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Old 04-23-2012, 09:49 PM   #1 (permalink)
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4-link front and rear design

Ok so I have searched around and have not really seen a good answer for my application. I am building a 1939 Dodge 1.5 Ton truck I will have a Cummins 12V 5.9L going to a Dana Spicer 19060s in the rear. I will have air bags all around and am trying to finalize the 4-link placement for the front and rear. My rear axle can handle 20,000lbs as can the airbags so I will want to calculate everything to not fail under this weight. I had planned to use 2” x .250 1020 DOM but that seems a bit light for the lowers especially. Since I already have the tube I am thinking to buy a section of 2.5” X .250 DOM and sleeve it over the smaller pipe for the lower bars.

On the front I am using a parallel 4-link with a pahard bar, on the rear I am using a triangulated 4-link. I have been playing around with the great 4-link calculator for the rears and think I have a fairly good setup. Unfortunately I had to make some compromises, so please take a look and let me know your thoughts (be nice this is the first time for me).


For the front I bought a parallel 4-link kit, but the bars seem a bit small for my application 1.25" od and I do not know the wall thickness but the threaded joint is .75" and that threads into a welded bung... so I assume 1/8" thickness. I was told it would work, but again think it is way too small for my weight load.

To get the lower links mounted I am going to have to make a mount that is about 10” below the frame rail, which seems like a bad idea but the only way I see to make it work without having a ton of over steer. Due to the size and potential weight of this truck I want it to stick to the ground, I do not want it wandering in the lane I want it solid. I will not be rock climbing but going over curbs or through the desert or logging roads I could see happening.

So my questions are;
What do you think of the rear design I have?
What would you change to make the rear better?
Is there a good calculator for the front and or the front and rear together?
If no calculator for the front 4-link + Panhard bar how do I know I am not f-ing everything up?

THANKS!!

Yeah I am new to this forum, I tried to post in the Newbe section but no replies... so here I am.

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Old 04-23-2012, 11:02 PM   #2 (permalink)
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Originally Posted by 1939dodge View Post
Ok so I have searched around and have not really seen a good answer for my application. I am building a 1939 Dodge 1.5 Ton truck I will have a Cummins 12V 5.9L going to a Dana Spicer 19060s in the rear. I will have air bags all around and am trying to finalize the 4-link placement for the front and rear. My rear axle can handle 20,000lbs as can the airbags so I will want to calculate everything to not fail under this weight. I had planned to use 2” x .250 1020 DOM but that seems a bit light for the lowers especially. Since I already have the tube I am thinking to buy a section of 2.5” X .250 DOM and sleeve it over the smaller pipe for the lower bars.

On the front I am using a parallel 4-link with a pahard bar, on the rear I am using a triangulated 4-link. I have been playing around with the great 4-link calculator for the rears and think I have a fairly good setup. Unfortunately I had to make some compromises, so please take a look and let me know your thoughts (be nice this is the first time for me).


For the front I bought a parallel 4-link kit, but the bars seem a bit small for my application 1.25" od and I do not know the wall thickness but the threaded joint is .75" and that threads into a welded bung... so I assume 1/8" thickness. I was told it would work, but again think it is way too small for my weight load.

To get the lower links mounted I am going to have to make a mount that is about 10” below the frame rail, which seems like a bad idea but the only way I see to make it work without having a ton of over steer. Due to the size and potential weight of this truck I want it to stick to the ground, I do not want it wandering in the lane I want it solid. I will not be rock climbing but going over curbs or through the desert or logging roads I could see happening.

So my questions are;
What do you think of the rear design I have?
What would you change to make the rear better?
Is there a good calculator for the front and or the front and rear together?
If no calculator for the front 4-link + Panhard bar how do I know I am not f-ing everything up?

THANKS!!

Yeah I am new to this forum, I tried to post in the Newbe section but no replies... so here I am.

looks like your going to get the same thing im problebly going to get crickets lol. from what i have read you want your anti squat around 70% and your bump steer around 0%

the rest im still trying to figure out. sorry that the best i could help.
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Old 04-23-2012, 11:09 PM   #3 (permalink)
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Thanks for trying to help, from what I understand the rear should be around 30-75% anti-squat and a little understeer to keep it on track... but I am not sure about the placement of the mounts or the front end stuff (along with the calculations I came up with).
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Old 04-23-2012, 11:40 PM   #4 (permalink)
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longer link couldnt hurt. what are u using it for mud/trail/rock?
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Old 04-23-2012, 11:45 PM   #5 (permalink)
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Longer links exert more force and are more likely to bend, compromise is pinion angle changes.

I am going to mostly use this on the road, gravel roads and in the dessert. Not going to go crazy off road, but this will be able to haul over 20,000lbs on the bed and tow my 16' dump trailer with another 20,000 to 40,000lbs.
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Old 04-24-2012, 09:32 AM   #6 (permalink)
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Originally Posted by 1939dodge View Post
Longer links exert more force and are more likely to bend, compromise is pinion angle changes.

I am going to mostly use this on the road, gravel roads and in the dessert. Not going to go crazy off road, but this will be able to haul over 20,000lbs on the bed and tow my 16' dump trailer with another 20,000 to 40,000lbs.
How exactly does a link exert more force if it's longer?

I agree that longer links can buckle under load easier but you need to understand the forces acting on the links first. For a normal rotation rear end the lowers are in compression most of the time to the uppers are in tension.

This is one of the reasons that you can use smaller lighter material for uppers. Now in braking that changes so a bit of compromise is needed.

Shooting from the hip I would say your sleeved idea for the lowers will be good and then just use the 2" dia 1/4" wall for the uppers. Your CG height is wrong I think. Seems too low, I would try to get the links a bit longer if possible.

I think you might want to use the 3 link calc. for the front end and just pretend that the fourth link doesn't exist. I "think" that will make things turn out right?

Keep shooting for 0 degrees of overtsteer/understeer. having a bit of roll understeer isn't so bad, makes things way more drivable than a bunch of roll oversteer.

Good thing you picked Tuesday to ask.

Last edited by miniwally; 04-24-2012 at 12:57 PM.
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Old 04-24-2012, 12:43 PM   #7 (permalink)
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How exactly does a link exert more force if it's longer?

I agree that linger links can buckle under load easier but you need to understand the forces acting on the links first. For a normal rotation rear end the lowers are in compression most of the time to the uppers are in tension...
Thanks for the heads up on the CG height... I was not sure how to calculate that.

You are correct I used the wrong term for the buckling forces and said on the links... meant the tubes. I am more worried about the buckling due to the extreme potential weight of everything.

I did have longer links (I still have not cut them shorter yet) but the mounts I have are already set with about a 33-45* angle (I forgot the exact amount) and the longer links need about a 22* angle so I would have to re-build the mounts for the uppers. I think having shorter links at the larger angle will also help to keep the axle more steady and centered. Since this is mostly for the road I am not as concerned with articulation and I have air bags to keep an even ride height at any weight.

Keep the comments coming and thanks for not flaming me yet
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Old 04-24-2012, 03:58 PM   #8 (permalink)
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60,000 lbs. oh that poor little 5.9L


sounds cool though, i want to see pics of it
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Last edited by BenE; 04-24-2012 at 03:58 PM.
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Old 04-24-2012, 05:46 PM   #9 (permalink)
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60,000 lbs. oh that poor little 5.9L


sounds cool though, i want to see pics of it
Ah, the engine will be ok, I am boosting it to about 500Hp compound turbos, better cam, lots of custom stuff and it will be bolted up to a Allison 3060 6 speed automatic transmission and a Dana Spicer 19060 rear axle... I think everything is going to be well overbuilt.

Here is one photo as from when I bought it... I have tons more on build threads and the site for the build 1939cummins.info

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Old 04-24-2012, 06:40 PM   #10 (permalink)
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If I increase the length of the upper links back to where I had them here are some calculations;


Suspension Geometry:
Upper Links x y z
Frame End 27.00 11.63 30.50 in
Axle End 2.00 2.50 30.50 in
Lower Links x y z
Frame End 37.50 15.00 16.00 in
Axle End 2.50 19.00 11.75 in


Geometry Summary:
Static Anti-Squat 48 % Travel Anti-Squat: 39%
Roll Center Height 31 in Travel Roll Center: 32.82
Roll Axis Angle 0 degrees (Roll Oversteer) Travel Roll Axis: -2.83°
Instant Center X-Axis 157 in Pinion Change: 0.81°
Instant Center Z-Axis 31 in Travel Amount: 4.00
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Old 04-26-2012, 11:38 PM   #11 (permalink)
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Here is the graph and calcs with the longer upper links,

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Old 04-27-2012, 06:01 AM   #12 (permalink)
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You will definaty kill nuns with those little ends on your heavy ass truck.
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Old 04-28-2012, 01:55 PM   #13 (permalink)
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You will definaty kill nuns with those little ends on your heavy ass truck.
Just avoid church and that takes care of that LOL

I hope you are saying the front ones are too small... I think the rear should be large enough
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