First, if you are confused about 3 link vs torque arm this might not be the thread for you. If you want to convince me to do something else, please understand cutting these cars up is one of the things that make me happiest in life.

Anyway. I'm running a ladder bar suspension right now with the 9", but as you know ladder bars bind when one wheel hits a bump, or body rolls in turns, etc.

I've been looking at a lot of 3-link setups lately, like the 2015-2019 mustang retrofit (everyone says "Mustang guys are going torque arm" - not true, they are going 3 link).

The main difference is that the 3 link pivots on one spot on the rear axle and one spot on the body, which allows the axle to move up and down without impacting the pinion angle as much as a torque arm (which causes the rear end to swing on an arc). The other thing is, a 3 link is similar to a four link where the top link(s) only provide pulling and pushing forces, not bending/leverage forces like a torque arm. High HP builds launching with sticky tires like to break the heim joints and where it threads in on torque arms simply because the forces are bending/prying forces at the joint. I can't remember who it was on here, but their torque arm let go and it ended up wiping out the transmission too.




What I am curious is those of you who do have experience, what have you found to be reasonable for a top link vs lower link ratio. I'm assuming you guys are running a shorter top link, which is horizontal, and using the bottom link angle to adjust for instant center. (and obviously top link length for pinion angle).

Here is an Art Morrison 3 link chassis. He's running a significantly shorter top link than the lower control arms.



The only visual calculator I have is for ladder bar setups, but I wonder if moving the top link high above the axle center line requires you to shorten it to keep the same ratio for instant center.

Like, if you ran it lower (like just above the tube) does it need to be longer so the intersection happens in a different spot or am I just over analyzing this.

 

i have a 3 link in my blazer.

lower bars going forward like the art pic above, and U shaped upper with mount on both sides of pumpkin into single mount like the art pic above.

When i had poly bushings in all link ends i had less body roll (i dont have a sway/roll bar)
when i rebuilt the links about 15k miles i installed ridetechs new ball joint ends, and it made the sway much more noticeable.
So much so, that i need to install a sway bar to make up for it.
My S blazer is lowered, tubbed, so its not a corner carving toy.
Pic is of my lbazer.

 

I put a 3 link in my 86 last summer, havent been able to drive it more than a loop around the development as im still working on wheel fitment.

From my research, an upper about 80% the length of the lowers is a good start. I ended up with about 25" lowers and 20" upper bars. The hurdle for most would be the back seats, but i lost them years ago when I did a minitub.

The height of the mounts above or below of the axle centering will affect how torque is applied and is limited by the gas tank so making them fairly even isnt hard to do.

 

So.. That's an interesting way you did the mount inside the passenger area. I was thinking of putting the mount basically in the same spot of the tunnel, but I thought about nut and bolting a plate on both sides rather than cutting out a section and mounting it entirely inside.

Do you think even with a sandwiched mount plate the sheet metal in the tunnel will flex too much?

I used to run a jegster torque arm, which just nut and bolted to the tunnel so I assumed a similar design, but sandwiched, would be sufficient.

 

That's interesting. I was thinking of using poly ends. I wonder why the ridetechs caused more sway?

 

I used the jegster tunnel saddle in my old 92 when i did a decoupled torque arm. The setup is a lot longer as the stress in the tunnel is reduced a bit. I dont see why a large saddle couldnt work but the angles required for the upper link put the arm inside the cabin so I didnt have much choice. Might be hard to tell but I raised the tunnel almost 4" over the 3rd link.

 

because they are that efficient.
no joke, they are awesome, i just didnt know it would have effected my ride like that.

Also, i realized i didnt put in my bar lenghts. But basically any suspension i build i mock up the lowers first, and then move the pumkin up and down through suspension cycle and position the pinion where i want it to be. -taking into consideration instant center, center of gravity etc..

Once you got the pinion angle, it's pretty simple after that to know the lenght of the uppers..

 

I'm on the fence about how to mount to the rear end. I could weld a mount to the top of the diff, but then I'd have to raise the body side significantly as you did.

I was thinking of making a plate that just mounts to my moser mount, which would put the link slightly offset. Basically right beside the driveshaft like a torqur arm is. I was looking at the floor layout and I was thinking I could weld a plate to the two rear seat belt mounts, and then through bolts it to the floor.

 

Thinking about this more. So if I use the 3 mounting points for the moser TA adapter, I can go a little lower in the tunnel beside the driveshaft, however, it would need to come off any time I remove the third member as it would be in the way.

If I do it like you did and put the mount on the pumpkin part of the housing, I'd need to raise the tunnel like you did. Which isn't a huge problem but a bit more fab plus I'd be welding on an assembled housing.

Unless of course, I could attach something to the top mount lug only. Hmm.

Decisions decisions.

 

Finally got back to messing with this last night. I made a mount for the top of the rear diff for the 3 link. After doing some measuring and calcs, I think I'm going with 12" on the upper arm and factory lower control arms (19-1/4).



This will sit at 12 o'clock on the diff, and will hold a 2-1/2" poly rod end. Using 3/4" adjuster.

I made the body side mount as well but I'm going to get the rear all welded and aligned back up before I figure out the front mount location. Going to need to cut the tunnel out, and then will probably triangulate the mount.

 

Mount welded up on the diff. I guess this weekend I'll cut the tunnel and figure out how I wan to run the mount.

I think I want the mount to bolt in vertically from the bottom so the horizontal rod end bolt is not trapped by the sides of the tunnel. (using 2-1/2" rod ends).

I went with rod ends rather than heims so it doesn't transmit as much noise from the 9" to the chassis.



The car doesn't have back seats. I kind of feel like I should tie it into the frame on both sides under where the arm rests are.

 

There is a lot of force on the upper link, so bracing it is important. Looking good so far, curious to see what you come up with as far as a mount.

Are you using the poly bushings on both side of the mount?

 

I am. Unless it drives me insane and I replace them with rubber. I think they should be ok.

I talked it over with a buddy tonight who builds much faster and expensive stuff than I do, and he suggested I use 3/16 to reform the tunnel and weld the mount to it. Then go over it with two 6x6 plates and tie it into the roll bar.
I think what I'm going to do is build a tunnel on the bench with some angle and 3/16 plate, test fit it a few times, then weld the mount to the bottom on the bench. Then I can weld the new tunnel in as a completed unit. Probably overlap the factory tunnel by several inches, roset weld it in a few spots, maybe through bolt where the seat mounts are, etc.

I cut the section of tunnel out tonight.



Found this photo online, but basically once the tunnel and mount is welded in place I'd tie it into the roll bar like this car:



The bars are naturally going to be angled back a bit since the mount will be behind the main hoop, but I don't think there is anything in the NHRA rulebook prohibiting that.

I was looking at the aftermarket S197 mounts and a lot of them have 3 hole positions for adjustability. I don't think I can really go DOWN any more because the mount might come in contact with the driveshaft over a huge bump, but I wonder if there ever is a benefit of going up.
In theory, all of the tuning should be done at the lower control arms.

 

Ive always been a fan of adding adjustment everywhere. Adding adjustment to the upper was the tricky part for me as well due to driveshaft clearance and thats why mine is offset to the passengerside a few inches. I wouldn't aim to have the upper link adjustment any higher than what would make the bar level at ride height or the lowest you can make the car if you were to decide to lower ir further.

The SW race cars main hoop is the best fittingnfrom my research. Im really trying to avoid putting a cage in my car as its a street car but i could really benifit for the added stability in chassis.

 

Yeah, I can see why that would give you a little more driveshaft clearance. I'm trying to find a reasonable balance between instant center and the driveshaft not striking the front mount on squat.

My car is not lowered, and I have some taller bump stops so I should be fine. I'm looking at about 19" on the rear and 16.5" on the front (from the ground). I guess the question is should I make it so I can set the front mounting point higher.

At 19/16.5 my instant center is 176.

I can reduce instant center to 154 by moving the lca up 1" in the back OR the front mount of the upper bar up 1".

 

Changing the distance from the axle centerline to the control arms mount changes how torque is applied on acceleration vs deceleration too so moving the lower control arm closer to the axle centerline 1" would create other changes that may not be desirable vs moving the front mount of the upper link higher 1".

 

Spent some time on this today. Bent the plate up using 3/16 sheet on the press brake. Two angles required. I spent some time making sure both mounts were completely parallel (with the road) so the ends wouldn't bind on the arc, but then I realized the rear end is going to articulate anyway. Maybe the rear joint should be swapped out to a heim. Right now it's bolted to the tunnel. Gonna weld it up tomorrow then finish the tunnel. Probably just finish it in 3/16 since I have a bunch in the shop. It would probably be strong enough as is but I think tying the roll bar into it makes sense.

 

The links need to be able to articulate, doesnt matter if they are the uppers or the lower. Factory used rubber for that reason. I used narrow jonnyjoints as they are rebuildable and greasable but rod ends work too. Originally i wanted to use rubber just to help with noise transfer but I couldn't find anything quality out there.

The saddle looks good. Hows the clearance to the driveshaft when the axle is on the bumpstops?

 

It's hard to tell from the photos but about 2-1/2" after the axle is on the bump stops.

Everything is finished and I seam sealed over the welds. I need to get the roll bar done next, but I think this is pretty strong as-is.