A 2-link question-

[Low Elco]

So, I just bought a 78 SWB, and have done several 67-72's. It will receive a cammed/tuned 5.3/4l60. I like the trailing arm ride and traction/handling advantages. But, I'm cheap, not a lot of dough here, and all of the kits are $$$$.

That has lead me to thinking. I intend to put the gas tank in the rear, which means nice, smooth rails all the way up under the cab. What If I took stock 67-72 trailing arm geometry, took the stock 78 forward spring hangers and flipped them, used basically a flip kit to mount the arms underneath (or just flipped the saddle over, or made saddles 67-72 style, only straight) and then adjusted for pinion angle. Make a bracket for the spring and a crossmember to reinforce at that point. Long travel shocks and a long panhard out back of the rear, a'la the No Limit kit.
3rd Gen WS6 swaybar somewhere in the mix. Wha-la, basically the same thing as a 67-72 setup, only outboard. I've been a fabricator for a long time, making the parts isn't a problem.

Anybody see anything glaringly wrong with this?

[SCOTI]

Originally Posted by Low Elco

So, I just bought a 78 SWB, and have done several 67-72's. It will receive a cammed/tuned 5.3/4l60. I like the trailing arm ride and traction/handling advantages. But, I'm cheap, not a lot of dough here, and all of the kits are $$$$.

That has lead me to thinking. I intend to put the gas tank in the rear, which means nice, smooth rails all the way up under the cab. What If I took stock 67-72 trailing arm geometry, took the stock 78 forward spring hangers and flipped them, used basically a flip kit to mount the arms underneath (or just flipped the saddle over, or made saddles 67-72 style, only straight) and then adjusted for pinion angle. Make a bracket for the spring and a crossmember to reinforce at that point. Long travel shocks and a long panhard out back of the rear, a'la the No Limit kit.
3rd Gen WS6 swaybar somewhere in the mix. Wha-la, basically the same thing as a 67-72 setup, only outboard. I've been a fabricator for a long time, making the parts isn't a problem.

Anybody see anything glaringly wrong with this?

I'm trying to picture what you're describing... Which 'link' style is your intent (leaf-spring or the T/A)?

Are you suggesting relocating the front leaf hangers inboard of the rails, using 67-72 T/A's as the suspension links/arms, & making a spring x-member to locate the coils @ the upper position?

[Low Elco]

Yes, but T/A outboard of the rails.

[SCOTI]

Originally Posted by Low Elco

Yes, but T/A outboard of the rails.

So T/A's instead of leaf springs in the leaf springs original mounting position?
The leaf springs over-all length is about the same as a T/A (leafs @ 52-56"; T/A @ ~51"). However, the leaf locates the rear housing mid-length of the spring pack where the T/A is much farther rear ward. This would require moving the hangers forward.

If this is what you meant, the difference is the original mounting position places the T/A's in a triangle configuration which allows for some articulation. Combing the triangulated front mounting w/the I-beams ability to slightly twist & return to form as well as rubber bushings @ the front mount allow the system to flex.

Mounting in an 'H' or 'U' pattern is going to significantly limit that small amount of flex.
It's also going to impact the pinion angle changes throughout suspension travel & would need to be kept in mind.

2-links can work w/some effort but there are better ways to get things done vs re-purposing OE T/A's.

[Low Elco]

Originally Posted by SCOTI

So T/A's instead of leaf springs in the leaf springs original mounting position?
The leaf springs over-all length is about the same as a T/A (leafs @ 52-56"; T/A @ ~51"). However, the leaf locates the rear housing mid-length of the spring pack where the T/A is much farther rear ward. This would require moving the hangers forward.

If this is what you meant, the difference is the original mounting position places the T/A's in a triangle configuration which allows for some articulation. Combing the triangulated front mounting w/the I-beams ability to slightly twist & return to form as well as rubber bushings @ the front mount allow the system to flex.

Mounting in an 'H' or 'U' pattern is going to significantly limit that small amount of flex.
It's also going to impact the pinion angle changes throughout suspension travel & would need to be kept in mind.

2-links can work w/some effort but there are better ways to get things done vs re-purposing OE T/A's.

Intention is to move spring mounts forward, to mirror stock 67-67 lengths.

[Ziegelsteinfaust]

Originally Posted by Low Elco

Yes, but T/A outboard of the rails.

TA's or trucks arms triangualte in the center crossmember, and work very well.

What you described is a parallel 2 link, and they work fine. If cruising or profiling is what your after. Due to the bars being parallel there is virtually no twist, and it makes the truck feel stiff if you take corners to fast. Along with a excessive amounts of understeer. Since the rear end will not allow the truck to rotate.

The TA gets away with this by large bushings, and the mythical connection point in front of the truck.

So if your goals are to cruise the truck, and haul trailers. The parallel 2 link will work fine. If you want to tear up some corners. I would save for a TA set up or swap one in if you can find the donor parts.

For the parallel 2 link the longer the bars are the better they comply. So if you can get 3 or 4 foot bars in the truck I would do it. Short one make for more extreme pinion angle changes. Also a fixed trans yoke with a slipper driveshaft supposedly helps out alot. Or I set the trans slip yoke dead center to help stop binding.

[Low Elco]

Originally Posted by Ziegelsteinfaust

TA's or trucks arms triangualte in the center crossmember, and work very well.

What you described is a parallel 2 link, and they work fine. If cruising or profiling is what your after. Due to the bars being parallel there is virtually no twist, and it makes the truck feel stiff if you take corners to fast. Along with a excessive amounts of understeer. Since the rear end will not allow the truck to rotate.

The TA gets away with this by large bushings, and the mythical connection point in front of the truck.

So if your goals are to cruise the truck, and haul trailers. The parallel 2 link will work fine. If you want to tear up some corners. I would save for a TA set up or swap one in if you can find the donor parts.

For the parallel 2 link the longer the bars are the better they comply. So if you can get 3 or 4 foot bars in the truck I would do it. Short one make for more extreme pinion angle changes. Also a fixed trans yoke with a slipper driveshaft supposedly helps out alot. Or I set the trans slip yoke dead center to help stop binding.

This truck won't be a road racer, but will have upgraded brakes (3/4 ton calipers and 2 1/2" drums) and big swaybars in urethane at each corner. Approximately 5/7 drop. I'm more of a Cannonball type of guy, but I do enjoy me some mountain/hilly roads.

Mainly looking for the better ride, ride height adjustability, and lack of axle wrap that T/A's provide.

Not arguing, just thinking through- Is not a leaf setup also a parallel 2-link by virtue of a more or less solid connection at the front hanger to the rear?

A lot of the big diesel guys use ladder bars to fight rotation in the leaves, which is nominally the same thing?

Also, this would also be panharded side/side.

Intention is to use the stock 67-72 T/A length, and move the front hangers forward, which would effectively lengthen the T/A's a tad by pulling them to perpendicular to the rearend, then mount the shocks off the end of the T/A's like the NO Limit kit, and notch the frame and do a long Panhard set level at ride height.

Then again, I might just get lazy and flip kit it and be done.

Thanks for the responses, just food for thought.

[SCOTI]

Originally Posted by Low Elco

This truck won't be a road racer, but will have upgraded brakes (3/4 ton calipers and 2 1/2" drums) and big swaybars in urethane at each corner. Approximately 5/7 drop. I'm more of a Cannonball type of guy, but I do enjoy me some mountain/hilly roads.

Mainly looking for the better ride, ride height adjustability, and lack of axle wrap that T/A's provide.

Not arguing, just thinking through- Is not a leaf setup also a parallel 2-link by virtue of a more or less solid connection at the front hanger to the rear?

A lot of the big diesel guys use ladder bars to fight rotation in the leaves, which is nominally the same thing?

Also, this would also be panharded side/side.

Intention is to use the stock 67-72 T/A length, and move the front hangers forward, which would effectively lengthen the T/A's a tad by pulling them to perpendicular to the rearend, then mount the shocks off the end of the T/A's like the NO Limit kit, and notch the frame and do a long Panhard set level at ride height.

Then again, I might just get lazy and flip kit it and be done.

Thanks for the responses, just food for thought.

You can make a suspension w/them as you described but it won't work (articulate) the way you desire 'as-is' for canyon/hilly drives. You could do a spherical bearing @ the front mounts for some ability to rotate.

[blazer2007]

I,ve seen ones like this but with air bags.Is that what your thinking ?

[SCOTI]

Originally Posted by blazer2007

I,ve seen ones like this but with air bags.Is that what your thinking ?

That's 'bind city' right there....

[Low Elco]

Originally Posted by blazer2007

I,ve seen ones like this but with air bags.Is that what your thinking ?

Nominally this idea, but with stock 67-72 length T/A's. Is this yours and do you like it?

[blazer2007]

Originally Posted by Low Elco

Nominally this idea, but with stock 67-72 length T/A's. Is this yours and do you like it?

No, is some pics I saved when I was looking for AOL air bags setups

[Low Elco]

I was considering Johnny Joints/those new ART joints. Hmm. It'll be interesting, I just got this thing Saturday. I'm also looking at the interesting idea of a Camaro IRS. We'll just have to wait and see what happens after the rust repair.

[Low Elco]

Sorry for the friction, Fellas! I was just looking at the basic bits and wondered, why not? I'm actually eyeing a 67 rear and t/a setup. Redrill axles, a posi and wide drums that I have on hand, 3/4 ton calipers up front. Wha-la, cheap narrowed rearend! Not trying to be cheap, as much as I kinda wanted to try a bit of fab work. That being said, it ain't like I can pony up for the QA1 kit anytime soon. Truck will be getting a 5.3/4l60 with a BTR stage 2 truck cam that is on hand. I have a 67-72 t/a xmember to mod/use to mock up. I'm also considering Z'ing the front. We'll see, I took in a 67 GMC to finish out over the weekend that'll take me a bit to deal with, so I've got time to ruminate.

[SCOTI]

Originally Posted by Low Elco

Sorry for the friction, Fellas! I was just looking at the basic bits and wondered, why not? I'm actually eyeing a 67 rear and t/a setup. Redrill axles, a posi and wide drums that I have on hand, 3/4 ton calipers up front. Wha-la, cheap narrowed rearend! Not trying to be cheap, as much as I kinda wanted to try a bit of fab work. That being said, it ain't like I can pony up for the QA1 kit anytime soon. Truck will be getting a 5.3/4l60 with a BTR stage 2 truck cam that is on hand. I have a 67-72 t/a xmember to mod/use to mock up. I'm also considering Z'ing the front. We'll see, I took in a 67 GMC to finish out over the weekend that'll take me a bit to deal with, so I've got time to ruminate.

This is how I would do it. The 67-72 x-member will get you the basic layout needs & can be modified to work within the Square rails or if you have the skill set I've seen guys graft the entire rear clip. Not sure that's any better IMHO. Stock T/A's cleaned-up w/some stitch welds in the seams & fresh front bushings. Fab (or buy) some front mounting brackets that allow tuning the pinion & Instant Center.

A front 'Z' done properly helps get the ride height @ a lower altitude w/o compromising ride quality. Do the Caster mods & taller upper BJ for a quicker Camber curve w/the OE suspension. Leaves $$ for better quality shocks as well.

[Low Elco]

That's pretty much the plan. What's the taller upper ball joint? I did the 3/4 mod (moved the joint and boxed the arm) on the 67 I just did, much improvement. No urge to swap the rear clip.

[SCOTI]

Originally Posted by Low Elco

That's pretty much the plan. What's the taller upper ball joint? I did the 3/4 mod (moved the joint and boxed the arm) on the 67 I just did, much improvement. No urge to swap the rear clip.

Taller upper BJ just makes the spindle 'taller'. A taller spindle gets you into the Camber curve quicker when the suspension compresses.

The Square set-up that they did the T/A rear clip was also a long to short conversion so they were cutting the frame in half anyway. Basically from the rear cab mount forward was 73-87 & from the front bed mount back was 67-72. I didn't see how they did the splicing so I'm not sure on specifics. I considered the T/A swap for my 74 before swapping it for my Dually. My plan was modding a 67-72 x-member. I had both OE & aftermarket so not sure what path it would have went (whichever was easiest/better fab wise).

[Low Elco]

I understand the geometry, my question was more toward Part Number. I wasn't aware of a taller part of these trucks and now I'm interested.

[SCOTI]

Originally Posted by Low Elco

I understand the geometry, my question was more toward Part Number. I wasn't aware of a taller part of these trucks and now I'm interested.

Low-friction & .500" taller...
https://www.summitracing.com/parts/qa1-1210-203b

[Low Elco]

Hmm. Interesting, thanks!