can we estimate where it is based on my quick drawing? Like I said, it is more about the process at this point rather than the exact measurements.

It's never too late to be what you might have been....
 

CRAIG_HALL

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here's mine
 

ntsqd

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As I recall you said your measurement is from the lower most surface of the block at it's rear-most edge. I'd estimate that the crank centerline is ~2" above that, and that the flywheel's friction surface is ~2" to the rear of that. I would say that we should adjust the dimensions so that we're closer to a real truck's dimensions.

Where the pivot points on the housing are going to be would be my next chore. I fully expect that they might get moved around some, but need to start with something. From observing various rear linkages it appears that the lower link axle pivots are always very close to the axle centerline. This makes the travel path easy to predict since it's dominated by the lower link. The axle will travel in a partial circular path of a radius very close to the length of the lower arm and centered about where the lower arm's frame pivot is.
When I worked out my friend's linkage (hasn't been built yet, no idea how it works) I started with the lower arm pivots 3" forward of the axle centerline and 3" down from the centerline. The upper pivots I put 9" above the centerline and on the fore/aft centerline.

The next chore is to draw a line btwn the IC and each of the pivot points. Wouldn't hurt to break out your Herb Adam's book at this point either. There are some good drawings in it on this topic.

TS

I used swerve around my halucinations, now I drive right thru them.
 

Curtis Guise

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This is just something that I thought of when looking at CRAIGHALL's drawing. What happens if you take both the upper and lower links front pivots and align them? I don't have a CAD program to try it.

Also I see alot of trucks with the rear lower pivot directly in front of the axle housing instead of below the housing. Wouldn't that be better because it would keep the arm higher off the ground?
 

billymanfroy

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<blockquote><font size=1>In reply to:</font><hr>

I see alot of trucks with the rear lower pivot directly in front of the axle housing instead of below the housing. Wouldn't that be better because it would keep the arm higher off the ground?

<hr></blockquote>


Curtis,

Here's the way I understand it. Ideally, you would want the force directly under the axle as CRAIGHALL has it. This is the direction you want the force acting on the axle to keep it from trying to twist. Straight out in front would be better for clearance, but ALL of the forces would be then trying to twist the axle forward on compression and back on rebound.

John Richer explains it a lot better here:
<A target="_blank" HREF=http://home.off-road.com/~jricher/newrearsusp.htm>http://home.off-road.com/~jricher/newrearsusp.htm</A>

Here's their Autocad drawing, too.
http://home.off-road.com/~jricher/images/white ranger/SUSPENSION.jpg


Thom,

I didn't see anywhere on Richer's build up where they considered the C of G, and I can't do it now because my truck is all torn apart. I can measure my crank from the ground and from the front wheels, but what do I do with that info? How do I use that to determine where my front pivots end up or how long my LCA's are going to be? Thanks

Billy
 

RacerX

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Enough of Bob Vilas's (sp?) "This old truck", how about we ask the builders of race winning vehicle's how it is done.
 

NorCal_Prerunner

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Hey Anthony,
How about you give Donahoe, H&M, and Camburg a call and tell them about the post. Otherwise, stop wasting everyones time with useless posts like that. This thread has more good info in it thus far than most. And if you feel like putting in your 0 cents again, why don't you just email me directly.

Here's some pics of some lower links for an F150 extended cab in progress, built by H&M. Anyone have an idea as to what diameter the tube looks like + possible thickness as well as the thickness of the plate? TIG welded Cromoly no doubt.






It's never too late to be what you might have been....
 

Kritter

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I am sure John has well thought out his design...he is a mechanical engineer and working in the design field by trade.

Kris
"Buy American before it's too late..."
 

ntsqd

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Have at it. See what they'll tell you. I know what I'd tell you where I in that possition: diddly squat. Why would I give up for free some hard earned knowlege that might be my competitive edge ?

TS

I used swerve around my halucinations, now I drive right thru them.
 

ntsqd

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Putting the LA's pivot directly forward of the axle CL makes that pivot point the center of torque reaction rotation and means that the UA has to resist all of the torque reaction. Moving the pivot down allows the LA to help a little. Does reduce clearence a little.

Rather than endlessly debating where to put the IC, I thot to put it right on the CG at static ride height. That avoids debating where it might better be put while still being demonstrative of the process of laying out the rear suspension. We're at the point where reading the rear suspension chapter in Herb Adam's chassis book will be really helpful. All we've done so far is duplicate his approach as applied to semi-real world truck.

Looking at the Richer dwgs it's odd, I'd started a layout and arbitrarily chosen a 50" long LA. From the measurements & my rough guess that puts the frame pivot of the LA just about equal to the front U-J which will minimize driveshaft plunge.

Those pockets under the damper mounts on the arm pictured are what I was worrying about catching just the right sized rock. I personally feel that such pockets should be open to the bottom. That creates some strength of design issues that need to be resolved.

TS

I used swerve around my halucinations, now I drive right thru them.
 
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