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evolution of a SAS - "Y-link" radius arms to 3 link

I told myself when I first did my SAS with the D30, it was a place holder for a D44 and when I was ready for the D44 I'd put the same brackets on it and bolt it in. Yeah right...

My "Y-link" long arms (technically radius arms) performed pretty decently and handled well on the road. I was able to get about 40" under the front tires flexing out. I could have kept them and been OK.

However, when I sold my D30 to a guy doing a Ranger SAS, he wanted my long arms too to make his conversion easy. I figured why not, I can make them better the next go around.

So now starts my 3 link project. I debated a long time what I should use, 4 link, 3 link or radius arms. In the end the 3 link won out. Better handling and flex than radius arms and less parts/cost in a tighter package than a 4 link.

Due to some major drivetrain changes, everything fits a bit different now. I'm ditching the stock tranny crossmember and upper link mounts welded to the frame. Instead I built a heavy duty bolt in crossmember/belly skid that will support the link mounts as well. It is a little farther back and also up, giving me about 2" more clearance than the stock x-member. It also stretches my long arms into the 36" range, where I was at about 32" before.

I'll be posting results from a link calculator, both from the planning stages and the execution. I'll add the old Y-link numbers in the mix as well for comparison. One major difference I already see is about 1/2 the anti-dive.

Materials will be Ballistic flex joints at the frame, poly bushings at the axle, with 1.5 ID/ 2.0 OD DOM tubing.
 



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damarble

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Well life happened and this didn't progress in the timeline I intended, but I'm back to it.

Here is pretty much how the new suspension will look, the way it is currently mocked up under the truck.

3_link-1.jpg
 






IZwack

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Assuming that the top half of the diagram is the top view (and not the bottom view):

I can't remember who pointed this out to me when I was designing my 3-link but basically you want the upper link on the same side as the differential (usually on the driver's side for RBVs) because if its not, then it will result in extreme pinion angles when one side is stuffed and the other is at full droop. Extreme pinion angles increases the chances of shearing the pinion gear's shaft (which has happened before due to not "cutting and turning" the inner knuckle for proper pinion and caster angle), and/or shearing a U-joint.

EDIT - Ouu I remember now who told me - Kirby N.
 






damarble

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I guess I can see how that's possible. I'm not sure it's possible to fit it in there but I'll look it over again.

Edit- I can make it work, but it's going to take a truss. Not necessarily a bad thing, I just didn't want to do it right now.
 






damarble

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This should do the trick.

PRE_2010-08-29-173911.jpg
 






IZwack

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Good stuff - make sure you get the pinion/caster angle correct.
 






damarble

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I'm staying low so I won't do a cut and turn and should still end up pretty good. Obviously there will some compromise, but it looks like I'll be ending up with 6-8* castor and the pinion will be 5* or less lower than straight at the transfer case. The lower links are adjustable on one end and the upper on both ends so I can fine tune quickly.

I should have 5-6" up travel all said and done, I only had 4" with the D30 and Y-link and it won't be sitting any higher, hopefully an inch lower even.
 






RockRanger

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When I did my 3 link from all the research I did I came up with some generalizations.

1. get the track bar as high and as flat as possible.
2. get the upper link as high as you can and if possible slanting backwards the better. the closer to center the better.
3. You can play with a computer program as much as you want, but unless you truely know the weight and real COG it aint worth a damn.
4. Just cause it fits on paper doesn't mean it will in the real world.
Just cause it clears with the wheels strait doesn't mean it will when the wheels are turned.

I played with that calculator for a little while. Once I crawled under the truck and saw where everything was, all the links went where they fit. My upper link misses the engine cross member by 1/2" on compression and the frame upper link mount misses the drive shaft by 1/4" . I had to put a bend in the track bar to clear the engine as well. The track bar also will just kiss the diff cover when fully flexed to the driverside. Just enough to scrape the paint on the cover. I couldn't move it forward cause I clear the steering links by 1/8" when the wheels are turned.

I really like how my three link works and seems very stable. I cant compare to a radius arms cause I had leafs first. I have less travel now but it feels more stable.

I do like your truss though. Interested to see how it turns out.
 






damarble

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Thanks for the tips.

1. I'm not doing high steer, just over the knuckle, so that dictates how high I can get the track bar (matching the drag link). As far as flat, it isn't, but it's less of an angle than before and much less than the Heeps around here run.

2. Pretty much as high as I can go, and there's no way to get it centered, the motor is kind of in the way. I *may* be able to slant it back a little but it will reduce my separation at the frame. Something I can play with after it's driving.

3. I have a pretty good idea of the weight, I had it weighed before I tore it apart and know roughly how much weight I'm adding. CoG is a guess, I'm just following the top-bellhousing-bolt method.

4. What I have on paper is pretty much the way it fits under the truck at this time. I need to update that graph, some of the numbers were rough and I've got exact numbers punched in now. (And the upper is now on the driver's side obviously.) My tires rubbed on the Y-links at full lock so I'm compensating and *shouldn't* have a problem this time.


When I did the Y-link I learned not to burn any brackets in until I'm sure everything clears, so I'm just tacking for now until it's all in and I can cycle the suspension. So far everything fits pretty good.


I almost have a graph of the old Y-link finished for a comparison, but I need get some D30 measurements off my buddy's Heep since I didn't measure the spacing of the brackets before. One major difference is the ridiculous anti-dive. Luckily it's not as big a factor as anti-squat in the rear which is why radius arms work pretty good for a lot of guys.


The truss is a loose copy of Ruffstuff's new design, except I wanted a smooth arch inside instead of angled bends. All 1/4" steel so plenty beefy. Let me tell you, it was NOT fun to cut out with a grinder. I made a cardboard mockup, notched the bends to make it flat, traced it on a straight piece of square tube, cut it out, bent with a ratchet strap and welded it up. The flat piece on the bottom I just worked with a hammer over a block of wood until it had the right curve. End result cost me about $20 in material.
 












damarble

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This:

PRE_2010-08-29-173952.jpg
 












RockRanger

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So with that setup if you need to pull the trans mission you have to pull the upper link. am I seeing that right? If so that is going to suck if the trans needs to come out. On my TTb truck ( yeah it is different then yours) I tried to do an upper link mount like that and the driveshaft would hit it. It ended up getting into it hard once I hooked the track bar up cause it pulled the axle that way on droop. I think there are some pictures in 90ranjo thread of his upper link mount. we built it similar to mine but with a few improvements I wish I had on mine. Hopefully someday he finishes it cause it should work real nice.
 






IZwack

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I had my upper link on that side - of course the trick is to get it as close to the chassis as much as possible w/o any binding (against the chassis). I got away with this because I had an upper link that was longer than the lower link which put the upper upper link mount behind the transfer case. At this point, the frame rail was an open "C" channel and I was able to get the link much closer to the frame rail (and it never binded).

obligatory pic with front axle at full droop:
upperlink_clearance.jpg
 






damarble

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I can't tell how close that is to the front driveshaft, but with a double cardon shaft it looks like it's gonna hit the mount.

It's hard to tell in the pic but the face of the t-case yoke is flush with the crossmember, so the entire double cardan assembly will hang outside it.


So with that setup if you need to pull the trans mission you have to pull the upper link. am I seeing that right? If so that is going to suck if the trans needs to come out. On my TTb truck ( yeah it is different then yours) I tried to do an upper link mount like that and the driveshaft would hit it. It ended up getting into it hard once I hooked the track bar up cause it pulled the axle that way on droop. I think there are some pictures in 90ranjo thread of his upper link mount. we built it similar to mine but with a few improvements I wish I had on mine. Hopefully someday he finishes it cause it should work real nice.

The lowers will also be attached to this crossmember so it would all need to drop if the tranny needs to come out. But! If the tranny ever needs to come out, it will come out the front with the engine, I'm designing it so it's easier to pull the entire drivetrain at once than each component.

I don't see any way the link can ever contact the driveshaft, there is a lot more room there than it looks.
 






damarble

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I can't tell how close that is to the front driveshaft, but with a double cardon shaft it looks like it's gonna hit the mount.

It's hard to tell in the pic but the face of the t-case yoke is flush with the crossmember, so the entire double cardan assembly will hang outside it.


So with that setup if you need to pull the trans mission you have to pull the upper link. am I seeing that right? If so that is going to suck if the trans needs to come out. On my TTb truck ( yeah it is different then yours) I tried to do an upper link mount like that and the driveshaft would hit it. It ended up getting into it hard once I hooked the track bar up cause it pulled the axle that way on droop. I think there are some pictures in 90ranjo thread of his upper link mount. we built it similar to mine but with a few improvements I wish I had on mine. Hopefully someday he finishes it cause it should work real nice.

The lowers will also be attached to this crossmember so it would all need to drop if the tranny needs to come out. But! If the tranny ever needs to come out, it will come out the front with the engine, I'm designing it so it's easier to pull the entire drivetrain at once than each component.

I don't see any way the link can ever contact the driveshaft, there is a lot more room there than it looks.


IZ, I think I have a lot more room between my frame t-case than you do. One, my drivetrain is heavily offset to the right and two I have a NP231D tcase, which seems to be a little narrower than the BW.
 






damarble

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I put in the driveshaft to check for clearances. Miraculously the stock first gen Explorer driveshaft fits perfectly.

The double cardan joint does clear the bracket and bolts throughout the full revolution, but not by much. Considering stuff does move around in real life, I'm going to move the bracket closer to the frame for good measure. I can get a solid 1/2" which should guarantee no contact.
 






damarble

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Here's the "final" specs on the 3 link. The UCA can be lowered up to 6" at the frame end, it's at it's highest point. All links can be lengthened slightly and the UCA can also be shortened a bit.

Still need to grab the numbers to compare to the old Y-link setup.

3_link_done.jpg
 









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damarble

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not sure there will be much for updates here on out. Just the specs of the Y-link and notes on how the 3 link performs when I get to drive it.
 






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